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Thermalization at lowest energies? A view from a transport model: Using the Isospin Quantum Molecular Dynamics (IQMD) model we analyzed the
production of pions and kaons in the energy range of 1-2 AGeV in order to study
the question why thermal models could achieve a successful description. For
this purpose we study the variation of pion and kaon yields using different
elementary cross sections. We show that several ratios appear to be rather
robust versus their variations. | nucl-th |
Geometrical symmetries of nuclear systems: D(3h) and T(d) symmetries in
light nuclei: The role of discrete (or point-group) symmetries in alpha-cluster nuclei is
discussed in the framework of the algebraic cluster model which describes the
relative motion of the alpha-particles. Particular attention is paid to the
discrete symmetry of the geometric arrangement of the alpha-particles, and the
consequences for the structure of the corresponding rotational bands. The
method is applied to study cluster states in the nuclei 12C and 16O. The
observed level sequences can be understood in a simple way as a consequence of
the underlying discrete symmetry that characterizes the geometrical
configuration of the alpha-particles, i.e. an equilateral triangle with D(3h)
symmetry for 12C, and a tetrahedron with T(d) symmetry for 16O. The structure
of rotational bands provides a fingerprint of the underlying geometrical
configuration of alpha-particles. | nucl-th |
Density-functional theory for the pairing Hamiltonian: We consider the pairing Hamiltonian and systematically construct its density
functional in the strong-coupling limit and in the limit of large particle
number. In the former limit, the functional is an expansion into central
moments of occupation numbers. In the latter limit, the functional is known
from BCS theory. Both functionals are nonlocal in structure, and the
nonlocalities are in the form of simple products of local functionals. We also
derive the relation between the occupation numbers and the Kohn-Sham density. | nucl-th |
Production of $a_0$-mesons in pp and pn reactions: We investigate the cross section for the reaction $NN \to NNa_0$ near
threshold and at medium energies. An effective Lagrangian approach with
one-pion exchange is applied to analyze different contributions to the cross
section for different isospin channels. The Reggeon exchange mechanism is also
considered. The results are used to calculate the contribution of the $a_0$
meson to the cross sections and invariant $K \bar K$ mass distributions of the
reactions $pp\to pn K^+\bar K^0$ and $pp\to pp K^+K^-$. It is found that the
experimental observation of $a_0^+$ mesons in the reaction $pp\to pn K^+\bar
K^0$ is much more promising than the observation of $a_0^0$ mesons in the
reaction $pp\to pp K^+K^-$. | nucl-th |
Femtometer Toroidal Structures in Nuclei: The two-nucleon density distributions in states with isospin $T=0$, spin
$S$=1 and projection $M_S$=0 and $\pm$1 are studied in $^2$H, $^{3,4}$He,
$^{6,7}$Li and $^{16}$O. The equidensity surfaces for $M_S$=0 distributions are
found to be toroidal in shape, while those of $M_S$=$\pm$1 have dumbbell shapes
at large density. The dumbbell shapes are generated by rotating tori. The
toroidal shapes indicate that the tensor correlations have near maximal
strength at $r<2$ fm in all these nuclei. They provide new insights and simple
explanations of the structure and electromagnetic form factors of the deuteron,
the quasi-deuteron model, and the $dp$, $dd$ and $\alpha d$ $L$=2 ($D$-wave)
components in $^3$He, $^4$He and $^6$Li. The toroidal distribution has a
maximum-density diameter of $\sim$1 fm and a half-maximum density thickness of
$\sim$0.9 fm. Many realistic models of nuclear forces predict these values,
which are supported by the observed electromagnetic form factors of the
deuteron, and also predicted by classical Skyrme effective Lagrangians, related
to QCD in the limit of infinite colors. Due to the rather small size of this
structure, it could have a revealing relation to certain aspects of QCD. | nucl-th |
The Unified Hydrodynamics and the Pseudorapidity Distributions in Heavy
Ion Collisions at BNL-RHIC and CERN-LHC Energies: The charged particles produced in nucleus-nucleus collisions are divided into
two parts. One is from the hot and dense matter created in collisions. The
other is from leading particles. The hot and dense matter is assumed to expand
according to unified hydrodynamics and freezes out into charged particles from
a space-like hypersurface with a fixed proper time of Tau_FO.The leading
particles are conventionally taken as the particles which inherit the quantum
numbers of colliding nucleons and carry off most of incident energy. The
rapidity distributions of the charged particles from these two parts are
formulated analytically, and a comparison is made between the theoretical
results and the experimental measurements performed in Au-Au and Pb-Pb
collisions at the respective BNL-RHIC and CERN-LHC energies. The theoretical
results are well consistent with experimental data. | nucl-th |
Onset of $η$ nuclear binding: Recent studies of $\eta$ nuclear quasibound states by the Jerusalem-Prague
Collaboration are reviewed, focusing on stochastic variational method self
consistent calculations of $\eta$ few-nucleon systems. These calculations
suggest that a minimum value Re$\,a_{\eta N} \approx 1$ fm (0.7 fm) is needed
to bind $\eta\,^3$He ($\eta\,^4$He). | nucl-th |
Spin-dependent correlations and the semi-exclusive ^{16}O(e,e'p)
reaction: The effect of central, tensor and spin-isospin nucleon-nucleon correlations
upon semi-exclusive ^{16}O(e,e'p) reactions is studied for Q^2 and Bjorken x
values in the range $0.2 \lesssim Q^2 \lesssim 1.1 (GeV/c)^2$ and 0.15
$\lesssim$ x $\lesssim$ 2. The fully unfactorized calculations are performed in
a framework that accounts not only for the dynamical coupling of virtual
photons to correlated nucleon pairs but also for meson-exchange and
$\Delta_{33}$-isobar currents. Tensor correlations are observed to produce
substantially larger amounts of semi-exclusive ^{16}O(e,e'p) strength than
central correlations do and are predominantly manifest in the proton-neutron
knockout channel. With the exception of the $x \approx 2$ case, in all
kinematical situations studied the meson-exchange and isobar currents are a
strong source of A(e,e'p) strength at deep missing energies. This feature gives
the A(e,e'p) strength at deep missing energies a pronounced transverse
character. | nucl-th |
Differential elliptic flow prediction at the LHC from parton transport: We predict how differential elliptic flow v2(pT) changes from RHIC to LHC
collision energies (Pb+Pb at 5.5 TeV/nucleon), ASSUMING that the quark-gluon
system created has a ``minimal'' shear viscosity eta/s = 1/(4*pi) at both RHIC
and the LHC. | nucl-th |
Predicting narrow states in the spectrum of a nucleus beyond the proton
drip line: Properties of particle-unstable nuclei lying beyond the proton drip line can
be ascertained by considering those (usually known) properties of its mirror
neutron-rich system. We have used a multi-channel algebraic scattering theory
to map the known properties of the neutron-${}^{14}$C system to those of the
proton-${}^{14}$O one from which we deduce that the particle-unstable
${}^{15}$F will have a spectrum of two low lying broad resonances of positive
parity and, at higher excitation, three narrow negative parity ones. A key
feature is to use coupling to Pauli-hindered states in the target. | nucl-th |
Enhancement of deuteron production in jets: A strong enhancement of deuteron production in jets has been recently
observed in proton-proton collisions at LHC. We show that the effect is due to
two independent factors: a collimation of jet nucleons and a smallness of
nucleon source. The coalescence parameter of jet deuterons is shown to acquire
its maximal possible value. | nucl-th |
Dynamical Model of Coherent Pion Production in Neutrino-Nucleus
Scattering: We study coherent pion production in neutrino-nucleus scattering in the
energy region relevant to neutrino oscillation experiments of current interest.
Our approach is based on a combined use of the Sato-Lee model of electroweak
pion production on a nucleon and the Delta-hole model of pion-nucleus
reactions. Thus we develop a model which describes pion-nucleus scattering and
electroweak coherent pion production in a unified manner. Numerical
calculations are carried out for the case of the 12C target. All the free
parameters in our model are fixed by fitting to both total and elastic
differential cross sections for pi-12C scattering. Then we demonstrate the
reliability of our approach by confronting our prediction for the coherent pion
photo-productions with data. Finally, we calculate total and differential cross
sections for neutrino-induced coherent pion production, and some of the results
are (will be) compared with the recent (forthcoming) data from K2K, SciBooNE
and MiniBooNE. We also study effect of the non-locality of the
Delta-propagation in the nucleus, and compare the elementary amplitudes used in
different microscopic calculations. | nucl-th |
Antiproton-nucleus electromagnetic annihilation as a way to access the
proton timelike form factors: Contrary to the reaction pbar + p --> e+ e- with a high momentum incident
antiproton on a free target proton at rest, in which the invariant mass M of
the (e+ e-) pair is necessarily much larger than the (pbar p) mass, in the
reaction pbar + d --> n e+ e- the value of M can take values near or below the
(pbar p) mass. In the antiproton-deuteron electromagnetic annihilation, this
allows to access the proton electromagnetic form factors in the time-like
region of q^2 near the (pbar p) threshold. We estimate the cross section
dsigma(pbar +d --> e+ e- n)/dM for an antiproton beam momentum of 1.5 GeV/c. We
find that near the (pbar p) threshold this cross section is about 1 pb/MeV. The
case of heavy nuclei target is also discussed. Elements of experimental
feasibility are presented for the process pbar + d --> n e+ e- in the context
of the Panda project. | nucl-th |
Bounding the ground-state energy of a many-body system with the
differential method: This paper promotes the differential method as a new fruitful strategy for
estimating a ground-state energy of a many-body system. The case of an
arbitrary number of attractive Coulombian particles is specifically studied and
we make some favorable comparison of the differential method to the existing
approaches that rely on variational principles. A bird's-eye view of the
treatment of more general interactions is also given. | nucl-th |
Nuclear Scission and Quantum Localization: We examine nuclear scission within a fully quantum-mechanical microscopic
framework, focusing on the non-local aspects of the theory. Using
$^{240}\textrm{Pu}$ hot fission as an example, we discuss the identification of
the fragments and the calculation of their kinetic, excitation, and interaction
energies, through the localization of the orbital wave functions. We show that
the "disentanglement" of the fragment wave functions is essential to the
quantum-mechanical definition of scission and the calculation of physical
observables. Finally, we discuss the fragments' pre-scission excitation
mechanisms and give a non-adiabatic description of their evolution beyond
scission. | nucl-th |
v4 from ideal and viscous hydrodynamic simulations of nuclear collisions
at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron
Collider (LHC): We compute v4/(v2)^2 in ideal and viscous hydrodynamics. We investigate its
sensitivity to details of the hydrodynamic model and compare the results to
experimental data from RHIC. Whereas v2 has a significant sensitivity only to
initial eccentricity and viscosity while being insensitive to freeze out
temperature, we find that v4/(v2)^2 is quite insensitive to initial
eccentricity. On the other hand, it can still be sensitive to shear viscosity
in addition to freeze out temperature, although viscous effects do not
universally increase v4/(v2)^2 as originally predicted. Consistent with data,
we find no dependence on particle species. We also make a prediction for
v4/(v2)^2 in heavy ion collisions at the LHC. | nucl-th |
Superscaling of Inclusive Electron Scattering from Nuclei: We investigate the degree to which the concept of superscaling, initially
developed within the framework of the relativistic Fermi gas model, applies to
inclusive electron scattering from nuclei. We find that data obtained from the
low energy loss side of the quasielastic peak exhibit the superscaling
property, i.e., the scaling functions f(\psi') are not only independent of
momentum transfer (the usual type of scaling: scaling of the first kind), but
coincide for A \geq 4 when plotted versus a dimensionless scaling variable
\psi' (scaling of the second kind). We use this behavior to study as yet poorly
understood properties of the inclusive response at large electron energy loss. | nucl-th |
On Probabilities of E2 Transitions between Positive-Parity States in
^160Dy Nucleus: Reduced probabilities B(E2) of \gamma transitions between states of positive
parity in the ^160Dy nucleus are calculated within the framework of the
interacting boson model (IBM-1). The results are compared with the experimental
data. | nucl-th |
Initial Conditions for Modified DGLAP Evolution of the Modified
Fragmentation Functions in Nuclear Medium: Initial conditions are required to solve medium modified DGLAP (mDGLAP)
evolution equations for modified fragmentation functions due to multiple
scatterings and parton energy loss. Such initial conditions should in principle
include energy loss for partons at scale $Q_0$ above which mDGLAP evolution
equations can be applied. Several models for the initial condition motivated by
induced gluon bremsstrahlung in perturbative QCD are used to calculate the
modified fragmentation functions in nuclear medium and to extract the jet
transport parameter $\hat q$ from fits to experimental data in deeply inelastic
scattering (DIS) off nuclei. The model with a Poisson convolution of multiple
gluon emissions is found to provide the overall best $\chi^2$/d.o.f. fit to the
HERMES data and gives a value of $\hat q_0 \approx 0.020 \pm 0.005$ GeV$^2$/fm
at the center of a large nucleus. | nucl-th |
A Reanalysis of Single Photon Data at CERN SPS: We reanalyze the WA98 single photon data at CERN SPS by incorporating several
recent developments in the study of prompt and thermal photon production from
relativistic heavy ion collisions. Isospin and shadowing corrected NLO pQCD,
along with an optimized scale for factorization, fragmentation and
renormalization are considered for prompt photon production. Photons from
thermal medium are estimated by considering a boost invariant azimuthally
anisotropic hydrodynamic expansion of the plasma along with a well tested
equation of state and initial conditions. A quantitative explanation of the
data is obtained by combining $\kappa \times$ prompt with thermal photons,
where $\kappa$ is an overall scaling factor. We show that, elliptic flow of
thermal photons can play a crucial role to distinguish between the `with' and
`without' phase transition scenarios at SPS energy. | nucl-th |
Thermal Effects for Quark and Gluon Distributions in Heavy-Ion
Collisions: In-medium effects for distributions of quarks and gluons in central A+A
collisions are considered. We suggest a duality principle, which means
similarity of thermal spectra of hadrons produced in heavy-ion collisions and
inclusive spectra which can be obtained within the dynamic quantum scattering
theory. Within the suggested approach we show that the mean square of the
transverse momentum for these partons grows and then saturates when the initial
energy increases. It leads to the energy dependence of hadron transverse mass
spectra which is similar to that observed in heavy ion collisions. | nucl-th |
Symmetry energy and nucleon-nucleon cross sections: The extension of the Boltzmann-Uehling-Uhlenbeck model of nucleus-nucleus
collision is presented. The isospin-dependent nucleon-nucleon cross sections
are estimated using the proper volume extracted from the equation of state of
the nuclear matter transformed into the form of the Van der Waals equation of
state. The results of such simulations demonstrate the dependence on symmetry
energy which typically varies strongly from the results obtained using only the
isospin-dependent mean-field. The evolution of the n/p multiplicity ratio with
angle and kinetic energy, in combination with the elliptic flow of neutrons and
protons, provides a suitable set of observables for determination of the
density dependence of the symmetry energy. The model thus provides an
environment for testing of equations of state, used for various applications in
nuclear physics and astrophysics. | nucl-th |
Symmetry Energy II: Isobaric Analog States: Using excitation energies to isobaric analog states (IAS) and charge
invariance, we extract nuclear symmetry coefficients, from a mass formula, on a
nucleus-by-nucleus basis. Consistently with charge invariance, the coefficients
vary weakly across an isobaric chain. However, they change strongly with
nuclear mass and range from a_a~10 MeV at mass A~10 to a_a~22 MeV at A~240.
Following the considerations of a Hohenberg-Kohn functional for nuclear
systems, we determine how to find in practice the symmetry coefficient using
neutron and proton densities, even when those densities are simultaneously
affected by significant symmetry-energy and Coulomb effects. These results
facilitate extracting the symmetry coefficients from Skyrme-Hartree-Fock (SHF)
calculations, that we carry out using a variety of Skyrme parametrizations in
the literature. For the parametrizations, we catalog novel short-wavelength
instabilities. In comparing the SHF and IAS results for the symmetry
coefficients, we arrive at narrow (+-2.4 MeV) constraints on the symmetry
energy values S(rho) at 0.04<rho<0.13 fm^-3. Towards normal density the
constraints significantly widen, but the normal value of energy a_a^V and the
slope parameter L are found to be strongly correlated. To narrow the
constraints, we reach for the measurements of asymmetry skins and arrive at
a_a^V=(30.2-33.7) MeV and L=(35-70) MeV, with those values being again strongly
positively correlated along the diagonal of their combined region. Inclusion of
the skin constraints allows to narrow the constraints on S(rho), at
0.04<rho<0.13 fm^-3, down to +-1.1 MeV. Several microscopic calculations,
including variational, Bruckner-Hartree-Fock and Dirac-Bruckner-Hartree-Fock,
are consistent with our constraint region on S(rho). | nucl-th |
Time-dependent generator coordinate method study of mass-asymmetric
fission of actinides: Low-energy positive and negative parity collective states in the equilibrium
minimum, and the dynamics of induced fission of actinide nuclei are
investigated in a unified theoretical framework based on the generator
coordinate method (GCM) with the Gaussian overlap approximation (GOA). The
collective potential and inertia tensor, both at zero and finite temperature,
are computed using the self-consistent multidimensionally constrained
relativistic mean field (MDC-RMF) model, based on the energy density functional
DD-PC1. Pairing correlations are treated in the BCS approximation with a
separable pairing force of finite range. A collective quadrupole-octupole
Hamiltonian characterized by zero-temperature axially-symmetric deformation
energy surface and perturbative cranking inertia tensor, is used to model the
low-lying excitation spectrum. The fission fragment charge distributions are
obtained by propagating the initial collective states in time with the
time-dependent GCM+GOA that uses the same quadrupole-octupole Hamiltonian, but
with the collective potential and inertia tensor computed at finite
temperature. The illustrative charge yields of $^{228}$Th, $^{234}$U,
$^{240}$Pu, $^{244}$Cm, and $^{250}$Cf are in very good agreement with
experiment, and the predicted mass asymmetry is consistent with the result of a
recent microscopic study that has attributed the distribution (peak) of the
heavier-fragment nuclei to shell-stabilized octupole deformations. | nucl-th |
Hadrons and Few-Body Physics: We present a selection of topics with an interplay of hadron and few-body
physics. This includes few-nucleon systems, light hypernuclei and quark
dynamics for baryons and multiquarks. It is stressed that standard quark models
predict very few stable multiquarks. | nucl-th |
Evaluation of the forward Compton scattering off protons: I.
Spin-independent amplitude: We evaluate the forward Compton scattering off the proton, based on
Kramers-Kronig kind of relations which express the Compton amplitudes in terms
of integrals of total photoabsorption cross sections. We obtain two distinct
fits to the world data on the unpolarized total photoabsorption cross section,
and evaluate the various spin-independent sum rules using these fits. For the
sum of proton electric and magnetic dipole polarizabilities, governed by the
Baldin sum rule, we obtain the following average (between the two fits):
$\alpha_{E1}+\beta_{M1}=14.0(2)\times 10^{-4}\,\mathrm{fm}^3$. An analogous sum
rule involving the quadrupole polarizabilities of the proton is evaluated too.
The spin-independent forward amplitude of proton Compton scattering is
evaluated in a broad energy range. The results are compared with previous
evaluations and the only experimental data point for this amplitude (at 2.2
GeV). We remark on sum rules for the elastic component of polarizabilities. | nucl-th |
PLATYPUS: a code for fusion and breakup in reactions induced by
weakly-bound nuclei within a classical trajectory model with stochastic
breakup: A self-contained Fortran-90 program based on a classical trajectory model
with stochastic breakup is presented, which should be a powerful tool for
quantifying complete and incomplete fusion, and breakup in reactions induced by
weakly-bound two-body projectiles near the Coulomb barrier. The code calculates
complete and incomplete fusion cross sections and their angular momentum
distribution, as well as breakup observables (angle, kinetic energy and
relative energy distributions). | nucl-th |
Effect of the symmetry energy and hyperon interaction on neutron stars: The joint effect of the density dependence of the symmetry energy and
strangeness content on the structure of cold neutron stars is studied within
the framework of a relativistic mean field theory. It is shown that 2$M_\odot$
are obtained for repulsive $YY$ interaction and preferably for a small or a
large slope $L$. An attractive $\Sigma$ potential in nuclear matter will favor
the appearance of strangeness in stars with a mass as small as $\sim 1
M_\odot$, if, however it is repulsive only stars with a mass $\gtrsim 1.4
M_\odot$ will contain strangeness. The joint effect of reducing the symmetry
energy slope and including hyperons is to farther reduce the radius. Neutron
star maximum mass evolve non-monotonically with the symmetry energy slope, and
the smallest masses are obtained for values $L\sim 80$ MeV. Other neutron star
variables evolve nonlinearly with the slope of the symmetry energy and depend
on the hyperon-nucleon and hyperon-hyperon couplings. The radius of a neutron
star is linearly correlated with the neutron star total strangeness fraction
and the slope is independent of the slope of the symmetry energy and the mass
of the star. | nucl-th |
On the isospin dependence of the mean spin-orbit field in nuclei: By the use of the latest experimental data on the spectra of $^{133}$Sb and
$^{131}$Sn and on the analysis of properties of other odd nuclei adjacent to
doubly magic closed shells the isospin dependence of a mean spin-orbit
potential is defined. Such a dependence received the explanation in the
framework of different theoretical approaches. | nucl-th |
Effects of nucleon-nucleon short-range correlations on inclusive
electron scattering: The nucleon-nucleon short-range correlation NN-SRC is one of the key issues
of nuclear physics, which typically manifest themselves in high-momentum
components of the nuclear momentum distributions. In this letter, the nuclear
spectral functions based on the axially deformed relativistic mean-field model
are developed to involve the NN-SRC. With the spectral functions, the inclusive
electron scattering $ (e,e^{\prime}) $ cross sections are calculated within the
PWIA framework, including the quasi-elastic (QE) part and $ \Delta $ production
part. Especially in the $ \Delta $ production region, we reconsider the
electromagnetic structures of the nucleon resonance $ \Delta $(1232) and the
scattering mechanisms, thereby the theoretical calculations are improved
effectively and the cross sections are well consistent with the experimental
data. The theoretical $ (e,e^{\prime}) $ cross sections are further divided
into NN-SRC and mean-field contributions. It is found that, at the kinematics $
0.5 \,{\rm GeV}^{2}<Q^{2}<1 \,{\rm GeV}^{2} $, the QE peak and $ \Delta $
production peak not only reflect the mean-field structure, but also are
sensitive to the NN-SRC information. Finally, we provide a new method to
extract the strengths of NN-SRC from experimental cross sections for selected
nuclei at the suitable kinematics. | nucl-th |
$α$ particles and the pasta phase: The effects of the $\alpha$ particles in nuclear matter at low densities are
investigated within three different parametrizations of relativistic models at
finite temperature. Both homogeneous and inhomogeneous matter (pasta phase) are
described for neutral nuclear matter with fixed proton fractions and stellar
matter subject to $\beta$-equilibrium and trapped neutrinos. In homogeneous
matter, $\alpha$ particles are only present at densities below 0.02 fm$^{-3}$
and their presence decreases with the increase of the temperature and, for a
fixed temperature, the $\alpha$ particle fraction decreases for smaller proton
fractions. A repulsive interaction is important to mimic the dissolution of the
clusters in homogeneous matter. The effects of the $\alpha$ particles on the
pasta structure is very small except close to the critical temperatures and /
or proton fractions when it may still predict a pasta phase while no pasta
phase would occur in the absence of light clusters. It is shown that for
densities above 0.01 fm$^{-3}$ the $\alpha$ particle fraction in the pasta
phase is much larger than the $\alpha$ particle fraction in homogeneous matter. | nucl-th |
Relativistic Contributions to Deuteron Photodisintegration in the
Bethe-Salpeter Formalism: In plane wave one-body approximation the reaction of deuteron
photodisintegration is considered in the framework of the Bethe-Salpeter
formalism for two-nucleon system. Results are obtained for deuteron vertex
function, which is the solution of the homogeneous Bethe-Salpeter equation with
a multi-rank separable interaction kernel, with a given analytical form. A
comparison is presented with predictions of non-relativistic, quasipotential
approaches and the equal time approximation. It is shown that important
contributions come from the boost in the arguments of the initial state vertex
function and the boost on the relative energy in the one-particle propagator
due to recoil. | nucl-th |
Effect of Inner Crust EoS on Neutron star properties: The neutron star maximum mass and the radius are investigated within the
framework of the relativistic mean-field (RMF) model. The variation in the
radius at the canonical mass, $R_{1.4}$, using different inner crust equation
of state (EoS) with different symmetry energy slope parameter is studied. It is
found that although the NS maximum mass and the corresponding radius do not
vary much with different inner crust EoSs, the radius and the tidal
deformability at 1.4$M_{\odot}$ vary with the different choice of crust EoS and
variation of about 1-2 km is seen in the radius at the canonical mass. For
non-unified EoSs, the crust with a low symmetry energy slope parameter produces
a low NS radius at the canonical mass. The properties of maximally rotating
neutron stars are also studied. The variation in the radius of rotating star at
the canonical mass 1.4$M_{\odot}$ is also seen with the slope parameter.
Similar to the static neutron star, the radius at 1.4$M_{\odot}$ of rotating
neutron star is affected by slope parameter of the inner crust. Other important
quantities like moment of inertia, frequency, rotational kinetic energy to
gravitational energy ratio are also calculated. The variation in these
quantities with the crust slope parameter is found to be more proportional to
the mass and the radius of NS. | nucl-th |
Future of Nuclear Fission Theory: There has been much recent interest in nuclear fission, due in part to a new
appreciation of its relevance to astrophysics, stability of superheavy
elements, and fundamental theory of neutrino interactions. At the same time,
there have been important developments on a conceptual and computational level
for the theory. The promising new theoretical avenues were the subject of a
workshop held at the University of York in October 2019; this report summarises
its findings and recommendations. | nucl-th |
Stability of the manifold boundary approximation method for reductions
of nuclear structure models: The framework of nuclear energy density functionals has been employed to
describe nuclear structure phenomena for a wide range of nuclei. Recently,
statistical properties of a given nuclear model, such as parameter confidence
intervals and correlations, have received much attention, particularly when one
tries to fit complex models. We apply information-theoretic methods to
investigate stability of model reductions by the manifold boundary
approximation method (MBAM). In an illustrative example of the
density-dependent point-coupling model of the relativistic energy density
functional, utilizing Monte Carlo simulations, it is found that main
conclusions obtained from the MBAM procedure are stable under variation of the
model parameters. Furthermore, we find that the end of the geodesic occurs when
the determinant of the Fisher information metric vanishes, thus effectively
separating the parameter space into two disconnected regions. | nucl-th |
Phase Transition and Hybrid Star in a Nonlinear $σ- ω$ model: The phase transition between the nuclear matter and the quark matter is
examined. The relativistic mean field theory(RMF) is consider with interacting
nucleons and mesons using TM1 parameter set for the nuclear matter equations of
state. It is found that the trasition point depends on coupling constant
$\alpha_s$ and bag pressure. From the study of the structure of a hybrid
neutron star, it is observed that the star contains quark matter in the
interior and neutron matter on the outer perifery. | nucl-th |
Shape coexistence in Sr isotopes: Sr isotopes are located in the mass region $A\approx 100$, where a very quick
onset of nuclear deformation exists, being other notable examples of this area
Yb, Zr, and Nb nuclei. The presence of the proton subshell closure $Z=40$
allows the existence of particle-hole excitations that produces low-lying
intruder bands.
Purpose: The goal of this work is the study of the nuclear structure of the
even-even $^{92-102}$Sr isotopes through the accurate description of excitation
energies, $B(E2)$ transition rates, nuclear radii and two-neutron separation
energies.
Method: The interacting boson model with configuration mixing will be the
framework to calculate all the observables of the Sr isotopes. Only two types
of configurations will be considered, namely, 0particle-0hole and
2particle-2hole excitations. The parameters of the model are determined using a
least-squares procedure for the excitation energies and the $B(E2)$ transition
rates.
Results: For the whole chain of isotopes, the value of excitation energies,
$B(E2)$'s, two-neutron separation energies, nuclear radii, and isotope shifts
have been obtained, with a good agreement between theory and experiment. Also,
a detailed analysis of the wave functions have been performed and, finally, the
mean-field energy surfaces and the value of the nuclear deformation, $\beta$,
have been obtained.
Conclusions: The presence of low-lying intruder states in even-even Sr
isotopes have been confirmed and its connection with the onset of deformation
has been clarified. Lightest Sr isotopes present a spherical structure while
the heaviest ones are clearly deformed. The rapid onset of deformation at
neutron number $60$ is due to the crossing of the regular and intruder
configurations and, moreover, both families of states present an increase of
deformation with the neutron number. | nucl-th |
Systematical Approach to the Exact Solution of the Dirac Equation for A
Special Form of the Woods-Saxon Potential: Exact solution of the Dirac equation for a special form of the Woods-Saxon
potential is obtained for the s-states. The energy eigenvalues and
two-component spinor wave functions are derived by using a systematical method
which is called as Nikiforov-Uvarov. It is seen that the energy eigenvalues
strongly depend on the potential parameters. In addition, it is also shown that
the non-relativistic limit can be reached easily and directly. | nucl-th |
Omega meson production in pp collisions with a polarized beam: Model independent formulae are derived for the beam analyzing power $A_y$ and
beam to meson spin transfers in $pp \to pp \omega$ taking into consideration
all the six threshold partial wave amplitudes covering the $Ss, Sp$ and $Ps$
channels. Attention is also focussed on the empirical determination of the
lowest three partial wave amplitudes $f_1, f_2, f_3$ without any discrete
ambiguities. | nucl-th |
Chiral SU(3) Symmetry and Strangeness: In this talk we review recent progress on the systematic evaluation of the
kaon and antikaon spectral functions in dense nuclear matter based on a chiral
SU(3) description of the low-energy pion-, kaon- and antikaon-nucleon
scattering data. | nucl-th |
Low energy n+t scattering and the NN forces: The Faddeev-Yakubovsky equations have been solved in configuration space for
the four nucleon system. The n+t elastic cross section has been calculated
using several realistic interactions and a phenomenological three-nucleon
force. Special attention is devoted to the description of the observed resonant
structure at $T_{lab}\approx 4$ MeV. In the present state of the calculations,
the realistic NN interactions are unable to describe the energy region
considered, i.e. n+t S- and P- waves. Whereas the inclusion of a three-nucleon
force improves the zero energy region, the disagreement in the resonant peak
remains. This failure contrasts with the results of a pure phenomenological
model. The origin of this disagreement as well as the possible issues are
discussed. | nucl-th |
Dependence of the BCS 1S0 superfluid pairing gap on nuclear interactions: We study in detail the dependence of the 1S0 superfluid pairing gap on
nuclear interactions and on charge-independence breaking at the BCS level.
Starting from chiral effective-field theory and conventional nucleon-nucleon
(NN) interactions, we use the renormalization group to generate low-momentum
interactions V_{low k} with sharp and smooth regulators. The resulting BCS gaps
are well constrained by the NN scattering phase shifts, and the cutoff
dependence is very weak for sharp or sufficiently narrow smooth regulators with
cutoffs Lambda > 1.6 fm^{-1}. It is therefore likely that the effect of
three-nucleon interactions on 1S0 superfluidity is small at the BCS level. The
charge dependence of nuclear interactions has a 10% effect on the pairing gap. | nucl-th |
Mean field effects in heavy-ion collisions at AGS energies: The question whether mean field effects exist in heavy-ion collisions at AGS
energies is studied in the framework of A Relativistic Transport (ART) model.
It is found that in central collisions of Au+Au at $P_{beam}/A=$11.6 GeV/c a
simple, Skyrme-type nuclear mean field satisfying the causality requirement
reduces the maximum baryon and energy densities reached in the cascade model by
about 30\% and 40\%, respectively. The mean field affects the inclusive, single
particle observables of various hadrons by at most 20\%. We show, however, that
the mean field causes a factor of 2.5 increase in the strength of the baryon
transverse collective flow. | nucl-th |
Relativistic Effects in Electroweak Nuclear Responses: The electroweak response functions for inclusive electron scattering are
calculated in the Relativistic Fermi Gas model, both in the quasi-elastic and
in the $\Delta$ peak regions. The impact of relativistic kinematics at high
momentum transfer is investigated through an expansion in the initial nucleonic
momentum, which is however exact in the four-momentum of the exchanged boson.
The same expansion is applied to the meson exchange currents in the
particle-hole sector: it is shown that the non-relativistic currents can be
corrected by simple kinematical factors to account for relativity. The
left-right asymmetry measured via polarized electron scattering is finally
evaluated in the quasi-elastic and $\Delta$ peaks. | nucl-th |
The quark condensate in relativistic nucleus-nucleus collisions: We compute the modification of the quark condensate $<\bar{q} q>$ in
relativistic nucleus-nucleus collisions and estimate the 4-volume, where the
quark condensate is small ($<\bar{q}q>/<\bar{q} q>_0\leq$ 0.1--0.3) using
hadron phase-space distributions obtained with the quark-gluon string model. As
a function of the beam energy the 4-volume rises sharply at a beam energy
$E_{lab}/A \simeq$ (2--5) GeV, remains roughly constant up to beam energies
$\simeq 20$ GeV and rises at higher energies. At low energies the reduction of
the condensate is mainly due to baryons, while at higher energies the rise of
the 4-volume is due to the abundant mesons produced. Based on our results we
expect that moderate beam energies on the order of 10 GeV per nucleon are
favourable for studying the restoration of chiral symmetry in a baryon-rich
environment in nucleus-nucleus collisions. | nucl-th |
Study of fusion dynamics using Skyrme energy density formalism with
different surface corrections: Within the framework of Skyrme energy density formalism, we investigate the
role of surface corrections on the fusion of colliding nuclei. For this, the
coefficient of surface correction was varied between 1/36 and 4/36, and its
impact was studied on about 180 reactions. Our detailed investigations indicate
a linear relationship between the fusion barrier heights and strength of the
surface corrections. Our analysis of the fusion barriers advocate the strength
of surface correction of 1/36. | nucl-th |
Phase Variation of Hadronic Amplitudes: The phase variation with angle of hadronic amplitudes is studied with a view
to understanding the underlying physical quantities which control it and how
well it can be determined in free space. We find that unitarity forces a
moderately accurate determination of the phase in standard amplitude analyses
but that the nucleon-nucleon analyses done to date do not give the phase
variation needed to achieve a good representation of the data in multiple
scattering calculations. Models are examined which suggest its behavior near
forward angles is related to the radii of the real and absorptive parts of the
interaction. The dependence of this phase on model parameters is such that if
these radii are modified in the nuclear medium (in combination with the change
due to the shift in energy of the effective amplitude in the medium) then the
larger magnitudes of the phase needed to fit the data might be attainable, but
only for negative values of the phase variation parameter. | nucl-th |
Effects of the ground state correlations on the structure of vibrational
states: A method to treat the ground state correlations beyond the RPA is presented.
A set of nonlinear equations taking into account effects of the ground state
correlations on the pairing and phonon-phonon coupling is derived. The
influence of such correlations on properties of the vibrational states in
spherical nuclei is studied. | nucl-th |
Note on neutron star equation of state in the light of GW170817: From the very first multimessenger event of GW170817, clean robust
constraints can be obtained for the tidal deformabilities of the two stars
involved in the merger, which provides us unique opportunity to study the
equation of states (EOSs) of dense stellar matter. In this contribution, we
employ a model from the quark level, describing consistently a nucleon and
many-body nucleonic system from a quark potential. We check that our sets of
EOSs are consistent with available experimental and observational constraints
at both sub-nuclear saturation densities and higher densities. The agreements
with ab-initio calculations are also good. Especially, we tune the density
dependence of the symmetry energy (characterized by its slope at nuclear
saturation $L$) and study its influence on the tidal deformability. The
so-called $QMF18$ EOS is named after the case of $L=40~\rm MeV$, and it gives
$M_{\rm TOV} =2.08~M_\odot$ and $R= 11.77~\rm km$, $\Lambda=331$ for a
$1.4\,M_\odot$ star. The tidal signals are demonstrated to be insensitive to
the uncertain crust-core matching, despite the good correlation between the
symmetry energy slope and the radius of the star. | nucl-th |
Two-photon exchange effect on deuteron electromagnetic form factors: Corrections of two-photon exchange to proton and neutron electromagnetic form
factors are employed to study the effect of two-photon exchange on the deuteron
electromagnetic form factors. Numerical results of the effect are given. It is
suggested to test the effect in the measurement of $P_z$ in a small angle
limit. | nucl-th |
Description of shape coexistence in $^{96}$Zr based on the collective
quadrupole Bohr Hamiltonian: Experimental data on $^{96}$Zr indicate coexisting spherical and deformed
structures with small mixing amplitudes. We investigate the properties of the
low-lying collective states of $^{96}$Zr based on the collective quadrupole
Bohr Hamiltonian. The $\beta$-dependent collective potential having two minima
-- spherical and deformed, is fixed so to describe experimental data in the
best way.Good agreement with the experimental data on the excitation energies,
$B(E2)$ and $B(M1)$ reduced transition probabilities is obtained. It is shown
that the low-energy structure of $^{96}$Zr can be reproduced in a satisfactory
way in the geometrical model with a potential function supporting shape
coexistence. However, the excitation energy of the $2^+_2$ state can be
reproduced only if the rotation inertia coefficient is taken five times smaller
then the vibrational one in the region of the deformed well. It is shown also
that shell effects are important for the description of the $B(M1;2^+_2
\rightarrow 2^+_1)$ value. An indication on the influence of the pairing
vibrational mode on the $\rho^2 (0^+_2 \rightarrow 0^+_1)$ value is obtained. | nucl-th |
Pairing, quasi-spin and seniority: We present our concise notes for the lectures and tutorials on pairing,
quasi-spin and seniority delivered at SERB school on Role of Symmetries in
Nuclear Physics, AMITY University, $2019$. Starting with some generic features
of residual nucleon-nucleon interactions, we provide detailed derivation of the
matrix elements for the $\delta$-interaction which is the basis for the
standard pairing Hamiltonian. The eigen values for standard pairing Hamiltonian
are then obtained within the quasi-spin formalism. The algebra involving
quasi-spin operators is performed explicitly using the annihilation and
creation operators for single nucleon together with the application of Wicks
theorem. These techniques are expected to be helpful in deriving the mean-field
equations for the $Hartree-Fock$, $Bardeen-Cooper-Schrieffer$ and
$Hartree-Fock$ Bogoliubov theories. | nucl-th |
Spectator induced electromagnetic effects in heavy-ion collisions and
space-time-momentum conditions for pion emission: We present our calculation of electromagnetic effects, induced by the
spectator charge on Feynman-$x_F$ distributions of charged pions in peripheral
$Pb+Pb$ collisions at CERN SPS energies, including realistic initial
space-time-momentum conditions for pion emission. The calculation is performed
in the framework of our simplified implementation of the fire-streak model,
adopted to the production of both $\pi^-$ and $\pi^+$ mesons. Isospin effects
are included to take into account the asymmetry in production of $\pi^+$ and
$\pi^-$ at high rapidity. A comparison to a simpler model from the literature
is made. We obtain a good description of the NA49 data on the $x_F$- and
$p_T$-dependence of the ratio of cross sections $\pi^+/\pi^-$. The experimental
data favors short times ($0.5<\tau<2$~fm/$c$) for fast pion creation in the
local fire-streak rest frame. The possibility of the expansion of the
spectators is considered in our calculation, and its influence on the
electromagnetic effect observed for the $\pi^+/\pi^-$ ratio is discussed. In
addition we discuss the relation between anisotropic flow and the
electromagnetic distortion of $\pi^+/\pi^-$ ratios, and study the influence of
transverse expansion of fire streaks as well as their vorticity on this
distortion. In this latter study we find that inclusion of rotation of fire
streaks in our model gives a satisfactory description of the rapidity
dependence of pion directed flow. We conclude that {our implementation of the}
fire-streak model, which properly describes the centrality dependence of
$\pi^-$ rapidity spectra at CERN SPS energies, also provides a quantitative
description of the electromagnetic effect on the $\pi^+/\pi^-$ ratio as a
function of $x_F$. | nucl-th |
Octet Spin Fractions and the Proton Spin Problem: The relatively small fraction of the spin of the proton carried by its quarks
presents a major challenge to our understanding of the strong interaction.
Traditional efforts to explore this problem have involved new and imaginative
experiments and QCD based studies of the nucleon. We propose a new approach to
the problem which exploits recent advances in lattice QCD. In particular, we
extract values for the spin carried by the quarks in other members of the
baryon octet in order to see whether the suppression observed for the proton is
a general property or depends significantly on the baryon structure. We compare
these results with the values for the spin fractions calculated within a model
that includes the effects of confinement, relativity, gluon exchange currents
and the meson cloud required by chiral symmetry, finding a very satisfactory
level of agreement given the precision currently attainable. | nucl-th |
Estimates of hyperon polarization in heavy-ion collisions at collision
energies $\sqrt{s_{NN}}=$ 4--40 GeV: Global polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons in Au+Au
collisions at collision energies $\sqrt{s_{NN}}=$ 4-40 GeV in the midrapidity
region and total polarization, i.e. averaged over all rapidities, are studied
within the scope of the thermodynamical approach. The relevant vorticity is
simulated within the model of the three-fluid dynamics (3FD). It is found that
the performed rough estimate of the global midrapidity polarization quite
satisfactorily reproduces the experimental STAR data on the polarization,
especially its collision-energy dependence. The total polarization increases
with the collision energy rise, which is in contrast to the decrease of the
midrapidity polarization. This suggests that at high collision energies the
polarization reaches high values in fragmentation regions. | nucl-th |
The nuclear fusion reaction rate based on relativistic equilibrium
velocity distribution: The Coulomb barrier is in general much higher than thermal energy. Nuclear
fusion reactions occur only among few protons and nuclei with higher relative
energies than Coulomb barrier. It is the equilibrium velocity distribution of
these high-energy protons and nuclei that participates in determining the rate
of nuclear fusion reactions. In the circumstance it is inappropriate to use the
Maxwellian velocity distribution for calculating the nuclear fusion reaction
rate. We use the relativistic equilibrium velocity distribution for this
purpose. The rate based on the relativistic equilibrium velocity distribution
has a reduction factor with respect to that based on the Maxwellian
distribution, which factor depends on the temperature, reduced mass and atomic
numbers of the studied nuclear fusion reactions. This signifies much to the
solar neutrino problem. | nucl-th |
Probing the symmetry energy and the degree of isospin equilibrium: The rapidity dependence of the single- and double- neutron to proton ratios
of nucleon emission from isospin-asymmetric but mass-symmetric reactions Zr+Ru
and Ru+Zr at energy range $100 \sim 800$ A MeV and impact parameter range
$0\sim 8$ fm is investigated. The reaction system with isospin-asymmetry and
mass-symmetry has the advantage of simultaneously showing up the dependence on
the symmetry energy and the degree of the isospin equilibrium. We find that the
beam energy- and the impact parameter dependence of the slope parameter of the
double neutron to proton ratio ($F_D$) as function of rapidity are quite
sensitive to the density dependence of symmetry energy, especially at energies
$E_b\sim 400$ A MeV and reduced impact parameters around 0.5. Here the symmetry
energy effect on the $F_D$ is enhanced, as compared to the single neutron to
proton ratio. The degree of the equilibrium with respect to isospin (isospin
mixing) in terms of the $F_D$ is addressed and its dependence on the symmetry
energy is also discussed. | nucl-th |
Soliton propagation in relativistic hydrodynamics: We study the conditions for the formation and propagation of Korteweg-de
Vries (KdV) solitons in nuclear matter. In a previous work we have derived a
KdV equation from Euler and continuity equations in non-relativistic
hydrodynamics. In the present contribution we extend our formalism to
relativistic fluids. We present results for a given equation of state, which is
based on quantum hadrodynamics (QHD). | nucl-th |
Thermalization through parton transport: A radiative transport model is used to study kinetic equilibration during the
early stage of a relativistic heavy ion collision. The parton system is found
to be able to overcome expansion and move toward thermalization via parton
collisions. Scaling behaviors show up in both the pressure anisotropy and the
energy density evolutions. In particular, the pressure anisotropy evolution
shows an approximate alpha_s scaling when radiative processes are included. It
approaches an asymptotic time evolution on a time scale of 1 to 2 fm/c. The
energy density evolution shows an asymptotic time evolution that decreases
slower than the ideal hydro evolution. These observations indicate that partial
thermalization can be achieved and viscosity is important for the evolution
during the early longitudinal expansion stage of a relativistic heavy ion
collision. | nucl-th |
Pairing-induced speedup of nuclear spontaneous fission: Collective inertia is strongly influenced at the level crossing at which
quantum system changes diabatically its microscopic configuration. Pairing
correlations tend to make the large-amplitude nuclear collective motion more
adiabatic by reducing the effect of those configuration changes. Competition
between pairing and level crossing is thus expected to have a profound impact
on spontaneous fission lifetimes. To elucidate the role of nucleonic pairing on
spontaneous fission, we study the dynamic fission trajectories of $^{264}$Fm
and $^{240}$Pu using the state-of-the-art self-consistent framework. We employ
the superfluid nuclear density functional theory with the Skyrme energy density
functional SkM$^*$ and a density-dependent pairing interaction. Along with
shape variables, proton and neutron pairing correlations are taken as
collective coordinates. The collective inertia tensor is calculated within the
nonperturbative cranking approximation. The fission paths are obtained by using
the least action principle in a four-dimensional collective space of shape and
pairing coordinates. Pairing correlations are enhanced along the minimum-action
fission path. For the symmetric fission of $^{264}$Fm, where the effect of
triaxiality on the fission barrier is large, the geometry of fission pathway in
the space of shape degrees of freedom is weakly impacted by pairing. This is
not the case for $^{240}$Pu where pairing fluctuations restore the axial
symmetry of the dynamic fission trajectory. The minimum-action fission path is
strongly impacted by nucleonic pairing. In some cases, the dynamical coupling
between shape and pairing degrees of freedom can lead to a dramatic departure
from the static picture. Consequently, in the dynamical description of nuclear
fission, particle-particle correlations should be considered on the same
footing as those associated with shape degrees of freedom. | nucl-th |
Kaon-nucleon scattering to one-loop order in heavy baryon chiral
perturbation theory: We calculate the T-matrices of kaon-nucleon ($KN$) and antikaon-nucleon
($\overline{K}N$) scattering to one-loop order in SU(3) heavy baryon chiral
perturbation theory (HB$\chi$PT). The low-energy constants (LECs) and their
combinations are then determined by fitting the phase shifts of $KN$ scattering
and the corresponding data. This leads to a good description of the phase
shifts below 200 MeV kaon laboratory momentum. We obtain the LEC uncertainties
through statistical regression analysis. We also determine the LECs through the
use of scattering lengths in order to check the consistency of the HB$\chi$PT
framework for different observables and obtain a consistent result. By using
these LECs, we predict the $\overline{K}N$ elastic scattering phase shifts and
obtain reasonable results. The scattering lengths are also predicted, which
turn out to be in good agreement with the empirical values except for the
isospin-0 $\overline{K}N$ scattering length that is strongly affected by the
$\Lambda(1405)$ resonance. As most calculations in the chiral perturbation
theory, the convergence issue is discussed in detail. Our calculations provide
a possibility to investigate the baryon-baryon interaction in HB$\chi$PT. | nucl-th |
Revisiting an extended-mean-field approach in heavy-ion collisions
around the Fermi energy: Static and dynamical aspects of nuclear systems are described through an
extended time-dependent mean-field approach. The foundations of the formalism
are presented, with highlights on the estimation of average values and their
corresponding dispersions. In contrast to semiclassical transport models, the
particular interest of this description lies on its intrinsic quantal
character. The reliability of this approach is discussed by means of
stopping-sensitive observables analysis in heavy-ion collisions in the range of
20 to 120 MeV per nucleon. | nucl-th |
Di-neutron correlation and soft dipole excitation in medium mass
neutron-rich nuclei near drip-line: The neutron pairing correlation and the soft dipole excitation in medium-mass
nuclei near drip-line are investigated from a viewpoint of the di-neutron
correlation. Numerical analyses by means of the coordinate-space HFB and the
continuum QRPA methods are performed for even-even $^{18-24}$O, $^{50-58}$Ca
and $^{80-86}$Ni. A clear signature of the di-neutron correlation is found in
the HFB ground state; two neutrons are correlated at short relative distances
$\lesim 2$ fm with large probability $\sim 50%$. The soft dipole excitation is
influenced strongly by the neutron pairing correlation, and it accompanies a
large transition density for pair motion of neutrons. This behavior originates
from a coherent superposition of two-quasiparticle configurations $[l\times
(l+1)]_{L=1}$ consisting of continuum states with high orbital angular momenta
$l$ reaching an order of $l\sim 10$. It raises a picture that the soft dipole
excitation under the influence of neutron pairing is characterized by motion of
di-neutron in the nuclear exterior against the remaining $A-2$ subsystem.
Sensitivity to the density dependence of effective pair force is discussed. | nucl-th |
What hard probes tell us about the quark-gluon plasma: Theory: In the study of the quark-gluon plasma in high-energy heavy-ion collisions,
hard and electromagnetic (EM) processes play an essential role as probes of the
properties of the dense medium. They can be used to study a wide range of
properties of the dense medium in high-energy heavy-ion collisions, from
space-time profiles of the dense matter, bulk transport coefficients to EM
responses and the jet transport parameter. I review in this talk these medium
properties, how they can be studied through hard and EM probes and the status
of recent theoretical and phenomenological investigations. | nucl-th |
Intermediate-Energy Semileptonic Probes of the Hadronic Neutral Current: The present and future prospects of intermediate-energy semileptonic neutral
current studies are reviewed. Possibilities for using neutrino and
parity-violating electron scattering from nucleons and nuclei to study hadron
structure and nuclear dynamics are emphasized, with particular attention paid
to probes of the nucleon's strangeness content. Connections are drawn between
such studies and tests of electroweak gauge theory using electron or neutrino
scattering. Outstanding theoretical issues in the interpretation of
semileptonic neutral current measurements are highlighted, and the prospects
for undertaking neutrino and parity-violating electron scattering experiments
in the near future are surveyed. | nucl-th |
Influence of the hadronic equation of state on the hadron-quark phase
transition in neutron stars: We study the hadron-quark phase transition in the interior of neutron stars.
The relativistic mean field (RMF) theory is adopted to describe the hadronic
matter phase, while the Nambu-Jona-Lasinio (NJL) model is used for the quark
matter phase. The influence of the hadronic equation of state on the phase
transition and neutron star properties are investigated. We find that a neutron
star possesses a large population of hyperons, but it is not dense enough to
possess a pure quark core. Whether the mixed phase of hadronic and quark matter
exist in the core of neutron stars depends on the RMF parameters used. | nucl-th |
Auxiliary Field Quantum Monte Carlo for Nuclear Physics on the Lattice: We employ constrained path Auxiliary Field Quantum Monte Carlo (AFQMC) in the
pursuit of studying physical nuclear systems using a lattice formalism. Since
AFQMC has been widely used in the study of condensed-matter systems such as the
Hubbard model, we benchmark our method against published results for both one-
and two-dimensional Hubbard model calculations. We then turn our attention to
cold-atomic and nuclear systems. We use an onsite contact interaction that can
be tuned in order to reproduce the known scattering length and effective range
of a given interaction. Developing this machinery allows us to extend our
calculations to study nuclear systems within a lattice formalism. We perform
initial calculations for a range of nuclear systems from two- to few-body
neutron systems. | nucl-th |
The Single State Dominance Hypothesis and the Two-Neutrino Double Beta
Decay of Mo100: The hypothesis of the single state dominance (SSD) in the calculation of the
two-neutrino double beta decay of Mo100 is tested by exact consideration of the
energy denominators of the perturbation theory. Both transitions to the ground
state as well as to the 0+ and 2+ excited states of the final nucleus Ru100 are
considered. We demonstrate, that by experimental investigation of the single
electron energy distribution and the angular correlation of the outgoing
electrons, the SSD hypothesis can be confirmed or ruled out by a precise
two-neutrino double beta decay measurement (e.g. by NEMO III collaboration). | nucl-th |
A novel treatment of the proton-proton Coulomb force in elastic
proton-deuteron Faddeev calculations: We propose a novel approach to incorporate the proton-proton (pp) Coulomb
force into the three-nucleon (3N) Faddeev calculations. The main new ingredient
is a 3-dimensional screened pp Coulomb t-matrix obtained by a numerical
solution of the 3-dimensional Lippmann-Schwinger (LS) equation. We demonstrate
numerically and provide analytical insight that the elastic proton-deuteron
(pd) observables can be determined directly from the resulting on shell 3N
amplitude increasing the screening radius. The screening limit exists without
the need of renormalisation not only for observables but for the elastic pd
amplitude itself. | nucl-th |
Thermalization through Hagedorn states - the importance of multiparticle
collisions: Quick chemical equilibration times of hadrons within a hadron gas are
explained dynamically using Hagedorn states, which drive particles into
equilibrium close to the critical temperature. Within this scheme master
equations are employed for the chemical equilibration of various hadronic
particles like (strange) baryon and antibaryons. A comparison of the Hagedorn
model to recent lattice results is made and it is found that for both Tc =176
MeV and Tc=196 MeV, the hadrons can reach chemical equilibrium almost
immediately, well before the chemical freeze-out temperatures found in thermal
fits for a hadron gas without Hagedorn states. | nucl-th |
Stellar weak-interaction rates for $rp$-process waiting-point nuclei
from projected shell model: We propose a projected shell model (PSM) for description of stellar
weak-interaction rates between even-even and odd-odd nuclei with extended
configuration space where up to six-quasiparticle (qp) configurations are
included, and the stellar weak-interaction rates for eight $rp$-process
waiting-point (WP) nuclei, $^{64}$Ge, $^{68}$Se, $^{72}$Kr, $^{76}$Sr,
$^{80}$Zr, $^{84}$Mo, $^{88}$Ru and $^{92}$Pd, are calculated and analyzed for
the first time within the model. Higher-order qp configurations are found to
affect the underlying Gamow-Teller strength distributions and the corresponding
stellar weak-interaction rates. Under $rp$-process environments with high
temperatures and densities, on one hand, thermal population of excited states
of parent nuclei tends to decrease the stellar $\beta^+$ decay rates. On the
other hand, the possibility of electron capture (EC) tends to provide
increasing contribution to the rates with temperature and density. The
effective half-lives of WP nuclei under the $rp$-process peak condition are
predicted to be reduced as compared with the terrestrial case, especially for
$^{64}$Ge and $^{68}$Se. | nucl-th |
Virtual Compton Scattering off the Nucleon in Chiral Perturbation Theory: We investigate the spin-independent part of the virtual Compton scattering
(VCS) amplitude off the nucleon within the framework of chiral perturbation
theory. We perform a consistent calculation to third order in external momenta
according to Weinberg's power counting. With this calculation we can determine
the second- and fourth-order structure-dependent coefficients of the general
low-energy expansion of the spin-averaged VCS amplitude based on gauge
invariance, crossing symmetry and the discrete symmetries. We discuss the
kinematical regime to which our calculation can be applied and compare our
expansion with the multipole expansion by Guichon, Liu and Thomas. We establish
the connection of our calculation with the generalized polarizabilities of the
nucleon where it is possible. | nucl-th |
Compton Scattering on 4He with Nuclear One- and Two-Body Densities: We present the first \emph{ab initio} calculation of elastic Compton
scattering from 4He. It is carried out to $\mathcal{O}(e^2 \delta^3)$ [N3LO] in
the $\delta$ expansion of $\chi$EFT. At this order and for this target, the
only free parameters are the scalar-isoscalar electric and magnetic dipole
polarisabilities of the nucleon. Adopting current values for these yields a
parameter-free prediction. This compares favourably with the world data from
HI$\gamma$S, Illinois and Lund for photon energies
$50\;\mathrm{MeV}\lesssim\omega\lesssim120\;\mathrm{MeV}$ within our
theoretical uncertainties of $\pm10\%$. We predict a cross section up to 7
times that for deuterium. As in 3He, this emphasises and tests the key role of
meson-exchange currents between np pairs in Compton scattering on light nuclei.
We assess the sensitivity of the cross section and beam asymmetry to the
nucleon polarisabilities, providing clear guidance to future experiments
seeking to further constrain them. The calculation becomes tractable by use of
the Transition Density Method. The one- and two-body densities generated from 5
chiral potentials and the AV18$+$UIX potential are available using the python
package provided at \url{https://pypi.org/project/nucdens/}. | nucl-th |
$α$ Decays in Superstrong Static Electric Fields: Superstrong static electric fields could deform Coulomb barriers between
$\alpha$ clusters and daughter nuclei, and bring up the possibility of speeding
up $\alpha$ decays. We adopt a simplified model for the spherical $\alpha$
emitter $^{212}$Po and study its responses to superstrong static electric
fields. We find that, superstrong electric fields with field strengths
$|\mathbf{E}|\sim0.1$ MV/fm could turn the angular distribution of $\alpha$
emissions from isotropic to strongly anisotropic, and speed up $\alpha$ decays
by more than one order of magnitude. We also study the influences of
superstrong electric fields along the Po isotope chains, and discuss the
implications of our studies on $\alpha$ decays in superstrong monochromatic
laser fields. The study here might be helpful for future theoretical studies of
$\alpha$ decay in realistic superstrong laser fields. | nucl-th |
Hadron-quark mixed phase in hyperon stars: We analyze the different possibilities for the hadron-quark phase transition
occurring in beta-stable matter including hyperons in neutron stars. We use a
Brueckner-Hartree-Fock approach including hyperons for the hadronic equation of
state and a generalized MIT bag model for the quark part. We then point out in
detail the differences between Maxwell and Gibbs phase transition constructions
including the effects of surface tension and electromagnetic screening. We find
only a small influence on the maximum neutron star mass, whereas the radius of
the star and in particular its internal structure are more affected. | nucl-th |
Estimating magnetar radii with an empirical meta-model: The presence of strong magnetic fields in neutron stars, such as in
magnetars, may significantly affect their crust-core transition properties and
the crust size. This knowledge is crucial in the correct interpretation of
astrophysical phenomena involving magnetars, such as glitches in observed
rotation frequencies, cooling, bursts and possibly tidal polarizabilities. A
recently developed meta-modelling technique allows exploring the model
dependence of density functional theory equation of state calculations. In this
work, we extend this meta-model to investigate the effect of strong magnetic
fields on spinodal instabilities of neutron star matter and the associated
crust-core properties. Both Tolman-Oppenheimer-Volkov and a full
self-consistent numerical calculations are performed for the neutron star
structure, the results being quantitatively different for strong magnetic
fields. | nucl-th |
Transport Coefficient to Trace Anomaly in the Clustering of Color
Sources Approach: From our previously obtained shear viscosity to entropy density ratio
($\eta/s$) in the framework of clustering of color sources (Color String
Percolation Model: CSPM), we calculate the jet quenching parameter $\hat {q}$
and trace anomaly $\Delta = (\varepsilon -3\it p)/T^{4}$ as a function of
temperature. It is shown that the scaled $\hat {q}/T^{3}$ is in agreement with
the recent JET Collaboration estimates. The inverse of $\eta/s$ is found to
represent $\Delta$. The results for $\Delta$ are in excellent agreement with
Lattice Quantum Chromo Dynamics (LQCD) simulations. From the trace anomaly and
energy density $\epsilon$, the equation of state is obtained as a function of
temperature and compared with LQCD simulations. It is possible that there is a
direct connection between the $\eta/s$ and $\Delta$. Thus the estimate of
transport coefficient $\eta/s$ provides $\hat {q}$ and $\Delta$ as a function
of temperature. Both $\Delta$ and $\eta/s$ describe the transition from a
strongly coupled QGP to a weakly coupled QGP. | nucl-th |
Collisional energy loss and the suppression of high $p_T$ hadrons: We calculate nuclear suppression factor ($R_{AA}$) for light hadrons by
taking only the elastic processes and argue that in the measured $p_T$ domain
of RHIC, collisional rather than the radiative processes is the dominant
mechanism for partonic energy loss. | nucl-th |
Constraining URCA cooling of neutron stars from the neutron radius of
208Pb: Recent observations by the Chandra observatory suggest that some neutron
stars may cool rapidly, perhaps by the direct URCA process which requires a
high proton fraction. The proton fraction is determined by the nuclear symmetry
energy whose density dependence may be constrained by measuring the neutron
radius of a heavy nucleus, such as 208Pb. Such a measurement is necessary for a
reliable extrapolation of the proton fraction to the higher densities present
in the neutron star. A large neutron radius in 208Pb implies a stiff symmetry
energy that grows rapidly with density, thereby favoring a high proton fraction
and allowing direct URCA cooling. Predictions for the neutron radius in 208Pb
are correlated to the proton fraction in dense matter by using a variety of
relativistic effective field-theory models. Models that predict a neutron (Rn)
minus proton (Rp) root-mean-square radius in 208Pb to be Rn-Rp<0.20 fm have
proton fractions too small to allow the direct URCA cooling of 1.4 solar-mass
neutron stars. Conversely, if Rn-Rp>0.25 fm, the direct URCA process is allowed
(by all models) to cool down a 1.4 solar-mass neutron star. The Parity Radius
Experiment at Jefferson Laboratory aims to measure the neutron radius in 208Pb
accurately and model independently via parity-violating electron scattering.
Such a measurement would greatly enhance our ability to either confirm or
dismiss the direct URCA cooling of neutron stars. | nucl-th |
Factorization Breaking of $A^T_d$ for polarized deuteron targets in a
relativistic framework: We discuss the possible factorization of the tensor asymmetry $A^T_d$
measured for polarized deuteron targets within a relativistic framework. We
define a reduced asymmetry and find that factorization holds only in plane wave
impulse approximation and if p-waves are neglected. Our numerical results show
a strong factorization breaking once final state interactions are included. We
also compare the d-wave content of the wave functions with the size of the
factored, reduced asymmetry and find that there is no systematic relationship
of this quantity to the d-wave probability of the various wave functions. | nucl-th |
Uncertainty Quantification for Optical Model Parameters: Although uncertainty quantification has been making its way into nuclear
theory, these methods have yet to be explored in the context of reaction
theory. For example, it is well known that different parameterizations of the
optical potential can result in different cross sections, but these differences
have not been systematically studied and quantified. The purpose of this work
is to investigate the uncertainties in nuclear reactions that result from
fitting a given model to elastic-scattering data, as well as to study how these
uncertainties propagate to the inelastic and transfer channels. We use
statistical methods to determine a best fit and create corresponding 95\%
confidence bands. A simple model of the process is fit to elastic-scattering
data and used to predict either inelastic or transfer cross sections. In this
initial work, we assume that our model is correct, and the only uncertainties
come from the variation of the fit parameters. We study a number of reactions
involving neutron and deuteron projectiles with energies in the range of 5-25
MeV/u, on targets with mass $A$=12-208. We investigate the correlations between
the parameters in the fit. The case of deuterons on $^{12}$C is discussed in
detail: the elastic-scattering fit and the prediction of $^{12}$C(d,p)$^{13}$C
transfer angular distributions, using both uncorrelated and correlated $\chi^2$
minimization functions. The general features for all cases are compiled in a
systematic manner to identify trends. Our work shows that, in many cases, the
correlated $\chi ^2$ functions (in comparison to the uncorrelated $\chi^2$
functions) provide a more natural parameterization of the process. These
correlated functions do, however, produce broader confidence bands. Further
optimization may require improvement in the models themselves and/or more
information included in the fit. | nucl-th |
Reduced transition probabilities for the gamma decay of the 7.8 eV
isomer in $^{229}$Th: The reduced magnetic dipole and electric quadrupole transition probabilities
for the radiative decay of the $^{229}$Th 7.8 eV isomer to the ground state are
predicted within a detailed nuclear-structure model approach. We show that the
presence and decay of this isomer can only be accounted for by the Coriolis
mixing emerging from a remarkably fine interplay between the coherent
quadrupole-octupole motion of the nuclear core and the single-nucleon motion
within a reflection-asymmetric deformed potential. We find that the magnetic
dipole transition probability which determines the radiative lifetime of the
isomer is considerably smaller than presently estimated. The so-far disregarded
electric quadrupole component may have non-negligible contributions to the
internal conversion channel. These findings support new directions in the
experimental search of the $^{229}$Th transition frequency for the development
of a future nuclear frequency standard. | nucl-th |
Exotic hadrons and hadron-hadron interactions in heavy ion collisions: We discuss the exotic hadron structure and hadron-hadron interactions in view
of heavy ion collisions. First, we demonstrate that a hadronic molecule with a
large spatial size would be produced more abundantly in the coalescence model
compared with the statistical model result. Secondly, we constrain the
Lambda-Lambda interaction by using the recently measured Lambda-Lambda
correlation data. We find that the RHIC-STAR data favor the Lambda-Lambda
scattering parameters in the range 1/a_0 <= -0.8 fm^{-1} and r_{eff} >= 3 fm. | nucl-th |
Fusion reactions in plasmas as probe of the high-momentum tail of
particle distributions: In fusion reactions, the Coulomb barrier selects particles from the
high-momentum part of the distribution. Therefore, small variations of the
high-momentum tail of the velocity distribution can produce strong effects on
fusion rates. In plasmas several potential mechanisms exist that can produce
deviations from the standard Maxwell-Boltzmann distribution. Quantum broadening
of the energy-momentum dispersion relation of the plasma quasi-particles
modifies the high-momentum tail and could explain the fusion-rate enhancement
observed in low-energy nuclear reaction experiments. | nucl-th |
Short-range correlations in semi-exclusive electron scattering
experiments: One-nucleon emission electron scattering experiments are studied with a model
that considers short--range correlations up to the first order in the number of
correlation lines. The proper normalization of the many-body wave functions
requires the evaluation of two- and three-point diagrams, the last ones usually
neglected in the literature. When all these diagrams are included the effects
of the short-range correlations are rather small. The results of our
calculations are compared with experimental data taken on $^{16}$O. | nucl-th |
Meson-induced pentaquark productions: Production cross sections of the pentaquark Theta+ baryon in the
meson-induced reactions are calculated for JP=1/2+- and 3/2+- cases. Through
the comparison with the previous measurements at KEK, several quantum numbers
are excluded. The remaining possibilities can be used to cast the upper limit
on the Theta+ width, combining with the result from the J-PARC E19 experiment. | nucl-th |
The Impact of Anisotropy on Neutron Star Properties: Insights from I-f-C
Universal Relations: This study presents a universal relation for anisotropic neutron stars,
called the $I-f-C$ relation, which accounts for the local anisotropic pressure
using the Quasi-Local (QL) Model proposed by Horvat et al. \cite{QL_Model} to
describe the anisotropy inside the neutron star. This study analyzes
approximately 60 unified tabulated EoS-ensembles, spanning from relativistic to
non-relativistic mean-field models, that comply with multimessenger constraints
and cover a broad range of stiffness. The results indicate that the
relationship between the parameters becomes more robust with positive
anisotropy, while it weakens with negative anisotropy. With the help of the
GW170817 \& GW190814 tidal deformability limit, a theoretical limit for the
canonical $f$-mode frequency for both isotropic and anisotropic stars is
established. For isotropic case the canonical $f$-mode frequency for event
GW170817 \& GW190814 is $f_{1.4} = 2.605^{+0.487} _ {-0.459}\ \mathrm{kHz}$ and
$ f_{1.4} = 2.093^{+0.150} _ {-0.125} \ \mathrm{kHz}$ respectively. These
established relationships have the potential to serve as a reliable tool to
limit the equation of state of nuclear matter when measurements of relevant
observables are obtained. | nucl-th |
The freeze-out mechanism and phase-space density in ultrarelativistic
heavy-ion collisions: We explore the consequences of a freeze-out criterion for heavy-ion
collisions, based on pion escape probabilities from the hot and dense but
rapidly expanding collision region. The influence of the expansion and the
scattering rate on the escape probability is studied. The temperature
dependence of this scattering rate favors a low freeze-out temperature of ~100
MeV. In general, our results support freeze-out along finite four-volumes
rather than sharp three-dimensional hypersurfaces, with high-pt particles
decoupling earlier from smaller volumes. We compare our approach to the
proposed universal freeze-out criteria using the pion phase-space density and
its mean free path. | nucl-th |
Isospin splitting of pion elliptic flow in relativistic heavy-ion
collisions: Based on the framework of an extended multiphase transport model with
mean-field potentials in both the partonic phase and the hadronic phase, we
explain the elliptic flow difference between $\pi^+$ and $\pi^-$ in the
beam-energy scan program at the relativistic heavy-ion collider by
incorporating the vector-isovector potential for quarks and antiquarks with
different isospins. It is found that the isospin splitting of pion elliptic
flow favors a strong vector-isovector interaction, and thus serves as a probe
of the quark matter equation of state as well as the QCD phase structure at
finite baryon and isospin chemical potentials. | nucl-th |
Efimov resonances above four-boson threshold: Four-boson Efimov physics is well known in the negative energy regime but far
less above the four-body breakup threshold. The part of this region with
negative two-boson scattering length is studied solving rigorous four-particle
scattering equations for transition operators in the momentum space. Moving
away from the unitary limit the Efimov tetramers evolve from unstable bound
states into resonances. Their energies and widths are studied as functions of
the two-boson scattering length; a universal behavior is established and given
in a dimensionless representation. The Efimov tetramers have finite width in
the whole regime; they broaden rapidly in the resonance regime but remain
narrower than the associated trimer. The resonant behavior is most clearly seen
in the four-particle recombination rate. | nucl-th |
Do deviations of neutron scattering widths distribution from the
Porter-Thomas law indicate on failure of the Random Matrix theory?: Deviations of neutron scattering width distributions from the Porter-Thomas
law due to resonances overlapping are calculated in the extended framework of
the random matrix approach. | nucl-th |
Kaon Energies in Dense Matter: We discuss the role of kaon-nucleon and nucleon-nucleon correlations in kaon
condensation in dense matter. Correlations raise the threshold density for kaon
condensation, possibly to densities higher than those encountered in stable
neutron stars. | nucl-th |
On the thermalization of quarkonia at the LHC: We argue that the relative yields of $\Upsilon$ states observed at the LHC
can be understood as bottomonium states coming to early thermal equilibrium and
then freezing out. The bottomonium freezeout temperature is approximately 250
MeV. We examine its systematics as a function of centrality. We remark on the
interesting differences seen by the CMS and ALICE experiments in the charmonium
sector. | nucl-th |
Strange Goings on in Quark Matter: We review recent work on how the superfluid state of three flavor quark
matter is affected by non-zero quark masses and chemical potentials. | nucl-th |
Effective field theory approaches to pion production in proton-proton
collisions: I critically review the status of computations of threshold pion production
in proton-proton collisions in the framework of effective field theory
approaches or variants thereof. I also present the results of a novel
diagrammatic scheme. | nucl-th |
Cross sections for Coulomb and nuclear breakup of three-body halo nuclei: All possible dissociation cross sections for the loosely bound three-body
halo nuclei $^6$He (n+n+$\alpha$) and $^{11}$Li (n+n+$^{9}$Li) are computed as
functions of target and beam energy. Both Coulomb and nuclear interactions are
included in the same theoretical framework. The measurements agree with the
calculations for energies above 100 Mev/nucleon. The largest cross sections
correspond to final states with zero or three particles for heavy and with two
neutrons for light targets. | nucl-th |
Clusterization and deformation of multi-$Λ$ hypernuclei within
relativistic mean-field model: Deformed multi-$\Lambda$ hypernuclei are studied within a relativistic
mean-field model. In this paper, we take some $N=Z$ "hyper isotope" chains,
i.e., $^{8+n}_{\ \ n\Lambda}{\rm Be}$, $^{20+n}_{\ \ \ n\Lambda}{\rm Ne}$, and
$^{28+n}_{\ \ \ n\Lambda}{\rm Si}$ systems where $n = 2$, $4$ for Be, and $n =
2$, $8$ for Ne and Si. A sign of two-$^6_{2\Lambda}$He cluster structure is
observed in the two-body correlation in $^{12}_{4\Lambda}$Be. In the Ne hyper
isotopes, the deformation is slightly reduced by addition of $\Lambda$ hyperons
whereas it is significantly reduced or even disappears in the Si hyper
isotopes. | nucl-th |
Observable consequences of event-by-event fluctuations of HBT radii: We explore the effects of event-by-event fluctuations of Hanbury Brown-Twiss
(HBT) radii and show how they can be observed experimentally. The relation of
measured HBT radii extracted from ensemble-averaged correlation functions to
the mean of their event-by-event probability distribution is clarified. We
propose a method to experimentally determine the mean and variance of this
distribution and test it on an ensemble of fluctuating events generated with
the viscous hydrodynamic code VISH2+1. Using the same code, the sensitivity of
the mean and variance of the HBT radii to the specific QGP shear viscosity
$\eta/s$ is studied. We report sensitivity of the mean pion HBT radii and their
variances to the temperature dependence of $\eta/s$ near the quark-hadron
transition at a level similar (10-20%) to that which was previously observed
for elliptic and quadrangular flow of charged hadrons [1]. | nucl-th |
Strangeness Balance in HADES Experiments and the Xi- Enhancement: HADES data on a strangeness production in Ar+KCl collisions at 1.76A GeV are
analyzed within a minimal statistical model. The total negative strangeness
content is fixed by the observed K^+ multiplicities on event-by-event basis.
Particles with negative strangeness are assumed to remain in chemical
equilibrium with themselves and in thermal equilibrium with the environment
until a common freeze-out. Exact strangeness conservation in each collision
event is explicitly preserved. This implies that Xi baryons can be released
only in events where two or more kaons are produced. An increase of the
fireball volume due to application of a centrality trigger in HADES experiments
is taken into account. We find that experimental ratios of K-/K+, Lambda/K+ and
Sigma/K+ can be satisfactorily described provided in-medium potentials are
taken into account. However, the calculated Xi-/Lambda/K+ ratio proves to be
significantly smaller compared to the measured value (8 times lower than the
experimental median value and 3 times lower than the lower error bar). Various
scenarios to explain observed Xi enhancement are discussed. Arguments are given
in favor of the Xi production in direct reactions. The rates of the possible
production processes are estimated and compared. | nucl-th |
Cluster and hyper-cluster production in relativistic heavy-ion
collisions within the Parton-Hadron-Quantum-Molecular-Dynamics approach: We study cluster and hypernuclei production in heavy-ion collisions at
relativistic energies employing the Parton-Hadron-Quantum-Molecular-Dynamics
(PHQMD) approach, a microscopic n-body transport model based on the QMD
propagation of the baryonic degrees of freedom with density dependent 2-body
potential interactions. All other ingredients of PHQMD, including the collision
integral and the treatment of the quark-gluon plasma (QGP) phase, are adopted
from the Parton-Hadron-String Dynamics (PHSD) approach. In PHQMD the cluster
formation occurs dynamically, caused by the interactions. The clusters are
recognized by the Minimum Spanning Tree (MST) algorithm. We present the PHQMD
results for cluster and hypernuclei formation in comparison with the available
experimental data at AGS, SPS, RHIC-BES and RHIC fixed target energies. We also
provide predictions on cluster production for the upcoming FAIR and NICA
experiments. PHQMD allows to study the time evolution of formed clusters and
the origin of their production, which helps to understand how such weakly bound
objects are formed and survive in the rather dense and hot environment created
in heavy-ion collisions. It offers therefore an explanation of the 'ice in the
fire' puzzle. | nucl-th |
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