Nuclear Theory

The self-consistent mean field approximation of two-flavor NJL model with introducing a free parameter α to reflect the competition between "direct" channel and the "exchange" channel, is employed to study QCD phase structure at finite isospin chemical potential μ I , finite baryon chemical potential μ B and finite temperature T , especially the location of the QCD critical point. It is found that, for fixed isospin chemical potentials the lower temperature of phase transition is obtained with α increasing in the T− μ I plane, and the largest difference of the phase transition temperature with different α 's appears at μ I ∼1.5 m π . At μ I =0 the temperature of the QCD critical end point (CEP) decreases with α increasing, while the critical baryon chemical potential increases. At high isospin chemical potential ( μ I =500 MeV), the temperature of the QCD tricritical point (TCP) increases with α increasing, and in the regions of low temperature the system will transit from pion superfluidity phase to the normal phase as μ B increases. At low temperatures, the critical temperature of QCD phase transition with different α 's rapidly increases with μ I at the beginning, and then increases smoothly around μ I >300 MeV. In high baryon density region, the increase of the isospin chemical potential will raise the critical baryon chemical potential of phase transition.

[Background] The BE2 rates of the Sn isotopes for N≤64 exhibit enhancements hitherto unexplained. The same is true for the Cd isotopes. [Purpose] Describe the electromagnetic properties of the Sn and Cd isotopes [Method] Shell model calculations with a minimally renormalized realistic interaction, supplemented by Quasi and Pseudo-SU3 symmetries and Nilsson-SU3 selfconsistent calculations. [Results for N≤64 ] Shell model calculations with the neutron effective charge as single free parameter describe well the BE2(2>0) and BE2(4>2) rates for N≤64 in the Cd and Sn isotopes. The former exhibit weak permanent deformation corroborating the prediction of a Pseudo-SU3 symmetry, which remains of heuristic value in the latter, where the pairing force erodes the quadrupole dominance. Calculations in 10 7 and 10 10 -dimensional spaces exhibit almost identical patterns: A vindication of the shell model. [Results for N≥64 ] Nilsson-SU3 calculations describe BE2 patterns in [112-120]Cd and [116-118]Sn isotopes having sizable quadrupole moment of non-rotational origin denoted as q-vibrations. No calculations are proposed for the heavier species, for which the conventional seniority dscription is assumed for Sn, while in Cd the quadrupole moments change sign. [Conclusion] A radical reexamination of traditional interpretations in the region has been shown to be necessary, in which quadrupole dominance plays a major role. What emerges is a bumpy but coherent view.

We study the properties of quantum cusp and butterfly catastrophes from an algebraic viewpoint. The analysis employs an interacting boson model Hamiltonian describing quantum phase transitions between specific quadrupole shapes by interpolating between two incompatible dynamical symmetry limits. The classical properties are determined by using coherent states to construct the complete phase diagrams associated with Landau potentials exhibiting such catastrophes.The quantum properties are determined by analyzing the spectra, transition rates and symmetry character of the eigenstates of critical Hamiltonians.

In this paper, we find the heat capacity of the magnetic dual chiral density wave (MDCDW) phase of dense quark matter and use it to explore the feasibility of this phase for a neutron star interior. MDCDW is a spatially inhomogeneous phase of quark matter known to be favored at intermediate densities over the chirally symmetric phase and the color-flavor-locked superconducting phase. By comparing our result to the lower limit of the core heat capacity established from observations of transiently accreting neutron stars, we show that the heat capacity of MDCDW quark matter is well above that lower limit and hence cannot be ruled out. This result adds to a wealth of complementary investigations, all of which has served to strengthen the viability of a neutron star interior made of MDCDW quark matter. For completeness, we review the contributions to the heat capacity of the main neutron star ingredients at low, high and intermediate densities, with and without the presence of a magnetic field.

Higher-order repulsive interactions are included in the three-flavor NJL model in order to describe the quark phase of an hybrid star. The effect of 4-quark and 8-quark vector-isoscalar interactions in the stability of hybrid star configurations is analyzed. The presence of a 8-quark vector-isoscalar channel is seen to be crucial in generating large quark branches in the M(R) diagram. This is due to its stiffening effect on the quark matter equation of state which arises from the non-linear density dependence of the speed of sound. This additional interaction channel allows for the appearance of a quark core at moderately low NS masses, ∼1 M ⊙ , and provides the required repulsion to preserve the star stability up to ∼2.1 M ⊙ . Furthermore, we show that both the heaviest NS mass generated, M max , and its radii, R max , are quite sensitive to the strength of 8-quark vector-isoscalar channel, leading to a considerable decrease of R max as the coupling increases. This behavior imprints a considerable deviation from the purely hadronic matter equation of state in the Λ(M) diagram, which might be a possible signature of the quark matter existence, even for moderately low NS masses, ∼1.4 M ⊙ . The resulting M(R) and Λ(R) relations are in accordance with the latest astrophysical constraints from NICER and Ligo/VIRGO observations, respectively.

Dissociation of quarkonium in quark-gluon plasma (QGP) is a long standing topic in relativistic heavy-ion collisions because it signals one of the fundamental natures of the QGP -- Debye screening due to the liberation of color degrees of freedom. Among recent new theoretical developments is the application of open quantum system framework to quarkonium in the QGP. Open system approach enables us to describe how dynamical as well as static properties of QGP influences the time evolution of quarkonium. Currently, there are several master equations for quarkonium corresponding to various scale assumptions, each derived in different theoretical frameworks. In this review, all of the existing master equations are systematically rederived as Lindblad equations in a uniform framework. Also, as one of the most relevant descriptions in relativistic heavy-ion collisions, quantum Brownian motion of heavy quark pair in the QGP is studied in detail. The quantum Brownian motion is parametrized by a few fundamental quantities of QGP such as real and imaginary parts of heavy quark potential (complex potential), heavy quark momentum diffusion constant, and thermal dipole self-energy constant. This indicates that the yields of quarkonia such as J/ψ and Υ in the relativistic heavy-ion collisions have the potential to determine these fundamental quantities.

In the context of the ongoing search for the QCD critical point at the Relativistic Heavy-Ion Collider, we study the equation of state near the critical point in the temperature and baryon chemical potential plane. We use the parametric representation introduced in earlier literature, which maps the universal 3D Ising equation of state onto the QCD phase diagram using several non-universal parameters. We focus on the quartic cumulant of the baryon number, or baryon number susceptibility~ χ B 4 , which can be accessed experimentally via net-proton fluctuation kurtosis measurements. It was originally predicted, through universality arguments based on the {\em leading} singular contribution, that χ B 4 and net-proton kurtosis should show a specific non-monotonic behavior due to the critical point. In particular, when following the freeze-out curve on the phase diagram by decreasing beam energy, the kurtosis is expected to dip, and then peak, when the beam energy scan passes close to the critical point. We study the effects of the non-universal and thus far unknown parameters of the Ising-to-QCD mapping on the behavior of~ χ B 4 . We find that, while the peak remains a solid feature, the presence of the critical point does not necessarily cause a dip in χ B 4 on the freezeout line {\em below} the transition temperature. The critical point contribution to the dip appears only for a narrow set of mapping parameters, when subleading singular terms are sufficiently suppressed.

In high energy nuclear collisions, heavy flavor tagged jets are useful hard probes to study the properties of the quark-gluon plasma (QGP). In this talk, we present the first theoretical prediction of the D 0 meson radial distributions in jets relative to the jet axis both in p+p and Pb+Pb collisions at 5.02 TeV, it shows a nice agreement with the available experimental data. The in-medium jet evolution in the study is described by a Monte Carlo transport model which has been incorporated with the initial events as input provided by the next-to-leading order (NLO) plus parton shower (PS) event generator SHERPA. In such evolution process, both elastic and inelastic parton energy loss in the hot and dense medium are taken into account. Within this same simulation framework, we predict different modification patterns of the radial profile of charm and bottom quarks in jets in Pb+Pb collisions: jet quenching effect will lead the charm quarks diffuse to lager radius while lead the bottom quarks distributed closer to jet axis.

We present a calculation of radiative pion photoproduction in the framework of covariant chiral perturbation theory with explicit \Delta(1232) degrees of freedom. The analysis is performed employing the small scale expansion scheme adjusted for the \Delta region. Depending on the channel, we include contributions up to next-to-next-to-leading order. We fit the available experimental data for the reaction \gamma p\to\gamma p\pi^0 and extract the value of the \Delta^+ magnetic moment. Errors from the truncation of the small scale expansion are estimated using the Bayesian approach. We compare our results both with the previous studies within the \delta-expansion scheme and with the \Delta-less theory. We also give predictions for radiative charged-pion photoproduction.

Motivated by the unknown nature of the 2.50−2.67 M ⊙ compact object in the binary merger event GW190814, we study the maximum neutron star mass based on constraints from low-energy nuclear physics, neutron star tidal deformabilities from GW170817, and simultaneous mass-radius measurements of PSR J0030+045 from NICER. Our prior distribution is based on a combination of nuclear modeling valid in the vicinity of normal nuclear densities together with the assumption of a maximally stiff equation of state at high densities, a choice that enables us to probe the connection between observed heavy neutron stars and the transition density at which conventional nuclear physics models must break down. We demonstrate that a modification of the highly uncertain supra-saturation density equation of state beyond 2.64 times normal nuclear density is required in order for chiral effective field theory models to be consistent with current neutron star observations and the existence of 2.6 M ⊙ neutron stars. We also show that the existence of very massive neutron stars strongly impacts the radii of ∼2.0 M ⊙ neutron stars (but not necessarily the radii of 1.4 M ⊙ neutron stars), which further motivates future NICER radius measurements of PSR J1614-2230 and PSR J0740+6620.