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Neutral weak currents in nucleon superfluid Fermi liquids: Larkin-Migdal
and Leggett approaches: Neutrino emission in processes of breaking and formation of nucleon Cooper
pairs is calculated in the framework of the Larkin-Migdal and the Leggett
approaches to the description of superfluid Fermi liquids at finite
temperatures. We explain peculiarities of both approaches and explicitly
demonstrate that they lead to the same expression for the emissivity in pair
breaking and formation processes. | nucl-th |
Fragments in Gaussian Wave-Packet Dynamics with and without correlations: Generalization of Gaussian trial wave functions in quantum molecular dynamics
models is introduced, which allows for long-range correlations characteristic
for composite nuclear fragments. We demonstrate a significant improvement in
the description of light fragments with correlations. Utilizing either type of
Gaussian wave functions, with or without correlations, however, we find that we
cannot describe fragment formation in a dynamic situation. Composite fragments
are only produced in simulations if they are present as clusters in the
substructure of original nuclei. The difficulty is traced to the delocalization
of wave functions during emission. Composite fragments are produced abundantly
in the Gaussian molecular dynamics in the limit $\hbar \rightarrow 0$. | nucl-th |
Multi-nucleon structure and dynamics via quantum computing: We propose a framework for computing the structure and dynamics for
second-quantized many-nucleon Hamiltonians on quantum computers. We develop an
oracle-based Hamiltonian input model that computes the many-nucleon states and
nonzero Hamiltonian matrix elements of the many-nucleon system. With our
Fock-state based input model, we show how to implement the sparse matrix
simulation algorithms to calculate the dynamics of the second-quantized
many-nucleon Hamiltonian. Based on the dynamics simulation methods, we also
present the methodology for structure calculations of the many-nucleon system.
In this work, we provide an explicit circuit design of our input model of the
second-quantized Hamiltonian within a direct encoding scheme that maps the
occupation of each available single-particle state in the many-nucleon state to
the state of specific qubit in a quantum register. We analyze our method and
provide the asymptotic cost in computing resources for structure and dynamics
calculations of many-nucleon systems. For pedagogical purposes, we demonstrate
our input model with two model problems in restricted model spaces. | nucl-th |
Aspects of Hadron Physics: Detailed investigations of the structure of hadrons are essential for
understanding how matter is constructed from the quarks and gluons of Quantum
chromodynamics (QCD), and amongst the questions posed to modern hadron physics,
three stand out. What is the rigorous, quantitative mechanism responsible for
confinement? What is the connection between confinement and dynamical chiral
symmetry breaking? And are these phenomena together sufficient to explain the
origin of more than 98% of the mass of the observable universe? Such questions
may only be answered using the full machinery of nonperturbative relativistic
quantum field theory. This contribution provides a perspective on progress
toward answering these key questions. In so doing it will provide an overview
of the contemporary application of Dyson-Schwinger equations in Hadron Physics.
The presentation assumes that the reader is familiar with the concepts and
notation of relativistic quantum mechanics, with the functional integral
formulation of quantum field theory and with regularisation and renormalisation
in its perturbative formulation. | nucl-th |
Nucleon resonances within a dynamical coupled-channels model of pi N and
gamma N reactions: The nucleon resonances are investigated within a dynamical coupled-channels
model of pi N and gamma N reactions up to the invariant mass W = 2 GeV. The
meson-baryon (MB) channels included in the calculations are MB = pi N, eta N, K
Lambda, K Sigma, and pi pi N that has pi Delta, rho N, and sigma N resonant
components. The meson-baryon amplitudes T_{M'B',MB}(W) are calculated from
solving a set of coupled-channels integral equations defined by an interaction
Hamiltonian consisting of (a) meson-exchange interactions v_{M'B',MB} derived
from phenomenological Lagrangian, and (b) vertex interactions N* --> MB for
describing the transition of a bare excited nucleon state N* to a channel MB.
The parameters of v_{M'B',MB} are mainly constrained by the fit to the data of
pi N --> pi N in the low energy region up to W =1.4 GeV. The bare masses of N*
and the N* --> MB parameters are then determined in simultaneous fits to the
data of pi N --> pi N up to W =2.3 GeV and those of pi N --> eta N, K Lambda, K
Sigma and gamma N --> pi N, eta N, K Lambda, K Sigma up to W = 2.1 GeV. The
pole positions and residues of nucleon resonances are extracted by analytically
continuing the meson-baryon amplitudes T_{M'B',MB}(W) to the complex Riemann
energy surface. From the extracted residues, we have determined the N* --> pi
N, gamma N, eta N, K Lambda, K Sigma transition amplitudes at resonance poles.
We compare the resonance pole positions from our analysis with those given by
Particle Data Group and the recent coupled-channels analyses by the Juelich and
Bonn-Gatchina groups. Four results agree well only for the first N* in each
spin-parity-isospin (J^P,I) channel. For higher mass states, the number of
states and their resonance positions from four results do not agree well. We
discuss the possible sources of the discrepancies and the need of additional
data from new hadron facilities such as J-PARC. | nucl-th |
Bose-Einstein correlations in thermal field theory: Two-particle correlation functions are calculated for bosons emitted from a
localized thermal source (the ``glow'' of a ``hot spot''). In contrast to
existing work, non-equilibrium effects up to first order in gradients of the
particle distribution function are taken into account. The spectral width of
the bosons is shown to be an important quantity: If it is too small, they do
not equilibrate locally and therefore strongly increase the measured
correlation radius. In memoriam of Eugene Wigner and Hiroomi Umezawa. | nucl-th |
Spin and pseudospin symmetries in the antinucleon spectrum of nuclei: Spin and pseudospin symmetries in the spectra of nucleons and antinucleons
are studied in a relativistic mean-field theory with scalar and vector
Woods-Saxon potentials, in which the strength of the latter is allowed to
change. We observe that, for nucleons and antinucleons, the spin symmetry is of
perturbative nature and it is almost an exact symmetry in the physical region
for antinucleons. The opposite situation is found in the pseudospin symmetry
case, which is better realized for nucleons than for antinucleons, but is of
dynamical nature and cannot be viewed in a perturbative way both for nucleons
and antinucleons. This is shown by computing the spin-orbit and
pseudospin-orbit couplings for selected spin and pseudospin partners in both
spectra. | nucl-th |
Isovector giant monopole and quadrupole resonances in a Skyrme energy
density functional approach with axial symmetry: [Background] Giant resonance (GR) is a typical collective mode of vibration.
The deformation splitting of the isovector (IV) giant dipole resonance is well
established. However, the splitting of GRs with other multipolarities is not
well understood. [Purpose] I explore the IV monopole and quadrupole excitations
and attempt to obtain the generic features of IV giant resonances in deformed
nuclei by investigating the neutral and charge-exchange channels
simultaneously. [Method] I employ a nuclear energy-density functional (EDF)
method: the Skyrme-Kohn-Sham-Bogoliubov and the quasiparticle random-phase
approximation are used to describe the ground state and the transition to
excited states. [Results] I find the concentration of the monopole strengths in
the energy region of the isobaric analog or Gamow-Teller resonance irrespective
of nuclear deformation, and the appearance of a high-energy giant resonance
composed of the particle-hole configurations of $2\hbar \omega_0$ excitation.
Splitting of the distribution of the strength occurs in the giant monopole and
quadrupole resonances due to deformation. The lower $K$ states of quadrupole
resonances appear lower in energy and possess the enhanced strengths in the
prolate configuration, and vice versa in the oblate configuration, while the
energy ordering depending on $K$ is not clear for the $J=1$ and $J=2$
spin-quadrupole resonances. [Conclusions] The deformation splitting occurs
generously in the giant monopole and quadrupole resonances. The $K$-dependence
of the quadrupole transition strengths is largely understood by the anisotropy
of density distribution. | nucl-th |
Low Energy Pion-Nucleus Interactions: Nuclear Deep Inelastic Scattering,
Drell-Yan and Missing Pions: The experimental discovery that the nucleus is approximately transparent to
low energy pions is reviewed. The consequences of this for nuclear deep
inelastic scattering and Drell-Yan interactions are discussed. I argue that low
energy nucleus data imply that there is little nuclear enhancement of the pion
cloud of a nucleon, and try to interpret this in terms of nucleon-nucleon
correlations. | nucl-th |
Light Front Theory Of Nuclear Matter: A relativistic light front formulation of nuclear dynamics is applied to
infinite nuclear matter. A hadronic meson-baryon Lagrangian, consistent with
chiral symmetry, leads to a nuclear eigenvalue problem which is solved,
including nucleon-nucleon (NN) correlations, in the one-boson-exchange
approximation for the NN potential. The nuclear matter saturation properties
are reasonably well reproduced, with a compression modulus of 180 MeV. We find
that there are about 0.05 excess pions per nucleon. | nucl-th |
Structure analysis of the virtual Compton scattering amplitude at low
energies: We analyze virtual Compton scattering off the nucleon at low energies in a
covariant, model-independent formalism.
We define a set of invariant functions which, once the irregular nucleon pole
terms have been subtracted in a gauge-invariant fashion, is free of poles and
kinematical zeros.
The covariant treatment naturally allows one to implement the constraints due
to Lorentz and gauge invariance, crossing symmetry, and the discrete
symmetries.
In particular, when applied to the $ep\to e'p'\gamma$ reaction,
charge-conjugation symmetry in combination with nucleon crossing generates four
relations among the ten originally proposed generalized polarizabilities of the
nucleon. | nucl-th |
Charged-particle rapidity density in Au+Au collisions in a quark
combination model: Rapidity/seudorapidity densities for charged particles and their centrality,
rapidity and energy dependence in Au+Au collisions at RHIC are studied in a
quark combination model. Using a Gaussian-type rapidity distribution for
constituent quarks as a result of Landau hydrodynamic evolution, the data at
$\sqrt{s_{NN}}=130, 200$ GeV at various centralities in full pseudorapidity
range are well described, and the charged particle multiplicity are reproduced
as functions of the number of participants. The energy dependence of the shape
of the $dN_{ch}/d\eta$ distribution is also described at various collision
energies $\sqrt{s_{NN}}=200, 130, 62.4$ GeV in central collisions with same
value of parameters except 19.6 GeV. The calculated rapidity distributions and
yields for the charged pions and kaons in central Au+Au collisions at
$\sqrt{s_{NN}}=200$ GeV are compared with experimental data of the BRAHMS
Collaboration. | nucl-th |
Meson Photoproductions of Nucleon In the Quark Model: The meson photoproductions off nucleons in the chiral quark model are
described. The role of the S-wave resonances in the second resonance region is
discussed, and it is particularly important for the Kaon, $\eta$ and $\eta'$
photoproductions. | nucl-th |
Single- & double-strangeness hypernuclei up to $ A=8 $ within chiral
effective field theory: We investigate $S=-1$ and $-2$ hypernuclei with $A=4-8$ employing the
Jacobi-NCSM approach and in combination with baryon-baryon interactions derived
within the frame work of chiral effective field theory. The employed
interactions are transformed using the similarity renormalization group (SRG)
so that the low- and high-momentum states are decoupled, and,
thereby,convergence of the binding energies with respect to model space can be
significantly speeded up. Such an evolution is however only approximately
unitary when the so-called SRG induced higher-body forces are omitted. We first
explore the impact of the SRG evolution on the $\Lambda$ separation energies
$B_{\Lambda}$ in $A=3-5$ hypernuclei when only SRG-evolved two-body and when
both two- and three-body forces are included. For the latter scenario, we
thoroughly study predictions of the two almost phase-equivalent NLO13 and NLO19
YN potentials for $A=4-7$ hypernuclei. The NLO19 interaction yields separation
energies that are comparable with experiment, whereas NLO13 underestimates all
the systems considered. We further explore CSB splittings in the $A=7,8$
multiplets employing the two NLO YN potentials that include also the leading
CSB potential in the $\Lambda$N channel, whose strength has been fitted to the
presently established CSB in $A=4$. Finally, we report on our recent study for
$\Xi$ hypernuclei based on the $\Xi$N interaction at NLO. | nucl-th |
Impact of Nucleon-Nucleon Bremsstrahlung Rates Beyond One-Pion Exchange: Neutrino-pair production and annihilation through nucleon-nucleon
bremsstrahlung is included in current supernova simulations by rates that are
based on the one-pion-exchange approximation. Here we explore the consequences
of bremsstrahlung rates based on a modern nuclear interactions for
proto-neutron star cooling and the corresponding neutrino emission. We find
that despite a reduction of the bremsstrahlung emission by a factor of 2-5 in
the neutrinospheric region, models with the improved treatment exhibit only
$\lesssim$5% changes of the neutrino luminosities and an increase of
$\lesssim$0.7 MeV of the average energies of the radiated neutrino spectra,
with the largest effects for the antineutrinos of all flavors and at late
times. Overall, the proto-neutron star cooling evolution is slowed down
modestly by $\lesssim$0.5-1 s. | nucl-th |
System stability and truncation schemes to the Dyson-Schwinger Equations: With decades of years development, although important progresses have been
made by the pioneers of this field, providing a sophisticated truncation scheme
is still a great challenge up to now if the Dyson-Schwinger Equations(DSEs) of
both quark and gluon propagators (or including even more DSEs) remain after
truncation. In this work we view the coupled reminiscent DSEs of the gluon and
quark propagators after truncation as a system with feedback. Then studying the
stability of this equation array gives useful results. Our calculation shows
that the sum of the gluon and ghost loops plays the most important role in
keeping this system stable and having reasonable solutions. The quark-gluon
vertex plays a relative smaller but also important role. Our method also could
give constraints and inspirations on fabricating a more sophisticated model of
the quark-gluon vertex. | nucl-th |
Shape phase mixing in critical point nuclei: Spectral properties of nuclei near the critical point of the quantum phase
transition between spherical and axially symmetric shapes are studied in a
hybrid collective model which combines the $\gamma$-stable and $\gamma$-rigid
collective conditions through a rigidity parameter. The model in the lower and
upper limits of the rigidity parameter recovers the X(5) and X(3) solutions
respectively, while in the equally mixed case it corresponds to the X(4)
critical point symmetry. Numerical applications of the model on nuclei from
regions known for critical behavior reveal a sizable shape phase mixing and its
evolution with neutron or proton numbers. The model also enables a better
description of energy spectra and electromagnetic transitions for these nuclei. | nucl-th |
Influence of anisotropic $Λ/Σ$ creation on the $Ξ^-$
mutiplicity in subthreshold proton-nucleus collisions: We present an analysis of $\Xi^-$ baryon production in subthreshold
proton--nucleus ($p+A$) collisions in the framework of a BUU type transport
model. We propose a new mechanism for $\Xi$ production in the collision of a
secondary $\Lambda$ or $\Sigma$ hyperon and a nucleon from the target nucleus.
We find that the $\Xi^-$ multiplicity in $p+A$ collisions is sensitive to the
angular distribution of hyperon production in the primary $N+N$ collision.
Using reasonable assumptions on the unknown elementary cross sections we are
able to reproduce the $\Xi^-$ multiplicity and the $\Xi^-/(\Lambda+\Sigma^0)$
ratio obtained in the HADES experiment in $p$+Nb collisions at $\sqrt{s_{NN}} =
$ 3.2 GeV energy. | nucl-th |
Influence of complete energy sorting on the characteristics of the
odd-even effect in fission-fragment element distributions: The characteristics of the odd-even effect in fission-fragment Z
distributions are compared to a model based on statistical mechanics. Special
care is taken for using a consistent description for the influence of pairing
correlations on the nuclear level density. The variation of the odd-even effect
with the mass of the fissioning nucleus and with fission asymmetry is explained
by the important statistical weight of configurations where the light nascent
fission fragment populates the lowest energy state of an even-even nucleus.
This implies that entropy drives excitation energy and unpaired nucleons
predominantly to the heavy fragment. Therefore, within our model, the odd-even
effect appears as an additional signature of the recently discovered
energy-sorting process in nuclear fission. | nucl-th |
Can only flavor-nonsinglet H dibaryons be stable against strong decays?: Using the QCD sum rule approach, we show that the flavor-nonsinglet $H$
dibaryon states with J$^{\pi} = 1^+$, J$^{\pi} = 0^+$, I=1 (27plet) are nearly
degenerate with the J$^{\pi} = 0^+$, I=0 singlet $H_0$ dibaryon, which has been
predicted to be stable against strong decay, but has not been observed. Our
calculation, which does not require an instanton correction, suggests that the
$H_0$ is slightly heavier than these flavor-nonsinglet $H$s over a wide range
of the parameter space. If the singlet $H_0$ mass lies above the $\Lambda
\Lambda$ threshold (2231~MeV), then the strong interaction breakup to $\Lambda
\Lambda$ would produce a very broad resonance in the $\Lambda \Lambda$
invariant mass spectrum which would be very difficult to observe. On the other
hand, if these flavor-nonsinglet J=0 and 1 $H$ dibaryons are also above the
$\Lambda \Lambda$ threshold, but below the $\Xi^0n$ breakup threshold (2254
MeV), then because the direct, strong interaction decay to the $\Lambda
\Lambda$ channel is forbidden, these flavor-nonsinglet states might be more
amenable to experimental observation. The present results allow a possible
reconciliation between the reported observation of $\Lambda \Lambda$
hypernuclei, which argue against a stable $H_0$, and the possible existence of
$H$ dibaryons in general. | nucl-th |
Impact of the symmetry energy on the outer crust of non-accreting
neutron stars: The composition and equation of state of the outer crust of non-accreting
neutron stars is computed using accurate nuclear mass tables. The main goal of
the present study is to understand the impact of the symmetry energy on the
structure of the outer crust. First, a simple "toy model" is developed to
illustrate the competition between the electronic density and the symmetry
energy. Then, realistic mass tables are used to show that models with a stiff
symmetry energy - those that generate large neutron skins for heavy nuclei -
predict a sequence of nuclei that are more neutron-rich than their softer
counterparts. This result may be phrased in the form of a correlation: the
larger the neutron skin of 208Pb, the more exotic the composition of the outer
crust. | nucl-th |
From 0 to 5000 in $2\times 10^{-24}$ seconds: Entropy production in
relativistic heavy-ion collisions: We review what is known about the contributions to the final entropy from the
different stages of a relativistic nuclear collision, including recent results
on the decoherence entropy and the entropy produced during the hydrodynamic
phase by viscous effects. We then present a general framework, based on the
Husimi distribution function, for the calculation of entropy growth in quantum
field theories, which is applicable to the earliest ("glasma") phase of the
collision during which most of the entropy is generated. The entropy calculated
from the Husimi distribution exhibits linear growth when the quantum field
contains unstable modes and is asymptotically equal to the Kolmogorov-Sina\"i
(KS) entropy. We outline how the approach can be used to investigate the
problem of entropy production in a relativistic heavy-ion reaction from first
principles. | nucl-th |
Estimates of dilepton spectra from open charm and bottom decays: The spectra of lepton pairs from correlated open charm and bottom decays in
ultrarelativistic heavy-ion collisions are calculated. Our approach includes
energy loss effects of the fast heavy quarks in deconfined matter which are
determined by temperature and density of the expanding parton medium. We find a
noticeable suppression of the initial transverse momentum spectrum of heavy
quarks due to the energy loss within the central rapidity covered by the PHENIX
detector system. As a result the dilepton yields from correlated decays of
heavy quarks are in the same order of magnitude as the Drell-Yan signal. | nucl-th |
A dynamical, confining model and hot quark stars: We explore the consequences of an equation of state (EOS) obtained in a
confining Dyson-Schwinger equation model of QCD for the structure and stability
of nonstrange quark stars at finite-T, and compare the results with those
obtained using a bag-model EOS. Both models support a temperature profile that
varies over the star's volume and the consequences of this are model
independent. However, in our model the analogue of the bag pressure is
(T,mu)-dependent, which is not the case in the bag model. This is a significant
qualitative difference and comparing the results effects a primary goal of
elucidating the sensitivity of quark star properties to the form of the EOS. | nucl-th |
The piNN system - recent progress: Recent progress towards an understanding of the piNN system within chiral
perturbation theory is reported. The focus lies on an effective field theory
calculation and its comparison to phenomenological calculations for the
reaction NN->d pi. In addition, the resulting absorptive and dispersive
corrections to the pi-d scattering length are discussed briefly. | nucl-th |
Sensitivity study of experimental measures for the nuclear liquid-gas
phase transition in the statistical multifragmentation model: The experimental measures of the multiplicity derivatives, the moment
parameters, the bimodal parameter, the fluctuation of maximum fragment charge
number (NVZ), the Fisher exponent ($\tau$) and Zipf's law parameter ($\xi$),
are examined to search for the liquid-gas phase transition in nuclear
multifragmention processes within the framework of the statistical
multifragmentation model (SMM). The sensitivities of these measures are
studied. All these measures predict a critical signature at or near to the
critical point both for the primary and secondary fragments. Among these
measures, the total multiplicity derivative and the NVZ provide accurate
measures for the critical point from the final cold fragments as well as the
primary fragments. The present study will provide a guide for future
experiments and analyses in the study of nuclear liquid-gas phase transition. | nucl-th |
The nuclear liquid-gas transition in QCD: We estimate the nuclear saturation density and the binding energy in a
nuclear liquid from precision data on the coupling of the four-quark scattering
vertex in the vector channel, computed within functional QCD. We show that this
coupling is directly related to the density-density potential and the latter is
used for the estimates. In a first qualitative computation we find a saturation
density of 0.2 fm${}^{-3}$ and an upper bound for the binding energy of 21.5
MeV, in agreement with the empirical values of 0.16 fm${}^{-3}$ and 16 MeV,
respectively. We also use the scattering vertex for constructing an emergent
low-energy effective theory for the liquid gas transition from QCD correlation
function, whose coupling parameters can be determined within QCD. As a first
consistency check of this construction we estimate the in-medium reduction of
the nucleon pole mass. | nucl-th |
CHIRAL SYMMETRY CONSTRAINTS ON THE $K^+$ INTERACTION WITH THE NUCLEAR
PION CLOUD: The real part of the $K^{+}$ selfenergy for the interaction of the $K^{+}$
with the pion nuclear cloud is evaluated in lowest order of chiral perturbation
theory and is found to be exactly zero in symmetric nuclear matter. This
removes uncertainties in that quantity found in former phenomenological
analyses and is supported by present experimental data on $K^{+}$ nucleus
scattering. | nucl-th |
Neutrino/antineutrino-$^{12}$C charged cross sections in the projected
QRPA formalism: The $\nu/\bar{\nu}-^{12}$C cross sections are evaluated in the projected
quasiparticle random phase approximation (PQRPA). The cross section for $\nu_e$
as a function of the incident neutrino energy is compared with recent
theoretical calculations of more sophisticated models. The $\bar{\nu}-^{12}$C
cross section is calculated for the first time with the PQRPA. The distribution
of cross sections averaged with the Michel spectrum as well as with other
estimated fluxes for future experiments is compared for both $\nu_e$ and
$\bar{\nu}_e$. Some astrophysical implications are addressed. | nucl-th |
Many-body nuclear Hamiltonian: Ab exitu approach: Fully-microscopic No-core Shell Model (NCSM) calculations of all stable $s$
and $p$ shell nuclei are used to determine realistic $NN$ interaction JISP16
describing not only the two-nucleon data but the binding energies and spectra
of nuclei with $A\leq 16$ as well. The JISP16 interaction, providing rapid
convergence of the NCSM calculations, is obtained in an {\em ab exitu} approach
by phase-equivalent transformations of the JISP6 $NN$ interaction. | nucl-th |
Multiplicities in Au-Au and Cu-Cu collisions at \sqrt{s_{NN}} = 62.4 and
200 GeV: Likelihood ratio tests are performed for the hypothesis that charged-particle
multiplicities measured in Au-Au and Cu-Cu collisions at $\sqrt{s_{NN}} = 62.4$
and 200 GeV are distributed according to the negative binomial form. Results
suggest that the hypothesis should be rejected in the all classes of collision
systems and centralities of PHENIX-RHIC measurements. However, the application
of the least-squares test statistic with systematic errors included shows that
for the collision system Au-Au at $\sqrt{s_{NN}} = 62.4$ GeV the hypothesis
could not be rejected in general. | nucl-th |
A quasiparticle equation of state with a phenomenological critical point: We propose a hybrid parameterization of a quasiparticle equation of state,
where a critical point is implemented phenomenologically. In this approach, a
quasiparticle model with finite chemical potential is used to describe the
quark-gluon plasma phase by fitting to the lattice quantum chromodynamics data
at high temperature. On the other hand, the hadronic resonance gas model with
excluded volume correction is employed for the hadronic phase. An interpolation
scheme is implemented so that the phase transition is a smooth crossover when
the chemical potential is smaller than a critical value, or otherwise
approximately of first order according to Ehrenfest's classification. Also, the
thermodynamic consistency is guaranteed for the equation of state related to
both the quasiparticle model and the implementation of the critical point. | nucl-th |
Smallness of the imaginary part of the eta-nucleus scattering length: In two recent analyses of eta meson production a very small imaginary part
was obtained for the eta-He3 scattering length, which is in contradiction with
most theoretical predictions. In this report a plausible explanation is given
to this unexpectedly weak absorption by suppression of the two main
inelasticity channels. It is stressed that the real and imaginary parts of the
elementary scattering length do not necessarily always have the same isospin
algebraic and spatial properties in a nuclear environment and caution should be
exercised in their use in multiple scattering calculations and even
constructing simple optical potentials. | nucl-th |
Macroscopic approximation to relativistic kinetic theory from a
nonlinear closure: We use a macroscopic description of a system of relativistic particles based
on adding a nonequilibrium tensor to the usual hydrodynamic variables. The
nonequilibrium tensor is linked to relativistic kinetic theory through a
nonlinear closure suggested by the Entropy Production Principle; the evolution
equation is obtained by the method of moments, and together with
energy-momentum conservation closes the system. Transport coefficients are
chosen to reproduce second order fluid dynamics if gradients are small. We
compare the resulting formalism to exact solutions of Boltzmann's equation in
0+1 dimensions and show that it tracks kinetic theory better than second order
fluid dynamics. | nucl-th |
Bose-Einstein condensation of pions in heavy-ion collisions at the CERN
Large Hadron Collider (LHC) energies: We analyse in detail the possibility of Bose-Einstein condensation of pions
produced in heavy-ion collisions at the beam energy $\sqrt{s_{\rm NN}}$ = 2.76
TeV. Our approach is based on the chemical non-equilibrium thermal model of
hadron production which has been generalised to include separately the
contribution from the local zero-momentum state. In order to study both the
hadronic multiplicities and the transverse-momentum spectra, we use the Cracow
freeze-out model which parameterises the flow and space-time geometry of the
system at freeze-out in a very economic way. Our analysis indicates that about
5% of all pions may form the Bose-Einstein condensate. | nucl-th |
Deformed Nuclei in a Chiral Model: We investigate the deformation properties of atomic nuclei in a hadronic
chiral SU_f(3) model approach. The parameters are fitted to hadron mass
properties and adjustments for spherical finite nuclei have been performed.
Using these parameters the deformation of a series of light and heavy nuclei
are obtained in a two-dimensional self-consistent calculation. In addition we
discuss a case of superdeformation in a heavy nucleus. | nucl-th |
Production of eta mesons in nucleon-nucleon collisions: A microscopic calculation of near-threshold eta-meson production in the
reaction NN -> NNeta is presented. It is assumed that the eta meson is produced
via direct emission and via elementary rescattering processes MN -> etaN of
various mesons M = pi, rho, etc. As a novel feature the amplitudes for the
latter production mechanism are taken from a multi-channel meson-exchange model
of the pi N system developed by the Juelich group which contains explicitly the
channels pi N, rho N, eta N, sigma N, and pi Delta. Furthermore, effects of the
NN interaction in the final as well as in the initial state are taken into
account microscopically. Our results are compared with recent data from the
COSY and CELSIUS accelerator facilities. Reasonable agreement with available
near-threshold cross section data for the reactions pp -> ppeta, pn -> pneta,
and pn -> deta is found. | nucl-th |
Threshold Two-Pion Photo- and Electroproduction: More neutrals than
expected: We present an exploratory study of two pion photo-- and electroproduction off
the nucleon in the threshold region. To calculate the pertinent amplitudes, we
make use of heavy baryon chiral perturbation theory. We show that due to finite
chiral loops the production cross section for final states with two neutral
pions is considerably enhanced. The experimental implications are briefly
discussed. | nucl-th |
Open-Shell Nuclei from No-Core Shell Model with Perturbative Improvement: We introduce a hybrid many-body approach that combines the flexibility of the
No-Core Shell Model (NCSM) with the efficiency of Multi-Configurational
Perturbation Theory (MCPT) to compute ground- and excited-state energies in
arbitrary open-shell nuclei in large model spaces. The NCSM in small model
spaces is used to define a multi-determinantal reference state that contains
the most important multi-particle multi-hole correlations and a subsequent
second-order MCPT correction is used to capture additional correlation effects
from a large model space. We apply this new ab initio approach for the
calculation of ground-state and excitation energies of even and odd-mass
carbon, oxygen, and fluorine isotopes and compare to large-scale NCSM
calculations that are computationally much more expensive. | nucl-th |
Complex phase structure of the meson-baryon $T$-matrix: The full complex phase structure of the meson-baryon reaction amplitude in
coupled channels approach is investigated, including also the photon-baryon
channel. The result may be viewed as a generalization of the well-known
Watson's theorem. Furthermore, the complex phase structure is exhibited for the
pole and nonpole parts of the reaction amplitude in such a way that it will
serve as a convenient common starting point for constructing models with
different levels of approximation, in particular, for building isobar models
where the basic properties of the $S$-matrix can be maintained. Such models
should be useful, especially, in coupled multichannel calculations, where a
large amount of experimental data are considered in resonance analyses, a
situation encountered in modern baryon spectroscopy. In particular, it is shown
that the unitarity of the pole part of the $T$-matrix arises automatically from
the dressing mechanism inherent in the basic scattering equation. This implies
that no separate conditions are required for making this part of the resonance
amplitude unitary as it has been done in some of the existing isobar models. | nucl-th |
Collective model for cluster motion in $^8$Be, $^{12}$C, and $^{16}$O
systems: A microscopic $n\alpha$ cluster model was applied to $^{8}$Be, $^{12}$C, and
$^{16}$O systems to investigate cluster motion in the ground state and radial
excitation. In the microscopic calculation of $^{12}$C and $^{16}$O using the
generator coordinate method with the coordinate $D$ of the $\alpha$-$\alpha$
distance, excited states were obtained as the large-amplitude mode built on the
ground state. A collective model was constructed to describe the cluster motion
of these states by utilizing inputs from the microscopic cluster model such as
the norm kernel and energy expectation values. Furthermore, the cluster model
was extended by introducing the imaginary part of the coordinate $D$ to
incorporate the dynamical effects on the collective mass. The collective wave
function obtained with the collective model was found to be in reasonable
agreement with the results of the generator coordinate method for energies,
root-mean-square radii, and amplitude functions. | nucl-th |
Location of the QCD critical point predicted by holographic Bayesian
analysis: We present results for a Bayesian analysis of the location of the QCD
critical point constrained by first-principles lattice QCD results at zero
baryon density. We employ a holographic Einstein-Maxwell-dilaton model of the
QCD equation of state, capable of reproducing the latest lattice QCD results at
zero and finite baryon chemical potential. Our analysis is carried out for two
different parametrizations of this model, resulting in confidence intervals for
the critical point location that overlap at one sigma. While samples of the
prior distribution may not even predict a critical point, or produce critical
points spread around a large region of the phase diagram, posterior samples
nearly always present a critical point at chemical potentials of $\mu_{Bc} \sim
550 - 630$ MeV. | nucl-th |
Heavy Flavor Suppression: Boltzmann vs Langevin: The propagation of heavy flavor through the quark gluon plasma has been
treated commonly within the framework of Langevin dynamics, i.e. assuming the
heavy flavor momentum transfer is much smaller than the light one. On the other
hand a similar suppression factor $R_{AA}$ has been observed experimentally for
light and heavy flavors. We present a thorough study of the approximations
involved by Langevin equation by mean of a direct comparison with the full
collisional integral within the framework of Boltzmann transport equation. We
have compared the results obtained in both approaches which can differ
substantially for charm quark leading to quite different values extracted for
the heavy quark diffusion coefficient. In the case of bottom quark the
approximation appears to be quite reasonable. | nucl-th |
Effect of cluster transfer on neutron-rich nuclide production around
N=126 in multinucleon transfer reactions: The cluster transfer in multinucleon transfer reactions near Coulomb barrier
energies is implemented into the master equations in dinuclear system model, in
which the deuteron, triton, $^{3}$He and $\alpha$ are taken into account. The
effects of cluster transfer and dynamical deformation on the formation of
primary and secondary fragments are systematically investigated. It is found
that the inclusion of cluster transfer is favorable the fragment formation with
increasing the transferring nucleons and leads to a broad mass distribution.
The isotopic cross sections of elements W, Os, Rn and Fr in the reaction of
$^{136}$Xe+$^{208}$Pb at the incident energy of E$_{c.m.}$ = 450 MeV are nicely
consistent with the Argonne data. The new neutron-rich isotopes of wolfram and
osmium are predicted with cross sections above 10 nb. The production mechanism
of neutron-rich heavy nuclei around N = 126 in the reactions of $^{58,64,72}$Ni
+ $^{198}$Pt is investigated thoroughly. The cross sections for producing the
neutron-rich isotopes of platinum, iridium, osmium and rhenium in the
multinucleon transfer reactions of $^{64}$Ni + $^{198}$Pt and $^{72}$Ni +
$^{198}$Pt at the center of mass energies of 220 MeV and 230 MeV are estimated
and proposed for the future experiments. | nucl-th |
Matter effects on $η$ and $η'$ mesons: We show how the nuclear medium affects the masses of the $\eta$ and $\eta'$
mesons. The change should be easily detectable for dense matter and/or strong
$\eta(\eta')N\bar N$ coupling. We also find that the $\eta-\eta'$ mixing angle
is less in magnitude in the nuclear matter than in vacuum. | nucl-th |
Momentum dependent nucleon-nucleon contact interaction from a
relativistic Lagrangian: A complete set of parity- and time-reversal conserving relativistic
nucleon-nucleon contact operators is identified up to the order $O(p^4)$ of the
expansion in soft momenta $p$. A basis is also provided for the corresponding
non-relativistic operators contributing in the general reference frame. We show
that the non-relativistic expansions of the relativistic operators involve
twenty-six independent combinations, two starting at $O(p^0)$, seven at order
$O(p^2)$ and seventeen at order $O(p^4)$. This gives supporting evidence to the
existence of two free low-energy constants which parametrize an interaction
depending on the total nucleon pair momentum ${\bf P}$, and were recently found
to be instrumental for the resolution of the long standing $A_y$ problem in
low-energy $p-d$ scattering. Furthermore, all remaining ${\bf P}$-dependent
interactions at the same order are uniquely determined as relativistic
corrections. | nucl-th |
Momentum-space calculation of proton-deuteron scattering including
Coulomb and irreducible three-nucleon forces: Three-nucleon scattering equations with irreducible three-nucleon force are
solved in momentum-space. The Coulomb interaction between the two protons is
included using the method of screening and renormalization. The need for the
renormalization of the scattering amplitudes is demonstrated numerically. The
Coulomb and Urbana IX three-nucleon force effects on the observables of elastic
proton-deuteron scattering and breakup are studied. | nucl-th |
Photon electroproduction off nuclei in the $Δ$-resonance region: The cross section for the $A(e,e'\gamma)A$ reaction is calculated,
investigating the contribution from the nuclear target with respect to the
radiative corrections from the electron. The reaction mechanism is studied for
photon emission in the $\Delta$-resonance region, varying the scattering
geometry and analyzing the most favourable kinematical conditions to extract
information on the nuclear system. | nucl-th |
Tracing baryon and electric charge transport in isobar collisions: It is of fundamental interest to understand the carrier of conserved quantum
charges within protons and nuclei at high energy. Preliminary data from isobar
collisions at RHIC reveal a scaled net-baryon to net-electric charge ratio
($B/\Delta Q \times \Delta Z/A$) at mid-rapidity between 1.2 and 2, consistent
with string junction model predictions. Here, we compute the initial stage
scaled net-baryon to net-electric charge ratio for isobar collisions. Our model
incorporates a realization of the string junction model and models the nuclear
structure. Our predictions identify the baseline expectations for such
measurement and quantify the impact of the nuclear structure. | nucl-th |
ADG: Automated generation and evaluation of many-body diagrams III.
Bogoliubov in-medium similarity renormalization group formalism: The goal of the present paper is twofold. First, a novel expansion many-body
method applicable to superfluid open-shell nuclei, the so-called Bogoliubov
in-medium similarity renormalization group (BIMSRG) theory, is formulated. This
generalization of standard single-reference IMSRG theory for closed-shell
systems parallels the recent extensions of coupled cluster, self-consistent
Green's function or many-body perturbation theory. Within the realm of IMSRG
theories, BIMSRG provides an interesting alternative to the already existing
multi-reference IMSRG (MR-IMSRG) method applicable to open-shell nuclei.
The algebraic equations for low-order approximations, i.e., BIMSRG(1) and
BIMSRG(2), can be derived manually without much difficulty. However, such a
methodology becomes already impractical and error prone for the derivation of
the BIMSRG(3) equations, which are eventually needed to reach high accuracy.
Based on a diagrammatic formulation of BIMSRG theory, the second objective of
the present paper is thus to describe the third version (v3.0.0) of the ADG
code that automatically (1) generates all valid BIMSRG(n) diagrams and (2)
evaluates their algebraic expressions in a matter of seconds. This is achieved
in such a way that equations can easily be retrieved for both the flow equation
and the Magnus expansion formulations of BIMSRG.
Expanding on this work, the first future objective is to numerically
implement BIMSRG(2) (eventually BIMSRG(3)) equations and perform ab initio
calculations of mid-mass open-shell nuclei. | nucl-th |
Asymptotics of neutron Cooper pair in weakly bound nuclei: Asymptotic form of neutron Cooper pair penetrating to the exterior of nuclear
surface is investigated with the Bogoliubov theory for the superfluid Fermions.
Based on a two-particle Schr\"{o}dinger equation governing the Cooper pair wave
function and systematic studies for both weakly bound and stable nuclei, the
Cooper pair is shown to be spatially correlated even in the asymptotic large
distance limit, and the penetration length of the pair condensate is revealed
to be universally governed by the two-neutron separation energy $S_{2n}$ and
the di-neutron mass $2m$. | nucl-th |
Exact versus Taylor-expanded energy density in the study of the neutron
star crust-core transition: The importance of the fourth and higher order terms in the Taylor series
expansion of the energy of the isospin asymmetric nuclear matter in the study
of the neutron star crust-core phase transition is investigated using the
finite range simple effective interaction. Analytic expressions for the
evaluation of the second and fourth order derivative terms in the Taylor series
expansion for any general finite range interaction of Yukawa, exponential or
Gaussian form have been obtained. The effect of the nuclear matter
incompressibility, symmetry energy and slope parameters on the predictions for
the crust-core transition density is examined. The crustal moment of inertia is
calculated and the prediction for the radius of the Vela pulsar is analyzed
using different equations of state. | nucl-th |
P and T odd effects in deuteron in the Reid potential: The $P$ and $T$ odd deuteron multipoles are calculated in the Reid
nucleon-nucleon potential in the chiral limit $m_{\pi}\to 0$. The contact
current generated by the $\pi$-meson exchange does not contribute to the
anapole moment. The contact current generated by the vector meson exchange is
negligible in comparison with other contributions of vector mesons. The result
for the deuteron electric dipole moment is of great interest because of the
experiment on its measurement discussed in Brookhaven. The deuteron
photodisintegration cross section asymmetry at the threshold is also
calculated. It is shown that its value strongly depends on the tensor forces
and d-wave contribution to the deuteron wave function. | nucl-th |
J/psi production at mid and forward rapidity at RHIC: We calculate the rapidity dependence of $J/\psi$ nuclear modification factor
and averaged transverse momentum square in heavy ion collisions at RHIC in a
3-dimensional transport approach with regeneration mechanism. | nucl-th |
Analysis of the pp-->pp, pid-->pid, and pid-->pp Scattering Data: A combined analysis of the main reactions of the two-baryon system (pp-->pp,
pid-->pid, and pid-->pp) over the sqrt{s} interval from pion threshold to 2.4
GeV has been completed. The overall phase in pid-->pp has now been determined.
The combined analysis has resulted in an improved fit to the pid elastic and
pid-->pp databases. | nucl-th |
Small-$x$ Asymptotics of the Gluon Helicity Distribution: We determine the small-$x$ asymptotics of the gluon helicity distribution in
a proton at leading order in perturbative QCD at large $N_c$. To achieve this,
we begin by evaluating the dipole gluon helicity TMD at small $x$. In the
process we obtain an interesting new result: in contrast to the unpolarized
dipole gluon TMD case, the operator governing the small-$x$ behavior of the
dipole gluon helicity TMD is different from the operator corresponding to the
polarized dipole scattering amplitude (used in our previous work to determine
the small-$x$ asymptotics of the quark helicity distribution). We then
construct and solve novel small-$x$ large-$N_c$ evolution equations for the
operator related to the dipole gluon helicity TMD. Our main result is the
small-$x$ asymptotics for the gluon helicity distribution: $\Delta G \sim
\left( \tfrac{1}{x} \right)^{\alpha_h^G}$ with $\alpha_h^G = \tfrac{13}{4
\sqrt{3}} \, \sqrt{\tfrac{\alpha_s \, N_c}{2 \pi}} \approx 1.88 \,
\sqrt{\tfrac{\alpha_s \, N_c}{2 \pi}}$. We note that the power $\alpha_h^G$ is
approximately 20$\%$ lower than the corresponding power $\alpha_h^q$ for the
small-$x$ asymptotics of the quark helicity distribution defined by $\Delta q
\sim \left( \tfrac{1}{x} \right)^{\alpha_h^q}$ with $\alpha_h^q =
\tfrac{4}{\sqrt{3}} \, \sqrt{\tfrac{\alpha_s \, N_c}{2 \pi}} \approx 2.31 \,
\sqrt{\tfrac{\alpha_s \, N_c}{2 \pi}}$ found in our earlier work. | nucl-th |
Electric Properties of One-Neutron Halo Nuclei in Halo EFT: We exploit the separation of scales in weakly-bound nuclei to compute E2
transitions and electric form factors in a Halo EFT framework. The relevant
degrees of freedom are the core and the halo neutron. The EFT expansion is
carried out in powers of $R_{core}/R_{halo}$, where $R_{core}$ and $R_{halo}$
denote the length scales of the core and halo, respectively. We include the
strong $s$-wave and $d$-wave interactions by introducing dimer fields. The
dimer propagators are regulated by employing the power divergence subtraction
scheme and matched to the effective range expansion in the respective
channel.Electromagnetic interactions are included via minimal substitution in
the Lagrangian. We demonstrate that, depending on the observable and respective
partial wave, additional local gauge-invariant operators contribute in LO, NLO
and higher orders. | nucl-th |
Spin observables in antiproton-proton to AntiLambda-Lambda and
density-matrix constraints: The positivity conditions of the spin density matrix constrain the spin
observables of the reaction antiproton-proton to AntiLambda-Lambda, leading to
model-independent, non-trivial inequalities. The formalism is briefly presented
and examples of inequalities are provided. | nucl-th |
Ion induced quark-gluon implosion: We investigate nuclear fragmentation in the central proton-nucleus and
nucleus - nucleus collisions at the energies of LHC. We argue that within the
semi-classical approximation because of fast increase with energy of cross
sections of soft and hard interactions each nucleon is stripped in the average
process off ``soft'' partons and fragments into a collection of leading quarks
and gluons with large $p_t$. Valence quarks and gluons are streaming in the
opposite directions when viewed in the c.m. of the produced system. The
resulting pattern of the fragmentation of the colliding nuclei leads to an
implosion of the quark and gluon constituents of the nuclei. The matter density
produced at the initial stage in the nucleus fragmentation region is estimated
to be $\geq$ 50 GeV/fm$^3$ at the LHC energies and probably $\geq$ 10
GeV/fm$^3$ at RHIC. | nucl-th |
Internal One-Particle Density Matrix for Bose-Einstein Condensates with
Finite Number of Particles in a Harmonic Potential: Investigations on the internal one-particle density matrix in the case of
Bose-Einstein condensates with a finite number ($N$) of particles in a harmonic
potential are performed. We solve the eigenvalue problem of the
Pethick-Pitaevskii-type internal density matrix and find a fragmented
condensate. On the contrary the condensate Jacobi-type internal density matrix
gives complete condensation into a single state. The internal one-particle
density matrix is, therefore, shown to be different in general for different
choices of the internal coordinate system. We propose two physically motivated
criteria for the choice of the adequate coordinate systems which give us a
unique answer for the internal one-particle density matrix. One criterion is
that in the infinite particle number limit ($N=\infty$) the internal
one-particle density matrix should have the same eigenvalues and eigenfunctions
as those of the corresponding ideal Bose-Einstein condensate in the laboratory
frame. The other criterion is that the coordinate of the internal one-particle
density matrix should be orthogonal to the remaining $(N - 2)$ internal
coordinates. This second criterion is shown to imply the first criterion. It is
shown that the internal Jacobi coordinate system satisfies these two criteria
while the internal coordinate system adopted by Pethick and Pitaevskii for the
construction of the internal one-particle density matrix does not. It is
demonstrated that these two criteria uniquely determine the internal
one-particle density matrix which is identical to that calculated with the
Jacobi coordinates. The relevance of this work concerning $\alpha$-particle
condensates in nuclei, as well as bosonic atoms in traps, is pointed out. | nucl-th |
Delayed Collapse of Protoneutron Stars with Kaon Condensate: Equation of state with kaon condensate is derived for isentropic and
neutrino-trapped matter. Both are important ingredients to study the delayed
collapse of protoneutron stars. Solving the TOV equation, we discuss the static
properties of protoneutron stars and implications for their delayed collapse. | nucl-th |
Relativistic fluctuating hydrodynamics with memory functions and colored
noises: Relativistic dissipative hydrodynamics including hydrodynamic fluctuations is
formulated by putting an emphasis on non-linearity and causality. As a
consequence of causality, dissipative currents become dynamical variables and
noises appeared in an integral form of constitutive equations should be colored
ones from fluctuation-dissipation relations. Nevertheless noises turn out to be
white ones in its differential form when noises are assumed to be Gaussian. The
obtained ifferential equations are very useful in numerical implementation of
relativistic fluctuating hydrodynamics. | nucl-th |
Superdeformation and clustering in $^{40}$Ca studied with
Antisymmetrized Molecular Dynamics: Deformed states in $^{40}$Ca are investigated with a method of
antisymmetrized molecular dynamics. Above the spherical ground state,
rotational bands arise from a normal deformation and a superdeformation as well
as an oblate deformation. The calculated energy spectra and $E2$ transition
strengths in the superdeformed band reasonably agree to the experimental data
of the superdeformed band starting from the $0^+_3$ state at 5.213 MeV. By the
analysis of single-particle orbits, it is found that the superdeformed state
has particle-hole nature of an $8p$-$8h$ configuration. One of new findings is
parity asymmetric structure with $^{12}$C+$^{28}$Si-like clustering in the
superdeformed band. We predict that $^{12}$C+$^{28}$Si molecular bands may be
built above the superdeformed band due to the excitation of inter-cluster
motion. They are considered to be higher nodal states of the superdeformed
state. We also suggest negative-parity bands caused by the parity asymmetric
deformation. | nucl-th |
Self-consistent description of the halo nature of 31Ne with continuum
and pairing correlations: Using a Glauber model with our relativistic fully microscopic structure model
input, we give a full description of the halo nature of 31Ne that includes a
self-consistent use of pairing and continuum contributions that makes
predictions consistent with reaction cross section measurements. Our
predictions of total reaction and one-neutron removal cross sections of 31Ne on
a Carbon target were significantly enhanced compared with those of neighboring
Neon isotopes, agreeing well with measurements at 240 MeV/nucleon and
consistent with a single neutron halo. Furthermore, our calculations of the
inclusive longitudinal momentum distribution of the 30Ne and valence neutron
residues from the 31Ne breakup reaction indicate a dilute density distribution
in coordinate space, another halo signature. | nucl-th |
Photoproduction of meson and baryon resonances in a chiral unitary
approach: By means of a coupled channel non-perturbative unitary approach, it is
possible to extend the strong constrains of Chiral Perturbation Theory to
higher energies. In particular, it is possible to reproduce the lowest lying
resonances in meson-meson scattering up to 1.2 GeV using the parameters of the
O(p^2) and O(p^4) Chiral Lagrangian. The meson baryon sector can also be
tackled along similar lines. We report on an update of these results showing
some examples of photon induced reactions where the techniques have been
recently applied. | nucl-th |
Freeze Out Process with In-Medium Nucleon Mass: We investigate the kinetic freeze out scenario of a nucleon gas through a
finite layer. The in-medium mass modification of nucleons and it's impact on
the freeze out process is studied. A considerable modification of the
thermodynamical parameters temperature, flow-velocity, energy density and
particle density has been found in comparison with evaluations which use a
constant vacuum nucleon mass. | nucl-th |
Nuclear interactions and net-proton number fluctuations in heavy ion
collisions at the SIS18 accelerator: The effect of nuclear interactions on measurable net-proton number
fluctuations in heavy ion collisions at the SIS18/GSI accelerator is
investigated. The state of the art UrQMD model including interaction potentials
is employed. It is found that the nuclear forces enhance the baryon number
cumulants, as predicted from grand canonical thermodynamical models. The effect
however is smeared out for proton number fluctuations due to iso-spin
randomization and global baryon number conservation, which decreases the
cumulant ratios. For a rapidity acceptance window larger than $\Delta y> 0.4$
the effects of global baryon number conservation dominate and all cumulant
ratios are significantly smaller than 1. | nucl-th |
Transport approaches for the Description of Intermediate-Energy
Heavy-Ion Collisions: The transport approach is a useful tool to study dynamics of non-equilibrium
systems. For heavy-ion collisions at intermediate energies, where both the
smooth nucleon potential and the hard-core nucleon-nucleon collision are
important, the dynamics are properly described by two families of transport
models, i.e., the Boltzmann-Uehling-Uhlenbeck approach and the quantum
molecular dynamics approach. These transport models have been extensively used
to extract valuable information of the nuclear equation of state, the nuclear
symmetry energy, and microscopic nuclear interactions from intermediate-energy
heavy-ion collision experiments. On the other hand, there do exist deviations
on the predications and conclusions from different transport models. Efforts on
the transport code evaluation project are devoted in order to understand the
model dependence of transport simulations and well control the main
ingredients, such as the initialization, the mean-field potential, the
nucleon-nucleon collision, etc. A new era of accurately extracting nuclear
interactions from transport model studies is foreseen. | nucl-th |
Statistical multifragmentation model with discretized energy and the
generalized Fermi breakup. I. Formulation of the model: The Generalized Fermi Breakup recently demonstrated to be formally equivalent
to the Statistical Multifragmentation Model, if the contribution of excited
states are included in the state densities of the former, is implemented. Since
this treatment requires the application of the Statistical Multifragmentation
Model repeatedly on the hot fragments until they have decayed to their ground
states, it becomes extremely computational demanding, making its application to
the systems of interest extremely difficult. Based on exact recursion formulae
previously developed by Chase and Mekjian to calculate the statistical weights
very efficiently, we present an implementation which is efficient enough to
allow it to be applied to large systems at high excitation energies. Comparison
with the GEMINI++ sequential decay code shows that the predictions obtained
with our treatment are fairly similar to those obtained with this more
traditional model. | nucl-th |
Evolution of $N=20,28,50$ shell closures in the $ 20 \leqslant Z
\leqslant 30$ region in deformed relativistic Hartree-Bogoliubov theory in
continuum: Magicity, or shell closure, plays an important role in our understanding of
complex nuclear phenomena. In this work, we employ one of the state-of-the-art
density functional theories, the deformed relativistic Hartree-Bogoliubov
theory in continuum (DRHBc) with the density functional PC-PK1, to investigate
the evolution of the $N=20,28,50$ shell closures in the $ 20 \leqslant Z
\leqslant 30$ region. We show how these three conventional shell closures
evolve from the proton drip line to the neutron drip line by studying the
charge radii, two-neutron separation energies, two-neutron gaps, quadrupole
deformations, and single-particle levels. In particular, we find that in the $
21 \leqslant Z \leqslant 27$ region, the $N=50$ shell closure disappears or
becomes quenched, mainly due to the deformation effects. Similarly, both
experimental data and theoretical predictions indicate that the $N=28$ shell
closure disappears in the Mn isotopic chain, also predominantly due to the
deformation effects. The DRHBc theory predicts the existence of the $N=20$
shell closure in the Ca, Sc, and Ti isotopic chains, but the existing data for
the Ti isotopes suggests the contrary, and therefore more investigations are
needed. | nucl-th |
Suprathermal viscosity of dense matter: Motivated by the existence of unstable modes of compact stars that eventually
grow large, we study the bulk viscosity of dense matter, taking into account
non-linear effects arising in the large amplitude regime, where the deviation
mu_Delta of the chemical potentials from chemical equilibrium fulfills mu_Delta
> T. We find that this supra-thermal bulk viscosity can provide a potential
mechanism for saturating unstable modes in compact stars since the viscosity is
strongly enhanced. Our study confirms previous results on strange quark matter
and shows that the suprathermal enhancement is even stronger in the case of
hadronic matter. We also comment on the competition of different weak channels
and the presence of suprathermal effects in various color superconducting
phases of dense quark matter. | nucl-th |
Strangeness $S=-1$ hyperon-nucleon interactions: chiral effective field
theory vs. lattice QCD: Hyperon-nucleon interactions serve as basic inputs to studies of hypernuclear
physics and dense (neutron) stars. Unfortunately, a precise understanding of
these important quantities have lagged far behind that of the nucleon-nucleon
interaction due to lack of high precision experimental data. Historically,
hyperon-nucleon interactions are either formulated in quark models or meson
exchange models. In recent years, lattice QCD simulations and chiral effective
field theory approaches start to offer new insights from first principles. In
the present work, we contrast the state of art lattice QCD simulations with the
latest chiral hyperon-nucleon forces and show that the leading order
relativistic chiral results can already describe the lattice QCD data
reasonably well. Given the fact that the lattice QCD simulations are performed
with pion masses ranging from the (almost) physical point to 700 MeV, such
studies provide a highly non-trivial check on both the chiral effective field
theory approaches as well as lattice QCD simulations. Nevertheless more precise
lattice QCD simulations are eagerly needed to refine our understanding of
hyperon-nucleon interactions. | nucl-th |
Relativistic viscous hydrodynamics for heavy-ion collisions: A
comparison between the Chapman-Enskog and Grad methods: Derivations of relativistic second-order dissipative hydrodynamic equations
have relied almost exclusively on the use of Grad's 14-moment approximation to
write $f(x,p)$, the nonequilibrium distribution function in the phase space.
Here we consider an alternative Chapman-Enskog-like method, which, unlike
Grad's, involves a small expansion parameter. We derive an expression for
$f(x,p)$ to second order in this parameter. We show analytically that while
Grad's method leads to the violation of the experimentally observed
$1/\sqrt{m_T}$ scaling of the longitudinal femtoscopic radii, the alternative
method does not exhibit such an unphysical behavior. We compare numerical
results for hadron transverse-momentum spectra and femtoscopic radii obtained
in these two methods, within the one-dimensional scaling expansion scenario.
Moreover, we demonstrate a rapid convergence of the Chapman-Enskog-like
expansion up to second order. This leads to an expression for $\delta f(x,p)$
which provides a better alternative to Grad's approximation for hydrodynamic
modeling of relativistic heavy-ion collisions. | nucl-th |
Faddeev Calculation of the Hypertriton using the SU_6 Quark-Model
Nucleon-Nucleon and Hyperon-Nucleon Interactions: Quark-model nucleon-nucleon and hyperon-nucleon interactions by the Kyoto-
Niigata group are applied to the hypertriton calculation in a new three-cluster
Faddeev formalism using the two-cluster resonating-group method kernels. The
most recent model, fss2, gives a reasonable result similar to the Nijmegen
soft-core model NSC89, except for an appreciable contributions of higher
partial waves. | nucl-th |
Baryon and meson screening masses: In a strongly-coupled quark-gluon plasma, collective excitations of gluons
and quarks should dominate over the excitation of individual quasi-free gluon
and quark modes. To explore this possibility, we computed screening masses for
ground-state light-quark mesons and baryons at leading-order in a
symmetry-preserving truncation scheme for the Dyson-Schwinger equations using a
confining formulation of a contact-interaction at nonzero temperature. Meson
screening masses are obtained from Bethe-Salpeter equations; and baryon
analogues from a novel construction of the Faddeev equation, which employs an
improved quark-exchange approximation in the kernel. Our treatment implements a
deconfinement transition that is coincident with chiral symmetry restoration in
the chiral limit, when both transitions are second order. Despite
deconfinement, in all T=0 bound-state channels, strong correlations persist
above the critical temperature, T>T_c; and, in the spectrum defined by the
associated screening masses, degeneracy between parity-partner correlations is
apparent for T >1.3T_c. Notwithstanding these results, there are reasons
(including Golberger-Treiman relations) to suppose that the inertial masses of
light-quark bound-states, when they may be defined, vanish at the deconfinement
temperature; and that this is a signal of bound-state dissolution. Where a
sensible comparison is possible, our predictions are consistent with results
from contemporary numerical simulations of lattice-regularised QCD. | nucl-th |
Symmetry-unrestricted Skyrme mean-field study of heavy nuclei: In the light of recent experimental developments, increasing attention is
devoted to nuclear phenomena related to rotational excitations of exotic
intrinsic nuclear configurations that often lack symmetries present in the
majority of nuclei. Examples include configurations with a non-vanishing
octupole moment. In order to describe this kind of states, we have developed a
new computer code to solve the self-consistent mean-field equations, able to
use most of today's effective Skyrme interactions and working in
coordinate-space. We report on the development of MOCCa, a code based on the
same principles as EV8, but offering the user individual control on many
symmetry assumptions. In addition, the HF+BCS pairing treatment of EV8 has been
generalised to the full machinery of Hartree-Fock-Bogoliubov transformations.
We discuss as example the static fission barrier of $^{226}$Ra, prefacing
extended studies in the region, using the recent series of Skyrme
parameterizations SLy5s1 through SLy5s8. | nucl-th |
Properties of superheavy nuclei with Z = 124: We employ Relativistic Mean Field (RMF) model with NL3 parametrization to
investigate the ground state properties of superheavy nucleus, Z = 124. The
nuclei selected (from among complete isotopic series) for detailed
investigation show that the nucleon density at the center is very low and
therefore, these nuclei can be treated as semi-bubble nuclei. The considerable
shell gap appears at neutron numbers N = 172, 184 and 198 showing the magicity
corresponding to these numbers. The results are compared with the
macro-microscopic Finite Range Droplet Model (FRDM) wherever possible. | nucl-th |
Chiral O(Q^4) two-body operators for s-wave pion photoproduction on the
NN system: The two-body currents for s-wave pion photoproduction on the NN system are
derived to O(Q^4) in chiral perturbation theory. For the interesting case of
3S1 <-> 1S0 transitions, we show that an axial isovector two-nucleon contact
term connects the short-distance physics of pion photoproduction to pion
production and several important electroweak reactions. We also find that the
standard chiral Lagrangian gives a gamma pi pi N N vertex that have not been
explicitly mentioned in previous literature. The corresponding Feynman rule is
presented here and some processes where it should be important are briefly
discussed. | nucl-th |
Backbending phenomena in light nuclei at A~60 mass region: Recent studies of the backbending phenomenon in medium light weight nuclei
near A~60 expanded greatly our interest about how the single particle orbits
are nonlinearly affected by the collective motion. As a consequence we have
applied a modi…ed version of the exponential model with the inclusion of
paring correlation to describe the energy spectra of the ground state bands
and/or the backbending phenomenon in mass region at A~60. A firm conclusion is
obtained concerning the successful validity of the proposed modified model in
describing the backbending phenomenon in this region. Comparison with different
theoretical descriptions is discussed. | nucl-th |
Quenching of Gamow-Teller strengths and two particle -- two hole
configurations: We apply the charge-exchange subtracted second random-phase approximation
(SSRPA), based on Skyrme functionals, to investigate Gamow-Teller resonances in
several closed-shell and closed-subshell nuclei, located in different regions
of the nuclear chart. After having discussed the SSRPA findings obtained within
different approximation schemes in $^{48}$Ca, we compare our results with
{\it{ab-initio}} coupled-cluster predictions available for C and O isotopes,
where two-body currents are included. Our integrated strenghts, obtained by
using one-body transition operators, are lower compared to the corresponding
{\it{ab-initio}} results. This indicates that, within our model, quenching
effects are mainly driven by the inclusion of two particle - two hole
configurations and that the role of a two-body contribution in the transition
operator is less important than in the coupled-cluster approach. By analyzing
heavier nuclei, $^{90}$ Zr and $^{132}$Sn, we confirm the same conclusions that
we have recently drawn for $^{48}$Ca: the inclusion of two particle - two hole
configurations is very effective in our model for providing strengths which are
significantly more quenched than in other theoretical models and, thus, in
better agreement with the experimental measurements. This occurs because two
particle - two hole configurations have a density which strongly increases with
the excitation energy. Their inclusion thus pushes a significant amount of the
strength to higher energies, compared to what happens in other theoretical
models, reducing in this way the cumulative sum of the strength up to
excitation energies around 20-30 MeV. | nucl-th |
Enhanced effect of quark mass variation in 229Th and limits from Oklo
data: The effects of the variation of the dimensionless strong interaction
parameter Xq=mq/Lambda{QCD} (mq is the quark mass, Lambda{QCD} is the QCD
scale) are enhanced about 1.5 x 10**5 times in the 7.6 eV "nuclear clock"
transition between the ground and first excited states in the 229Th nucleus and
about 1 x 10**8 times in the relative shift of the 0.1 eV compound resonance in
150Sm.The best terrestrial limit on the temporal variation of the fundamental
constants, |delta(Xq)/Xq| < 4 x 10**-9 at 1.8 billion years ago (|d(Xq/Xq)/dt|
< 2.2 x 10**-18 y**-1), is obtained from the shift of this Sm resonance derived
from the Oklo natural nuclear reactor data. The results for 229Th and 150Sm are
obtained by extrapolation from light nuclei where the many-body calculations
can be performed more accurately. The errors produced by such extrapolation may
be smaller than the errors of direct calculations in heavy nuclei. The
extrapolation results are compared with the "direct" estimates obtained using
the Walecka model. A number of numerical relations needed for the calculations
of the variation effects in nuclear physics and atomic spectroscopy have been
obtained: for the nuclear binding energy delta(E)/E ~ -1.45 delta(mq)/mq, for
the spin-orbit intervals delta(Eso)/Eso ~ -0.22 delta(mq)/mq, for the nuclear
radius delta(r)/r ~ 0.3 delta(mq)/mq (in units of Lambda{QCD}); for the shifts
of nuclear resonances and weakly bound energy levels delta(Er) ~ 10
delta(Xq)/Xq MeV. | nucl-th |
The structure of the QED-Vacuum and Electron-Positron Pair Production in
Super-Intense, pulsed Laser Fields: We discuss electron-positron pair-production by super-intense, short laser
pulses off the physical vacuum state locally deformed by (stripped) nuclei with
large nuclear charges. Consequences of non-perturbative vacuum polarisation
resulting from such a deformation are shortly broached. Production
probabilities per pulse are calculated. | nucl-th |
Scale Dependence of Nucleon-Nucleon Potentials: The scale-dependence of the nucleon-nucleon interaction, which in recent
years has been extensively analysed within the context of chiral effective
field theory, is, in fact, inherent in any potential models constrained by a
fit to scattering data. A comparison between a purely phenomenological
potential and local interactions derived from chiral effective field theory
suggests that--thanks to the ability to describe nucleon-nucleon scattering at
higher energies, as well as the deuteron momentum distribution extracted from
electro-disintegration data--phenomenological potentials are best suited for
the description of nuclear dynamics at the scale relevant to neutron star
matter. | nucl-th |
The optical model potential of the $Σ$ hyperon in nuclear matter: We present our attempts to determine the optical model potential $U_\Sigma =
V_\Sigma -iW_\Sigma$ of the $\Sigma$ hyperon in nuclear matter. We analyze the
following sources of information on $U_\Sigma$: $\Sigma N$ scattering,
$\Sigma^-$ atoms, and final state interaction of $\Sigma$ hyperons in the
$(\pi,K^+)$ and $(K^-.\pi)$ reactions on nuclear targets. We conclude that
$V_\Sigma$ is repulsive inside the nucleus and has a shallow a tractive pocket
at the nuclear surface. These features of $V_\Sigma$ are consistent with the
Nijmegen model F of the hyperon-nucleon interaction. | nucl-th |
Meson-exchange currents and quasielastic predictions for
neutrino-nucleus scattering: We review some recent progress in the study of electroweak interactions in
nuclei within the SuSAv2-MEC model. The model has the capability to predict
(anti)neutrino scattering observables on different nuclei. The theoretical
predictions are compared with the recent T2K $\nu_\mu-^{16}$O data and good
agreement is found at all kinematics. The results are very similar to those
obtained for $\nu_\mu-^{12}$C scattering, except at low energies, where some
differences emerge. The role of meson-exchange currents in the two-particle
two-hole channel is analyzed in some detail. In particular it is shown that the
density dependence of these contributions is different from what is found for
the quasielastic response. | nucl-th |
Thermal twin stars within a hybrid equation of state based on a nonlocal
chiral quark model compatible with modern astrophysical observations: We investigate the extension to finite temperatures and neutrino chemical
potentials of a recently developed nonlocal chiral quark model approach to the
equation of state of neutron star matter. We consider two light quark flavors
and current-current interactions in the scalar-pseudoscalar, vector, and
diquark pairing channels, where the nonlocality of the currents is taken into
account by a Gaussian form factor that depends on the spatial components of the
4-momentum. Within this framework, we analyze order parameters, critical
temperatures, phase diagrams, equations of state, and mass-radius relations for
different temperatures and neutrino chemical potentials. For parameters of the
model that are constrained by recent multi-messenger observations of neutron
stars, we find that the mass-radius diagram for isothermal hybrid star
sequences exhibits the thermal twin phenomenon for temperatures above 30 MeV. | nucl-th |
Linearly stable and causal relativistic first-order spin hydrodynamics: We derive equations of motion for dissipative spin hydrodynamics from kinetic
theory up to first order in a gradient expansion. Choosing a specific form of
the matching conditions, relating the change in the spin potential to the spin
diffusion and spin energy, we then show that the equations of motion,
linearized around homogeneous global equilibrium, are causal and stable in any
Lorentz frame, if certain sufficient conditions on the transport coefficients
are fulfilled. | nucl-th |
Effective pseudopotential for energy density functionals with higher
order derivatives: We derive a zero-range pseudopotential that includes all possible terms up to
sixth order in derivatives. Within the Hartree-Fock approximation, it gives the
average energy that corresponds to a quasi-local nuclear Energy Density
Functional (EDF) built of derivatives of the one-body density matrix up to
sixth order. The direct reference of the EDF to the pseudopotential acts as a
constraint that divides the number of independent coupling constants of the EDF
by two. This allows, e.g., for expressing the isovector part of the functional
in terms of the isoscalar part, or vice versa. We also derive the analogous set
of constraints for the coupling constants of the EDF that is restricted by
spherical, space-inversion, and time-reversal symmetries. | nucl-th |
Nonmesonic Weak Decay of $Λ$ Hypernuclei: The Three--Nucleon
Induced Mode: The nonmesonic weak decay of $\Lambda$ hypernuclei is studied within a
microscopic diagrammatic approach which is extended to include the
three--nucleon induced mechanism. We adopt a nuclear matter formalism which,
through the local density approximation, allows us to model finite hypernuclei,
a one--meson--exchange weak transition potential and a Bonn nucleon--nucleon
strong potential. One--, two-- and three--nucleon induced weak decay rates are
predicted for $^{12}_\Lambda$C by including ground state correlations up to
second order in the nucleon--nucleon potential and the recoil of the residual
nucleus. Three--nucleon stimulated decays, $\Lambda NNN\to nNNN$ ($N=n$ or
$p$), are considered here for the first time. The obtained decay rates compare
well with the latest KEK and FINUDA data. The three--nucleon induced rate turns
out to be dominated by $nnp$-- and $npp$--induced decays, it amounts to $\sim$
7\% of the total nonmesonic rate and it is $\sim 1/2$ of the neutron--induced
decay rate. The reduction effect of the nuclear recoil is particularly relevant
for the three--nucleon induced rates ($\sim$ 15\%), less important for the
two--nucleon induced rates ($\sim$ 4\%) and negligible for the one--nucleon
induced rates. Given the non--negligible size of the three--nucleon induced
contribution and consequently its importance in the precise determination of
the complete set of decay rates, new measurements and/or experimental analysis
are encouraged. | nucl-th |
The isospin quartic term in the kinetic energy of neutron-rich nucleonic
matter: The energy of a free gas of neutrons and protons is well known to be
approximately isospin parabolic with a negligibly small quartic term of only
$0.45$ MeV at the saturation density of nuclear matter $\rho_0=0.16/\rm{fm}^3$.
Using an isospin-dependent single-nucleon momentum distribution including a
high (low) momentum tail (depletion) with its shape parameters constrained by
recent high-energy electron scattering and medium-energy nuclear
photodisintegration experiments as well as the state-of-the-art calculations of
the deuteron wave function and the equation of state of pure neutron matter
near the unitary limit within several modern microscopic many-body theories, we
show for the first time that the kinetic energy of interacting nucleons in
neutron-rich nucleonic matter has a significant quartic term of
$7.18\pm2.52\,\rm{MeV}$. Such a large quartic term has significant
ramifications in determining the equation of state of neutron-rich nucleonic
matter using both terrestrial and astrophysical observables. | nucl-th |
Ab-initio no-core shell model study of $^{18-24}$Ne isotopes: We report \textit{ab initio} no-core shell model (NCSM) study of $^{18-24}$Ne
isotopes for energy spectra, electromagnetic properties, and point-proton radii
using three realistic $NN$ interactions. We have used inside nonlocal outside
Yukawa (INOY), charge-dependent Bonn 2000 (CDB2K) and the chiral
next-to-next-to-next-to-leading order (N$^3$LO) interactions. We are able to
reach basis size up to $N_{max}$ = 6 for $^{18}$Ne and $N_{max}$ = 4 for the
$^{19-24}$Ne isotopes with m-scheme dimensions up to 1.0 $\times$ $10^9$ in
case of $^{24}$Ne. We observed better results for INOY interaction in terms of
the binding energies of ground state (g.s.), and overall all three interactions
provide good agreement with the experimental low-energy spectra. Our results
for reduced $M1$ transition strengths and magnetic moments are close to the
experimental values. We found that for long-range observables such as the $E2$
transition strengths, the electric quadrupole moments, and the point-proton
radii ($r_p$), we need higher $N_{max}$ calculations to obtain results
comparable to the experimental data. We have observed almost 6 \% increment in
the converged $r_p$ as we increase the model space from $N_{max}$ = 4 to
$N_{max}$ = 6. | nucl-th |
Diffusion of hidden charm mesons in hadronic medium: The drag and diffusion coefficients of a hot hadronic medium have been
evaluated by using hidden charm mesons as probes. The matrix elements for the
evaluation of these coefficients are calculated using an effective theory as
well as from scattering lengths. Although the transport coefficients show a
significant rise with temperature its effects on the suppression of $J/\psi$ in
hadronic matter is not significant. | nucl-th |
Quantum Fluctuations Driving the Generation and Strong Correlations of
Fission Fragment Angular Momenta: Two critical issues in the study of the fission mechanism are how the fission
fragment angular momenta (FFAM) develop dynamically from equilibrium and how
they are correlated with each other. To this end, we construct a time-dependent
generator coordinate method that incorporates crucial quantum fluctuations --
multiple rotations, vibrations, and their couplings -- based on covariant
density functional theory, providing for the first time a global, microscopic,
and dynamical study on the FFAM distribution. The calculated probability
distributions of FFAM are in good agreement with the experimental measurements,
and the sawtooth-like mass dependence of average FFAM is reproduced very well.
It is noteworthy to find that the quantum fluctuations drive the generation and
chaotic evolution of FFAM during fission fragment formation and induce the
strong correlations of FFAM orientations at the small, medium, and large
opening angles ($\phi_{\rm LH}\approx 30^{\rm o}$, $90^{\rm o}$, $160^{\rm
o}$). | nucl-th |
Systematics of dynamic moment of inertia in super-deformed bands in Mass
~150 region: An empirical semi-classical model have been proposed to investigate the
nature of dynamic moment-of-inertia , of the super-deformed (SD) bands in
nuclei of mass 150 region. The model incorporates an additional frequency
dependent distortion, to the dynamic moment-of-inertia term akin to a
vibrational component to explain the extreme spin structure of these bands.
Using this model two separate components to the dynamic moment of inertia,
$\Im^{(2)}$ have been identified for the SD band structure for the mass 150
region. Three distinct nature of the moment-of-inertia, also have been
identified using the two parameter model. | nucl-th |
Near-threshold $η$ production in $pp$ collisions: We study near-threshold $\eta$ meson production in $pp$ collisions within an
effective Lagrangian approach combined with the isobar model, by allowing for
the various intermediate nucleon resonances due to the $\pi$, $\eta$, and
$\rho$-meson exchanges. It is shown that the $\rho$-meson exchange is the
dominant excitation mechanism for these resonances, and the contribution from
the $N^*(1720)$ is dominant. The total cross section data can be reasonably
reproduced, and the anisotropic angular distributions of the emitted $\eta$
meson are consistent with experimental measurements. Besides, the invariant
mass spectra of $pp$ and $p\eta$ explain the data well at excess energy of 15
MeV, and are basically consistent with the data at excess energy of 40 MeV.
However, our model calculations cannot reasonably account for the two-peak
structure in the $p\eta$ distribution at excess energies of 57 and 72 MeV,
which suggests that a more complicated mechanism is needed at higher energy
region. | nucl-th |
Few-body calculations of $η$-nuclear quasibound states: We report on precise hyperspherical-basis calculations of $\eta NN$ and $\eta
NNN$ quasibound states, using energy dependent $\eta N$ interaction potentials
derived from coupled-channel models of the $S_{11}$ $N^{\ast}(1535)$ nucleon
resonance. The $\eta N$ attraction generated in these models is too weak to
generate a two-body bound state. No $\eta NN$ bound-state solution was found in
our calculations in models where Re $a_{\eta N}\lesssim 1$ fm, with $a_{\eta
N}$ the $\eta N$ scattering length, covering thereby the majority of
$N^{\ast}(1535)$ resonance models. A near-threshold $\eta NNN$ bound-state
solution, with $\eta$ separation energy of less than 1 MeV and width of about
15 MeV, was obtained in the 2005 Green-Wycech model where Re $a_{\eta N}\approx
1$ fm. The role of handling self consistently the subthreshold $\eta N$
interaction is carefully studied. | nucl-th |
Effective forces between quantum bound states: Recent ab initio lattice studies have found that the interactions between
alpha particles (4He nuclei) are sensitive to seemingly minor details of the
nucleon-nucleon force such as interaction locality. In order to uncover the
essential physics of this puzzling phenomenon without unnecessary
complications, we study a simple model involving two-component fermions in one
spatial dimension. We probe the interaction between two bound dimers for
several different particle-particle interactions and measure an effective
potential between the dimers using external point potentials which act as
numerical tweezers. We find that the strength and range of the local part of
the particle-particle interactions play a dominant role in shaping the
interactions between the dimers and can even determine the overall sign of the
effective potential. | nucl-th |
Treatment of the proton-proton Coulomb force in proton-deuteron breakup
Faddeev calculations: We extend our approach to incorporate the proton-proton (pp) Coulomb force
into the three-nucleon (3N) Faddeev calculations from elastic proton-deuteron
(pd) scattering to the breakup process. The main new ingredient is a
3-dimensional screened pp Coulomb t-matrix obtained by a numerical solution of
the 3-dimensional Lippmann-Schwinger equation. We demonstrate numerically that
the proton-deuteron breakup observables can be determined from the resulting
on-shell 3N amplitudes increasing the screening radius. However, contrary to
the pd elastic scattering, the screening limit exists only after
renormalisation of the pp t-matrices. | nucl-th |
RPA equations and the instantaneous Bethe-Salpeter equation: We give a derivation of the particle-hole RPA equations for an interacting
multi-fermion system by applying the instantaneous approximation to the
amputated two-fermion propagator of the system. In relativistic field theory
the same approximation leads from the fermion-antifermion Bethe-Salpeter
equation to the Salpeter equation. We show that RPA equations and Salpeter
equation are indeed equivalent. | nucl-th |
Quantum Monte Carlo calculations of six-quark states: The variational Monte Carlo method is used to find the ground state of six
quarks confined to a cavity of diameter R_c, interacting via an assumed
non-relativistic constituent quark model (CQM) Hamiltonian. We use a flux-tube
model augmented with one-gluon and one-pion exchange interactions, which has
been successful in describing single hadron spectra. The variational wave
function is written as a product of three-quark nucleon states with
correlations between quarks in different nucleons. We study the role of quark
exchange effects by allowing flux-tube configuration mixing. An accurate
six-body variational wave function is obtained. It has only ~13% rms
fluctuation in the total energy and yields a standard deviation of ~<.1%; small
enough to be useful in discerning nuclear interaction effects from the large
rest mass of the two nucleons. Results are presented for three values of the
cavity diameter, R_c=2, 4, and 6 fm. They indicate that the flux-tube model
Hamiltonian with gluon and pion exchange requires revisions in order to obtain
agreement with the energies estimated from realistic two-nucleon interactions.
We calculate the two-quark probability distribution functions and show how they
may be used to study and adjust the model Hamiltonian. | nucl-th |
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