Nuclear Theory·nucl-th

Thursday·October 31, 2019

11 papers—6 primary·5 cross-listed

01
Fission in a microscopic framework: from basic science to support for applications
I. Stetcu · A. Bulgac · S. Jin · K. J. Roche · N. Schunck
Recent developments, both in theoretical modeling and computational power, have allowed us to make progress on a goal not fully achieved yet in nuclear theory: a microscopic theory of nuclear fission. Even if the complete microscopic description remains a computationally demanding task, the information that can be provided by current calculations can be extremely useful to guide and constrain more phenomenological approaches, which are simpler to implement. First, a microscopic model that describes the real-time dynamics of the fissioning system can justify or rule out some of the approximations. Second, the microscopic approach can be used to obtain trends, e.g., with increasing excitation energy of the fissioning system, or even to compute observables that cannot be otherwise calculated in phenomenological approaches or that can be hindered by the limitations of the method. We briefly present in this contribution the time-dependent superfluid local density approximation (TDSLDA) approach to nuclear fission, approach that has become a very successful theoretical model in many areas of many-body research. The TDSLDA incorporates the effects of the continuum, the dynamics of the pairing field, and the numerical solution is implemented with controlled approximations and negligible numerical corrections. The main part of the current contribution will be dedicated to discussing the method, and recent results concerning the fission dynamics. In addition, we present results on the excitation energy sharing between the fragments, which are in agreement with a qualitative conclusions extracted from a limited number of experimental measurements of properties of prompt neutrons.
nucl-thnucl-exEPJ Web Conf.(2021)·1 citation
02
What can we learn from global spin alignment of $ϕ$ meson in heavy-ion collisions?
Xin-Li Sheng🇨🇳 · Lucia Oliva🇩🇪 · Qun Wang🇨🇳
We propose that a significant positive deviation from 1/3 for the spin density matrix element $ρ_{00}$ of the $ϕ$ meson may indicate the existence of a mean field of the $ϕ$ meson generated in heavy-ion collisions. This explains why STAR preliminary data for the $ϕ$ meson's $ρ_{00}$ are much larger than 1/3 while the data of $Λ$ and $Λ ˉ$ polarization seem not to allow such a significant and positive deviation. The contribution may be from the polarization of the strange quark and antiquark through the $ϕ$ field, an effective mode of the gluon field in strong interaction. We show that $ρ_{00}$ for the $ϕ$ meson is a good analyzer for fields even if they may strongly fluctuate in space-time.
nucl-thPRD(2020)·154 citations
03
Color transparency of $K^{+}$ meson produced in the inclusive $(e, e^{'})$ reaction on nuclei
Swapan Das🇮🇳
Color transparency is studied for the $K^{+}$ meson produced due to large four-momentum transfer in the $(e, e^{'})$ reaction on nuclei. The variation of the $K^{+}$ meson color transparency ( $K^{+}$ CT) with the photon virtuality, and kaon momentum is investigated. The calculated results for $K^{+}$ CT are compared with the data reported from Jefferson Laboratory.
nucl-thnucl-exPRC(2019)·5 citations
04
Hamiltonian flow equations for a Dirac particle in large scalar and vector potentials
Z. X. Ren · P. W. Zhao
An efficient solution of the Dirac Hamiltonian flow equations has been proposed through a novel expandsion with the inverse of the Dirac effective mass. The efficiency and accuracy of this new expansion have been demonstrated by reducing a radial Dirac Hamiltonian with large scalar and vector potentials to two nonrelativistic Hamiltonians corresponding to particles and antiparticles, respectively. By solving the two nonrelativistic Hamiltonians, it is found that the exact solutions of the Dirac equation, for both particles and antiparticles, can be reproduced with a high accuracy up to only a few lowest order terms in the expansion. This could help compare and bridge the relativistic and nonrelativistic nuclear energy density functional theories in the future.
nucl-thquant-phPRC(2019)·6 citations
05
Equivalence of the phenomenological Tsallis distribution to the transverse momentum distribution of $q$ -dual statistics
A.S. Parvan🇷🇺
In the present work, we have found that the phenomenological Tsallis distribution (which nowadays is largely used to describe the transverse momentum distributions of hadrons measured in $pp$ collisions at high energies) is consistent with the basis of the statistical mechanics if it belongs to the $q$ -dual nonextensive statistics instead of the Tsallis one. We have defined the $q$ -dual statistics based on the $q$ -dual entropy which was obtained from the Tsallis entropy under the multiplicative transformation of the entropic parameter $q \to 1/ q$ . We have found that the phenomenological Tsallis distribution is equivalent to the transverse momentum distribution of the $q$ -dual statistics in the zeroth term approximation. Since the $q$ -dual statistics is properly defined, it provides a correct link between the phenomenological Tsallis distribution and the second law of thermodynamics.
nucl-thhep-phEPJA(2020)·21 citations
06
Signatures of Chiral Magnetic Effect in the Collisions of Isobars
Shuzhe Shi🇨🇦 · Hui Zhang🇨🇳 · Defu Hou🇨🇳 · Jinfeng Liao🇺🇸
Quantum anomaly is a fundamental feature of chiral fermions. In chiral materials the microscopic anomaly leads to nontrivial macroscopic transport processes such as the Chiral Magnetic Effect (CME), which has been in the spotlight lately across disciplines of physics. The quark-gluon plasma (QGP) created in relativistic nuclear collisions provides the unique example of a chiral material consisting of intrinsically relativistic chiral fermions. Potential discovery of CME in QGP is of utmost significance, with extensive experimental searches carried out over the past decade. A decisive new collider experiment, dedicated to detecting CME in the collisions of isobars, was performed in 2018 with analysis now underway. In this paper, we develop the state-of-the-art theoretical tool for describing CME phenomenon in these collisions and propose an appropriate isobar subtraction strategy for best background removal. Based on that, we make quantitative predictions for signatures of CME in the collisions of isobars. A new and robust observable that is independent of axial charge uncertainty -- the ratio between isobar-subtracted $γ -$ and $δ -$ correlators, is found to be $- (0.41 \pm 0.27)$ for event-plane measurement and $- (0.90 \pm 0.45)$ for reaction-plane measurement.
nucl-thhep-phnucl-exPRL(2020)·69 citations
07
Hybrid and quark star matter based on a non-perturbative equation of state
Konstantin Otto🇩🇪 · Micaela Oertel🇫🇷 · Bernd-Jochen Schaefer🇩🇪
With the recent dawn of the multi-messenger astronomy era a new window has opened to explore the constituents of matter and their interactions under extreme conditions. One of the pending challenges of modern physics is to probe the microscopic equation of state (EoS) of cold and dense matter via macroscopic neutron star observations such as their masses and radii. Still unanswered issues concern the detailed composition of matter in the core of neutron stars at high pressure and the possible presence of e.g. hyperons or quarks. By means of a non-perturbative functional renormalization group approach the influence of quantum and density fluctuations on the quark matter EoS in $β$ -equilibrium is investigated within two- and three-flavor quark-meson model truncations and compared to results obtained with common mean-field approximations where important fluctuations are usually ignored. We find that they strongly impact the quark matter EoS.
↳ hep-phastro-ph.HEnucl-thPRD(2020)·72 citations
08
On the Topic of Emergence from an Effective Field Theory Perspective
Thomas Luu🇩🇪 · Ulf-G. Meißner🇩🇪
Effective Field Theories have been used successfully to provide a "bottom-up" description of phenomena whose intrinsic degrees of freedom behave at length scales far different from their effective degrees of freedom. An example is the emergent phenomenon of bound nuclei, whose constituents are neutrons and protons, which in turn are themselves composed of more fundamental particles called quarks and gluons. In going from a fundamental description that utilizes quarks and gluons to an effective field theory description of nuclei, the length scales traversed span at least two orders of magnitude. In this article we provide an Effective Field Theory viewpoint on the topic of emergence, arguing on the side of reductionism and weak emergence. We comment on Anderson's interpretation of constructionism and its connection to strong emergence.
↳ physics.hist-phhep-thnucl-th3 citations
09
Role of chiral symmetry in the nucleon excitation spectrum
Adam Virgili🇦🇺 · Waseem Kamleh🇦🇺 · Derek Leinweber (University of Adelaide)🇦🇺
The origin of the low-lying nature of the $N$ *(1440), or Roper resonance, has been the subject of significant interest for many years, including several investigations using lattice QCD. The majority of lattice studies have not observed a low-lying excited state energy level in the region of the Roper resonance. However, it has been claimed that chiral symmetry could play an important role in our understanding of this resonance. The purpose of this study is to systematically examine the role of chiral symmetry in the low-lying nucleon spectrum by directly comparing the clover and overlap fermion actions. To ensure any differences in results are attributable to the choice of fermion action, simulations are performed on the same set of gauge field configurations at matched pion masses. Correlation matrix techniques are employed to determine the excitation energy of the first positive-parity excited state for each action. The clover and overlap actions show a remarkable level of agreement. We do not find any evidence that fermion action chiral symmetry plays a significant role in understanding the Roper resonance on the lattice.
↳ hep-lathep-phnucl-thPRD(2020)·11 citations
10
On the Deconfinement Phase Transition in Neutron-Star Mergers
Elias R. Most🇺🇸 · L. Jens Papenfort🇩🇪 · Veronica Dexheimer🇺🇸 · Matthias Hanauske🇩🇪 · Horst Stöcker🇩🇪 · Luciano Rezzolla🇩🇪
We study in detail the nuclear aspects of a neutron-star merger in which deconfinement to quark matter takes place. For this purpose, we make use of the Chiral Mean Field (CMF) model, an effective relativistic model that includes self-consistent chiral symmetry restoration and deconfinement to quark matter and, for this reason, predicts the existence of different degrees of freedom depending on the local density/chemical potential and temperature. We then use the out-of-chemical-equilibrium finite-temperature CMF equation of state in full general-relativistic simulations to analyze which regions of different QCD phase diagrams are probed and which conditions, such as strangeness and entropy, are generated when a strong first-order phase transition appears. We also investigate the amount of electrons present in different stages of the merger and discuss how far from chemical equilibrium they can be and, finally, draw some comparisons with matter created in supernova explosions and heavy-ion collisions.
↳ astro-ph.HEgr-qcnucl-thEPJA(2020)·126 citations
11
Nuclear deformation effects on charge radius measurements of the proton and deuteron
Yonghui Lin🇨🇳 · Bingsong Zou🇨🇳
Up to now, all charge radius measurements of the proton and deuteron assumed uniform spheroidal charge distribution. We investigate the nuclear deformation effects on these charge radius measurements by assuming a uniform prolate charge distribution for the proton and deuteron. We solve the energy levels of the corresponding muonic and electric atoms with such deformed nucleus and present how the purely quadruple deformation of proton and deuteron affects their Lamb shifts. The numerical results suggest that the deformation of proton and deuteron leads to that the charge radius extracted from the electronic measurement should be smaller than the corresponding one in the muonic measurement which assumed uniform spheroidal charge distribution. If the central values of newest measurements for the proton are adopted, the proton would have a prolate structure with the 0.91 $fm$ long axis and 0.73 $fm$ short axis. Further improved precise charge radius measurements of the proton and deuteron will help us to pin down their shape deformation.
↳ hep-phnucl-exnucl-th1 citation

Affiliations

first authorsco-authorsvia INSPIRE