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Bottomonium production in pp and heavy-ion collisions: We study bottomonium $b\bar b$ production in pp collisions as well as in
heavy-ion collisions, using a quantal density matrix approach. The initial
bottom (anti)quarks are provided by the PYTHIA event generator. We solve the
Schr\"odinger equation for the $b\bar b$ pair, identifying the potential with
the free energy, calculated with lattice QCD, to obtain the temperature
dependent $b\bar b$ density matrix as well as the dissociation temperature. The
formation of bottomonium is given by projection of the bottomonium density
matrix onto the density matrix of the system. With this approach we describe
the rapidity and transverse momentum distribution of the $\Upsilon $(nS) in pp
collisions at $\sqrt{s_{\rm NN}}=$ 5.02 TeV extending a similar calculation for
the charmonium states \cite{Song:2017phm}. We employ the Remler formalism to
study the $b\bar b$ production in heavy ion collisions in which the heavy
quarks scatter elastically with partons from the quark gluon plasma (QGP). The
elastic scattering of heavy (anti)quark in QGP is realized by the dynamical
quasi-particle model (DQPM) and the expanding QGP is modeled by PHSD. We find
that a reduction to 10 \% of the scattering cross section for a (anti)bottom
quark with a QGP parton reproduces the experimental data. This suggests that
due to color neutrality the scattering cross section of the small $b\bar b$
system with a parton is considerably smaller than twice the bottom-parton
scattering cross section. | nucl-th |
Self-energy Effects in the Superfluidity of Neutron Matter: The superfluidity of neutron matter in the channel $^1 S_0$ is studied by
taking into account the effect of the ground-state correlations in the
self-energy. To this purpose the gap equation has been solved within the
generalized Gorkov approach. A sizeable suppression of the energy gap is driven
by the quasi-particle strength around the Fermi surface. | nucl-th |
Exactly solvable Richardson-Gaudin models for many-body quantum systems: The use of exactly-solvable Richardson-Gaudin (R-G) models to describe the
physics of systems with strong pair correlations is reviewed. We begin with a
brief discussion of Richardson's early work, which demonstrated the exact
solvability of the pure pairing model, and then show how that work has evolved
recently into a much richer class of exactly-solvable models. We then show how
the Richardson solution leads naturally to an exact analogy between such
quantum models and classical electrostatic problems in two dimensions. This is
then used to demonstrate formally how BCS theory emerges as the large-N limit
of the pure pairing Hamiltonian and is followed by several applications to
problems of relevance to condensed matter physics, nuclear physics and the
physics of confined systems. Some of the interesting effects that are discussed
in the context of these exactly-solvable models include: (1) the crossover from
superconductivity to a fluctuation-dominated regime in small metallic grains,
(2) the role of the nucleon Pauli principle in suppressing the effects of high
spin bosons in interacting boson models of nuclei, and (3) the possibility of
fragmentation in confined boson systems. Interesting insight is also provided
into the origin of the superconducting phase transition both in two-dimensional
electronic systems and in atomic nuclei, based on the electrostatic image of
the corresponding exactly-solvable quantum pairing models. | nucl-th |
Isoscalar M1 and E2 Amplitudes in n+p -> d+gamma: The low energy radiative capture process n+p -> d+gamma provides a sensitive
probe of the two-nucleon system. The cross section for this process is
dominated by the isovector M1 amplitude for capture from the 1S0 channel via
the isovector magnetic moment of the nucleon. In this work we use effective
field theory to compute the isoscalar M1 and isoscalar E2 amplitudes that are
strongly suppressed for cold neutron capture. The actual value of the isoscalar
E2 amplitude is expected to be within 15% of the value computed in this work.
In contrast, due to the vanishing contribution of the one-body operator at
leading order and next-to-leading order, the isoscalar M1 amplitude is
estimated to have a large uncertainty. We discuss in detail the deuteron
quadrupole form factor and SD mixing. | nucl-th |
Axial vector diquark correlations in the nucleon: Structure functions
and static properties: In order to extract information on the strength of quark-quark correlations
in the axial vector (a.v.) diquark channel ($J^P=1^+, T=1$), we analyze the
quark light cone momentum distributions in the nucleon, in particular their
flavor dependencies, and the static properties of the nucleon. To construct the
nucleon as a relativistic 3-quark bound state, we use a simple 'static'
approximation to the full Faddeev equation in the Nambu-Jona-Lasinio model,
including correlations in the scalar ($J^P=0^+, T=0$) and a.v. diquark
channels. It is shown that the a.v. diquark correlations should be rather weak
compared to the scalar ones. From our analysis we extract information on the
strength of the correlations as well as on the probability of the a.v. diquark
channel. | nucl-th |
Impact of the neutron-star deformability on equation of state parameters: We use a Bayesian inference analysis to explore the sensitivity of Taylor
expansion parameters of the nuclear equation of state (EOS) to the neutron star
dimensionless tidal deformability ($\Lambda$) on 1 to 2 solar masses neutron
stars. A global power law dependence between tidal deformability and
compactness parameter (M/R) is verified over this mass region. To avoid
superfluous correlations between the expansion parameters, we use a
correlation-free EOS model based on a recently published meta-modeling
approach. We find that assumptions in the prior distribution strongly influence
the constraints on $\Lambda$. The $\Lambda$ constraints obtained from the
neutron star merger event GW170817 prefer low values of $L_\text{sym}$ and
$K_\text{sym}$, for a canonical neutron star with 1.4 solar mass. For neutron
star with mass $<1.6$ solar mass, $L_\text{sym}$ and $K_\text{sym}$ are highly
correlated with the tidal deformability. For more massive neutron stars, the
tidal deformability is more strongly correlated with higher order Taylor
expansion parameters. | nucl-th |
On the quark mass dependence of nucleon-nucleon S-wave scattering
lengths: In the framework of a Chiral effective theory with dibaryon fields, we
calculate the pion mass dependence of the inverse scattering length of the
nucleon-nucleon system in the $^3S_1$ channel at order ${(m_\pi^3 /
\Lambda_\chi^2)}\times (m_\pi^{1/2}m_N^{3/2}/8\pi f_\pi^2)^n$ for all $n\ge 0$.
We show that certain sets of potentially large higher order contributions
vanish. We discuss the difficulties of extending the proof to the $^1S_0$
channel. We apply our results to chiral extrapolations of current lattice data. | nucl-th |
Low energy proton reactions of astrophysical interest in A$\sim90-100$
region: Semimicroscopic optical potentials for low energy proton reactions in mass
90-100 region have been obtained by folding the density dependent M3Y
interaction with relativistic mean field densities. Certain parameters in the
potential have been deduced by comparing calculated results with the data for
elastic scattering. Low energy proton reactions in this mass region have been
studied in the formalism with success. Rates of important astrophysical
reaction in the mass region have been calculated. | nucl-th |
Perturbative approaches in relativistic kinetic theory and the emergence
of first-order hydrodynamics: Hydrodynamics can be formulated in terms of a perturbative series in
derivatives of the temperature, chemical potential, and flow velocity around an
equilibrium state. Different formulations for this series have been proposed
over the years, which consequently led to the development of various
hydrodynamic theories. In this work, we discuss the relativistic
generalizations of the perturbative expansions put forward by Chapman and
Enskog, and Hilbert, using general matching conditions in kinetic theory. This
allows us to describe, in a comprehensive way, how different out-of-equilibrium
definitions for the hydrodynamic fields affect the development of the
hydrodynamic perturbative series. We provide a perturbative method for
systematically deriving the hydrodynamic formulation recently proposed by
Bemfica, Disconzi, Noronha, and Kovtun (BDNK) from relativistic kinetic theory.
The various transport coefficients that appear in BDNK (at first-order) are
explicitly computed using a new formulation of the relaxation time
approximation for the Boltzmann equation. Assuming Bjorken flow, we also
determine the hydrodynamic attractors of BDNK theory and compare the overall
hydrodynamic evolution obtained using this formulation with that generated by
the Israel-Stewart equations of motion and also kinetic theory. | nucl-th |
Nuclear constraints on gravitational waves from deformed pulsars: The recent direct detection of gravitational waves (GWs) from binary black
hole mergers (2016, Phys. Rev. Lett. 116, no. 6, 061102; no. 24, 241103) opens
up an entirely new non-electromagnetic window into the Universe making it
possible to probe physics that has been hidden or dark to electromagnetic
observations. In addition to cataclysmic events involving black holes, GWs can
be triggered by physical processes and systems involving neutron stars.
Properties of neutron stars are largely determined by the equation of state
(EOS) of neutron-rich matter, which is the major ingredient in calculating the
stellar structure and properties of related phenomena, such as gravitational
wave emission from elliptically deformed pulsars and neutron star binaries.
Although the EOS of neutron-rich matter is still rather uncertain mainly due to
the poorly known density dependence of nuclear symmetry energy at high
densities, significant progress has been made recently in constraining the
symmetry energy using data from terrestrial nuclear laboratories. These
constraints could provide useful information on the limits of GWs expected from
neutron stars. Here after briefly reviewing our previous work on constraining
gravitational radiation from elliptically deformed pulsars with terrestrial
nuclear laboratory data in light of the recent gravitational wave detection, we
estimate the maximum gravitational wave strain amplitude, using an optimistic
value for the breaking strain of the neutron star crust, for 15 pulsars at
distances 0.16 kpc to 0.91 kpc from Earth, and find it to be in the range of
$\sim[0.2-31.1]\times 10^{-24}$, depending on the details of the EOS used to
compute the neutron star properties. Implications are discussed. | nucl-th |
Isospin dependent kaon and antikaon optical potentials in dense hadronic
matter: Isospin effects on the optical potentials of kaons and antikaons in dense
hadronic matter are investigated using a chiral SU(3) model. These effects are
important for asymmetric heavy ion collision experiments. In the present work
the dispersion relations are derived for kaons and antikaons, compatible with
the low energy scattering data, within our model approach. The relations result
from the kaonic interactions with the nucleons, vector mesons and scalar mesons
in the asymmetric nuclear matter. The isospin asymmetry effects arising from
the interactions with the vector-isovector $\rho$- meson as well as the scalar
isovector $\delta$ mesons are considered. The density dependence of the isospin
asymmetry is seen to be appreciable for the kaon and antikaon optical
potentials. This can be particularly relevant for the future accelerator
facility FAIR at GSI, where experiments using neutron rich beams are planned to
be used in the study of compressed baryonic matter. | nucl-th |
Effets de structure dans la diffusion des ions lourds: Nous avons analyse les distributions angulaires de la diffusion elastique
pour differents systemes a des energies proches de la barriere de Coulomb au
moyen d'un potentiel semi phenomenologique. Les distributions radiales
calculees au moyen de ces potentiels montrent sans ambiguite qu'aux energies
proches de la barriere de Coulomb, l'absorption se produit dans un etroit
domaine de distances de la surface du potentiel nucleaire. Utilisant une
modelisation simple de la theorie de Feshbach du potentiel optique, nous avons
calcule la contribution a l'absorption due a un nombre reduit d'etats
collectifs de surface facilement excitables. L'inclusion d'un terme
d'absorption phenomenologique pour decrire des processus plus peripheriques que
les excitations inelastiques, nous a permis de reproduire de maniere
satisfaisante les distributions angulaires experimentales de la diffusion
elastique. Aux plus hautes energies (793 MeV et 1503 MeV), et pour le systeme
16O+208Pb, nous avons utilise un potentiel reel obtenu moyennant une
modelisation simple de la relation de dispersion et nous avons fait usage du
modele de fermeture propose par N. Vinh Mau pour calculer le terme d'absorption
du potentiel. Nos calculs a 793 MeV conduisent a des resultats identiques a
ceux obtenus avec les potentiels de reference. Par contre a 1503 MeV, les
calculs ne reproduisent pas convenablement les donnees experimentales indiquant
qu'a cette energie l'absorption n'est plus controlee par les seuls processus
collectifs. | nucl-th |
Core-excitation effects in three-body breakup reactions studied using
the Faddeev formalism: Previous studies of $(d,p)$ reactions in three-body (proton, neutron, nuclear
core) systems revealed a nontrivial effect of the core excitation: the transfer
cross section cannot be factorized into the spectroscopic factor and the
single-particle cross section obtained neglecting the core excitation. This
observable, up to a kinematic factor, is the angular distribution of the core
nucleus in the $(p,d)$ reaction. The study of the core excitation effect for
the most closely related observable in the $(p,pn)$ three-body breakup, i.e.,
the core angular distribution, is aimed in the present work. Breakup of the
one-neutron halo nucleus in the collision with the proton is described using
three-body Faddeev-type equations extended to include the excitation of the
nuclear core. The integral equations for transition operators are solved in the
momentum-space partial-wave representation. Breakup of 11Be nucleus as well as
of model $A=11$ $p$-wave nuclei is studied at beam energies of 30, 60, and 200
MeV per nucleon. Angular and momentum distributions for the 10Be core in ground
and excited states is calculated. In sharp contrast to $(p,d)$ reactions, the
differential cross section in most cases factorizes quite well into the
spectroscopic factor and the single-particle cross section. Due to different
reaction mechanisms the core excitation effect in the breakup is very different
from transfer reactions. A commonly accepted approach to evaluate the cross
section, i.e., the rescaling of single-particle model results by the
corresponding spectroscopic factor, appears to be reliable for breakup though
it fails in general for transfer reactions. | nucl-th |
Modeling Cluster Production at the AGS: Deuteron coalescence, during relativistic nucleus-nucleus collisions, is
carried out in a model incorporating a minimal quantal treatment of the
formation of the cluster from its individual nucleons by evaluating the overlap
of intial cascading nucleon wave packets with the final deuteron wave function.
In one approach the nucleon and deuteron center of mass wave packet sizes are
estimated dynamically for each coalescing pair using its past light-cone
history in the underlying cascade, a procedure which yields a parameter free
determination of the cluster yield. A modified version employing a global
estimate of the deuteron formation probability, is identical to a general
implementation of the Wigner function formalism but can differ from the most
frequent realisation of the latter. Comparison is made both with the extensive
existing E802 data for Si+Au at 14.6 GeV/c and with the Wigner formalism. A
globally consistent picture of the Si+Au measurements is achieved. In light of
the deuteron's evident fragility, information obtained from this analysis may
be useful in establishing freeze-out volumes and help in heralding the presence
of high-density phenomena in a baryon-rich environment. | nucl-th |
Validity of the one-body current for the calculation of form factors in
the point form of relativistic quantum mechanics: Form factors are calculated in the point form of relativistic quantum
mechanics for the lowest energy states of a system made of two scalar particles
interacting via the exchange of a massless boson. They are compared to the
exact results obtained by using solutions of the Bethe-Salpeter equation which
are well known in this case (Wick-Cutkosky model). Deficiencies of the
point-form approach together with the single-particle current are emphasised.
They point to the contribution of two-body currents which are required in any
case to fulfil current conservation. | nucl-th |
Latest results from lattice QCD for the Roper resonance: The present status of the Roper resonance in lattice QCD is reviewed. Some of
the latest lattice results are discussed with particular emphasis on a large
systematic error stemming from the finite size effect. These results suggest
that the Roper resonance can be described by the simple three quark excitation
of sizable extent. | nucl-th |
Complete inclusion of parity-dependent level densities in the
statistical description of astrophysical reaction rates: Microscopic calculations show a strong parity dependence of the nuclear level
density at low excitation energy of a nucleus. Previously, this dependence has
either been neglected or only implemented in the initial and final channels of
Hauser-Feshbach calculations. We present an indirect way to account for a full
parity dependence in all steps of a reaction, including the one of the compound
nucleus formed in a reaction. To illustrate the impact on astrophysical
reaction rates, we present rates for neutron captures in isotopic chains of Ni
and Sn. Comparing with the standard assumption of equipartition of both
parities, we find noticeable differences in the energy regime of astrophysical
interest caused by the parity dependence of the nuclear level density found in
the compound nucleus even at sizeable excitation energies. | nucl-th |
Scaling within the Spectral Function approach: Scaling features of the nuclear electromagnetic response functions unveil
aspects of nuclear dynamics that are crucial for interpretating neutrino- and
electron-scattering data. In the large momentum-transfer regime, the
nucleon-density response function defines a universal scaling function, which
is independent of the nature of the probe. In this work, we analyze the
nucleon-density response function of $^{12}$C, neglecting collective
excitations. We employ particle and hole spectral functions obtained within two
distinct many-body methods, both widely used to describe electroweak reactions
in nuclei. We show that the two approaches provide compatible nucleon-density
scaling functions that for large momentum transfers satisfy first-kind scaling.
Both methods yield scaling functions characterized by an asymmetric shape,
although less pronounced than that of experimental scaling functions. This
asymmetry, only mildly affected by final state interactions, is mostly due to
nucleon-nucleon correlations, encoded in the continuum component of the hole
SF. | nucl-th |
Algebraic treatment of the hyper-Coulomb problem: A completely algebraic treatment of the six-dimensional hypercoulomb problem
is discussed in terms of an oscillator realization of the dynamical algebra of
SO(7,2). Closed expressions are derived for the energy spectrum and form
factors. | nucl-th |
Correlated $\bbox{πρ}$ Exchange in the $\bbox{NN}$ Interaction: We evaluate the contribution to the nucleon-nucleon interaction due to
correlated $\pi\rho$ exchange in the $\pi$, $\omega$, and $A_1$/$H_1$ channels
by means of dispersion-theoretic methods based on a realistic meson exchange
model for the interaction between $\pi$ and $\rho$ mesons. These processes have
substantial effects: In the pionic channel it counterbalances the suppression
generated by a soft $\pi NN$ form factor of monopole type with a cutoff mass of
about 1 GeV; in the $\omega$-channel it provides nearly half of the empirical
repulsion, leaving little room for explicit quark-gluon effects. | nucl-th |
${\barΛ}/{\bar p}$ ratios in heavy ion collisions at 11.6 AGeV/c: We attempt to explain the ${\bar \Lambda}/\bar p$ ratios measured in heavy
ion collisions at $11.6~{\rm A\cdot GeV}/c$ beam momentum within a hadronic
framework. This ratio is enhanced relative to corresponding ratios in $pp$
collisions, and is large when compared with thermal fits to heavy ion data.
Using a detailed cascade calculation, we show that different annihilation
cross--sections of $\bar \Lambda$'s and $\bar p$'s, and the net conversion of
$\bar p$'s to $\bar \Lambda$'s, do not account for the enhancement in central
collisions. For larger impact parameters, however, hadronic mechanisms may well
suffice to produce the observed enhancement. Uncertainties in elementary
cross--sections and formation times are considered. | nucl-th |
Parity-Dependence in the Nuclear Level Density: Astrophysical reaction rates are sensitive to the parity distribution at low
excitation energies. We combine a formula for the energy-dependent parity
distribution with a microscopic-macroscopic nuclear level density. This
approach describes well the transition from low excitation energies, where a
single parity dominates, to high excitations where the two densities are equal. | nucl-th |
$\bar K^*$ meson in dense matter: We study the properties of $\bar K^*$ mesons in nuclear matter using a
unitary approach in coupled channels within the framework of the local hidden
gauge formalism and incorporating the $\bar K \pi$ decay channel in matter. The
in-medium $\bar K^* N$ interaction accounts for Pauli blocking effects and
incorporates the $\bar K^*$ self-energy in a self-consistent manner. We also
obtain the $\bar K^*$ (off-shell) spectral function and analyze its behaviour
at finite density and momentum. At normal nuclear matter density, the $\bar
K^*$ meson feels a moderately attractive potential while the $\bar K^*$ width
becomes five times larger than in free space. We estimate the transparency
ratio of the $\gamma A \to K^+ K^{* -} A^\prime$ reaction, which we propose as
a feasible scenario at present facilities to detect the changes of the
properties of the $\bar K^*$ meson in the nuclear medium. | nucl-th |
Asymmetry in the neutrino and anti-neutrino reactions in a nuclear
medium: We study the effect of the density-dependent axial and vector form factors on
the electro-neutrino ($\nu_e$) and anti-neutrino $({\bar \nu}_e)$ reactions for
a nucleon in nuclear matter or in $^{12}$C. The nucleon form factors in free
space are presumed to be modified for a bound nucleon in a nuclear medium. We
adopt the density-dependent form factors calculated by the quark-meson coupling
(QMC) model, and apply them to the $\nu_e$ and ${\bar \nu}_e$ induced reactions
with the initial energy $E = $ 8 $\sim$ 80 MeV. We find that the total
${\nu}_e$ cross sections on $^{12}$C as well as a nucleon in nuclear matter are
reduced by about 5% at the nuclear saturation density, $\rho_0$. This reduction
is caused by the modification of the nucleon structure in matter. Although the
density effect for both cases is relatively small, it is comparable with the
effect of Coulomb distortion on the outgoing lepton in the $\nu$-reaction. In
contrast, the density effect on the ${\bar \nu}_e$ reaction reduces the cross
section significantly in both nuclear matter and $^{12}$C cases, and the amount
maximally becomes of about 35% around $\rho_0$. Such large asymmetry in the
$\nu_e$ and ${\bar \nu}_e$ cross sections, which seems to be nearly independent
of the target, is originated from the difference in the helicities of ${\bar
\nu}_e$ and ${\nu}_e$. It is expected that the asymmetry influences the
r-process and also the neutrino-process nucleosynthesis in core-collapse
supernovae. | nucl-th |
Mean Field Effect on J/ψProduction in Heavy Ion Collisions: The mean field effect in quark-gluon plasma on J/\psi production in heavy ion
collisions is perturbatively calculated in a transport approach. While the
global nuclear modification factor R_{AA} is not sensitive to the mean field,
the reduced threshold for J/\psi regeneration leads to a significant
enhancement of R_{AA} at low transverse momentum at RHIC and LHC energies. | nucl-th |
Comparison of GiBUU calculations with MiniBooNE pion production data: Background. Neutrino-induced pion production can give important informationon
the axial coupling to nucleon resonances. Furthermore, pion production
represents a major background to quasielastic-like events. Single pion
production data from the MiniBooNE in charged current neutrino scattering in
mineral oil appeared higher than expected within conventional theoretical
approaches.
Purpose. We aim to investigate which model parameters affect the calculated
cross section and how they do this.
Method. The Giessen Boltzmann--Uehling--Uhlenbeck (GiBUU) model is used for
an investigation of neutrino-nucleus reactions.
Results. Presented are integrated and differential cross sections for 1\pi^+
and 1\pi^0 production before and after final state interactions in comparison
with the MiniBooNE data.
Conclusions. For the MiniBooNE flux all processes (QE, 1\pi-background,
\Delta, higher resonance production, DIS) contribute to the observed final
state with one pion of a given charge. The uncertainty in elementary pion
production cross sections leads to a corresponding uncertainty in the nuclear
cross sections. Final state interactions change the shape of the muon-related
observables only slightly, but they significantly change the shape of pion
distributions. | nucl-th |
A theoretical approach to study J/$Ψ$ suppression in relativistic
heavy ion collisions: With a view to understanding J/$\Psi$ suppression in relativistic heavy ion
collisions, we compute the suppression rate within the framework of
hydrodynamical evolution model. For this, we consider an ellipsoidal flow and
use an ansatz for temperature profile function which accounts for time and the
three dimensional space evolution of the quark-gluon plasma. We have calculated
the survival probability separately as the function of transverse and
longitudinal momentum. We have shown that previous calculations are special
cases of this model. | nucl-th |
Separability of a Low-Momentum Effective Nucleon-Nucleon Potential: A realistic nucleon-nucleon potential is transformed into a low-momentum
effective one (LMNN) using the Okubo theory. The separable potentials are
converted from the LMNN with a universal separable expansion method and a
simple Legendre expansion. Through the calculation of the triton binding
energies, the separability for the convergence of these ranks is evaluated. It
is found that there is a tendency for the lower momentum cutoff parameter
$\Lambda$ of LMNN to gain good separability. | nucl-th |
Hydrodynamic fluctuations and two-point correlations: We examine correlations of energy density induced by initial state
fluctuations, which are localized in both transverse and longitudinal extent.
The hotspots are evolved according to hydrodynamics in a background which
includes radial flow. Two-point energy density correlations from these hotspots
are computed as a function of the difference in azimuthal angle and rapidity.
Such localized perturbations occur naturally in the theory of hydrodynamic
fluctuations and may provide insight into some features of the two-particle
correlation data from RHIC and the LHC. | nucl-th |
Superfluid neutron matter in the s-channel exchange nucleon-nucleon
interaction models: The superfluid pairing gap of neutron matter is calculated in the framework
of Quark Compound Bag model with nucleon-nucleon interactions generated by the
s-channel exchange of Jaffe-Low primitives (6-quark states). | nucl-th |
Quasinormal modes of scalar field coupled to Einstein's tensor in the
non-commutative geometry inspired black hole: We investigate the quasinormal modes (QNMs) of the scalar field coupled to
the Einstein's tensor in the non-commutative geometry inspired black hole
spacetime. It is found that the lapse function of the non-commutative black
hole metric can be represented by a Kummer's confluent hypergeometric function,
which can effectively solve the problem that the numerical results of the QNMs
are sensitive to the model parameters and make the QNMs values more reliable.
We make a careful analysis of the scalar QNM frequencies by using several
numerical methods, and find that the numerical results obtained by the new WKB
method (the Pad\'e approximants) and the Mashhoon method
(P$\ddot{\text{o}}$schl-Teller potential method) are quite different from those
obtained by the asymptotic iterative method (AIM) and time-domain integration
method when the non-commutative parameter $\theta$ and coupling parameter
$\eta$ are large. The most obvious difference is that the numerical results
obtained by the AIM and the time-domain integration method appear a critical
value $\eta_c$ with an increase of $\eta$, which leads to the dynamical
instability. After carefully analyzing the numeral results, we conclude that
the numerical results obtained by the AIM and the time-domain integration
method are closer to the theoretical values than those obtained by the WKB
method and the Mashhoon method, when the $\theta$ and $\eta$ are large.
Moreover, through a numerical fitting, we obtain that the functional
relationship between the threshold $\eta_c$ and the non-commutative parameter
$\theta$ satisfies $\eta_{c}=a\theta^{b}+c$ for a fixed $l$ approximately. We
find that the stability of dynamics can be ensured in the $\eta<\eta_c(\theta,
l)$ region. | nucl-th |
Flow Coefficients and Jet Characteristics in Heavy Ion Collisions: Identifying jets in heavy ion collisions is of significant interest since the
properties of jets are expected to get modified because of the formation of
quark gluon plasma. The detection of jets is, however, difficult because of
large number of non-jet hadrons produced in the collision process. In this work
we propose a method of identifying a jet and determining its transverse
momentum by means of flow analysis. This has been done an event-by-event basis. | nucl-th |
Hadron Physics from the Global Color Model of QCD: We review recent progress in modeling the quark-gluon content of mesons and
their low-energy interactions through the Global Color Model field theory. An
emphasis is placed on techniques that are shared with the approach based on
truncations of the Dyson-Schwinger equations of QCD. In contrast to most other
field theory models for QCD degrees of freedom in hadron physics, this approach
directly deals with the derived intrinsic space-time extent of the meson modes
in their role as field variables and can accommodate confinement as well as
dynamical breaking of chiral symmetry. Various theoretical techniques and
approximations found useful in this approach are described. Selected
applications reviewed here include the properties and interactions of the
Goldstone bosons, interaction vertex functions, low energy chiral observables,
electromagnetic interactions and form factors, and transition form factors.
Some initial considerations of Vector Meson Dominance and pion loop processes
are discussed. | nucl-th |
Surface-integral formalism of deuteron stripping: The purpose of this paper is to develop an alternative theory of deuteron
stripping to resonance states based on the surface integral formalism of
Kadyrov et al. [Ann. Phys. 324, 1516 (2009)] and continuum-discretized coupled
channels (CDCC).
First we demonstrate how the surface integral formalism works in the
three-body model and then we consider a more realistic problem in which a
composite structure of target nuclei is taken via optical potentials. We
explore different choices of channel wave functions and transition operators
and show that a conventional CDCC volume matrix element can be written in terms
of a surface-integral matrix element, which is peripheral, and an auxiliary
matrix element, which determines the contribution of the nuclear interior over
the variable $r_{nA}$. This auxiliary matrix element appears due to the
inconsistency in treating of the $n-A$ potential: this potential should be real
in the final state to support bound states or resonance scattering and complex
in the initial state to describe $n-A$ scattering. Our main result is
formulation of the theory of the stripping to resonance states using the prior
form of the surface integral formalism and CDCC method. It is demonstrated that
the conventional CDCC volume matrix element coincides with the surface matrix
element, which converges for the stripping to the resonance state. Also the
surface representation (over the variable $r_{nA}$ of the stripping matrix
element enhances the peripheral part of the amplitude although the internal
contribution doesn't disappear and increases with increase of the deuteron
energy. We present calculations corroborating our findings for both stripping
to the bound state and the resonance. | nucl-th |
Spin-tensor decomposition of nuclear transition matrix elements for
neutrinoless double-$β$ decay of $^{76}$Ge and $^{82}$Se nuclei within
PHFB approach: Employing the PHFB model, nuclear transition matrix elements $M^{\left(
K\right) }$ for the neutrinoless double-$\beta^{-} $ decay of $\ ^{76}$Ge and
$^{82}$Se isotopes are calculated within mechanisms involving light as well as
heavy Majorana neutrinos, and classical Majorons by considering the spin-tensor
decomposition of realistic KUO and empirical JUN45 effective two-body
interaction. It is noticed that the effects due to the SRC on NTMEs $M^{\left(
0\nu \right) }$ and $M^{\left( 0N\right) }$ due to the exchange of light and
heavy Majorana neutrinos, respectively, is maximally incorporated by the
central part of the effective two-body interaction, which varies by a small
amount with the inclusion of spin-orbit and tensor components. The maximum
uncertainty in the average NTMEs $\overline{M}^{(0\nu)}$ and
$\overline{M}^{(0N)}$ turns out to be about 10\% and 37\%, respectively. | nucl-th |
Specific features and symmetries for magnetic and chiral bands in nuclei: Magnetic and chiral bands have been a hot subject for more than twenty years.
Therefore, quite large volumes of experimental data as well as theoretical
descriptions have been accumulated. Although some of the formalisms are not so
easy to handle, the results agree impressively well with the data. The
objective of this paper is to review the actual status of both experimental and
theoretical investigations. Aiming at making this material accessible to a
large variety of readers, including young students and researchers, I gave some
details on the schematic models which are able to unveil the main features of
chirality in nuclei. Also, since most formalisms use a rigid triaxial rotor for
the nuclear system's core, I devoted some space to the semi-classical
description of the rigid triaxial as well as of the tilted triaxial rotor. In
order to answer the question whether the chiral phenomenon is spread over the
whole nuclear chart and whether it is specific only to a certain type of
nuclei, odd-odd, odd-even or even-even, the current results in the mass regions
of $A\sim 60,80,100,130,180,200$ are briefly described for all kinds of
odd/even-odd/even systems. The chiral geometry is a sufficient condition for a
system of proton-particle, neutron-hole and a triaxial rotor to have the
electromagnetic properties of chiral bands. In order to prove that such
geometry is not unique for generating magnetic bands with chiral features, I
presented a mechanism for a new type of chiral bands. One tries to underline
the fact that this rapidly developing field is very successful in pushing
forward nuclear structure studies. | nucl-th |
Partonic effects on the elliptic flow at relativistic heavy ion
collisions: The elliptic flow in heavy ion collisions at RHIC is studied in a multiphase
transport model. By converting the strings in the high energy density regions
into partons, we find that the final elliptic flow is sensitive to the parton
scattering cross section. To reproduce the large elliptic flow observed in
Au+Au collisions at $\sqrt s=130A$ GeV requires a parton scattering cross
section of about 6 mb. We also study the dependence of the elliptic flow on the
particle multiplicity, transverse momentum, and particle mass. | nucl-th |
Parity violation and dynamical relativistic effects in $(\vec{e},e'N)$
reactions: It is well known that coincidence quasielastic $(\vec{e},e'N)$ reactions are
not appropriate to analyze effects linked to parity violation due the presence
of the fifth electromagnetic (EM) response $R^{TL'}$. Nevertheless, in this
work we develop a fully relativistic approach to be applied to parity-violating
(PV) quasielastic $(\vec{e},e'N)$ processes. This is of importance as a
preliminary step in the subsequent study of inclusive quasielastic PV
$(\vec{e},e')$ reactions. Moreover, our present analysis allows us to
disentangle effects associated with the off-shell character of nucleons in
nuclei, gauge ambiguities and the role played by the lower components in the
nucleon wave functions, i.e., dynamical relativistic effects. This study can
help in getting clear information on PV effects. Particular attention is paid
to the relativistic plane-wave impulse approximation where the explicit
expressions for the PV single-nucleon responses are shown for the first time. | nucl-th |
Production of multi-strangeness hypernuclei and the YN-interaction: We investigate for the first time the influence of hyperon-nucleon (YN)
interaction models on the strangeness dynamics of antiproton- and $\Xi$-nucleus
interactions. Of particular interest is the formation of bound
multi-strangeness hypermatter in reactions relevant for \panda. The main
features of two well-established microscopic approaches for YN-scattering are
first discussed and their results are then analysed such that they can be
applied in transport-theoretical simulations. The transport calculations for
reactions induced by antiproton beams on a primary target including also the
secondary cascade beams on a secondary target show a strong sensitivity on the
underlying YN-interaction. In particular, we predict the formation of
$\Xi$-hypernuclei with an observable sensitivity on the underlying
$\Xi$N-interaction. We conclude the importance of our studies for the
forthcoming research plans at FAIR. | nucl-th |
Comment on "Neutron Skin of $^{208}$Pb from Coherent Pion
Photoproduction": We argue that the reaction mechanism for the coherent pion production is not
known with sufficient accuracy to determine the neutron radius of 208Pb to the
claimed precision of 0.03 fm. | nucl-th |
A microscopic rotational cranking model and its connection to
conventional cranking and other collective rotational models: A microscopic time-reversal invariant cranking model (MCRM) for nuclear
collective rotation about a single axis and its coupling to intrinsic motion is
derived. The MCRM is derived by transforming the stationary nuclear Schrodinger
equation using a collective rotation-intrinsic product wavefunction, imposing
no constraints on the wavefunction and the nucleon coordinates, and using no
relative co-ordinates. The derivatives of the collective-rotation angle are
defined in terms of a combination of rigid and irrotational collective flows of
the nucleons. The collective wavefunction is chosen to be an eigenstate of the
angular momentum, yielding a MCRM Schrodinger equation for the intrinsic
wavefunction that contains a cranking Coriolis energy term that is linear in
the angular momentum and shear operators, a collective centrifugal energy term,
and a rotation-fluctuation energy term. In absence of the irrotational-flow
component and fluctuation energy term, the MCRM equation reduces to that of the
conventional cranking model (CCRM), but with a dynamic rigid-flow angular
velocity and rigid-flow centrifugal-energy term. The expectation of the angular
momentum operator, which is the sum of the collective rotation angular momentum
and the expectation of the angular momentum in the intrinsic state, would
reduce to that in the CCRM if the collective rotation angular momentum were
small. However, it is shown that, even for the simple case of the anisotropic
harmonic oscillator mean-field potential in , the collective rotation angular
momentum is not small in the current version of the MCRM, and that this problem
needs further study. It is also shown that the MCRM Schrodinger equation is
reducible to the equations of the particle-plus-rotor, phenomenological and
microscopic collective rotation-vibration, and two-fluid semi-classical
collective models. | nucl-th |
Description of electromagnetic and favored $α$-transitions in heavy
odd-mass nuclei: We describe electromagnetic and favored \alpha-transitions to rotational
bands in odd-mass nuclei built upon a single particle state with angular
momentum projection $\Omega=\frac{1}{2}$ in the region $88 \le Z \le 98$. We
use the particle coupled to an even-even core approach described by the
Coherent State Model (CSM) and the coupled channels method to estimate partial
$\alpha$-decay widths. We reproduce the energy levels of the rotational band
where favored $\alpha$-transitions occur for 26 nuclei and predict B (E2)
values for electromagnetic transitions to the bandhead using a deformation
parameter and a Hamiltonian strength parameter for each nucleus, together with
an effective collective charge depending linearly on the deformation parameter.
Where experimental data is available, the contribution of the single particle
effective charge to the total B (E2) value is calculated. The Hamiltonian
describing the $\alpha$- nucleus interaction contains two terms, a spherically
symmetric potential given by the double-folding of the M3Y nucleon-nucleon
interaction plus a repulsive core simulating the Pauli principle and a
quadrupole-quadrupole (QQ) interaction. The $\alpha$-decaying state is
identified as a narrow outgoing resonance in this potential. The intensity of
the transition to the first excited state is reproduced by the QQ coupling
strength. It depends linearly both on the nuclear deformation and the square of
the reduced width for the decay to the bandhead, respectively. Predicted
intensities for transitions to higher excited states are in a reasonable
agreement with experimental data. This formalism offers a unified description
of energy levels, electromagnetic and favored $\alpha$-transitions for known
heavy odd-mass $\alpha$-emitters. | nucl-th |
Lambda collective flow in heavy ion reactions: Collective flow of Lambda hyperons in heavy ion reactions at SIS energies is
investigated. It is found that a $\Lambda$ mean field constructed on the basis
of the quark model leads to a good description of the experimental data of the
in-plane transverse flow of $\Lambda$'s. The attractive mean field can also
give rise to an additional "virtual" $\Lambda$ radial flow directed inwards,
which is reflected by a "concave" structure of the transverse mass spectrum of
the $\Lambda$ hyperons emitted at midrapidity. The $\Lambda$ radial flow is
found to exhibit a strong mass dependence: The flow is visible in the Ni+Ni
system, but is strongly reduced in the system of Au on Au. | nucl-th |
One-body Langevin dynamics in heavy-ion collisions at intermediate
energies: We present a new framework to treat the dissipation and fluctuation dynamics
associated with nucleon-nucleon scattering in heavy-ion collisions. The
two-body collision processes are effectively described in terms of the
diffusion of nucleons in viscous nuclear media, governed by a set of Langevin
equations in momentum space. The new framework combined with the usual mean
field dynamics can be used to simulate heavy-ion collisions at intermediate
energies. As a proof of principle, we simulate Au + Au reactions and obtain
results consistent with other existing codes under the same constrained
conditions. We also study the formation of fragments in Sn + Sn reactions at 50
MeV/nucleon, and results are discussed and compared with two other models
commonly employed for collisions. | nucl-th |
Reaction Operator Approach to Non-Abelian Energy Loss: A systematic expansion of the induced inclusive gluon radiation associated
with jet production in a dense QCD plasma is derived using a reaction operator
formalism. Analytic expressions for the transverse momentum and light-cone
momentum distributions are derived to all orders in powers of the gluon opacity
of the medium, $N\sigma_g/A=L/\lambda_g$. The reaction operator approach also
leads to a simple algebraic proof of the ``color triviality'' of single
inclusive distributions and to a solvable set of recursion relations. The
analytic solution generalizes previous continuum solutions (BDMPS) for
applications to mesoscopic QCD plasmas. The solution is furthermore not
restricted to uncorrelated geometries and allows for evolving screening scales
as well as the inclusion of finite kinematic constraints. The later is
particularly important because below LHC energies the kinematic constraints
significantly decrease the non-abelian energy loss. Our solution for the
inclusive distribution also generalizes the finite order exclusive (tagged)
distribution case studied previously (GLV1). The form of the analytic solution
is well suited for numerical implementation in Monte Carlo event generators to
enable more accurate calculations of jet quenching in ultra-relativistic
nuclear collisions. Numerical results illustrating the constributions of the
first three orders in opacity are compared to the ``self-quenching'' hard
radiation intensity. A surprising result is that the induced gluon radiation
intensity is dominated by the (quadratic in $L$) first order opacity
contribution for realistic geometries and jet energies in nuclear collisions. | nucl-th |
Calculation Energy levels and charge radius for odd $^{41-49}$Ca
Isotopes by using the analytical approach: In the present study, some static properties of odd isotopes of Ca were
investigated in the non-relativistic shell model. We also suggested a novel
suitable local potential model for the non-microscopic investigation of the
mentioned nuclei. We modeled the odd $^{41-49}$Ca nuclei as doubly-magic
isotopes, with further nucleons (valence) in the lf7/2 and 2p3/2 levels. Then
the modified Eckart potential as well as Hulthen potential were chosen for the
interaction between core and nucleons. We also used the Parametric Nikiforov
Uvarov method to calculate the values of energy, the radius of charge and wave
function. The obtained results showed a good agreement with the experimental
data, so this model is applicable for the similar nuclei. | nucl-th |
Semiempirical Shell Model Masses with Magic Number Z = 126 for
Superheavy Elements: A semiempirical shell model mass equation applicable to superheavy elements
up to Z = 126 is presented and shown to have a high predictive power. The
equation is applied to the recently discovered superheavy nuclei Z = 118, A =
293 and Z = 114, A = 289 and their decay products. | nucl-th |
Collective Hamiltonian for chiral modes: A collective model is proposed to describe the chiral rotation and vibration
and applied to a system with one $h_{11/2}$ proton particle and one $h_{11/2}$
neutron hole coupled to a triaxial rigid rotor. The collective Hamiltonian is
constructed from the potential energy and mass parameter obtained in the tilted
axis cranking approach. By diagonalizing the collective Hamiltonian with a box
boundary condition, it is found that for the chiral rotation, the partner
states become more degenerate with the increase of the cranking frequency, and
for the chiral vibrations, their important roles for the collective excitation
are revealed at the beginning of the chiral rotation region. | nucl-th |
Application of the Kerman-Klein method to the solution of a spherical
shell model for a deformed rare-earth nucleus: Core-particle coupling models are made viable by assuming that core
properties such as matrix elements of multipole and pairing operators and
excitation spectra are known independently. From the completeness relation, it
is seen, however, that these quantities are themselves algebraic functions of
the calculated core-particle amplitudes. For the deformed rare-earth nucleus
158Gd, we find that these sum rules are well-satisfied for the ground state
band, implying that we have found a self-consistent solution of the non-linear
Kerman-Klein equations. | nucl-th |
Variational Monte Carlo study of pentaquark states in a correlated quark
model: Accurate numerical solution of the five-body Schrodinger equation is effected
via variational Monte Carlo in a correlated quark model. The spectrum is
assumed to exhibit a narrow resonance with strangeness S=+1. A fully
antisymmetrized and pair-correlated five-quark wave function is obtained for
the assumed non-relativistic Hamiltonian which has spin, isospin, and color
dependent pair interactions and many-body confining terms which are fixed by
the non-exotic spectra. Gauge field dynamics are modeled via flux tube exchange
factors. The energy determined for the ground states with spin-parity 1/2-
(1/2+) is 2.22 GeV (2.50 GeV). A lower energy negative parity state is
consistent with recent lattice results. | nucl-th |
A unified approach for nucleon knock-out, coherent and incoherent pion
production in neutrino interactions with nuclei: We present a theory of neutrino interactions with nuclei aimed at the
description of the partial cross-sections, namely quasi-elastic and
multi-nucleon emission, coherent and incoherent single pion production. For
this purpose, we use the theory of nuclear responses treated in the random
phase approximation, which allows a unified description of these channels. It
is particularly suited for the coherent pion production where collective
effects are important whereas they are moderate in the other channels. We also
study the evolution of the neutrino cross-sections with the mass number from
carbon to calcium. We compare our approach to the available neutrino
experimental data on carbon. We put a particular emphasis on the multi-nucleon
channel, which at present is not easily distinguishable from the quasi-elastic
events. This component turns out to be quite relevant for the interpretation of
experiments (K2K, MiniBooNE, SciBooNE). It can account in particular for the
unexpected behavior of the quasi-elastic cross-section. | nucl-th |
A Study of Charge Radii and Neutron Skin Thickness near Nuclear Drip
Lines: We studied the charge radius, rms radius and neutron skin thickness $\Delta
r_{np}$ in even-even isotopes of Si, S, Ar and Ca and isotones of N =20, 28, 50
and 82. The $\Delta r_{np}$ in doubly-magic $^{48}$Ca, $^{68}$Ni,
$^{120,132}$Sn and $^{208}$Pb nuclei has also been calculated. Theoretical
calculations are done with the Hartree-Fock-Bogoliubov theory with the
effective Skyrme interactions. Calculated theoretical estimates are in good
agreement with the recently available experimental data. The charge radii for
Si, S, Ar and Ca isotopes is observed to be minimum at neutron number N =14.
The theoretically computed results with UNEDF0 model parameterization of
functional are reasonably reproducing the experimental data for $\Delta r_{np}$
in $^{48}$Ca, $^{68}$Ni and $^{120,132}$Sn. The energy density functional of
UNEDF1 model provides much improved result of $\Delta r_{np}$ for $^{208}$Pb. | nucl-th |
Solutions of the Faddeev-Yakubovsky equations for the four nucleons
scattering states: The Faddeev-Yakubowsky equations in configuration space have been solved for
the four nucleon system. The results with an S-wave interaction model in the
isospin approximation are presented. They concern the bound and scattering
states below the first three-body threshold. The elastic phase-shifts for the
N+NNN reaction in different ($S,T$) channels are given and the corresponding
low energy expansions are discussed. Particular attention is payed to the n+t
elastic cross section. Its resonant structure is well described in terms of a
simple NN interaction. First results concerning the S-matrix for the coupled
N+NNN-NN+NN channels and the strong deuteron-deuteron scattering length are
obtained. | nucl-th |
Solution of the Skyrme-Hartree-Fock-Bogolyubov equations in the
Cartesian deformed harmonic-oscillator basis. (VI) HFODD (v2.38j): a new
version of the program: We describe the new version (v2.38j) of the code HFODD which solves the
nuclear Skyrme-Hartree-Fock or Skyrme-Hartree-Fock-Bogolyubov problem by using
the Cartesian deformed harmonic-oscillator basis. In the new version, we have
implemented: (i) projection on good angular momentum (for the Hartree-Fock
states), (ii) calculation of the GCM kernels, (iii) calculation of matrix
elements of the Yukawa interaction, (iv) the BCS solutions for state-dependent
pairing gaps, (v) the HFB solutions for broken simplex symmetry, (vi)
calculation of Bohr deformation parameters, (vii) constraints on the Schiff
moments and scalar multipole moments, (viii) the D2h transformations and
rotations of wave functions, (ix) quasiparticle blocking for the HFB solutions
in odd and odd-odd nuclei, (x) the Broyden method to accelerate the
convergence, (xi) the Lipkin-Nogami method to treat pairing correlations, (xii)
the exact Coulomb exchange term, (xiii) several utility options, and we have
corrected two insignificant errors. | nucl-th |
Collective flow and two-pion correlations from a relativistic
hydrodynamic model with early chemical freeze out: We investigate the effect of early chemical freeze-out on radial flow,
elliptic flow and HBT radii by using a fully three dimensional hydrodynamic
model. When we take account of the early chemical freeze-out, the space-time
evolution of temperature in the hadron phase is considerably different from the
conventional model in which chemical equilibrium is always assumed. As a
result, we find that radial and elliptic flows are suppressed and that the
lifetime and the spatial size of the fluid are reduced. We analyze the p_t
spectrum, the differential elliptic flow, and the HBT radii at the RHIC energy
by using hydrodynamics with chemically non-equilibrium equation of state. | nucl-th |
Two-particle spatial correlations in superfluid nuclei: We discuss the effect of pairing on two-neutron space correlations in
deformed nuclei. The spatial correlations are described by the pairing tensor
in coordinate space calculated in the HFB approach. The calculations are done
using the D1S Gogny force. We show that the pairing tensor has a rather small
extension in the relative coordinate, a feature observed earlier in spherical
nuclei. It is pointed out that in deformed nuclei the coherence length
corresponding to the pairing tensor has a pattern similar to what we have found
previously in spherical nuclei, i.e., it is maximal in the interior of the
nucleus and then it is decreasing rather fast in the surface region where it
reaches a minimal value of about 2 fm. This minimal value of the coherence
length in the surface is essentially determined by the finite size properties
of single-particle states in the vicinity of the chemical potential and has
little to do with enhanced pairing correlations in the nuclear surface. It is
shown that in nuclei the coherence length is not a good indicator of the
intensity of pairing correlations. This feature is contrasted with the
situation in infinite matter. | nucl-th |
Antiproton-deuteron annihilation at low energies: Recent experimental studies of the antiproton-deuteron system at low energies
have shown that the imaginary part of the antiproton-deuteron scattering length
is smaller than the antiproton-proton one. Two- and three-body systems with
strong annihilation are investigated and a mechanism explaining this unexpected
relation between the imaginary parts of the scattering lengths is proposed. | nucl-th |
Resolving the plasma profile via differential single inclusive
suppression: The ability of experimental signatures to resolve the spatio-temporal profile
of an expanding quark gluon plasma is studied. In particular, the single
inclusive suppression of high momentum hadrons versus the centrality of a
heavy-ion collision and with respect to the reaction plane in non-central
collisions is critically examined. Calculations are performed in the higher
twist formalism for the modification of the fragmentation functions. Radically
different nuclear geometries are used. The influence of different initial gluon
distributions as well as different temporal evolution scenarios on the single
inclusive suppression of high momentum pions are outlined. It is demonstrated
that the modification versus the reaction plane is quite sensitive to the
initial spatial density. Such sensitivity remains even in the presence of a
strong elliptic flow. | nucl-th |
Energy dependence of fission-fragment neutron multiplicity in
$^{235}\textrm{U}(n,f)$: A consistent framework for treating the energy dependence of fission-fragment
neutron multiplicities is presented. The shape evolution of the compound
nucleus towards scission is treated in the strong damping limit using the
Metropolis walk method. The available excitation energy at scission is then
divided statistically between the two fragments using microscopic level
densities. Deformation energies, which contribute to the excitation energy when
the fragments relax to their ground-state shapes, are also computed. From the
total fragment excitation energies, the number of emitted neutrons is obtained
and illustrated for neutron-induced fission of $^{235}\textrm{U}$. | nucl-th |
Cluster radioactivity of Th isotopes in the mean-field HFB theory: Cluster radioactivity is described as a very mass asymmetric fission process.
The reflection symmetry breaking octupole moment has been used in a mean field
HFB theory as leading coordinate instead of the quadrupole moment usually used
in standard fission calculations. The procedure has been applied to the study
of the ``very mass asymmetric fission barrier'' of several even-even Thorium
isotopes. The masses of the emitted clusters as well as the corresponding
half-lives have been evaluated on those cases where experimental data exist. | nucl-th |
Nuclear structure and decay properties of even-even nuclei in $Z=70-80$
drip-line region: We study nuclear structure properties for various isotopes of Ytterbium (Yb),
Hafnium(Hf), Tungsten(W), Osmium(Os), Platinum(Pt) and Mercury(Hg) in $Z = 70 -
80$ drip-line region starting from $N =80$ to $N=170$ within the formalism of
relativistic mean field (RMF) theory. The pairing correlation is taken care by
using BCS approach. We compared our results with Finite Range Droplet
Model(FRDM) and experimental data and found that the calculated results are in
good agreement. Neutron shell closure are obtained at $N=82$ and $126$ in this
region. We have also studied probable decay mechanisms of these elements. | nucl-th |
Anharmonic double-$γ$ vibrations in nuclei and their description in
the interacting boson model: Double-$\gamma$ vibrations in deformed nuclei are studied in the context of
the interacting boson model with special reference to their anharmonic
character. It is shown that large anharmonicities can be obtained with
interactions that are (at least) of three-body nature between the bosons. As an
example the $\gamma$ vibrations of the nucleus
$^{166}_{\phantom{0}68}$Er$^{\phantom{00}}_{98}$ are studied in detail. | nucl-th |
Hadronic resonance production and interaction in partonic and hadronic
matter in EPOS3 with and without the hadronic afterburner UrQMD: We study the production of hadronic resonances and their interaction in the
partonic and hadronic medium using the EPOS3 model, which employs the UrQMD
model for the description of the hadronic phase. We investigate the centrality
dependence of the yields and momentum distributions for various resonances
(rho(770),K(892),phi(1020),Delta(1232),Sigma(1385),Lambda(1520),Xi(1530) and
their antiparticles) in Pb-Pb collisions at sNN= 2.76 TeV. The predictions for
K(892) and phi(1020) will be compared with the experimental data from the ALICE
collaboration. The observed signal suppression of the K(892) with increasing
centrality will be discussed with respect to the resonance interaction in the
hadronic medium. The mean transverse momentum and other particle ratios such as
phi(1020)/p and Omega/phi(1020) will be discussed with respect to additional
contributions from the hadronic medium interactions. | nucl-th |
Nuclear energy density functional from chiral pion-nucleon dynamics: We calculate the nuclear energy density functional relevant for N=Z even-even
nuclei in the systematic framework of chiral perturbation theory. The
calculation includes the one-pion exchange Fock diagram and the iterated
one-pion exchange Hartree and Fock diagrams. From these few leading order
contributions in the small momentum expansion one obtains already a very good
equation of state of isospin symmetric nuclear matter. We find that in the
region below nuclear matter saturation density the effective nucleon mass
$\widetilde M^*(\rho)$ deviates by at most 15% from its free space value $M$,
with $0.89M<\widetilde M^*(\rho)<M$ for $\rho < 0.11 {\rm fm}^{-3}$ and
$\widetilde M^*(\rho)>M$ for higher densities. The parameterfree strength of
the $(\vec\nabla \rho)^2$-term, $F_\nabla(k_f)$, is at saturation density
comparable to that of phenomenological Skyrme forces. The magnitude of
$F_J(k_f)$ accompanying the squared spin-orbit density $\vec J ^2$ comes out
somewhat larger. The strength of the nuclear spin-orbit interaction,
$F_{so}(k_f)$, as given by iterated one-pion exchange is about half as large as
the corresponding empirical value, however, with the wrong negative sign. The
novel density dependencies of $\widetilde M^*(\rho)$ and $F_{\nabla,so,J}(k_f)$
as predicted by our parameterfree calculation should be examined in nuclear
structure calculations (after introducing an additional short range spin-orbit
contribution constant in density). | nucl-th |
Rapidity correlations test stochastic hydrodynamics: We show that measurements of the rapidity dependence of transverse momentum
correlations can be used to determine the characteristic time $\tau_{\pi}$ that
dictates the rate of isotropization of the stress energy tensor, as well as the
shear viscosity $\nu = \eta/sT$. We formulate methods for computing these
correlations using second order dissipative hydrodynamics with noise. Current
data are consistent with $\tau_{\pi}/\nu \sim 10$ but targeted measurements can
improve this precision. | nucl-th |
Nucleons and nuclei in the context of low-energy QCD: This presentation reports on recent developments concerning basic aspects of
low-energy QCD as they relate to the understanding of the nucleon mass and the
nuclear many-body problem. | nucl-th |
Quark-meson coupling model for a nucleon: We considered the quark-meson coupling model for a nucleon. The model
describes a nucleon as an MIT bag, in which quarks are coupled to the scalar
and the vector mesons. A set of coupled equations for the quark and the meson
fields are obtained and are solved in a self-consistent manner. We show that
the mass of a dressed MIT bag interacting with $\sigma$- and $\omega$-meson
fields differs considerably from the mass of the free MIT bag. The effects of
the density-dependent bag constant are investigated. The results of our
calculations imply that the self-energy of the bag in the quark-meson coupling
model is significant and needs to be considered in doing the calculations for
nuclear matter or finite nuclei. | nucl-th |
Event-by-event distributions of azimuthal asymmetries in
ultrarelativistic heavy-ion collisions: Relativistic dissipative fluid dynamics is a common tool to describe the
space-time evolution of the strongly interacting matter created in
ultrarelativistic heavy-ion collisions. For a proper comparison to experimental
data, fluid-dynamical calculations have to be performed on an event-by-event
basis. Therefore, fluid dynamics should be able to reproduce, not only the
event-averaged momentum anisotropies, $<v_{n}>$, but also their distributions.
In this paper, we investigate the event-by-event distributions of the
initial-state and momentum anisotropies $\epsilon_n$ and $v_n$, and their
correlations. We demonstrate that the event-by-event distributions of relative
$v_n$ fluctuations are almost equal to the event-by-event distributions of
corresponding $\epsilon_n$ fluctuations, allowing experimental determination of
the relative anisotropy fluctuations of the initial state. Furthermore, the
correlation $c(v_2,v_4)$ turns out to be sensitive to the viscosity of the
fluid providing an additional constraint to the properties of the strongly
interacting matter. | nucl-th |
Phases of Dense Quark Matter and the Structure of Compact Objects: The presence of quark matter in neutron stars may affect several neutron star
observables and the neutrino signal in core-collapse supernovae. These
observables are sensitive to the phase of quark matter that is present in
compact objects. We present the first calculation of the phase structure of
dense quark matter which includes a six-fermion color-superconducting
interaction and show that the effect of this term can destabilize the pairing
interaction, favoring phases where fewer quarks are paired. In turn, this
modification of the phase structure can modify the neutrino signal, the
structure of the neutron star, and the long-term cooling. We also show that,
contrary to the 20-year old paradigm of the surface structure of the
"strange-quark stars", the surface of these objects may consist of nuggets of
strange quark matter screened by the electron gas. | nucl-th |
Supplemental note for "Two-fermion emission from spin-singlet and
triplet resonances in one dimension": Time-dependent calculation has been a suitable method to investigate the
quantum dynamical processes. In Ref. [1] = [T. Oishi et al., J. of Phys. G 45,
105101 (2018)], we applied this method to the one-dimensional two-fermion
tunneling in the nuclear-physics scale. Beside the specific results presented
therein, some basic formalism and methods, which can be helpful for further
discussions and developments to investigate time-dependent quantum systems,
have been awaiting our description. This note is devoted to describe those
supplemental contents. We do not limit the story to the nuclear physics, but
keep it applicable to other scales and/or targets. | nucl-th |
Does quark-gluon plasma feature an extended hydrodynamic regime?: We investigate the response of the near-equilibrium quark-gluon plasma (QGP)
to perturbation at non-hydrodynamic gradients. We propose a conceivable
scenario under which sound mode continues to dominate the medium response in
this regime. Such a scenario has been observed experimentally for various
liquids and liquid metals. We further show this extended hydrodynamic regime
(EHR) indeed exists for both the weakly-coupled kinetic equation in the
relaxation time approximation (RTA) and the strongly-coupled ${\cal N}=4$
supersymmetric Yang-Mills (SYM) theory. We construct a simple but nontrivial
extension of M{\"u}eller-Isareal-Stewart (MIS) theory, namely MIS*, and
demonstrate that it describes EHR response for both RTA and SYM theory. This
indicates that MIS* equations can potentially be employed to search for QGP EHR
via heavy-ion collisions. | nucl-th |
A percolation transition in Yang-Mills matter at finite number of
colours: We examine baryonic matter at quark chemical potential of the order of the
confinement scale, $\mu_q\sim \lqcd$. In this regime, quarks are supposed to be
confined but baryons are close to the ``tightly packed limit'' where they
nearly overlap in configuration space. We show that this system will exhibit a
percolation phase transition {\em when varied in the number of colours} $N_c$:
at high $N_c$, large distance correlations at quark level are possible even if
the quarks are essentially confined. At low $N_c$, this does not happen. We
discuss the relevance of this for dense nuclear matter, and argue that our
results suggest a new ``phase transition'', varying $N_c$ at constant $\mu_q$. | nucl-th |
Pairing and specific heat in hot nuclei: The thermodynamics of pairing phase-transition in nuclei is studied in the
canonical ensemble and treating the pairing correlations in a
finite-temperature variation after projection BCS approach (FT-VAP). Due to the
restoration of particle number conservation, the pairing gap and the specific
heat calculated in the FT-VAP approach vary smoothly with the temperature,
indicating a gradual transition from the superfluid to the normal phase, as
expected in finite systems. We have checked that the predictions of the FT-VAP
approach are very accurate when compared to the results obtained by an exact
diagonalization of the pairing Hamiltonian. The influence of pairing
correlations on specific heat is analysed for the isotopes $^{161,162}$Dy and
$^{171,172}$Yb. It is shown that the FT-VAP approach, applied with a level
density provided by mean field calculations and supplemented, at high energies,
by the level density of the back-shifted Fermi gas model, can approximate
reasonably well the main properties of specific heat extracted from
experimental data. However, the detailed shape of the calculated specific heat
is rather sensitive to the assumption made for the mean field. | nucl-th |
Model independent study of massive lepton elastic scattering on the
proton, beyond the Born approximation: Model independent expressions for all polarization observables in $\mu+p\to
\mu+p$ elastic scattering are obtained, taking into account the lepton mass and
including the two-photon exchange contribution. The spin structure of the
matrix element is parametrized in terms of six independent complex amplitudes,
functions of two independent kinematical variables. General statements about
the influence of the two--photon--exchange terms on the differential cross
section and on polarization observables are given. Polarization effects have
been investigated for the case of a longitudinally polarized lepton beam and
polarized nucleon in the final state. | nucl-th |
The Structure of the Hadron-Quark Reaction Zone: Hadron-quark combustion in dense matter is a central topic in the study of
phases in compact stars and their high-energy astrophysics. We critically
review the literature on hadron-quark combustion, dividing them into a "first
wave" that treats the problem as a steady-state burning with or without
constraints of mechanical equilibrium, and a "second wave" which uses numerical
techniques to resolve the burning front and solves the underlying Partial
Differential Equations for the chemistry of the burning front under less
restrictive conditions. We detail the inaccuracies that the second wave amends
over the first wave, and highlight crucial differences between various
approaches in the second wave. We also include results from time-dependent
simulations of the reaction zone that include a hadronic EOS, neutrinos, and
self-consistent thermodynamics without using parameterized shortcuts. | nucl-th |
Universal behavior of $p$-wave proton-proton fusion near threshold: We calculate the $p$-wave contribution to the proton-proton fusion $S$ factor
and its energy derivative in pionless effective field theory (EFT) up to
next-to-leading order. The leading contributions are given by a recoil piece
from the Gamow-Teller and Fermi operators, and from relativistic $1/m$
suppressed weak interaction operators. We obtain the value of $(2.5\pm0.3
)\times 10^{-28}~\mathrm{MeV\ fm^2}$ for the $S$ factor and $(2.2\pm0.2) \times
10^{-26}~\mathrm{fm^2}$ for its energy derivative at threshold. These are
smaller than the results of a prior study that employed chiral EFT by several
orders of magnitude. We conclude that, contrary to what has been previously
reported, the $p$-wave contribution does not need to be considered in a
high-precision determination of the $S$ factor at astrophysical energies.
Combined with the chiral EFT calculation of Acharya {\it et al.} [Phys. Lett. B
\bf{760}, 584 (2016)] for the $s$-wave channel, this gives a total threshold
$S$ factor of $S(0) = (4.047^{+0.024}_{-0.032}) \times 10^{-23}~{\rm
MeV~fm}^2$. | nucl-th |
In-Medium Vector Mesons, Dileptons and Chiral Restoration: Medium modifications of the electromagnetic spectral function in hadronic and
quark-gluon matter are reviewed. A strong broadening of the $\rho$ meson, which
dominates the spectral function in the low-mass regime, is quantitatively
consistent with dilepton excess spectra measured in photoproduction off cold
nuclei (CLAS/JLab) and in fixed-target ultrarelativistic heavy-ion collisions
(NA45,NA60/CERN-SPS). The large excess observed by PHENIX at RHIC remains
unexplained to date, but is most likely not due to emission from the
Quark-Gluon Plasma. Connections to thermal lattice QCD promise progress in the
search for chiral symmetry restoration. | nucl-th |
Fission-fragment mass distributions from strongly damped shape evolution: Random walks on five-dimensional potential-energy surfaces were recently
found to yield fission-fragment mass distributions that are in remarkable
agreement with experimental data. Within the framework of the Smoluchowski
equation of motion, which is appropriate for highly dissipative evolutions, we
discuss the physical justification for that treatment and investigate the
sensitivity of the resulting mass yields to a variety of model ingredients,
including in particular the dimensionality and discretization of the shape
space and the structure of the dissipation tensor. The mass yields are found to
be relatively robust, suggesting that the simple random walk presents a useful
calculational tool. Quantitatively refined results can be obtained by including
physically plausible forms of the dissipation, which amounts to simulating the
Brownian shape motion in an anisotropic medium. | nucl-th |
Applications of the Similarity Renormalization Group to the Nuclear
Interaction: The Similarity Renormalization Group (SRG) is investigated as a powerful yet
practical method to modify nuclear potentials so as to reduce computational
requirements for calculations of observables. The key feature of SRG
transformations that leads to computational benefits is the decoupling of
low-energy nuclear physics from high-energy details of the inter-nucleon
interaction. We examine decoupling quantitatively for two-body observables and
few-body binding energies. The universal nature of this decoupling is
illustrated and errors from suppressing high-momentum modes above the
decoupling scale are shown to be perturbatively small. To explore the SRG
evolution of many-body forces, we use as a laboratory a one-dimensional system
of bosons with short-range repulsion and mid-range attraction, which emulates
realistic nuclear forces. The free-space SRG is implemented for few-body
systems in a symmetrized harmonic oscillator basis using a recursive
construction analogous to no-core shell model implementations. Building on
one-dimensional results we performed the first practical evolution of
three-dimensional many-body forces within the No-Core Shell Model basis.
Results for the 3H binding energy are consistent with previous calculations
involving momentum-space evolution of only two-body forces, and validate
expectations from calculations in the one-dimensional oscillator basis. When
applied to 4He calculations, the two- and three-body oscillator matrix elements
yield rapid convergence of the ground-state energy with a small net
contribution of the induced four-body force. The radius of light nuclei is also
explored in the three-dimensional basis. | nucl-th |
The generalised relativistic Lindhard functions: We present here analytic expressions for the generalised Lindhard function,
also referred to as Fermi Gas polarisation propagator, in a relativistic
kinematic framework and in the presence of various resonances and vertices.
Particular attention is payed to its real part, since it gives rise to
substantial difficulties in the definition of the currents entering the
dynamics. | nucl-th |
Soft two-meson-exchange nucleon-nucleon potentials. II. One-pair and
two-pair diagrams: Two-meson-exchange nucleon-nucleon potentials are derived where either one or
both nucleons contains a pair vertex. Physically, the meson-pair vertices are
meant to describe in an effective way (part of) the effects of heavy-meson
exchange and meson-nucleon resonances. {}From the point of view of ``duality,''
these two kinds of contribution are roughly equivalent. The various
possibilities for meson pairs coupling to the nucleon are inspired by the
chiral-invariant phenomenological Lagrangians that have appeared in the
literature. The coupling constants are fixed using the linear $\sigma$ model.
We show that the inclusion of these two-meson exchanges gives a significant
improvement over a potential model including only the standard one-boson
exchanges. | nucl-th |
Mechanisms producing fissionlike binary fragments in heavy collisions: The mixing of the quasifission component to the fissionlike cross section
causes ambiguity in the quantitative estimation of the complete fusion cross
section from the observed angular and mass distributions of the binary
products. We show that the partial cross section of quasifission component of
binary fragments covers the whole range of the angular momentum values leading
to capture. The calculated angular momentum distributions for the compound
nucleus and dinuclear system going to quasifission may overlap: competition
between complete fusion and quasifission takes place at all values of initial
orbital angular momentum. Quasifission components formed at large angular
momentum of the dinuclear system can show isotropic angular distribution and
their mass distribution can be in mass symmetric region similar to the
characteristics of fusion-fission components. As result the unintentional
inclusion of the quasifission contribution into the fusion-fission fragment
yields can lead to overestimation of the probability of the compound nucleus
formation. | nucl-th |
Mass dependence and isospin dependence of short-range correlated pairs: The target-mass number dependence of nucleon-nucleon pairs with short-range
correlations is explored in a physically transparent geometrical model within a
zero-range approximation. The observed $A$ dependence of 2-nucleon ejection
cross sections in $(e,e')$ reactions is found to reflect the mass dependence of
nuclear density distributions. A parametrization of this $A$ dependence is
given. The $A$ dependence of proton-proton vs.\ proton-neutron pairs relative
to $^{12}$C is also analyzed in this model. It can be understood using simple
combinatorics without any additional isospin dependence. | nucl-th |
A comparative analysis of in-medium spectral functions for $N(940)$ and
$N^*(1535)$ in real-time thermal field theory: In the real-time thermal field theory, the nucleon self-energy at finite
temperature and density is evaluated where an extensive set of pion-baryon
($\pi B$) loops are considered. On the other side the in-medium self-energy of
$N^*(1535)$ for $\pi N$ and $\eta N$ loops is also determined in the same
framework. The detail branch cut structures for these different $\pi B$ loops
for nucleon $N(940)$ and $\pi N$, $\eta N$ loops for $N^*(1535)$ are addressed.
Using the total self-energy of $N(940)$ and $N^*(1535)$, which contain the
contributions of their corresponding loop diagrams, the complete structures of
their in-medium spectral functions have been obtained. The Landau and unitary
cut contributions provide two separate peak structures in the nucleon spectral
function while $N^*(1535)$ has single peak structure in its unitary cuts. At
high temperature, the peak structures of both at their individual poles are
attenuated while at high density Landau peak structure of nucleon is completely
suppressed and its unitary peak structure is tending to be shifted towards the
melted peak of $N^*(1535)$. The non-trivial modifications of these chiral
partners may indicate some association of chiral symmetry restoration. | nucl-th |
Resonances from Baryon decuplet-Meson octet interaction: The s-wave interactions of the baryon decuplet with the octet of pseudoscalar
mesons is studied in a unitarized coupled channel approach. We obtain a fair
agreement for mass and width of several 3/2- resonances. In particular, the
Xi(1820), the Lambda(1520) and the Sigma(1670) states are well reproduced.
Other resonances are predicted and also the couplings of the observed
resonances to the various channels are evaluated. | nucl-th |
Quantum Monte Carlo calculations of electromagnetic transitions in 8Be
with meson-exchange currents derived from chiral effective field theory: We report quantum Monte Carlo calculations of electromagnetic transitions in
8Be. The realistic Argonne v18 two-nucleon and Illinois-7 three-nucleon
potentials are used to generate the ground state and nine excited states, with
energies that are in excellent agreement with experiment. A dozen M1 and eight
E2 transition matrix elements between these states are then evaluated. The E2
matrix elements are computed only in impulse approximation, with those
transitions from broad resonant states requiring special treatment. The M1
matrix elements include two-body meson-exchange currents derived from chiral
effective field theory, which typically contribute 20--30% of the total
expectation value. Many of the transitions are between isospin-mixed states;
the calculations are performed for isospin-pure states and then combined with
empirical mixing coefficients to compare to experiment. Alternate mixings are
also explored. In general, we find that transitions between states that have
the same dominant spatial symmetry are in reasonable agreement with experiment,
but those transitions between different spatial symmetries are often
underpredicted. | nucl-th |
The Disappearance of Flow: We investigate the disappearance of collective flow in the reaction plane in
heavy-ion collisions within a microscopic model (QMD). A systematic study of
the impact parameter dependence is performed for the system Ca+Ca. The balance
energy strongly increases with impact parameter. Momentum dependent
interactions reduce the balance energies for intermediate impact parameters
$b\approx4.5$ fm. Dynamical negative flow is not visible in the laboratory
frame but does exist in the contact frame for the heavy system Au+Au. For
semi-peripheral collisions of Ca+Ca with $b\approx6.5$ fm a new two-component
flow is discussed. Azimuthal distributions exhibit strong collectiv flow
signals, even at the balance energy. | nucl-th |
Analysis of the data on spin density matrix elements for $γp \to
K^{*+}Λ$: In our previous work [Phys. Rev. C {\bf 96}, 035206 (2017)], the
high-precision differential cross-section data for $\gamma p \to K^{*+}\Lambda$
reported by the CLAS Collaboration has been analyzed within an effective
Lagrangian approach. It was found that apart from the $t$-channel $K$, $K^*$,
and $\kappa$ exchanges, the $u$-channel $\Lambda$, $\Sigma$, and $\Sigma^*$
exchanges, the $s$-channel $N$ exchange, and the interaction current, one needs
to introduce at least two nucleon resonances in the $s$ channel in constructing
the reaction amplitudes to describe the cross-section data. One of the needed
resonances is $N(2060)5/2^-$, and the other one could be one of the
$N(2000)5/2^+$, $N(2040)3/2^+$, $N(2100)1/2^+$, $N(2120)3/2^-$, and
$N(2190)7/2^-$ resonances. In this paper, we further include in our analysis
the data on spin density matrix elements for $K^*$ meson reported recently by
the CLAS Collaboration, with the purpose being to impose further constraints on
extracting the resonance contents and to gain a better understanding of the
reaction mechanism. It turns out that with the new data on spin density matrix
elements taken into account, only the set with the $N(2060)5/2^-$ and
$N(2000)5/2^+$ resonances among those five possible solutions extracted from
the analysis of the differential cross-section data can satisfactorily describe
the data on both the differential cross sections and the spin density matrix
elements. Further analysis shows that this reaction is dominated by the
$t$-channel $K$ exchange and $s$-channel $N(2060)5/2^-$ and $N(2000)5/2^+$
exchanges. | nucl-th |
Spectral Function of rho in Dense and Hot Hadronic Matter: The spectral function of rho meson in hot/dense hadronic matter is studied by
taking into account the nucleon-loop on quantum hadrondynamics model level.
Different from the hot pion gas effect which changes the spectral function
slightly, the nucleon-antinucleon polarization (Dirac sea) makes the spectral
function very sharp and shifted towards the low invariant mass region
significantly due to the decreasing effective nucleon mass. | nucl-th |
Collectivity in Ultra-Peripheral Pb+Pb Collisions at the Large Hadron
Collider: We present the first full (3+1)D dynamical simulations of ultra-peripheral
Pb+Pb collisions at the Large Hadron Collider. Extrapolating from p+Pb
collisions, we explore whether a quasi-real photon $\gamma^*$ interacting with
the lead nucleus in an ultra-peripheral collision can create a many-body system
exhibiting fluid behavior. Assuming strong final-state interactions, we provide
model results for charged hadron multiplicity, identified particle mean
transverse momenta, and charged hadron anisotropic flow coefficients, and
compare them with experimental data from the ALICE and ATLAS collaborations.
The elliptic flow hierarchy between p+Pb and $\gamma^*$+Pb collisions is
dominated by the difference in longitudinal flow decorrelations and reproduces
the experimental data well. We have demonstrated that our theoretical framework
provides a quantitative tool to study particle production and collectivity for
all system sizes, ranging from central heavy-ion collisions to small asymmetric
collision systems at the Relativistic Heavy-Ion Collider and the Large Hadron
Collider and even at the future Electron-Ion Collider. | nucl-th |
The Magnetic Moments of the Octet Baryons in Quenched Chiral
Perturbation Theory: We compute the magnetic moments of the octet baryons up to two orders in
quenched chiral perturbation theory. In addition to the $\sim\sqrt{m_q}$
contributions that arise in QCD, there are lower-order contributions of the
form $M_0^2\log m_q$ from loop diagrams involving hairpin interactions. | nucl-th |
Non-equilibrium approaches to the pre-thermal and post-hadronisation
stages of A+A collisions: The results related to non-equilibrium phenomena at the very early and late
stages of the processes of A+A collisions are presented. A good description of
the hadron momentum spectra as well as pion and kaon interferometry data at
RHIC is reached within the realistic dynamical picture of A+A collisions:
HydroKinetic Model (HKM). The model accumulates the following features: not too
early thermalization time; $\tau\geq 1$ fm/c; a developing of the pre-thermal
transverse flows; the effectively more hard, than in the case of chemical
equilibrium, equation of state of expanding chemically non-equilibrated
multi-hadronic gas; a continuous non-equilibrated emission of hadrons. All
these factors lead to a good description of the mentioned RHIC data, in
particular, the observed $R_{out}/R_{side}$ ratios, solving, therefore, the HBT
puzzle in detailed realistic model. | nucl-th |
Target mass number dependence of subthreshold antiproton production in
proton-, deuteron- and alpha-particle-induced reactions: Data from KEK on subthreshold $\bar{\mrm{p}}$ as well as on $\pi^\pm$ and
$\mrm{K}^\pm$ production in proton-, deuteron- and $\alpha$-induced reactions
at energies between 2.0 and 12.0 A GeV for C, Cu and Pb targets are described
within a unified approach. We use a model which considers a nuclear reaction as
an incoherent sum over collisions of varying numbers of projectile and target
nucleons. It samples complete events and thus allows for the simultaneous
consideration of all final particles including the decay products of the
nuclear residues. The enormous enhancement of the $\bar{\mrm{p}}$ cross
section, as well as the moderate increase of meson production in deuteron and
$\alpha$ induced compared to proton-induced reactions, is well reproduced for
all target nuclei. In our approach, the observed enhancement near the
production threshold is mainly due to the contributions from the interactions
of few-nucleon clusters by simultaneously considering fragmentation processes
of the nuclear residues. The ability of the model to reproduce the target mass
dependence may be considered as a further proof of the validity of the cluster
concept. | nucl-th |
Proton-Proton and Proton-Neutron Correlations in Medium-Weight Nuclei:
Role of the Tensor Force within a Many-Body Cluster Expansion: A detailed analysis of the effect of tensor correlations on one- and two-body
densities and momentum distributions of complex nuclei is presented within a
linked cluster expansion providing reliable results for the ground state
properties of nuclei calculated with realistic interactions. | nucl-th |
Femtoscopy in Relativistic Heavy Ion Collisions and its Relation to Bulk
Properties of QCD Matter: Using a viscous hydrodynamic model coupled to a hadronic cascade code,
numerous features of the dynamics and equilibrium properties are explored for
their impact on femtoscopic measurements. The equation of state, viscous
parameters and initial conditions are investigated. We find that femtoscopy is
affected by numerous model features at the 10% level, and that by including
features and adjusting unknown parameters, one can explain experimental source
size measurements to better than 10%. | nucl-th |
Probing the pairing interaction through two-neutron transfer reactions: Cross sections for ($p,t$) two-neutron transfer reactions are calculated in
the one-step zero-range distorted-wave Born approximation for the tin isotopes
$^{124}$Sn and $^{136}$Sn and for incident proton energies from 15 to 35 MeV.
Microscopic quasiparticle random-phase approximation form factors are provided
for the reaction calculation and phenomenological optical potentials are used
in both the entrance and the exit channels. Three different surface/volume
mixings of a zero-range density-dependent pairing interaction are employed in
the microscopic calculations and the sensitivity of the cross sections to the
different mixings is analyzed. Since absolute cross sections cannot be obtained
within our model, we compare the positions of the diffraction minima and the
shapes of the angular distributions. No differences are found in the position
of the diffraction minima for the reaction $^{124}$Sn($p,t$)$^{122}$Sn. On the
other side, the angular distributions obtained for the reaction
$^{136}$Sn($p,t$)$^{134}$Sn with surface and mixed interactions differ at large
angles for some values of the incident proton energy. For this reaction, we
compare the ratios of the cross sections associated to the ground state and the
first excited state transitions. Differences among the three different
theoretical predictions are found and they are more important at the incident
proton energy of 15 MeV. As a conclusion, we indicate ($p,t$) two-neutron
transfer reactions with very neutron-rich Sn isotopes and at proton energies
around 15 MeV as good experimental cases where the surface/volume mixing of the
pairing interaction may be probed. | nucl-th |
Statistical aspects of nuclear coupling to continuum: Various global characteristics of the coupling between the bound and
scattering states are explicitly studied based on realistic Shell Model
Embedded in the Continuum. In particular, such characteristics are related to
those of the scattering ensemble. It is found that in the region of higher
density of states the coupling to continuum is largely consistent with the
statistical model. However, assumption of channel equivalence in the
statistical model is, in general, violated. | nucl-th |
Measuring the Rate of Isotropization of Quark-Gluon Plasma Using
Rapidity Correlations: We propose that rapidity dependent momentum correlations can be used to
extract the shear relaxation time $\tau_\pi$ of the medium formed in high
energy nuclear collisions. The stress-energy tensor in an equilibrium
quark-gluon plasma is isotropic, but in nuclear collisions it is likely very
far from this state. The relaxation time $\tau_\pi$ characterizes the rate of
isotropization and is a transport coefficient as fundamental as the shear
viscosity. We show that fluctuations emerging from the initial anisotropy
survive to freeze-out, in excess of thermal fluctuations, influencing rapidity
correlation patterns. We show that these correlations can be used to extract
$\tau_\pi$. We describe a method for calculating the rapidity dependence of
two-particle momentum correlations with a second order, causal, diffusion
equation that includes Langevin noise as a source of thermal fluctuations. The
causality requirement introduces the relaxation time and we link the shape of
the rapidity correlation pattern to its presence. Here we examine how different
equations of state and temperature dependent transport coefficients in the
presence of realistic hydrodynamic flow influence the estimate of $\tau_\pi$.
In comparison to RHIC data, we find that the ratio $\tau_\pi/\nu \approx 5-6$
where $\nu=\eta/sT$ is the kinematic viscosity. | nucl-th |
Convergence and efficiency of angular momentum projection for many-body
systems: In many so-called "beyond-mean-field" many-body methods, one creates
symmetry-breaking states and then projects out states with good quantum
number(s); the most important example is angular momentum. Motivated by the
computational intensity of symmetry restoration, we investigate the numerical
convergence of two competing methods for angular momentum projection with
rotations over Euler angles, the textbook-standard projection through
quadrature, and a recently introduced projection through linear algebra. We
find well-defined patterns of convergence with increasing number of mesh points
(for quadrature) and cut-offs (for linear algebra). Because the method of
projection through linear algebra requires inverting matrices generated on a
mesh of Euler angles, we discuss two methods for robustly reducing the number
of required evaluations. Reviewing the literature, we find our inversion
involving rotations about the $z$-axis is equivalent to trapezoidal
"quadrature" commonly used as well as Fomenko projection used for
particle-number projection. The efficiency depends upon the number of angular
momentum $J$ to be projected, but in general inversion methods, including
Fomenko projection/trapezoidal "quadrature" dramatically improve the
efficiency. | nucl-th |
v4 for identified particles at RHIC from viscous hydrodynamics: Using ideal and viscous hydrodynamics, the ratio of azimuthal moments
v4/(v2)^2 is calculated for pions, protons, and kaons in sqrt{s}=200 A*GeV
Au+Au collisions. For any value of viscosity here is little dependence on
particle species. Ideal hydrodynamics and data show a flat curve as a function
of pt. Adding viscosity in the standard way destroys this flatness. However, it
can be restored by replacing the standard quadratic ansatz for delta f (the
viscous correction to the distribution function at freeze-out) with a weaker
momentum dependence. | nucl-th |
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