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Nuclear Theory·nucl-th

Thursday·September 2, 2021

10 papers—3 primary·7 cross-listed

All10Primary3Cross-lists7
  1. 04

    Lepton pair production from a hot and dense QCD medium in the presence of an arbitrary magnetic field

    Aritra Das🇮🇳 · Aritra Bandyopadhyay🇨🇳 · Chowdhury Aminul Islam🇨🇳

    In this article, we have explored the very important quantity of lepton pair production from a hot and dense QCD medium in presence of an arbitrary external magnetic field for simultaneous nonzero values of both the parallel (along the direction of the external field) and perpendicular (lying on the transverse plane to the external field) components of the dilepton momentum. As opposed to the zero magnetic field case (the so-called Born rate) or the lowest Landau level approximated rate, where only the annihilation process contributes, here we observe contributions also arising out of the quark and antiquark decay processes. We found the encouraging result of considerable enhancement of lepton pair production in presence of an arbitrary magnetic field. We decompose the total rate into different physical processes and discuss their behaviors for both zero and nonzero baryon density. The whole analysis is then subjected to an effective model treatment, where we have incorporated the magnetic field induced novel effects of magnetic catalysis (MC) and inverse MC (IMC) through a medium dependent scalar coupling, which leads to some further interesting observations.

    ↳ hep-phnucl-thPRD(2022)·29 citations
  2. 05

    Bayesian Estimation of the D(p,)He Thermonuclear Reaction Rate

    Joseph Moscoso (1 and 2)🇺🇸 · Rafael S. de Souza (3)🇨🇳 · Alain Coc (4)🇫🇷 · Christian Iliadis (1 and 2) ((1) Department of Physics & Astronomy University of North Carolina at Chapel Hill,(2) Triangle Universities Nuclear Laboratory (TUNL), Durham, (3) Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, (4) CNRS/IN2P3, IJCLab, Université Paris-Saclay, Bâtiment)🇺🇸

    Big bang nucleosynthesis (BBN) is the standard model theory for the production of the light nuclides during the early stages of the universe, taking place for a period of about 20 minutes after the big bang. Deuterium production, in particular, is highly sensitive to the primordial baryon density and the number of neutrino species, and its abundance serves as a sensitive test for the conditions in the early universe. The comparison of observed deuterium abundances with predicted ones requires reliable knowledge of the relevant thermonuclear reaction rates, and their corresponding uncertainties. Recent observations reported the primordial deuterium abundance with percent accuracy, but some theoretical predictions based on BBN are at tension with the measured values because of uncertainties in the cross section of the deuterium-burning reactions. In this work, we analyze the S-factor of the D(p,)He reaction using a hierarchical Bayesian model. We take into account the results of eleven experiments, spanning the period of 1955--2021; more than any other study. We also present results for two different fitting functions, a two-parameter function based on microscopic nuclear theory and a four-parameter polynomial. Our recommended reaction rates have a 2.2\% uncertainty at ~GK, which is the temperature most important for deuterium BBN. Differences between our rates and previous results are discussed.

    ↳ astro-ph.COnucl-exnucl-thphysics.data-anApJ(2021)·26 citations
  3. 06

    Search for the Chiral Magnetic Effect with Isobar Collisions at = 200 GeV by the STAR Collaboration at RHIC

    STAR Collaboration: M. S. Abdallah · B. E. Aboona · J. Adam · L. Adamczyk · J. R. Adams · J. K. Adkins · G. Agakishiev · I. Aggarwal · M. M. Aggarwal · Z. Ahammed · I. Alekseev · D. M. Anderson and 385 other authors

    The chiral magnetic effect (CME) is predicted to occur as a consequence of a local violation of and symmetries of the strong interaction amidst a strong electro-magnetic field generated in relativistic heavy-ion collisions. Experimental manifestation of the CME involves a separation of positively and negatively charged hadrons along the direction of the magnetic field. Previous measurements of the CME-sensitive charge-separation observables remain inconclusive because of large background contributions. In order to better control the influence of signal and backgrounds, the STAR Collaboration performed a blind analysis of a large data sample of approximately 3.8 billion isobar collisions of Ru+Ru and Zr+Zr at GeV. Prior to the blind analysis, the CME signatures are predefined as a significant excess of the CME-sensitive observables in Ru+Ru collisions over those in Zr+Zr collisions, owing to a larger magnetic field in the former. A precision down to 0.4% is achieved, as anticipated, in the relative magnitudes of the pertinent observables between the two isobar systems. Observed differences in the multiplicity and flow harmonics at the matching centrality indicate that the magnitude of the CME background is different between the two species. No CME signature that satisfies the predefined criteria has been observed in isobar collisions in this blind analysis.

    ↳ nucl-exhep-exhep-phnucl-thPRC(2022)·327 citations
  4. 07

    Quantum Kinetic Theory for Quantum Electrodynamics

    Shu Lin🇨🇳

    We derive a quantum kinetic theory for QED based on Kadanoff-Baym equations for Wigner functions. By assuming parity invariance and considering a complete set of self-energy diagrams, we find the resulting kinetic theory expanded to lowest order in generalizes the well-known classical kinetic theory to massive case. It contains elastic and inelastic collision terms and integrates screening effect naturally. For a given solution to the classical kinetic theory, we find at next order in a non-dynamical quantum correction to Wigner functions for both fermions and photons, which gives rise to spin polarization for fermion and photon respectively. The approach allows us to study the non-dynamical part of collisional effect on spin polarization phenomenon.

    ↳ hep-phnucl-thPRD(2022)·44 citations
  5. 08

    Conserved charge fluctuations at vanishing net-baryon density from Lattice QCD

    Jishnu Goswami🇩🇪 · Frithjof Karsch🇩🇪 · Swagato Mukherjee🇺🇸 · Peter Petreczky🇺🇸 · Christian Schmidt🇩🇪

    We present here continuum extrapolated results for all 2nd order cumulants using the most recent results obtained by the HotQCD collaboration in (2+1)-flavor QCD. We constrain the applicability of various HRG models by presenting a detailed comparison of our results based on different sets of hadron spectra as well as with virial expansion based model calculations. A comparison with our lattice QCD results for 2nd order cumulants with models that parametrize repulsive interactions among baryons and anti-baryons in a hadron resonance gas through a single excluded volume parameter (EVHRG) is also shown.

    ↳ hep-lathep-phnucl-thEPJ Web Conf.(2022)·4 citations
  6. 09

    The intermediate neutron capture process II.Nuclear uncertainties

    S. Goriely · L. Siess · A. Choplin

    Carbon-enhanced metal-poor (CEMP) r/s-stars show surface-abundance distributions characteristic of the so-called intermediate neutron capture process (i-process) of nucleosynthesis. We previously showed that the ingestion of protons in the convective helium-burning region of a low-mass low-metallicity star can explain the surface abundance distribution observed in CEMP r/s stars relatively well. Such an i-process requires detailed reaction network calculations involving hundreds of nuclei for which reaction rates have not yet been determined experimentally. We investigate the nuclear physics uncertainties affecting the i-process during the AGB phase of low-metallicity low-mass stars by propagating the theoretical uncertainties in the radiative neutron capture cross sections, as well as the 13C(a,n)16O reaction rate, and estimating their impact on the surface-abundance distribution. It is found that considering systematic uncertainties on the various nuclear ingredients affecting the radiative neutron capture rates, surface elemental abundances are typically predicted within +/-0.4 dex. The 56 < Z < 59 region of the spectroscopically relevant heavy-s elements of Ba-La-Ce-Pr as well as the r-dominated Eu element remain relatively unaffected by nuclear uncertainties. In contrast, the inclusion of the direct capture contribution impacts the rates in the neutron-rich A~45, 100, 160, and 200 regions, and the i-process production of the Z~45 and 65-70 elements. Uncertainties in the photon strength function also impact the overabundance factors by typically 0.2-0.4 dex. Nuclear level densities tend to affect abundance predictions mainly in the Z=74-79 regions. The uncertainties associated with the neutron-producing reaction 13C(a,n)16O and the unknown beta-decay rates are found to have a low impact on the overall surface enrichment

    ↳ astro-ph.SRnucl-thAstron.Astrophys.(2021)·17 citations
  7. 10

    Accelerating an Iterative Eigensolver for Nuclear Structure Configuration Interaction Calculations on GPUs using OpenACC

    Pieter Maris · Chao Yang · Dossay Oryspayev · Brandon Cook

    To accelerate the solution of large eigenvalue problems arising from many-body calculations in nuclear physics on distributed-memory parallel systems equipped with general-purpose Graphic Processing Units (GPUs), we modified a previously developed hybrid MPI/OpenMP implementation of an eigensolver written in FORTRAN 90 by using an OpenACC directives based programming model. Such an approach requires making minimal changes to the original code and enables a smooth migration of large-scale nuclear structure simulations from a distributed-memory many-core CPU system to a distributed GPU system. However, in order to make the OpenACC based eigensolver run efficiently on GPUs, we need to take into account the architectural differences between a many-core CPU and a GPU device. Consequently, the optimal way to insert OpenACC directives may be different from the original way of inserting OpenMP directives. We point out these differences in the implementation of sparse matrix-matrix multiplications (SpMM), which constitutes the main cost of the eigensolver, as well as other differences in the preconditioning step and dense linear algebra operations. We compare the performance of the OpenACC based implementation executed on multiple GPUs with the performance on distributed-memory many-core CPUs, and demonstrate significant speedup achieved on GPUs compared to the on-node performance of a many-core CPU. We also show that the overall performance improvement of the eigensolver on multiple GPUs is more modest due to the communication overhead among different MPI ranks.

    ↳ cs.DCcs.MScs.NAmath.NA+11 citation

Affiliations

first authorsco-authorsvia INSPIRE