Nuclear Theory·nucl-th

Friday·October 28, 2016

14 papers—8 primary·6 cross-listed

01
[Submitted on 27 Oct 2016]
Importance of volume corrections on the net-charge distributions at the RHIC BES energies
Hao-jie Xu🇨🇳
The paper presents my recent investigations of volume corrections on the cumulant products of net-charge distributions in statistical model, corresponding to the data reported by the STAR collaboration. The corrected statistical expectations, under simple Poisson approximations, can reasonably explain the data measured in experiment. The results indicate that volume corrections play crucial role in event-by-event multiplicity fluctuation studies.
Comments:
5 pages, 2 figures, contribution to the proceedings of Critical Point and Onset of Deconfinement 2016 (CPOD2016), Wrocław, Poland, May 30 - June 4, 2016
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1610.08591 [pdf]
Acta Phys.Polon.Supp.(2017)·2 citations
02
[Submitted on 27 Oct 2016]
Gap-bridging enhancement of modified Urca processes in nuclear matter
Mark G. Alford · Kamal Pangeni
In nuclear matter at neutron-star densities and temperatures, Cooper pairing leads to the formation of a gap in the nucleon excitation spectra resulting in exponentially strong Boltzmann suppression of many transport coefficients. Previous calculations have shown evidence that density oscillations of sufficiently large amplitude can overcome this suppression for flavor-changing $β$ processes, via the mechanism of "gap bridging". We address the simplifications made in that initial work, and show that gap bridging can counteract Boltzmann suppression of neutrino emissivity for the realistic case of modified Urca processes in matter with $^{3} P_{2}$ neutron pairing.
Comments:
8 pages, 9 figures. Additional references and corrections from proof-reading implemented
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
1610.08617 [pdf]
PRC(2017)·6 citations
03
[Submitted on 27 Oct 2016]
$Λ$ polarization in peripheral collisions at moderate relativistic energies
Y.L. Xie🇳🇴 · M. Bleicher🇩🇪 · H. Stöcker🇩🇪 · D.J. Wang🇨🇳 · L.P. Csernai🇳🇴
The polarization of $Λ$ hyperons from relativistic flow vorticity is studied in peripheral heavy ion reactions at FAIR and NICA energies, just above the threshold of the transition to the Quark-Gluon Plasma. Previous calculations at higher energies with larger initial angular momentum, predicted significant $Λ$ polarization based on the classical vorticity term in the polarization, while relativistic modifications decreased the polarization and changed its structure in the momentum space. At the lower energies studied here, we see the same effect namely that the relativistic modifications decrease the polarization arising from the initial shear flow vorticity.
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1610.08678 [pdf]
PRC(2016)·58 citations
04
[Submitted on 27 Oct 2016]
Equilibrium and non-equilibrium properties of the QGP in a magnetic field: a holographic approach
Renato Critelli🇧🇷
This manuscript reviews recent theoretical progress on the understanding of the quark gluon plasma in a magnetic field that I presented on the conference Hot Quarks 2016, held at South Padre Island, Texas, USA, 12-17 September 2016. It is shown that, using a holographic bottom-up Einstein-Maxwell-Dilaton model, one can have a good quantitative agreement with Lattice data for QCD equation of state and Polyakov loop with nonzero magnetic field. I also present results for the anisotropic shear viscosity ratio $η_{∥} / η_{⊥}$ , with the conclusion that $η_{∥} < η_{⊥}$ for $B > 0$ .
Comments:
4 pages. Contribution to the proceedings of Hot Quarks 2016 conference at South Padre Island, TX, USA
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th)
arXiv:
1610.08751 [pdf]
J.Phys.Conf.Ser.(2017)·2 citations
05
[Submitted on 27 Oct 2016]
New scenarios for hard-core interactions in a hadron resonance gas
L. M. Satarov🇩🇪 · V. Vovchenko🇩🇪 · P. Alba🇩🇪 · M. I. Gorenstein🇺🇦 · H. Stoecker🇩🇪
The equation of state of a baryon-symmetric hadronic matter with hard-sphere interactions is studied. It is assumed that mesons are point-like, but baryons and antibaryons have the same hard-core radius rB. Three possibilities are considered: 1) the baryon-baryon and antibaryon-baryon interactions are the same; 2) baryons do not interact with antibaryons; 3) the baryon-antibaryon and meson-(anti)baryon interactions are negligible. By choosing the parameter rB=0.3-0.6 fm, we calculate the nucleon to pion ratio as a function of temperature and perform the fit of hadron yields measured in central Pb+Pb collisions at the bombarding energy Ecm=2.76 TeV per nucleon pair. New nontrivial effects in the interacting hadron resonance gas at temperatures 150-200 MeV are found.
Comments:
30 pages, 11 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1610.08753 [pdf]
PRC(2017)·46 citations
06
[Submitted on 26 Oct 2016]
$γ^{*} N \to N^{*} (1520)$ form factors in the timelike regime
G. Ramalho🇧🇷 · M.T. Peña🇵🇹
The covariant spectator quark model, tested before in a variety of electromagnetic baryon excitations, is applied here to the $γ^{*} N \to N^{*} (1520)$ reaction in the timelike regime. The transition form factors are first parametrized in the spacelike region in terms of a valence quark core model together with a parametrization of the meson cloud contribution. The form factor behavior in the timelike region is then predicted, as well as the $N^{*} (1520) \to γ N$ decay width and the $N^{*} (1520)$ Dalitz decay, $N^{*} (1520) \to e^{+} e^{-} N$ . Our results may help in the interpretation of dielectron production from elementary $pp$ collisions and from the new generation of HADES results using a pion beam. In the $q^{2} = 0$ --1 GeV $^{2}$ range we conclude that the {\it QED approximation} (a $q^{2}$ independent form factor model) underestimates the electromagnetic coupling of the $N^{*} (1520)$ from 1 up to 2 orders of magnitude. We conclude also that the $N^{*} (1520)$ and the $Δ (1232)$ Dalitz decay widths are comparable.
Comments:
Published version. 12 pages, 10 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1610.08788 [pdf]
PRD(2017)·40 citations
07
[Submitted on 26 Oct 2016]
Recent progress in understanding deconfinement and chiral restoration phase transitions
Edward Shuryak🇺🇸
Paradigme shift in gauge topology, from instantons to their constituents -- instanton-dyons -- has recently lead to very significant advances. Like instantons, they have fermionic zero modes, and their collectivization at sufficiently high density explains the chiral symmetry breaking. Unlike instantons, these objects have electric and magnetic charges. Their back reaction on the mean value of the Polyakov line (holonomy) allows to explain the deconfinement transition. The talk summarizes recent works on the dyon ensemble, done in the mean field approximation (MFA), and also by direct numerical statistical simulation. Introduction of non-trivial quark periodicity conditions leads to drastic changes in both deconfinement and chiral transitions. In particulaly, in the so called Z(N_c)-QCD model the former gets much stronger, while the latter does not seem to occur at all.
Comments:
XIIth Quark Confinement and the Hadron Spectrum, 28 Aug to 4 Sep 2016
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th)
arXiv:
1610.08789 [pdf]
EPJ Web Conf.(2017)·7 citations
08
[Submitted on 27 Oct 2016]
Particle-number projection in the finite-temperature mean-field approximation
P. Fanto · Y. Alhassid · G.F. Bertsch
Calculation of statistical properties of nuclei in a finite-temperature mean-field theory requires projection onto good particle number, since the theory is formulated in the grand canonical ensemble. This projection is usually carried out in a saddle-point approximation. Here we derive formulas for an exact particle-number projection of the finite-temperature mean-field solution. We consider both deformed nuclei, in which the pairing condensate is weak and the Hartree-Fock (HF) approximation is the appropriate mean-field theory, and nuclei with strong pairing condensates, in which the appropriate theory is the Hartree-Fock-Bogoliubov (HFB) approximation, a method that explicitly violates particle-number conservation. For the HFB approximation, we present a general projection formula for a condensate that is time-reversal invariant and a simpler formula for the Bardeen-Cooper-Schrieffer (BCS) limit, which is realized in nuclei with spherical condensates. We apply the method to three heavy nuclei: a typical deformed nucleus $^{162}$ Dy, a typical spherical nucleus $^{148}$ Sm, and a transitional nucleus $^{150}$ Sm in which the pairing condensate is deformed. We compare the results of this projection with results from the saddle-point approximation and exact shell model Monte Carlo calculations. We find that the approximate canonical HF entropy in the particle-number projection decreases monotonically to zero in the limit when the temperature goes to zero. However, in a nucleus with a strong pairing condensate, the approximate canonical HFB entropy in the particle-number projection decreases monotonically to a negative value, reflecting the violation of particle-number conservation. Computationally, the exact particle-number projection is more efficient than calculating the derivatives required in the saddle-point approximation.
Comments:
11 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
arXiv:
1610.08954 [pdf]
PRC(2017)·16 citations
09
[Submitted on 27 Oct 2016] (cross-list from hep-lat)
Multiresolution decomposition of quantum field theories using wavelet bases
Tracie Michlin🇺🇸 · W.N. Polyzou🇺🇸 · Fatih Bulut🇹🇷
We investigate both theoretical and computational aspects of using wavelet bases to decouple physics on different scales in quantum field theory.
Comments:
21 pages, 16 figures, significant additions from original submission
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1610.08612 [pdf]
PRD(2017)·14 citations
10
[Submitted on 27 Oct 2016] (cross-list from hep-ph)
Fluctuation-induced modifications of the phase structure in (2+1)-flavor QCD
Fabian Rennecke🇩🇪 · Bernd-Jochen Schaefer🇩🇪
The low-energy sector of QCD with $N_{f} = 2 + 1$ dynamical quark flavors at non-vanishing chemical potential and temperature is studied with a non-perturbative functional renormalization group method. The analysis is performed in different truncations in order to explore fluctuation-induced modifications of the quark-meson correlations as well as quark and meson propagators on the chiral phase transition of QCD. Depending on the chosen truncation significant quantitative implications on the phase transition are found. In the chirally symmetric phase, the quark flavor composition of the pseudoscalar $(η, η^{'})$ -meson complex turns out to be drastically sensitive to fluctuation-induced modifications in the presence of the axial $U (1)_{A}$ anomaly. This has important phenomenological consequences for the assignment of chiral partners to these mesons.
Comments:
21 pages, 9 figures; v2: published version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1610.08748 [pdf]
PRD(2017)·85 citations
11
[Submitted on 26 Oct 2016] (cross-list from astro-ph.HE)
Note on fast spinning neutron stars with unified equations of states
A. Li · N. B. Zhang · B. Qi · G. F. Burgio
For the propose of confronting updated pulsar observations with developed neutron star equation of states (EoSs), we employ four unified EoSs for both the core and the crust, namely BCPM, BSk20, BSk21, Shen-TM1, as well as two non-unified EoSs widely used in the literature, i.e. APR and GM1 EoS, which are commonly matched with the Negele-Vautherin and the Baym-Pethick-Sutherland crust EoS. All the core EoSs satisfy the recent observational constraints of the two massive pulsars whose masses are precisely measured. We show that the NS mass-equatorial radius relations are slightly affected by the smoothness at the core-crust matching interface. Moreover, the uncertainties in the crust EoS and the matching interface bring insignificant changes, even at maximally rotating (Keplerian) configurations. We also find that for all four unified EoSs, rotation can increase the star's gravitational mass up to $18% - 19%$ and the equatorial radius by $29% - 36%$ , which are consistent with the previous calculations using non-unified EoSs. For stars as heavy as 1.4 M $_{⊙}$ , the radius increase is more pronounced, reaching $41% - 43%$ , i.e. $5 - 6$ km. Moreover, by confronting the results using unified EoSs, which give the correct empirical values at saturation density, with two controversial determinations of the radius for the fast rotator 4U 1608-52, we address that a small radius may be better justified for this source.
Comments:
11 pages, 6 figures, 3 tables
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)
arXiv:
1610.08770 [pdf]
3 citations
12
[Submitted on 27 Oct 2016] (cross-list from hep-ph)
Meson cloud effects on the pion quark distribution function in the chiral constituent quark model
Akira Watanabe🇹🇼 · Chung Wen Kao🇹🇼 · Katsuhiko Suzuki🇯🇵
We investigate the valence quark distribution function of the pion $v^{π} (x, Q^{2})$ in the framework of the chiral constituent quark model and evaluate the meson cloud effects on $v^{π} (x, Q^{2})$ . We explicitly demonstrate how the meson cloud effects affect $v^{π} (x, Q^{2})$ in detail. We find that the meson cloud correction causes an overall 32\% reduction of the valence quark distribution and an enhancement at the small Bjorken $x$ regime. Besides, we also find that the dressing effect of the meson cloud will make the valence quark distribution to be softer in the large $x$ region.
Comments:
8 pages, 4 figures, version accepted by Phys. Rev. D
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1610.08817 [pdf]
PRD(2016)·23 citations
13
[Submitted on 27 Oct 2016] (cross-list from hep-ph)
Groomed jets in heavy-ion collisions: sensitivity to medium-induced bremsstrahlung
Yacine Mehtar-Tani🇺🇸 · Konrad Tywoniuk🇨🇭
We argue that contemporary jet substructure techniques might facilitate a more direct measurement of hard medium-induced gluon bremsstrahlung in heavy-ion collisions, and focus specifically on the "soft drop declustering" procedure that singles out the two leading jet substructures. Assuming coherent jet energy loss, we find an enhancement of the distribution of the energy fractions shared by the two substructures at small subjet energy caused by hard medium-induced gluon radiation. Departures from this approximation are discussed, in particular, the effects of colour decoherence and the contamination of the grooming procedure by soft background. Finally, we propose a complementary observable, that is the ratio of the two-pronged probability in Pb-Pb to proton-proton collisions and discuss its sensitivity to various energy loss mechanisms.
Comments:
20 pages, 5 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1610.08930 [pdf]
JHEP(2017)·126 citations
14
[Submitted on 27 Oct 2016] (cross-list from hep-ph)
Lifetime and mass of rho meson in correlation with magnetic-dimensional reduction
Mamiya Kawaguchi🇯🇵 · Shinya Matsuzaki🇯🇵
It is simply anticipated that in a strong magnetic configuration, the Landau quantization ceases the neutral rho meson to decay to the charged pion pair, so the neutral rho meson will be long-lived. To closely access this naive observation, we explicitly compute the charged pion-loop in the magnetic field at the one-loop level, to evaluate the magnetic dependence of the lifetime for the neutral rho meson as well as its mass.Due to the dimensional reduction induced by the magnetic field (violation of the Lorentz invariance), the polarization (spin $s_{z} = - 1, 0, + 1$ ) modes of the rho meson, as well as the corresponding pole mass and width, are decomposed in a nontrivial manner compared to the vacuum case. To see the significance of the reduction effect, we simply take the lowest-Landau level approximation to analyze the spin-dependent rho masses and widths. We find that the "fate" of the rho meson may be more complicated because of the magnetic-dimensional reduction: as the magnetic field increases, the rho width for the spin $s_{z} = 0$ starts to develop, reach a peak, to be vanishing at the critical magnetic field to which the folklore refers. On the other side, the decay rates of the other rhos for $s_{z} = - 1, + 1$ monotonically increase as the magnetic field develops. The correlation between the polarization dependence and the Landau-level truncation is also addressed.
Comments:
10 pages, 2 figures, typos corrected
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1610.08942 [pdf]
EPJA(2017)·11 citations

Affiliations

first authorsco-authorsvia INSPIRE