Nuclear Theory·nucl-th

Wednesday·November 17, 2021

10 papers—6 primary·4 cross-listed

01
Skyrme-based extrapolation for the static response of neutron matter
Mateusz Buraczynski · Samuel Martinello · Alexandros Gezerlis
The study of inhomogeneous neutron matter can provide insights into the structure of neutron stars as well as their dynamics in neutron-star mergers. In this work we tackle pure neutron matter in the presence of a periodic external field by considering a finite (but potentially large) number of particles placed in periodic boundary conditions. We start with the simpler setting of a noninteracting gas and then switch to a Skyrme-Hartree-Fock approach, showing static-response results for five distinct Skyrme parametrizations. We explain both the technical details of our computational approach, as well as the significance of these results as a general finite-size extrapolation scheme that may be used by ab initio practitioners to approach the static-response problem of neutron matter in the thermodynamic limit.
nucl-thastro-ph.HEcond-mat.quant-gasPRC(2022)·3 citations
02
Dependence of total kinetic energy of fission fragments on the excitation energy of fissioning systems
Kazuya Shimada · Chikako Ishizuka · Fedir A. Ivanyuk · Satoshi Chiba
We elucidated the reason why the average total kinetic energy (TKE) of fission fragments decreases when the excitation energy of the fissioning systems increases as indicated by experimental data for the neutron-induced fission events. To explore this problem, we used a method based on the four-dimensional Langevin equations we have developed. We have calculated the TKE of fission fragments for fissioning systems $^{236}$ U $^{*}$ and $^{240}$ Pu $^{*}$ excited above respective fission barriers, and compared the results with experimental data for n + $^{235}$ U and n + $^{239}$ Pu reactions, respectively. From the Langevin-model analysis, we have found that the shape of the abundant heavy fragments changes from almost spherical for low excitation domain to highly prolate shape for high excitation energy, while that of the light fragments does not change noticeably. The change of the "shape" of the heavy fragments causes an increase of a distance between the charge centers of the nascent fragments just after scission as excitation energy increases. Accordingly, the Coulomb repulsion between the two fragments decreases with an increase of the excitation energy, which causes the decrease of the average TKE. In this manner, we found that the change of the shape of the heavy fragment as a function of the excitation energy is the key issue for the TKE of fission fragments to decrease as the excitation energy of the fissioning nuclei increases. In other words, washing out of the shell effects which affect the shape of the heavy fragments is the key reason for the decreasing energy dependence of the average TKE of the fission fragments.
nucl-thnucl-exPRC(2021)·13 citations
03
Coherent elastic neutrino-nucleus scattering (CE $ν$ NS) event rates for Ge, Zn and Si detector materials
T. S. Kosmas🇬🇷 · V. K. B. Kota🇮🇳 · D. K. Papoulias🇬🇷 · R. Sahu🇮🇳
Realistic nuclear structure calculations are presented for the event rates due to coherent elastic neutrino-nucleus scattering (CE $ν$ NS), assuming neutrinos from pion-decay at-rest, from nuclear reactors and from Earth's interior. We focus on the currently interesting Germanium isotopes, $^{70, 73, 76}$ Ge, which constitute detector materials of the recently planned CE $ν$ NS experiments. We study in addition the potential use of $^{64, 70}$ Zn and $^{28}$ Si isotopes as promising CE $ν$ NS detectors. From nuclear physics perspectives, recently, calculations have been carried out within the framework of the deformed shell-model (DSM), based on realistic nuclear forces, and assessed on the reproducibility of spectroscopic nuclear properties. The high confidence level acquired by their agreement with experimental results and by their comparison with other mostly phenomenological calculations encouraged the use of DSM to extract predictions for the CE $ν$ NS event rates of the above isotopes. Our detailed estimation of the nuclear physics aspects of the recently observed neutral current coherent neutrino-nucleus scattering may shed light on unravelling the still remaining uncertainties for the CE $ν$ NS process within and beyond the Standard Model.
nucl-thPRC(2021)·13 citations
04
$B_{c}^{+}$ Formation from Random Charm and Anti-bottom Quarks in the Quark-Gluon Plasma
Baoyi Chen🇨🇳 · Liuyuan Wen🇨🇳 · Yunpeng Liu🇨🇳
We study the $B_{c}^{+}$ production in Pb-Pb collisions at $s_{N N} = 5.02$ TeV. In the quark-gluon plasma (QGP) produced in heavy-ion collisions, heavy quarks make random motions with the energy loss. We employ the Langevin equations to study the non-equilibrium distributions of heavy quarks and the Instantaneous Coalescence Model (ICM) to study the hadronization process. Due to abundant charm and bottom quarks in the QGP, their coalescence probability is significantly enhanced compared with the situations in proton-proton collisions. We find that the final production of $B_{c}^{+}$ is increased by the coalescence process, which makes the nuclear modification factor ( $R_{AA}$ ) of $B_{c}^{+}$ larger than the unit. Our model explains the experimental data well at semi-central and central collisions. The observation of $R_{AA} (B_{c}^{+}) > 1$ is regarded as an evident and strong signal of the existence of the deconfined medium generated in heavy-ion collisions.
nucl-thPLB(2022)·13 citations
05
Hydrodynamization times of a holographic fluid far from equilibrium
Romulo Rougemont🇧🇷 · Willians Barreto🇧🇷 · Jorge Noronha🇺🇸
We investigate several hydrodynamization times for an ensemble of different far-from-equilibrium solutions of the strongly coupled $N = 4$ Supersymmetric Yang-Mills plasma undergoing Bjorken flow. For the ensemble of initial data analyzed in the present work, we find that, with typical tolerances between $3%$ to $5%$ , the average hydrodynamization time associated with the late time convergence of the pressure anisotropy to the corresponding Borel resummed hydrodynamic attractor is approximately equal to the average hydrodynamization time associated with the Navier-Stokes result, while both are shorter than the average hydrodynamization time associated with second-order hydrodynamics. On the other hand, we find that the entropy density of the different solutions coalesces to second-order hydrodynamics long before entering in the Navier-Stokes regime. A clear hierarchy between the different average hydrodynamization times of the Bjorken expanding fluid is established for the set of analyzed initial data, comprising also some solutions which, whilst satisfying the dominant and the weak energy conditions at the initial time, evolve such as to transiently violate one or both conditions when the fluid is still far from equilibrium. In particular, solutions violating the weak energy condition are generally found to take a longer time to enter in the hydrodynamic regime than the other solutions.
nucl-thhep-phhep-thPRD(2022)·12 citations
06
Evolution of low-lying M1 modes in germanium isotopes
S. Frauendorf · R. Schwengner
Magnetic dipole strength functions are determined for the series of germanium isotopes from $N = Z = 32$ to $N$ = 48 on the basis of a large number of transition strengths calculated within the shell model. The evolution of the strength with increasing neutron number in the $1 g_{9/2}$ orbital is analyzed. A bimodal structure comprising an enhancement toward low transition enery and a resonance in the region of the scissors mode is identified. The low-energy enhancement is strongest near closed shells, in particular at the almost completely filled $1 g_{9/2}$ orbital, while the scissorslike resonance is most pronounced in the middle of the open shell, which correlates with the magnitude of the also deduced electric quadrupole transition strengths. The results are consistent with previous findings for the shorter series of iron isotopes and proves the occurrence and correlation of the two low-lying magnetic dipole modes as a global structural feature.
nucl-thnucl-exPRC(2022)·9 citations
07
Resurrecting the Strong KSS Conjecture
Scott Lawrence🇺🇸
Many counterexamples to the proposed KSS bound $\frac{η}{s} \geq \frac{1}{4 π}$ depend on constructing systems with large numbers of species. As a result, the entropy density grows large and $\frac{η}{s}$ can be made arbitrarily small. However, these constructions do not affect the dimensionless shear viscosity $\frac{η T}{ϵ + P}$ , which agrees with the traditional $\frac{η}{s}$ only for vanishing chemical potential. This raises the possibility that a KSS-like bound holds for all systems, not just UV-complete quantum field theories, contrary to the previous understanding.
↳ hep-thnucl-th3 citations
08
Spectral functions of heavy quarkonia in a bulk-viscous quark gluon plasma
Lata Thakur🇰🇷 · Yuji Hirono🇰🇷
We study the properties of quarkonia inside a bulk-viscous quark gluon plasma. The non-equilibrium nature of the medium is encoded in the deformed distribution functions of thermal quarks and gluons, with which we compute the dielectric permittivity within the hard thermal loop approximation at one-loop. The modified dielectric permittivity is used to calculate the in-medium heavy quark potential, and using the potential we compute spectral functions, which reflect the physical properties of heavy quarkonia. We discuss how the bulk viscous effect influences quantities such as binding energies and thermal widths. Based on those properties, we discuss the implications of the bulk viscous effect on the physical observables such as $ψ^{'}$ to $J / ψ$ ratio and the nuclear modification factor, $R_{AA}$ . In particular, we argue that the nuclear modification factors of excited and ground states show different sensitivities to the bulk viscous nature of a plasma, which is potentially useful for the critical point search.
↳ hep-phhep-exnucl-thJHEP(2022)·14 citations
09
Neutrino flavor evolution in dense environments and the r-process
Maria Cristina Volpe🇫🇷
In dense environments, standard and non-standard neutrino interactions with the background particles trigger a variety of flavor mechanisms, which can impact r-process nucleosynthetic abundances. Future observations of a(n) (extra)galactic supernova will tell us about properties of neutrinos and of the astrophysical source that produce them. The upcoming measurement of the diffuse supernova neutrino background constitute a unique source of information. We highlight some recent developments.
↳ hep-phastro-ph.SRnucl-thPoS(2022)·0 citations
10
Quantum mechanics of radiofrequency-driven coherent beam oscillations in storage rings
J. Slim🇩🇪 · N.N. Nikolaev🇷🇺 · F. Rathmann🇩🇪 · A. Wirzba🇩🇪
Precision searches for the electric dipole moment of protons in storage ring experiments call for beam-position monitoring in the picometer range. We present the relevant fully quantum mechanical derivation of radiofrequency-driven collective oscillations of a beam in a storage ring.
↳ physics.acc-phhep-phnucl-exnucl-th+1Phys.Rev.Accel.Beams(2023)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE