Nuclear Theory·nucl-th

Tuesday·February 21, 2023

10 papers—6 primary·4 cross-listed

01
Third-order relativistic dissipative fluid dynamics from the method of moments
Caio V. P. de Brito🇧🇷 · Gabriel S. Denicol🇧🇷
We derive a linearly causal and stable third-order relativistic fluid-dynamical theory from the Boltzmann equation using the method of moments. For this purpose, we demonstrate that such theory must include novel degrees of freedom, corresponding to irreducible tensors of rank 3 and 4. The equations of motion derived in this work are compared with numerical solutions of the Boltzmann equation, considering an ultrarelativistic, classical gas in the highly symmetric Bjorken flow scenario. These solutions are shown to be in good agreement for a wide range of values of shear viscosity and initial temperatures.
nucl-thphysics.flu-dynPRD(2023)·29 citations
02
Bayesian quantification of strongly-interacting matter with color glass condensate initial conditions
Matthew R. Heffernan🇨🇦 · Charles Gale🇨🇦 · Sangyong Jeon🇨🇦 · Jean-François Paquet🇺🇸
A global Bayesian analysis of relativistic Pb + Pb collisions at $s_{NN}$ = 2.76 TeV is performed, using a multistage model consisting of an IP-Glasma initial state, a viscous fluid dynamical evolution, and a hadronic transport final state. The observables considered are from the soft sector hadronic final state. Posterior and Maximum a Posteriori parameter distributions that pertain to the IP-Glasma and hydrodynamic phases are obtained, including the shear and bulk specific viscosity of strong interacting matter. The first use of inference with transfer learning in heavy-ion analyses is presented, together with Bayes Model Averaging.
nucl-thhep-phnucl-exPRC(2024)·55 citations
03
Phenomenological Relativistic Second-Order Hydrodynamics for Multiflavor Fluids
Arus Harutyunyan🇦🇲 · Armen Sedrakian🇩🇪
In this work, we perform a phenomenological derivation of the first- and second-order relativistic hydrodynamics of dissipative fluids. To set the stage, we start with a review of the ideal relativistic hydrodynamics from energy-momentum and particle number conservation equations. We then go on to discuss the matching conditions to local thermodynamical equilibrium, symmetries of the energy-momentum tensor, decomposition of dissipative processes according to their Lorentz structure, and finally, the definition of the fluid velocity in the Landau and Eckart frames. With this preparatory work, we first formulate the first-order (Navier-Stokes) relativistic hydrodynamics from the entropy flow equation, keeping only the first-order gradients of thermodynamical forces. A generalized form of diffusion terms is found with a matrix of diffusion coefficients describing the relative diffusion between various flavors. The procedure of finding the dissipative terms is then extended to the second order to obtain the most general form of dissipative function for multiflavor systems up to the second order in dissipative fluxes. The dissipative function now includes in addition to the usual second-order transport coefficients of Israel-Stewart theory also second-order diffusion between different flavors. The relaxation-type equations of second-order hydrodynamics are found from the requirement of positivity of the dissipation function, which features the finite relaxation times of various dissipative processes that guarantee the causality and stability of the fluid dynamics. These equations contain a complete set of nonlinear terms in the thermodynamic gradients and dissipative fluxes arising from the entropy current, which are not present in the conventional Israel-Stewart theory.
nucl-thastro-ph.HEhep-phSymmetry(2023)·6 citations
04
Optical potential for incident and emitted low-energy $α$ particles. III. Non-statistical processes induced by neutrons on Zr, Nb, and Mo nuclei
Marilena Avrigeanu · Vlad Avrigeanu
The reliability of a previous $α$ -particle optical-model potential (OMP) on nuclei with mass number 45 $\leq$ $A$ $\leq$ 209 was proved for emitted $α$ particles as well, for proton--induced reactions on Zn isotopes [Phys. Rev. C {\bf 91}, 064611 (2015), Paper I]. However, the same was not the case of neutrons on Zr stable isotopes [Phys. Rev. C {\bf 96}, 044610 (2017), Paper II]. A recent assessment of this potential also for nucleon--induced $α$ -emission on $A$ $\sim$ 60 nuclei, including pickup direct reaction and eventual Giant Quadrupole Resonance (GQR) $α$ -emission, is completed for neutrons incident on Zr, Nb, and Mo stable isotopes. Consistent sets of input parameters, determined through analysis of independent data, is involved while no further empirical rescaling factors of the $γ$ and nucleon widths have been involved. A suitable account of all competitive reaction channels is confirmed by careful uncertainty analysis, to avoid parameter ambiguities and/or error compensation. Additional validation of this potential is also supported by recently measured $(α, γ)$ and $(α, n)$ cross--sections of Zr and Mo nuclei. An increase of the $α$ -emission beyond the statistical predictions, through consideration of additional reaction channels of the pickup direct interaction and {\it like}--GQR decay, makes possible the description of both absorption and emission of $α$ particles by the same optical potential.
nucl-thnucl-exPRC(2023)·7 citations
05
Pion production in intermediate-energy heavy-ion collisions with a relativistic quantum molecular dynamics model
Si-Na Wei🇨🇳 · Zhao-Qing Feng🇨🇳
The relativistic mean field approach by distinguishing \com{the slope of symmetry energy} is implemented into the Lanzhou quantum molecular dynamics transport model (LQMD.RMF). The collective flows in the isotopic nuclear reactions are systematically investigated by the relativistic quantum molecular dynamics model \com{with various slopes of symmetry energy}. The structure of the directed and elliptic flows is consistent with the results of the nonrelativistic transportation of nucleon system. \com{The directed flow difference between free neutrons and protons appears in the midrapidity region. The transverse momentum spectra of $π^{+}$ production is close to each other in the nearly symmetric $^{108} Sn +^{112} Sn$ system and the neutron-rich $^{132} Sn +^{124} Sn$ system. However, since there are more neutron-neutron scatterings in neutron-rich system, the transverse momentum spectra of $π^{-}$ production in the neutron-rich system are higher than one in the nearly symmetric system. For a given reaction system, the transverse momentum spectra of $π^{+}$ and $π^{-}$ production are independent on the stiffness of symmetry energy. This leads to the fact that the single ratio and the double ratio are independent on the stiffness of symmetry energy. Moreover, the double ratio without the $π$ -nucleon potential decreases with increasing the transverse momentum. However, the double ratio with the inclusion of $π$ potential increases with increasing the transverse momentum.
nucl-th0 citations
06
Revisiting the Gamow Factor of Reactions on Light Nuclei
Eunseok Hwang · Heamin Ko · Kyoungsu Heo · Myung-Ki Cheoun · Dukjae Jang
This study provides an improved understanding of the penetration probabilities (PPs) in nuclear reactions of light nuclei by correcting the assumptions used in the conventional Gamow factor. The Gamow factor effectively describes the PP in nuclear reactions based on two assumptions: low particle energy than the Coulomb barrier and neglecting the dependence of nuclear interaction potential. However, we find that the assumptions are not valid for light nuclei. As a result of a calculation that excludes the assumptions, we obtain the PP that depends on the nuclear interaction potential depth for the light nuclei. For the potential depth fitted by the experimental fusion cross-section, we present that PPs of light nuclei (D+D, D+T, D+ $^{3}$ He, p+D, p+ $^{6}$ Li, and p+ $^{7}$ Li) become higher than the conventional one near the Coulomb barrier. We also discuss the implications of the modified PP, such as changes in the Gamow peak energy, which determine the measurement of the energy range of the nuclear cross-section in experiments, and the electron screening effect.
nucl-thastro-ph.SRnucl-exApJ(2023)·3 citations
07
Light front synchronization and rest frame densities of the proton: Electromagnetic densities
Adam Freese🇺🇸 · Gerald A. Miller🇺🇸
We clarify the physical origin and meaning of the two-dimensional relativistic densities of the light front formalism. The densities are shown to originate entirely from the use of light front time instead of instant form time, which physically corresponds to using an alternative synchronization convention. This is shown by using tilted light front coordinates, which consist of light front time and ordinary spatial coordinates, and which are also used to show that the obtained densities describe a system at rest rather than at infinite momentum. These coordinates allow all four components of the electromagnetic current density to be given clear physical meanings. We explicate the formalism for spin-half targets, obtaining charge and current densities of the proton and neutron using empirical form factor parametrizations, as well as up and down quark densities and currents. Angular modulations in the densities of transversely-polarized states are explained as originating from redshifts and blueshifts due to quarks moving in different longitudinal directions.
↳ hep-phnucl-thPRD(2023)·13 citations
08
QCD Thermodynamics and Neutral Pion in a Uniform Magnetic Field: Finite Volume Effects
Prabal Adhikari🇺🇸 · Brian C. Tiburzi🇺🇸
We address finite volume effects of lattice QCD calculations in background magnetic fields. Using chiral perturbation theory at next-to-leading order, volume effects are calculated for thermodynamic quantities: the chiral condensate, pressure anisotropy, and magnetization. The neutral pion effective action in a finite volume is additionally derived. For these charge neutral observables, volume and source averaging are shown to capitalize on magnetic periodicity, which is the remnant translational invariance of the finite-volume theory. For a fixed magnetic field strength, certain volume and source averaged quantities are independent of the size of the lattice transverse to the magnetic field. Despite this simplifying feature, finite volume corrections to the magnetic field dependence of the chiral condensate and neutral pion magnetic polarizability can be non-negligible. The pressure anisotropy at fixed magnetic flux, moreover, appears acutely sensitive to the lattice volume.
↳ hep-lathep-phnucl-thPRD(2023)·16 citations
09
Study of the threshold anomaly in the elastic scattering of d+ $^{197}$ Au
T. Giudice · D. Abriola · A. Arazi · E. de Barbará · M.A. Cardona · J. Gómez · D. Hojman · R.M. Id Betan · M.S. Kohen · N. Llaneza · G.V. Martí · B. Paes and 3 other authors
Measurements of the elastic scattering angular distribution for the d+ $^{197}$ Au system were carried out covering deuteron incident energies in the range from 5 to 16 MeV, i.e. approximately 50% below and above the Coulomb barrier. A critical interaction distance of $d_{I}$ = 2.49 fm was determined from these distributions, which is comparable to that of the radioactive halo nucleus $^{6}$ He. The experimental angular distributions were systematically analyzed using two alternative models: the semi-microscopic Sao Paulo and the effective Woods-Saxon optical potentials, for which the best-fitting parameters were determined. These potentials, integrated in the vicinity of the sensitivity radius, were calculated for each energy. For both models, the energy dependence of these integrals presented the breakup threshold anomaly around the coulomb barrier, a typical signature of weakly bound nuclei.
↳ nucl-exnucl-thJ.Phys.G(2023)·3 citations
10
Implementation of Cluster expansion for hot QCD matter
Niels-Uwe Friedrich Bastian🇵🇱 · Pasi Huovinen🇵🇱 · Elizaveta Nazarova🇷🇺
We present a cluster expansion EoS model for strongly-interacting matter based on the generalized Beth-Uhlenbeck formalism to describe hadrons as bound clusters of quarks. This formalism can describe both confined and deconfined phases. Our emphasis is on the region of vanishing baryon densities, where numerical solutions available from Lattice QCD predict a smooth crossover transition from hadron to quark matter. Medium effects are taken into account as self energies, which are motivated from both perturbative QCD calculations and phenomenological models. Parameters are tuned to Lattice QCD data and result in a good agreement of the thermodynamics.
↳ hep-phnucl-thNPA(2023)·2 citations

Affiliations

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