Nuclear Theory·nucl-th

Friday·March 19, 2021

13 papers—4 primary·9 cross-listed

01
Exploring theoretical uncertainties in the hydrodynamic description of relativistic heavy-ion collisions
Cheng Chiu🇺🇸 · Chun Shen🇺🇸
We explore theoretical uncertainties in the hydrodynamic description of relativistic heavy-ion collisions by examining the full non-linear causality conditions and quantifying the second-order transport coefficients' role on flow observables. The causality conditions impose physical constraints on the maximum allowed values of inverse Reynolds numbers during the hydrodynamic evolution. Including additional second-order gradient terms in the Denicol-Niemi-Molnár-Rischke (DNMR) theory significantly shrinks the casual regions compared to those in the Israel-Stewart hydrodynamics. For Au+Au collisions, we find the variations of flow observables are small with and without imposing the necessary causality conditions, suggesting a robust extraction of the Quark-Gluon Plasma's transport coefficients in previous model-to-data comparisons. However, sizable sensitivity is present in small p+Au collisions, which poses challenges to study the small systems' collectivity.
nucl-thhep-phnucl-exPRC(2021)·53 citations
02
Delta Baryons in Neutron-Star Matter under Strong Magnetic Fields
Veronica Dexheimer🇺🇸 · Kauan D. Marquez🇧🇷 · Débora P. Menezes🇧🇷
In this work, we study magnetic field effects on neutron star matter containing the baryon octet and additional heavier spin 3/2 baryons (the $Δ$ 's). We make use of two different relativistic hadronic models that contain an additional vector-isovector self interaction for the mesons: one version of a relativistic mean field (RMF) model and the Chiral Mean Field (CMF) model. We find that both the additional interaction and a strong magnetic field enhance the $Δ$ baryon population in dense matter, while decreasing the relative density of hyperons. At the same time that the vector-isovector meson interaction modifies neutron-star masses very little ( $< 0.1 M_{⊙}$ ), it decreases their radii considerably, allowing both models to be in better agreement with observations. Together, these features indicate that magnetic neutron stars are likely to contain $Δ$ baryons in their interior.
nucl-thastro-ph.HEhep-thEPJA(2021)·35 citations
03
Nuclear energy density functionals from empirical ground-state densities
Giacomo Accorto🇭🇷 · Tomoya Naito🇯🇵 · Haozhao Liang🇯🇵 · Tamara Niksic🇭🇷 · Dario Vretenar🇭🇷
A model is developed, based on the density functional perturbation theory and the inverse Kohn-Sham method, that can be used to improve relativistic nuclear energy density functionals towards an exact but unknown Kohn-Sham exchange-correlation functional. The improved functional is determined by empirical exact ground-state densities of finite systems. A test of the model and an illustrative calculation are performed, starting from two different approximate functionals, to reproduce the parameters and density dependence of a target functional, using exact ground-state densities of symmetric N=Z systems.
nucl-thPRC(2021)·5 citations
04
Quarkyonic stars with isospin-flavor asymmetry
J. Margueron🇫🇷 · H. Hansen🇫🇷 · P. Proust🇫🇷 · G. Chanfray🇫🇷
We suggest an extension to isospin asymmetric matter of the quarkyonic model from McLerran and Reddy. This extension allows us to construct the $β$ -equilibrium between quarks, nucleons and leptons. The concept of the quarkyonic matter originates from the large number of color limit for which nucleons are the correct degrees of freedom near the Fermi surface -- reflecting the confining forces -- while deep inside the Fermi sea quarks naturally appear. In isospin asymmetric matter, we suggest that this new concept can be implemented within a global isoscalar relation between the shell gaps differentiating the nucleon and the quark sectors. In addition, we impose the conservation of the isospin-flavor asymmetry in the nucleon and the quark phases. Within this model, several quarkyonic stars are constructed on top of the SLy4 model for the nucleon sector, producing a bump in the sound speed, which implies that quarkyonic stars are systematically bigger and have a larger maximum mass than the associated neutron stars. They also predict lower proton fraction at $β$ -equilibrium, which potentially quenches fast cooling in massive compact stars.
nucl-thastro-ph.HEhep-phPRC(2021)·54 citations
05
Implications of Lithium to Oxygen AMS-02 spectra on our understanding of cosmic-ray diffusion
Michael Korsmeier🇸🇪 · Alessandro Cuoco🇮🇹
We analyze recent AMS-02 comic-ray measurements of Lithium, Beryllium, Boron, Carbon, Nitrogen and Oxygen. The emphasis of the analysis is on systematic uncertainties related to propagation and nuclear cross sections. To investigate the uncertainties in the propagation scenario, we consider five different frameworks, differing with respect to the inclusion of a diffusion break at a few GV, the presence of reacceleration, and the presence of a break in the injection spectra of primaries. For each framework we fit the diffusion equations of cosmic rays and explore the parameter space with Monte Carlo methods. At the same time, the impact of the uncertainties in the nuclear production cross sections of secondaries is explicitly considered and included in the fit through the use of nuisance parameters. We find that all the considered frameworks are able to provide a good fit. In particular, two competing scenarios, one including a break in diffusion but no reacceleration and the other with reacceleration but no break in diffusion are both allowed. The inclusion of cross-section uncertainties is, however, crucial, to this result. Thus, at the moment, these uncertainties represent a fundamental systematic preventing a deeper understanding of the properties of CR propagation. We find, nonetheless, that the slope of diffusion at intermediate rigidities is robustly constrained in the range $δ ≃ 0.45 - 0.5$ in models without convection, or $δ ≃ 0.4 - 0.5$ if convection is included in the fit. Furthermore, we find that the use of the AMS-02 Beryllium data provides a lower limit on the vertical size of the Galactic propagation halo of $z_{h} ≳ 3$ kpc.
↳ astro-ph.HEnucl-thPRD(2021)·63 citations
06
On the transition form factors of the axial-vector resonance $f_{1} (1285)$ and its decay into $e^{+} e^{-}$
Marvin Zanke🇩🇪 · Martin Hoferichter🇨🇭 · Bastian Kubis🇩🇪
Estimating the contribution from axial-vector intermediate states to hadronic light-by-light scattering requires input on their transition form factors (TFFs). Due to the Landau-Yang theorem, any experiment sensitive to these TFFs needs to involve at least one virtual photon, which complicates their measurement. Phenomenologically, the situation is best for the $f_{1} (1285)$ resonance, for which information is available from $e^{+} e^{-} \to e^{+} e^{-} f_{1}$ , $f_{1} \to 4 π$ , $f_{1} \to ρ γ$ , $f_{1} \to ϕ γ$ , and $f_{1} \to e^{+} e^{-}$ . We provide a comprehensive analysis of the $f_{1}$ TFFs in the framework of vector meson dominance, including short-distance constraints, to determine to which extent the three independent TFFs can be constrained from the available experimental input, a prerequisite for improved calculations of the axial-vector contribution to hadronic light-by-light scattering. In particular, we focus on the process $f_{1} \to e^{+} e^{-}$ , evidence for which has been reported recently by SND for the first time, and discuss the impact that future improved measurements will have on the determination of the $f_{1}$ TFFs.
↳ hep-phhep-exnucl-thJHEP(2021)·97 citations
07
$N^{*}$ states with hidden charm and a three-body nature
Brenda B. Malabarba🇧🇷 · K. P. Khemchandani🇧🇷 · A. Martinez Torres🇧🇷
In this work we study the formation of $N^{*}$ 's as a consequence of the dynamics involved in the $N D D ˉ^{*} - N D ˉ D^{*}$ system when the $D D ˉ^{*} - D ˉ D^{*}$ subsystem generates $X (3872)$ in isospin 0 and $Z_{c} (3900)$ in isospin 1. States with isospin $I = 1/2$ and mass in the energy region $4400 - 4600$ MeV are found to arise with spin-parity $J^{P} = 1/ 2^{+}$ and $3/ 2^{+}$ , leading to predictions in this way of the existence of $N^{*}$ resonances with hidden charm and a three-body nature. We also discuss the possibility of the existence of $Δ_{c}$ states, i.e., $Δ$ 's with hidden charm.
↳ hep-phnucl-thEPJA(2022)·13 citations
08
Light-front holography with chiral symmetry breaking
Yang Li🇨🇳 · James P. Vary🇺🇸
We present an analytically solvable 3D light-front Hamiltonian model for hadrons that extends light-front holography by including finite mass quarks and a longitudinal confinement term. We propose that the model is suitable as an improved analytic approximation to QCD at a low resolution scale. We demonstrate that it preserves desired Lorentz symmetries and it produces improved agreement with the experimental mass spectroscopy and other properties of the light mesons. Importantly, the model also respects chiral symmetry and the Gell-Mann-Oakes-Renner relation.
↳ hep-phnucl-thPLB(2022)·50 citations
09
Relativistic spin sum rules and the role of the pivot
Cédric Lorcé (Ecole Polytechnique, CPHT)🇫🇷
Spin sum rules depend on the choice of a pivot, i.e. the point about which the angular momentun is defined, usually identified with the center of the nucleon. The latter is however not unique in a relativistic theory and has led to apparently contradictory results in the literature. Using the recently developed phase-space approach, we compute for the first time the contribution associated with the motion of the center of the nucleon, and we derive a general spin sum rule which reduces to established results after appropriate choices for the pivot and the spin component.
↳ hep-phnucl-thEPJC(2021)·24 citations
10
Microscopic derivation of the Boltzmann equation for transport coefficients of resonating fermions at high temperature
Keisuke Fujii🇯🇵 · Yusuke Nishida🇯🇵
Motivated by the recently observed failure of the kinetic theory for the bulk viscosity, we in turn revisit the shear viscosity and the thermal conductivity of two-component fermions with a zero-range interaction both in two and three dimensions. In particular, we show that their Kubo formula evaluated exactly in the high-temperature limit to the lowest order in fugacity is reduced to the linearized Boltzmann equation. Previously, such a microscopic derivation of the latter was achieved only incompletely corresponding to the relaxation-time approximation. Here, we complete it by resuming all contributions that are naively higher orders in fugacity but become comparable in the zero-frequency limit due to the pinch singularity, leading to a self-consistent equation for a vertex function identical to the linearized Boltzmann equation. We then compute the shear viscosity and the thermal conductivity in the high-temperature limit for an arbitrary scattering length and find that the Prandtl number exhibits a nonmonotonic behavior slightly below the constant value in the relaxation-time approximation.
↳ cond-mat.quant-gascond-mat.stat-mechnucl-thPRA(2021)·5 citations
11
Half-integer anomalous currents in 2D materials from a QFT viewpoint
D. Dudal🇧🇪 · F. Matusalem🇧🇷 · A. J. Mizher🇨🇱 · A. R. Rocha🇧🇷 · C. Villavicencio🇨🇱
Charge carriers in Dirac/Weyl semi-metals exhibit a relativistic-like behavior. In this work we propose a novel type of intrinsic half-integer Quantum Hall effect in 2D materials, thereby also offering a topological protection mechanism for the current. Its existence is rooted in the 2D parity anomaly, without any need for a perpendicular magnetic field. We conjecture that it may occur in disturbed honeycomb lattices where both spin degeneracy and time reversal symmetry are broken. These configurations harbor two distinct gap-opening mechanisms that, when occurring simultaneously, drive slightly different gaps in each valley, causing a net anomalous conductivity when the chemical potential is tuned to be between the distinct gaps. Some examples of promising material setups that fulfill the prerequisites of our proposal are also listed to motivate looking for the effect at the numerical and experimental level.
↳ cond-mat.mes-hallhep-phhep-thnucl-thSci.Rep.(2022)·11 citations
12
Revisit the Chiral Magnetic Effect Expectation in Isobaric Collisions at the Relativistic Heavy Ion Collider
Yicheng Feng🇺🇸 · Yufu Lin🇨🇳 · Jie Zhao🇺🇸 · Fuqiang Wang🇺🇸
Isobaric $_{44}^{96}$ Ru+ $_{44}^{96}$ Ru and $_{40}^{96}$ Zr+ $_{40}^{96}$ Zr collisions at $s_{_{N N}} = 200$ GeV have been conducted at the Relativistic Heavy Ion Collider to circumvent the large flow-induced background in searching for the chiral magnetic effect (CME), predicted by the topological feature of quantum chromodynamics (QCD). Considering that the background in isobar collisions is approximately twice that in Au+Au collisions (due to the smaller multiplicity) and the CME signal is approximately half (due to the weaker magnetic field), we caution that the CME may not be detectable with the collected isobar data statistics, within $\sim$ 2 $σ$ significance, if the axial charge per entropy density ( $n_{5} / s$ ) and the QCD vacuum transition probability are system independent. This expectation is generally verified by the Anomalous-Viscous Fluid Dynamics (AVFD) model. While our estimate provides an approximate "experimental" baseline, theoretical uncertainties on the CME remain large.
↳ nucl-exnucl-thPLB(2021)·22 citations
13
Shear-induced spin polarization in heavy-ion collisions
Baochi Fu🇨🇳 · Shuai Y. F. Liu🇨🇳 · Longgang Pang🇨🇳 · Huichao Song🇨🇳 · Yi Yin🇨🇳
We study the spin polarization generated by the hydrodynamic gradients. In addition to the widely studied thermal vorticity effects, we identify an undiscovered contribution from the fluid shear. This shear-induced polarization (SIP) can be viewed as the fluid analog of strain-induced polarization observed in elastic and nematic materials. We obtain the explicit expression for SIP using the quantum kinetic equation and linear response theory. Based on a realistic hydrodynamic model, we compute the differential spin polarization along both the beam direction $z^$ and the out-plane direction $y^$ in non-central heavy-ion collisions at $s_{N N} = 200$ GeV, including both SIP and thermal vorticity effects. We find that SIP contribution always shows the same azimuthal angle dependence as experimental data and competes with thermal vorticity effects. In the scenario that $Λ$ inherits and memorizes the spin polarization of strange quark, SIP wins the competition, and the resulting azimuthal angle dependent spin polarization $P_{y}$ and $P_{z}$ agrees qualitatively with the experimental data.
↳ hep-phnucl-thPRL(2021)·238 citations

Affiliations

first authorsco-authorsvia INSPIRE