Nuclear Theory·nucl-th

Friday·July 26, 2019

13 papers—8 primary·5 cross-listed

01
[Submitted on 24 Jul 2019]
Relaxation Time for Strange Quark Spin in Rotating Quark-Gluon Plasma
Joseph I. Kapusta🇺🇸 · Ermal Rrapaj🇺🇸 · Serge Rudaz🇺🇸
Experiments at the Relativistic Heavy Ion Collider (RHIC) have measured the net polarization of $Λ$ and $Λ ˉ$ hyperons and attributed it to a coupling between their spin and the vorticity of the fluid created in heavy ion collisions. Equipartition of energy is generally assumed, but the dynamical mechanism which polarizes them has yet to be determined. We consider two such mechanisms: vorticity fluctuations and helicity flip in scatterings between strange quarks and light quarks and gluons. With reasonable parameters both mechanisms lead to equilibration times orders of magnitude too large to be relevant to heavy ion collisions. Our conclusion is that strange quark spin or helicity is unchanged from the time they are created to the time they hadronize. A corollary is that vorticity fluctuations do not affect the hyperon spin either.
Comments:
31 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Theory (hep-th)
arXiv:
1907.10750 [pdf]
PRC(2020)·58 citations
02
[Submitted on 24 Jul 2019]
Underlying structure of collective bands and self-organization in quantum systems
Takaharu Otsuka · Yusuke Tsunoda · Takashi Abe · Noritaka Shimizu · Piet Van Duppen
The underlying structure of low-lying collective bands of atomic nuclei is discussed from a novel perspective on the interplay between single-particle and collective degrees of freedom, by utilizing state-of-the-art configuration interaction calculations on heavy nuclei. Besides the multipole components of the nucleon-nucleon interaction that drive collective modes forming those bands, the monopole component is shown to control the resistance against such modes. The calculated structure of 154Sm corresponds to coexistence between prolate and triaxial shapes, while that of 166Er exhibits a deformed shape with a strong triaxial instability. Both findings differ from traditional views based on beta/gamma vibrations. The formation of collective bands is shown to be facilitated from a self-organization mechanism.
Comments:
4 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1907.10759 [pdf]
PRL(2019)·66 citations
03
[Submitted on 25 Jul 2019]
Pseudorapidity dependent hydrodynamic response in heavy-ion collisions
Hui Li🇨🇳 · Li Yan🇨🇳
We propose a differential hydrodynamic response relation, $V_{2} (ζ) = \int d ξ G (ζ - ξ) E_{2} (ξ)$ , to describe the formation of a pseudorapidity dependent elliptic flow in heavy-ion collisions, in response to a fluctuating three-dimensional initial density profile. By analyzing the medium expansion using event-by-event simulations of 3+1D MUSIC, with initial conditions generated via the AMPT model, the differential response relation is verified. Given the response relation, we are able to separate the two-point correlation of elliptic flow in pseudorapidity into fluid response and two-point correlation of initial eccentricity. The fluid response contains information of the speed of sound and shear viscosity of the medium. From the pseudorapidity dependent response relation, a finite radius of convergence of hydrodynamic gradient expansion is obtained with respect to realistic fluids in heavy-ion collisions.
Comments:
The published version, 7 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1907.10854 [pdf]
PLB(2020)·11 citations
04
[Submitted on 25 Jul 2019]
Primordial fluctuations in heavy-ion collisions
François Gelis🇫🇷 · Giuliano Giacalone🇫🇷 · Pablo Guerrero-Rodríguez🇪🇸 · Cyrille Marquet🇫🇷 · Jean-Yves Ollitrault🇫🇷
We present a simple description of the energy density profile created in a nucleus-nucleus collision, motivated by high-energy QCD. The energy density is modeled as the sum of contributions coming from elementary collisions between localized charges and a smooth nucleus. Each of these interactions creates a sharply-peaked source of energy density falling off at large distances like $1/ r^{2}$ , corresponding to the two-dimensional Coulomb field of a point charge. Our model reproduces the one-point and two-point functions of the energy density field calculated in the framework of the color glass condensate effective theory, to leading logarithmic accuracy. We apply it to the description of eccentricity fluctuations. Unlike other existing models of initial conditions for heavy-ion collisions, it allows us to reproduce simultaneously the centrality dependence of elliptic and triangular flow.
Comments:
6 pages, 2 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1907.10948 [pdf]
21 citations
05
[Submitted on 25 Jul 2019]
Nucleon momentum distributions in asymmetric nuclear matter
Z. X. Yang🇨🇳 · X. L. Shang🇨🇳 · G. C. Yong🇨🇳 · W. Zuo🇨🇳 · Y. Gao🇨🇳
Nucleon momentum distributions at various densities and isospin-asymmetries for nuclear matter are investigated systematically within the extended Bruecker-Hartree-Fock approach.The shapes of the normalized momentum distributions varying with $k / k_{F}$ are practically identical, while the density and isospin dependent magnitude of the distribution is directly related to the depletion of the Fermi sea. Based on these properties, a parameterized formula is proposed with the parameters calibrated to the calculated result.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.10977 [pdf]
PRC(2019)·27 citations
06
[Submitted on 25 Jul 2019]
Neutron-proton pairing in Nuclear Matter
Xiao-Hua Fan · Xin-le Shang · Jian-Min Dong · Wei Zuo
The self-energy effect on the neutron-proton (np) pairing gap is investigated up to the third order within the framework of the extend Bruecker-Hartree-Fock (BHF) approach combined with the BCS theory. The self-energy up to the second-order contribution turns out to reduce strongly the effective energy gap, while the \emph{renormalization} term enhances it significantly. In addition, the effect of the three-body force on the np pairing gap is shown to be negligible. To connect the present results with the np pairing in finite nuclei, an effective density-dependent zero-range pairing force is established with the parameters calibrated to the microscopically calculated energy gap.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.10986 [pdf]
PRC(2019)·12 citations
07
[Submitted on 25 Jul 2019]
Macroscopic manifestations of rotating triaxial superfluid nuclei
P. Schuck🇫🇷 · M. Urban🇫🇷
Recently, Allmond and Wood [Phys. Lett. B 767, 226 (2017)] were able to extract the three moments of inertia $I_{k}$ of a dozen of superfluid triaxial nuclei from experimental data. The observed dependence of the $I_{k}$ on the deformation parameters is rather smooth. Here we show that these moments of inertia can be surprisingly well explained by a semiclassical cranked Hartree-Fock-Bogoliubov (HFB) calculation in which the velocity field is a simple superposition of rigid and irrotational flows.
Comments:
5 pages; v2: minor revision (pairing gaps from 5-point formula and improved figures)
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.11008 [pdf]
PRC(2019)·8 citations
08
[Submitted on 25 Jul 2019]
Studies of quasiclassical approach applicability to true three-body decays
O.M. Sukhareva · L.V. Grigorenko · D.A. Kostyleva · M.V. Zhukov
Within the hyperspherical harmonics approach the three-body problem is reduced to a motion of one effective particle in a "strongly deformed" field, which is described in coupled-channel formalism. This method is especially suited to studies of phenomena characterized by genuine three-body dynamics, e.g. Borromean haloes and true three-body decays. The reduction of the hyperspherical equations set to a single-channel Schrödinger equation provides the basis for the use of the standard quasiclassical expression for calculations of widths for true three-body decays. We demonstrate that the quasiclassical approach by itself is quite precise in application to typical profiles of the three-body effective potentials. However, the reduction to single-channel formalism leads to significant overestimation of the two-proton width $Γ_{2 p}$ . This is demonstrated by the example of the $^{17}$ Ne first excited $3/ 2^{-}$ state decay, questioning, however, the applicability of such an approximation in general.
Comments:
12 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.11013 [pdf]
0 citations
09
[Submitted on 24 Jul 2019] (cross-list from hep-ph)
(Not as) Big as a Barn: Upper Bounds on Dark Matter-Nucleus Cross Sections
Matthew C. Digman🇺🇸 · Christopher V. Cappiello🇺🇸 · John F. Beacom🇺🇸 · Christopher M. Hirata🇺🇸 · Annika H. G. Peter🇺🇸
Critical probes of dark matter come from tests of its elastic scattering with nuclei. The results are typically assumed to be model-independent, meaning that the form of the potential need not be specified and that the cross sections on different nuclear targets can be simply related to the cross section on nucleons. For point-like spin-independent scattering, the assumed scaling relation is $σ_{χ A} \propto A^{2} μ_{A}^{2} σ_{χ N} \propto A^{4} σ_{χ N}$ , where the $A^{2}$ comes from coherence and the $μ_{A}^{2} ≃ A^{2} m_{N}^{2}$ from kinematics for $m_{χ} ≫ m_{A}$ . Here we calculate where model independence ends, i.e., where the cross section becomes so large that it violates its defining assumptions. We show that the assumed scaling relations generically fail for dark matter-nucleus cross sections $σ_{χ A} \sim 1 0^{- 32} - 1 0^{- 27} cm^{2}$ , significantly below the geometric sizes of nuclei, and well within the regime probed by underground detectors. Last, we show on theoretical grounds, and in light of existing limits on light mediators, that point-like dark matter cannot have $σ_{χ N} ≳ 1 0^{- 25} cm^{2}$ , above which many claimed constraints originate from cosmology and astrophysics. The most viable way to have such large cross sections is composite dark matter, which introduces significant additional model dependence through the choice of form factor. All prior limits on dark matter with cross sections $σ_{χ N} > 1 0^{- 32} cm^{2}$ with $m_{χ} ≳ 1 GeV$ must therefore be re-evaluated and reinterpreted.
Comments:
18 pages, 7 figures, revised to match journal version including erratum, comments are welcome
Subjects:
High Energy Physics — Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Nuclear Theory (nucl-th)
arXiv:
1907.10618 [pdf]
PRD(2019)·92 citations
10
[Submitted on 24 Jul 2019] (cross-list from astro-ph.HE)
Bayesian Inference of High-density Nuclear Symmetry Energy from Radii of Canonical Neutron Stars
Wen-Jie Xie🇺🇸 · Bao-An Li🇺🇸
The radius $R_{1.4}$ of neutron stars (NSs) with a mass of 1.4 M $_{⊙}$ has been extracted consistently in many recent studies in the literature. Using representative $R_{1.4}$ data, we infer high-density nuclear symmetry energy $E_{sym} (ρ)$ and the associated nucleon specific energy $E_{0} (ρ)$ in symmetric nuclear matter (SNM) within a Bayesian statistical approach using an explicitly isospin-dependent parametric Equation of State (EOS) for nucleonic matter. We found that: (1) The available astrophysical data can already improve significantly our current knowledge about the EOS in the density range of $ρ_{0} - 2.5 ρ_{0}$ . In particular, the symmetry energy at twice the saturation density $ρ_{0}$ of nuclear matter is determined to be $E_{sym} (2 ρ_{0})$ =39.2 $_{- 8.2}^{+ 12.1}$ MeV at 68\% confidence level. (2) A precise measurement of the $R_{1.4}$ alone with a 4\% 1 $σ$ statistical error but no systematic error will not improve much the constraints on the EOS of dense neutron-rich nucleonic matter compared to what we extracted from using the available radius data. (3) The $R_{1.4}$ radius data and other general conditions, such as the observed NS maximum mass and causality condition introduce strong correlations for the high-order EOS parameters. Consequently, the high-density behavior of $E_{sym} (ρ)$ inferred depends strongly on how the high-density SNM EOS $E_{0} (ρ)$ is parameterized, and vice versa. (4) The value of the observed maximum NS mass and whether it is used as a sharp cut-off for the minimum maximum mass or through a Gaussian distribution affect significantly the lower boundaries of both the $E_{0} (ρ)$ and $E_{sym} (ρ)$ only at densities higher than about $2.5 ρ_{0}$ .
Comments:
Discussions added. The Astrophysical Journal (2019) in press
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1907.10741 [pdf]
ApJ(2019)·125 citations
11
[Submitted on 25 Jul 2019] (cross-list from hep-ph)
Temperature and fluid velocity on the freeze-out surface from $π$ , $K$ , $p$ spectra in pp, p--Pb and Pb--Pb collisions
Aleksas Mazeliauskas🇩🇪 · Vytautas Vislavicius🇩🇰
We present a new approach to take into account resonance decays in the blast-wave model fits of identified hadron spectra. Thanks to pre-calculated decayed particle spectra, we are able to extract, in a matter of seconds, the multiplicity dependence of the single freeze-out temperature $T_{fo}$ , average fluid velocity $⟨ β_{T} ⟩$ , velocity exponent $n$ , and the volume $d V / d y$ of an expanding fireball. In contrast to blast-wave fits without resonance feed-down, our approach results in a freeze-out temperature of $T_{fo} \approx 150 MeV$ , which has only weak dependence on multiplicity and collision system. Finally, we discuss separate chemical and kinetic freeze-outs separated by partial chemical equilibrium.
Comments:
8 pages, 6 figures; v2 analysis redone with PDG2016 resonance list, typos corrected, published version
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1907.11059 [pdf]
PRC(2020)·49 citations
12
[Submitted on 25 Jul 2019] (cross-list from hep-ph)
Collinear Drop
Yang-Ting Chien🇺🇸 · Iain W. Stewart🇺🇸
We introduce collinear drop jet substructure observables, which are unaffected by contributions from collinear radiation, and systematically probe soft radiation within jets. These observables can be designed to be either sensitive or insensitive to process-dependent soft radiation originating from outside the jet. Such collinear drop observables can be exploited as variables to distinguish quark, gluon, and color neutral initiated jets, for testing predictions for perturbative soft radiation in Monte Carlo simulations, for assessing models and universality for hadronization corrections, for examining the efficiency of pileup subtraction methods, and for any other application that leaves an imprint on soft radiation. We discuss examples of collinear drop observables that are based both on clustering and on jet shapes. Using the soft-collinear effective theory we derive factorization expressions for collinear drop observables from QCD jets, and carry out a resummation of logarithmically enhanced contributions at next-to-leading-logarithmic order. We also identify an infinite class of collinear drop observables for which the leading double logarithms are absent.
Comments:
60 pages, 20 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1907.11107 [pdf]
JHEP(2020)·29 citations
13
[Submitted on 25 Jul 2019] (cross-list from hep-ph)
Shear viscosity and electrical conductivity of relativistic fluid in presence of magnetic field: a massless case
Jayanta Dey🇮🇳 · Sarthak Satapathy🇮🇳 · Prasanta Murmu🇮🇳 · Sabyasachi Ghosh🇮🇳
We have explored the shear viscosity and electrical conductivity calculations for bosonic and fermionic medium, which goes from without to with magnetic field picture and then their simplified massless expressions. In presence of magnetic field, 5 independent velocity gradient tensors can be designed, so their corresponding proportional coefficients, connected with the viscous stress tensor provide us 5 shear viscosity coefficients. In existing litterateurs, two sets of tensors are available. Starting from them, present work has obtained two sets of expressions for 5 shear viscosity coefficients, which can be ultimately classified into three basic components: parallel, perpendicular and Hall components as one get same for electrical conductivity at finite magnetic field. Our calculations are based on kinetic theory approach in relaxation time approximation. Repeating same mathematical steps for finite magnetic field picture, which traditionally practiced for without field case, we have obtained 2 sets of 5 shear viscosity components, whose final expressions are in well agreements with earlier references, although a difference in methodology or steps can be clearly noticed. Realizing the massless results of viscosity and conductivity for Maxwell-Boltzmann, Fermi-Dirac and Bose-Einstein distribution function, we have applied them for massless quark gluon plasma and hadronic matter phases, which can provide us a rough order of strength, within which actual results will vary during quark-hadron phase transition. Present work also indicates that magnetic field might have some role for building perfect fluid nature in RHIC or LHC matter. The lower bound expectation of shear viscosity to entropy density ratio is also discussed.
Comments:
page 20, 15 figures (Here expressions of 5 shear viscosity components for two sets of tensor structure are addressed)
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1907.11164 [pdf]
Pramana(2021)·47 citations

Affiliations

first authorsco-authorsvia INSPIRE