Nuclear Theory·nucl-th

Thursday·June 6, 2019

7 papers—3 primary·4 cross-listed

01
[Submitted on 4 Jun 2019]
Neutron matter at the interface(s): static response and effective mass
Mateusz Buraczynski🇨🇦 · Nawar Ismail🇨🇦 · Alexandros Gezerlis🇨🇦
Neutron matter is interesting both as an extension of terrestrial nuclear physics and due to its significance for the study of neutron stars. In this work, after some introductory comments on nuclear forces, nuclear ab initio theory, and nuclear phenomenology, we employ two techniques, Quantum Monte Carlo (QMC) and Energy Density Functionals, to practically handle an extended system composed of strongly interacting neutrons. We start by summarizing work on the static response of neutron matter, which considers the impact of external influences on the time-independent system. We then proceed to discuss new results of the energy of quasiparticle excitations in neutron matter, including QMC calculations with chiral or phenomenological nucleon-nucleon interactions. As part of this study, we carefully study the approach of our finite-number computations toward the infinite-system limit.
Comments:
12 pages, 8 figures; v2 corresponds to published version
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Quantum Gases (cond-mat.quant-gas)
arXiv:
1906.01674 [pdf]
EPJA(2020)·8 citations
02
[Submitted on 5 Jun 2019]
Superfluid Phase Transitions and Effects of Thermal Pairing Fluctuations in Asymmetric Nuclear Matter
Hiroyuki Tajima · Tetsuo Hatsuda · Pieter van Wyk · Yoji Ohashi
We investigate superfluid phase transitions of asymmetric nuclear matter at finite temperature ( $T$ ) and density ( $ρ$ ) with a low proton fraction ( $Y_{p} \leq 0.2$ ) which is relevant to the inner crust and outer core of neutron stars. A strong-coupling theory developed for two-component atomic Fermi gases is generalized to the four-component case and is applied to the system of spin- $1/2$ neutrons and protons. The empirical phase shifts of neutron-neutron (nn), proton-proton (pp) and neutron-proton (np) interactions up to $k = 2$ $fm^{- 1}$ are described by multi-rank separable potentials. We show that (i) the critical temperature of the neutron superfluidity $T_{c}^{nn}$ at $Y_{p} = 0$ agrees well with Monte Carlo data at low densities and takes a maximum value $T_{c}^{nn} = 1.68$ MeV at $ρ / ρ_{0} = 0.14$ with $ρ_{0} = 0.17$ fm $^{- 3}$ , (ii) the critical temperature of the proton superconductivity $T_{c}^{pp}$ for $Y_{p} \leq 0.2$ is substantially suppressed at low densities due to np-pairing fluctuations and starts to dominate over $T_{c}^{nn}$ only above $ρ / ρ_{0} = 0.70$ $(0.77)$ for $Y_{p} = 0.1$ $(0.2)$ , and (iii) the deuteron condensation temperature $T_{c}^{d}$ is suppressed at $Y_{p} \leq 0.2$ due to the large mismatch of the two Fermi surfaces.
Comments:
23 pages, 12 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Quantum Gases (cond-mat.quant-gas); Superconductivity (cond-mat.supr-con)
arXiv:
1906.02098 [pdf]
Sci.Rep.(2019)·21 citations
03
[Submitted on 5 Jun 2019]
Renormalizing random-phase approximation by using exact pairing
L. Tan Phuc · N. Quang Hung · N. Dinh Dang
A fully self-consistent renormalized random-phase approximation is constructed based on the self-consistent Hartree-Fock mean field plus exact pairing solutions (EP). This approach exactly conserves the particle number and restores the energy-weighted sum rule, which is violated in the conventional renormalized particle-hole random-phase approximation for a given multipolarity. The numerical calculations are carried out for several light, medium, and heavy-mass nuclei such as $^{22}$ O, $^{60}$ Ni, and $^{90}$ Zr by using an effective MSk3 interaction. To study the pygmy dipole resonance (PDR), the calculations are also performed for the two light and neutron-rich $^{24, 28}$ O isotopes, whose PDRs are known to be dominant. The results obtained show that the inclusion of ground-state correlations beyond the random-phase approximation (RPA) by means of the occupation numbers obtained from the EP affects the RPA solutions within the whole mass range, although this effect decreases with increasing the mass number. At the same time, the anti-pairing effect is observed via a significant reduction of pairing in neutron-rich nuclei. The enhancement of PDR is found in most of neutron-rich nuclei under consideration within our method.
Comments:
26 pages and 10 figures. Accepted in Physical Review C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1906.02137 [pdf]
PRC(2019)·2 citations
04
[Submitted on 28 May 2019] (cross-list from hep-th)
Nonuniqueness of Green's functions at special points
Makoto Natsuume🇯🇵 · Takashi Okamura🇯🇵
We investigate a new property of retarded Green's functions using AdS/CFT. The Green's functions are not unique at special points in complex momentum space. This arises because there is no unique incoming mode at the horizon and is similar to the "pole-skipping" phenomenon in holographic chaos. Our examples include the bulk scalar field, the bulk Maxwell vector and scalar modes, and the shear mode of gravitational perturbations. In these examples, the special points are always located at $ω_{⋆} = - i (2 π T)$ with appropriate values of complex wave number.
Comments:
18 pages, JHEP; v2: added discussion, published version
Subjects:
High Energy Physics — Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
arXiv:
1905.12015 [pdf]
JHEP(2019)·72 citations
05
[Submitted on 4 Jun 2019] (cross-list from hep-ph)
Quark Flavour Dependence of the Shear Viscosity in a Quasiparticle Model
Valeriya Mykhaylova🇵🇱 · Marcus Bluhm🇵🇱 · Krzysztof Redlich🇵🇱 · Chihiro Sasaki🇵🇱
We study the temperature-dependence of the shear viscosity to entropy density ratio in pure Yang-Mills theory and in QCD with light and strange quarks within kinetic theory in the relaxation time approximation. As effective degrees of freedom in a deconfined phase we consider quasiparticle excitations with quark and gluon quantum numbers and dispersion relations that depend explicitly on the temperature. The quasiparticle relaxation times are obtained by computing the microscopic two-body scattering amplitudes for the elementary scatterings among the quasiparticles. For pure Yang-Mills theory we show that the shear viscosity to entropy density ratio exhibits a characteristic non-monotonicity with a minimum at the first-order phase transition. In the presence of dynamical quarks the ratio smoothens while still exhibiting a minimum near confinement. Furthermore, there is a significant increase of the shear viscosity to entropy density ratio in QCD resulting from the quark contributions. This observation differs from previously reported estimates based on functional methods but is in line with perturbative QCD expectations at higher temperatures.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1906.01697 [pdf]
PRD(2019)·39 citations
06
[Submitted on 5 Jun 2019] (cross-list from hep-ph)
Chemical freeze-out conditions and fluctuations of conserved charges in heavy-ion collisions within quantum van der Waals model
R. Poberezhnyuk🇺🇦 · V. Vovchenko🇩🇪 · A. Motornenko🇩🇪 · M. I. Gorenstein🇺🇦 · H. Stoecker🇩🇪
The chemical freeze-out parameters in central nucleus-nucleus collisions are extracted consistently from hadron yield data within the quantum van der Waals (QvdW) hadron resonance gas model. The beam energy dependences for skewness and kurtosis of net baryon, net electric, and net strangeness charges are predicted. The QvdW interactions in asymmetric matter, $Q / B \neq = 0.5$ , between (anti)baryons yield a non-congruent liquid-gas phase transition, together with a nuclear critical point (CP) with critical temperature of $T_{c} = 19.5$ MeV. The nuclear CP yields the collision energy dependence of the skewness and the kurtosis to both deviate significantly from the ideal hadron resonance gas baseline predictions even far away, in $(T, μ_{B})$ -plane, from the CP. These predictions can readily be tested by STAR and NA61/SHINE Collaborations at the RHIC BNL and the SPS CERN, respectively, and by HADES at GSI. The results presented here offer a broad opportunity for the search for signals of phase transition in dense hadronic matter at the future NICA and FAIR high intensity facilities.
Comments:
20 pages, 21 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1906.01954 [pdf]
PRC(2019)·44 citations
07
[Submitted on 5 Jun 2019] (cross-list from astro-ph.HE)
Equation of state effects in the core collapse of a $20$ - $M_{⊙}$ star
A. S. Schneider · L. F. Roberts · C. D. Ott · E. O'connor
Uncertainties in our knowledge of the properties of dense matter near and above nuclear saturation density are among the main sources of variations in multi-messenger signatures predicted for core-collapse supernovae (CCSNe) and the properties of neutron stars (NSs). We construct 97 new finite-temperature equations of state (EOSs) of dense matter that obey current experimental, observational, and theoretical constraints and discuss how systematic variations in the EOS parameters affect the properties of cold nonrotating NSs and the core collapse of a $20 M_{⊙}$ progenitor star. The core collapse of the $20 M_{⊙}$ progenitor star is simulated in spherical symmetry using the general-relativistic radiation-hydrodynamics code GR1D where neutrino interactions are computed for each EOS using the NuLib library. We conclude that the effective mass of nucleons at densities above nuclear saturation density is the largest source of uncertainty in the CCSN neutrino signal and dynamics even though it plays a subdominant role in most properties of cold NS matter. Meanwhile, changes in other observables affect the properties of cold NSs, while having little effect in CCSNe. To strengthen our conclusions, we perform six octant three-dimensional CCSN simulations varying the effective mass of nucleons at nuclear saturation density. We conclude that neutrino heating and, thus, the likelihood of explosion is significantly increased for EOSs where the effective mass of nucleons at nuclear saturation density is large.
Comments:
21 pages, 13 figures, 2 tables
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1906.02009 [pdf]
PRC(2019)·107 citations

Affiliations

first authorsco-authorsvia INSPIRE

Neutron matter at the interface(s): static response and effective mass

Superfluid Phase Transitions and Effects of Thermal Pairing Fluctuations in Asymmetric Nuclear Matter

Renormalizing random-phase approximation by using exact pairing

Nonuniqueness of Green's functions at special points

Quark Flavour Dependence of the Shear Viscosity in a Quasiparticle Model

Chemical freeze-out conditions and fluctuations of conserved charges in heavy-ion collisions within quantum van der Waals model

Equation of state effects in the core collapse of a 20-M⊙​ star

Affiliations

Equation of state effects in the core collapse of a $20$ - $M_{⊙}$ star