Nuclear Theory·nucl-th

Wednesday·July 10, 2019

10 papers—6 primary·4 cross-listed

01
Damping of density oscillations in neutrino-transparent nuclear matter
Mark G. Alford🇺🇸 · Steven P. Harris🇺🇸
We calculate the bulk-viscous dissipation time for adiabatic density oscillations in nuclear matter at densities of 1-7 times nuclear saturation density and at temperatures ranging from 1 MeV, where corrections to previous low-temperature calculations become important, up to 10 MeV, where the assumption of neutrino transparency is no longer valid. Under these conditions, which are expected to occur in neutron star mergers, damping of density oscillations arises from beta equilibration via weak interactions. We find that for 1 kHz oscillations the shortest dissipation times are in the 5 to 20 ms range, depending on the equation of state, which means that bulk viscous damping could affect the dynamics of a neutron star merger. For higher frequencies the dissipation time can be even shorter.
nucl-thastro-ph.HEgr-qchep-phPRC(2019)·82 citations
02
Scaling properties of direct photon yields in heavy ion collisions
Vladimir Khachatryan🇺🇸 · Michal Praszalowicz🇵🇱
A recent analysis from the PHENIX collaboration of available direct photon measurement results in collisions of various systems such as Au+Au, Cu+Cu, and Pb+Pb, at different beam energies ranging from 39 to 2760 GeV, has shown a universal, within experimental uncertainties, $m u l t i pl i c i t y$ scaling, in which direct photon $p_{T}$ -spectra for transverse momenta up to 2 GeV/ $c$ are scaled with charged hadron pseudorapidity density at midrapidity raised to power $α = 1.25$ . On the other hand, those direct photon $p_{T}$ -spectra also exhibit $g eo m e t r i c a l$ scaling in the similar $p_{T}$ range. Assuming power-law dependence of the scaled photon spectra for both scaling laws, we formulate two independent conditions for the power $α$ , which overshoot experimental data by $\sim 10%$ on average. We discuss possible sources that might improve this estimate.
nucl-thhep-phEPJC(2020)·12 citations
03
Parton-Hadron-Quantum-Molecular Dynamics (PHQMD) -- A Novel Microscopic N-Body Transport Approach for Heavy-Ion Collisions, Dynamical Cluster Formation and Hypernuclei Production
J. Aichelin🇫🇷 · E. Bratkovskaya🇩🇪 · A. Le Fevre🇩🇪 · V. Kireyeu🇷🇺 · V. Kolesnikov🇷🇺 · Y. Leifels🇩🇪 · V. Voronyuk🇷🇺 · G. Coci🇩🇪
Cluster and hypernuclei production in heavy-ion collisions is presently under active experimental and theoretical investigation. Since clusters are weekly bound objects, their production is very sensitive to the dynamical evolution of the system and its interactions. The theoretical description of cluster formation is related to the n-body problem. Here we present the novel n-body dynamical transport approach PHQMD (Parton-Hadron-Quantum-Molecular Dynamics) which is designed to provide a microscopic description of nuclear cluster and hypernucleus formation as well as of general particle production in heavy-ion reactions at relativistic energies. In difference to the coalescence or statistical models, often used for the cluster formation, in PHQMD clusters are formed dynamically due to the interactions between baryons described on a basis of Quantum Molecular Dynamics (QMD)which allows to propagate the n-body Wigner density and n-body correlations in phase-space, essential for the cluster formation. The clusters are identified by the MST (Minimum Spanning Tree) or the SACA ('Simulated Annealing Cluster Algorithm') algorithm which finds the most bound configuration of nucleons and clusters. Collisions among hadrons as well as Quark-Gluon-Plasma formation and parton dynamics in PHQMD are treated in the same way as in the established PHSD (Parton-Hadron-String Dynamics)transport approach. In order to verify our approach with respect to the general dynamics we present here the first PHQMD results for general 'bulk' observables such as rapidity distributions and transverse mass spectra for hadrons ( $π, K, K ˉ, p, p ˉ, Λ, Λ ˉ$ ) from SIS to RHIC energies. We find a good description of the 'bulk' dynamics which allows us to proceed with the results on cluster production, including hypernuclei.
nucl-thhep-phPRC(2020)·132 citations
04
Structure Factors of The Unitary Gas Under Supernova Conditions
Andrei Alexandru🇺🇸 · Paulo F. Bedaque🇺🇸 · Neill C. Warrington🇺🇸
We compute with lattice field theory the vector and axial static structure factors of the unitary gas for arbitrary temperature above the superfluid transition and for fugacities 0.1 < z < 1.0. Using the lattice formulation, we calculate beyond the validity of the virial expansion, a commonly used technique in many-body physics. We find qualitative differences in the behavior of the structure factors at high fugacity compared to the predictions of the virial expansion. Due to the large scattering length of neutrons, we expect the unitary gas structure factors to approximate the structure factors of hot neutron gases, and we therefore expect our calculations to be useful in supernova simulations, where neutron gas structure factors are needed to compute in-medium neutrino-neutron scattering rates.
nucl-thastro-ph.HEcond-mat.quant-gashep-lat+1PRC(2020)·9 citations
05
Effect of anomalous magnetic moment of quarks on the phase structure and mesonic properties in the NJL model
Nilanjan Chaudhuri🇮🇳 · Snigdha Ghosh🇮🇳 · Sourav Sarkar🇮🇳 · Pradip Roy🇮🇳
Employing a field dependent three-momentum cut-off regularization technique, we study the phase structure and mesonic masses using the $2$ -flavour Nambu-Jona Lasinio model at finite temperature and density in presence of arbitrary external magnetic field. This approach is then applied to incorporate the effects of the anomalous magnetic moment(AMM) of quarks on constituent quark mass and thermodynamic observables as a function of temperature/baryonic density. The critical temperature for transition from chiral symmetry broken to the restored phase is observed to decrease with the external magnetic field, which can be classified as inverse magnetic catalysis, while an opposite behaviour is realized in the case of a vanishing magnetic moment, implying magnetic catalysis. These essential features are also reflected in the phase diagram. Furthermore, the properties of the low lying scalar and neutral pseudoscalar mesons are also studied in presence of a hot and dense magnetized medium including AMM of the quarks using random phase approximation. For non-zero values of magnetic field, we notice a sudden jump in the mass of the Goldstone mode at and above the Mott transition temperature which is found to decrease substantially with the increase in magnetic field when the AMM of the quarks are taken into consideration.
nucl-thhep-phPRD(2019)·67 citations
06
Uncertainty quantification and falsification of Chiral Nuclear Potentials
Rodrigo Navarro Perez🇺🇸 · Enrique Ruiz Arriola🇪🇸
Are chiral theories at present describing experimental NN scattering data satisfactorily ?. Will the chiral approach offer a framework where fitting and selecting the existing np and pp data can be done without theoretical bias ?. While predictive power in theoretical nuclear physics has been a major concern in the study of nuclear structure and reactions, the Effective Field Theory (EFT) based on chiral expansions has emerged after Weinberg as a model independent hierarchy for many body forces and much progress has been achieved over the last decades. We review some of the issues involved which point to being close to the solution, but also that work remains still to be done to validate the theory. We analyze several examples including zero energy NN scattering and perturbative counterterm -- free peripheral scattering where one would expect these methods to work best and unveil relevant systematic discrepancies when a fair comparison to the Granada-2013 NN-database and partial wave analysis (PWA) based on coarse graining the interaction is undertaken.
nucl-thhep-ph2 citations
07
Charged-lepton-flavor violation in $∣Δ S ∣ = 1$ hyperon decays
Xiao-Gang He🇨🇳 · Jusak Tandean🇹🇼 · German Valencia🇦🇺
Studies of lepton-flavor violation in strangeness-changing ( $∣Δ S ∣ = 1$ ) transitions have a~long tradition in the kaon sector where they provide some of the strongest limits on physics beyond the standard model. Recent hints of violation of lepton-flavor universality in $B$ -meson decays have revived interest in lepton-flavor violation as the two phenomena appear simultaneously in many extensions of the standard model. At the same time, the LHCb experiment has produced new results for the hyperon process $Σ^{+} \to p μ^{+} μ^{-}$ and may be in a position to study other rare hyperon decay modes. With this in mind, we investigate $∣Δ S ∣ = 1$ hyperon decays into different-flavor lepton pairs $e^{\pm} μ^{\mp}$ in a model-independent manner and contrast the coverage of parameter space that can be achieved with what is known from kaon modes. We include a comparison with selected two-body leptonic decays of charged mesons, with $K \to π ν ν ˉ$ modes, with $μ \to e$ conversion, and with lepton-flavor violating decays of other neutral mesons, all of which constrain the same parameter space in a complementary~way.
↳ hep-phhep-exnucl-thJHEP(2019)·10 citations
08
Linearly polarized gluons at next-to-next-to leading order and the Higgs transverse momentum distribution
Daniel Gutierrez-Reyes🇪🇸 · Sergio Leal-Gomez🇪🇸 · Ignazio Scimemi🇪🇸 · Alexey Vladimirov🇩🇪
We calculate the small-b (or large-qT) matching of transverse momentum dependent (TMD) distribution for linearly polarized gluons to the integrated gluon distributions at the next-to-next-to-leading order (NNLO). This is the last missing part for the complete NNLO prediction of the Higgs spectrum within TMD factorization. We discuss the numerical impact of the correction so derived to the qT-differential cross-section for Higgs boson production and to the positivity bound for linearly polarized gluon transverse momentum distribution.
↳ hep-phhep-exhep-latnucl-ex+1JHEP(2019)·79 citations
09
Charged pion condensation and duality in dense and hot chirally and isospin asymmetric quark matter in the framework of NJL $_{2}$ model
T. G. Khunjua🇷🇺 · K. G. Klimenko🇷🇺 · R. N. Zhokhov🇷🇺
In this paper we investigate in the large- $N_{c}$ limit ( $N_{c}$ is the number of colored quarks) the phase structure of a massless (1+1)-dimensional quark model with four-quark interaction and in the presence of baryon ( $μ_{B}$ ), isospin ( $μ_{I}$ ) and chiral isospin ( $μ_{I 5}$ ) chemical potentials as well as at nonzero temperature. It is established that chiral isospin chemical potential leads to the generation of charged pion condensation (PC) in dense (nonzero baryon density) and chiral asymmetric quark matter for a wide range of isospin densities. It is shown that there exists a duality correspondence between the chiral symmetry breaking and the charged PC phenomena at any values of temperature even for very hot quark gluon plasma. Moreover, it is shown that charged PC phase with nonzero baryon density can be induced in the model at comparatively high temperatures. This opens up new possible physical systems, where it can be of importance, such as heavy ion collisions, just born neutron stars (proto-neutron stars), supernovas as well as neutron star mergers.
↳ hep-phhep-thnucl-thPRD(2019)·36 citations
10
Bulk viscosity of baryonic matter with trapped neutrinos
Mark Alford🇺🇸 · Arus Harutyunyan🇦🇲 · Armen Sedrakian🇩🇪
We study bulk viscosity arising from weak current Urca processes in dense baryonic matter at and beyond nuclear saturation density. We consider the temperature regime where neutrinos are trapped and therefore have nonzero chemical potential. We model the nuclear matter in a relativistic density functional approach, taking into account the trapped neutrino component. We find that the resonant maximum of the bulk viscosity would occur at or below the neutrino trapping temperature, so in the neutrino trapped regime the bulk viscosity decreases with temperature as $T^{- 2}$ , this decrease being interrupted by a drop to zero at a special temperature where the proton fraction becomes density-independent and the material scale-invariant. The bulk viscosity is larger for matter with lower lepton fraction, i.e., larger isospin asymmetry. We find that bulk viscosity in the neutrino-trapped regime is smaller by several orders of magnitude than in the neutrino-transparent regime, which implies that bulk viscosity in neutrino-trapped matter is probably not strong enough to affect significantly the evolution of neutron star mergers. This also implies weak damping of gravitational waves emitted by the oscillations of the postmerger remnant in the high-temperature, neutrino-trapped phase of evolution.
↳ astro-ph.HEastro-ph.SRnucl-thPRD(2019)·79 citations

Affiliations

first authorsco-authorsvia INSPIRE