Nuclear Theory·nucl-th

Wednesday·August 28, 2019

11 papers—3 primary·8 cross-listed

01
Exact hydrodynamic attractor of an ultrarelativistic gas of hard spheres
Gabriel S. Denicol🇧🇷 · Jorge Noronha🇺🇸
We derive the general analytical solution of the viscous hydrodynamic equations for an ultrarelativistic gas of hard spheres undergoing Bjorken expansion, taking into account effects from particle number conservation, and use it to analytically determine its attractor at late times. Differently than all the cases considered before involving rapidly expanding fluids, in this example the gradient expansion converges. We exactly determine the hydrodynamic attractor of this system when its microscopic dynamics is modeled by the Boltzmann equation with a fully nonlinear collision kernel. The exact late time attractor of this system can be reasonably described by hydrodynamics even when the gradients are large.
nucl-thhep-phPRL(2020)·72 citations
02
Back-to-back relative-excess observable in search for the chiral magnetic effect
Yicheng Feng🇺🇸 · Jie Zhao🇺🇸 · Fuqiang Wang🇺🇸
$Background:$ The chiral magnetic effect (CME) is extensively studied in heavy-ion collisions at RHIC and LHC. In the commonly used reaction plane (RP) dependent, charge dependent azimuthal correlator ( $Δ γ$ ), both the close and back-to-back pairs are included. Many backgrounds contribute to the close pairs (e.g. resonance decays, jet correlations), whereas the back-to-back pairs are relatively free of those backgrounds. $Purpose:$ In order to reduce those backgrounds, we propose a new observable which only focuses on the back-to-back pairs, namely, the relative back-to-back opposite-sign (OS) over same-sign (SS) pair excess ( $r_{BB}$ ) as a function of the pair azimuthal orientation with respect to the RP ( $φ_{BB}$ ). $Methods:$ We use analytical calculations and toy model simulations to demonstrate the sensitivity of $r_{BB} (φ_{BB})$ to the CME and its insensitivity to backgrounds. $Results:$ With finite CME, the $φ_{BB}$ distribution of $r_{BB}$ shows a clear characteristic modulation. Its sensitivity to background is significantly reduced compared to the previous $Δ γ$ observable. The simulation results are consistent with our analytical calculations. $Conclusions:$ Our studies demonstrate that the $r_{BB} (φ_{BB})$ observable is sensitive to the CME signal and rather insensitive to the resonance backgrounds.
nucl-thnucl-exPRC(2020)·3 citations
03
Influence of the neutron-skin effect on nuclear isobar collisions at RHIC
Jan Hammelmann🇩🇪 · Alba Soto-Ontoso🇺🇸 · Massimiliano Alvioli🇮🇹 · Hannah Elfner🇩🇪 · Mark Strikman🇺🇸
The unambiguous observation of a Chiral Magnetic Effect (CME)-driven charge separation is the core aim of the isobar program at RHIC consisting of $_{40}^{96}$ Zr+ $_{40}^{96}$ Zr and $_{44}^{96}$ Ru+ $_{44}^{96}$ Ru collisions at $s_{NN} = 200$ GeV. We quantify the role of the spatial distributions of the nucleons in the isobars on both eccentricity and magnetic field strength within a relativistic hadronic transport approach (SMASH, Simulating Many Accelerated Strongly-interacting Hadrons). In particular, we introduce isospin-dependent nucleon-nucleon spatial correlations in the geometric description of both nuclei, deformation for $_{44}^{96}$ Ru and the so-called neutron skin effect for the neutron-rich isobar i.e. $_{40}^{96}$ Zr. The main result of this study is a reduction of the magnetic field strength difference between $_{44}^{96}$ Ru+ $_{44}^{96}$ Ru and $_{40}^{96}$ Zr+ $_{40}^{96}$ Zr by a factor of 2, from $10%$ to $5%$ in peripheral collisions when the neutron-skin effect is included. Further, we find an increase of eccentricity by up to 10 $%$ when deformation is taken into account while neither the neutron skin effect nor the nucleon-nucleon correlations result into a significant modification of this observable with respect to the traditional Woods-Saxon modeling. Our results suggest a significantly smaller CME signal to background ratio for the experimental charge separation measurement in peripheral collisions with the isobar systems than previously expected.
nucl-thhep-phnucl-exPRC(2020)·44 citations
04
Thermal free energy of large Nf QED in 2+1 dimensions from weak to strong coupling
Paul Romatschke🇺🇸 · Matias Säppi🇫🇮
In 2+1 dimensions, QED becomes exactly solvable for all values of the fermion charge $e$ in the limit of many fermions $N_{f} ≫ 1$ . We present results for the free energy density at finite temperature $T$ to next-to-leading-order in large $N_{f}$ . In the naive large $N_{f}$ limit, we uncover an apparently UV-divergent contribution to the vacuum energy at order $O (e^{6} N_{f}^{3})$ , which we argue to become a finite contribution of order $O (N_{f}^{4} e^{6})$ when resumming formally higher-order $1/ N_{f}$ contributions. We find the finite-temperature free energy to be well-behaved for all values of the dimensionless coupling $e^{2} N_{f} / T$ , and to be bounded by the free energy of $N_{f}$ free fermions and non-interacting QED3, respectively. We invite follow-up studies from finite-temperature lattice gauge theory at large but fixed $N_{f}$ to test our results in the regime $e^{2} N_{f} / T ≫ 1$ .
↳ hep-thcond-mat.str-elhep-latnucl-thPRD(2019)·12 citations
05
Quadrupole moments of baryons
A. J. Buchmann🇩🇪 · E. M. Henley🇺🇸
Quadrupole moments of decuplet baryons and the octet-decuplet transition quadrupole moments are calculated using Morpurgo's general QCD parameterization method. Certain relations among the decuplet and the octet to decuplet transition quadrupole moments are derived. These can be used to predict the $Δ$ quadrupole moments which are difficult to measure.
↳ hep-phnucl-thPRD(2002)·64 citations
06
Vector analyzing powers in the $d (p, pp) n$ and $d (p,^{2} He) n$ channels at 135 MeV
H. Tavakoli-Zaniani · M. Eslami-Kalantari · M. T. Bayat · N. Kalantar-Nayestanaki · St. Kistryn · A. Kozela · J.G. Messchendorp · M. Mohammadi-Dadkan · R. Ramazani-Sharifabadi · E. Stephan
Vector analyzing powers, $A_{x}$ and $A_{y}$ , of the proton-deuteron break-up reaction have been measured by using a polarized-proton beam at 135 MeV impinging on a liquid-deuterium target. For the experiment, the Big Instrument for Nuclear-polarization Analysis (BINA) was used at KVI, Groningen, the Netherlands. The data are compared to the predictions of Faddeev calculations using state-of-the-art two- and three-nucleon potentials. Our data are reasonably well described by calculations for the kinematical configurations at which the three-nucleon force (3NF) effect is predicted to be small. However, striking discrepancies are observed at specific configurations, in particular in the cases of symmetric configurations, where the relative azimuthal angle between the two protons is small which corresponds to the $d (p,^{2} He) n$ channel. The vector analyzing powers of these configurations are compared to the proton deuteron elastic scattering to study the spin-isospin sensitivity of the 3NF models. The results are compared to the earlier results of the proton-deuteron break-up reaction at 190 MeV proton-beam energy \cite{Mardanpour2010}. A disagreement is observed for both proton-beam energies between data and calculations which points to a deficiency in the treatment of spin-isospin part of the 3NF.
↳ nucl-exnucl-thEPJA(2020)·12 citations
07
On the Charge Dependence of the Pion-Nucleon Coupling Constant and Nucleon-Nucleon Low-Energy Scattering Parameters
V. A. Babenko🇺🇦 · N. M. Petrov🇺🇦
The simple model describing charge independence and charge symmetry breaking of the pion-nucleon coupling constant is proposed. The model, which has simple physical meaning and foundation, suggests directly proportional dependence of the pion-nucleon coupling constants on the masses of interacting nucleons and pions. Charge dependence of the pion-nucleon coupling constant and the $^{1} S_{0}$ -state low-energy nucleon-nucleon ( $N N$ ) scattering parameters are studied on the basis of the Yukawa meson theory. The values of the $n p$ and $nn$ interaction characteristics calculated by the proposed model agree quite well with the experimental data.
↳ hep-phnucl-th0 citations
08
Light-front wave functions of mesons, baryons and pentaquarks, with topology-induced local 4-quark interaction
Edward Shuryak🇺🇸
We calculate light-front wave functions of mesons, baryons and pentaquarks in a model including constituent mass (representing chiral symmetry breaking), harmonic confining potential, and 4-quark local interaction of 't Hooft type. The model is a simplified version of that used by Jia and Vary. The method used is numerical diagonalization of the Hamiltonian matrix, with certain functional basis. We found that the nucleon wave function displays strong diquar correlations, unlike that for Delta (decuplet) baryon. We also calculate 3-quark-5-quark admixture to baryons, and the resulting antiquark sea PDF.
↳ hep-phnucl-thPRD(2019)·12 citations
09
Neutral pion mass in the linear sigma model coupled to quarks at arbitrary magnetic field
Aritra Das🇮🇳 · Najmul Haque🇮🇳
We calculate the neutral pion mass in the presence of an external magnetic field of arbitrary strength in the framework of the linear sigma model coupled to quarks at zero temperature. We find nonmonotonic behavior of the pion mass as a function of magnetic field. We are also able to reproduce existing results for the weak-field approximation.
↳ hep-phnucl-thPRD(2020)·37 citations
10
Stringent constraints on neutron-star radii from multimessenger observations and nuclear theory
Collin D. Capano🇩🇪 · Ingo Tews🇺🇸 · Stephanie M. Brown🇩🇪 · Ben Margalit🇺🇸 · Soumi De🇺🇸 · Sumit Kumar🇩🇪 · Duncan A. Brown🇺🇸 · Badri Krishnan🇩🇪 · Sanjay Reddy🇺🇸
The properties of neutron stars are determined by the nature of the matter that they contain. These properties can be constrained by measurements of the star's size. We obtain stringent constraints on neutron-star radii by combining multimessenger observations of the binary neutron-star merger GW170817 with nuclear theory that best accounts for density-dependent uncertainties in the equation of state. We construct equations of state constrained by chiral effective field theory and marginalize over these using the gravitational-wave observations. Combining this with the electromagnetic observations of the merger remnant that imply the presence of a short-lived hyper-massive neutron star, we find that the radius of a $1.4 M_{⊙}$ neutron star is $R_{1.4 M_{⊙}} = 11. 0_{- 0.6}^{+ 0.9} km$ (90% credible interval). Using this constraint, we show that neutron stars are unlikely to be disrupted in neutron-star black-hole mergers; subsequently, such events will not produce observable electromagnetic emission.
↳ astro-ph.HEgr-qchep-phnucl-thNature Astron.(2020)·474 citations
11
Probing up-down quark matter via gravitational waves
Chen Zhang🇨🇦
Recently, it was shown that quark matter with only $u$ and $d$ quarks ( $u d$ QM) can be the ground state of matter for baryon numbers $A > A_{min}$ with $A_{min} ≳ 300$ . In this paper, we explore $u d$ quark stars ( $u d$ QSs) that are composed of $u d$ QM, in the context of the two-families scenario in which $u d$ QSs and hadronic stars (HSs) can coexist. Distinct signatures are discussed compared to the conventional study regarding strange quark stars (SQSs). We show that the requirements of $A_{min} ≳ 300$ and the most massive compact star observed being a $u d$ QS together may put stringent constraints on the allowed parameter space of $u d$ QSs. Then, we study the related gravitational-wave probe of the tidal deformability in binary star mergers, including the $u d$ QS- $u d$ QS and $u d$ QS-HS cases. The obtained values of the tidal deformability at 1.4 solar masses and the average tidal deformability are all in good compatibility with the experimental constraints of GW170817. This study points to a new possible interpretation of the GW170817 binary merger event, where $u d$ QS may be at least one component of the binary system detected.
↳ astro-ph.HEgr-qchep-phnucl-thPRD(2020)·49 citations

Affiliations

first authorsco-authorsvia INSPIRE