Nuclear Theory·nucl-th

Friday·July 26, 2019

13 papers—8 primary·5 cross-listed

09
(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.
↳ hep-phastro-ph.COnucl-thPRD(2019)·92 citations
10
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 $2.5 ρ_{0}$ .
↳ astro-ph.HEastro-ph.SRnucl-exnucl-thApJ(2019)·125 citations
11
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.
↳ hep-phnucl-exnucl-thPRC(2020)·49 citations
12
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.
↳ hep-phhep-exnucl-thJHEP(2020)·29 citations
13
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.
↳ hep-phnucl-thPramana(2021)·47 citations

Affiliations

first authorsco-authorsvia INSPIRE

(Not as) Big as a Barn: Upper Bounds on Dark Matter-Nucleus Cross Sections

Bayesian Inference of High-density Nuclear Symmetry Energy from Radii of Canonical Neutron Stars

Temperature and fluid velocity on the freeze-out surface from π, K, p spectra in pp, p--Pb and Pb--Pb collisions

Collinear Drop

Shear viscosity and electrical conductivity of relativistic fluid in presence of magnetic field: a massless case

Affiliations

Temperature and fluid velocity on the freeze-out surface from $π$ , $K$ , $p$ spectra in pp, p--Pb and Pb--Pb collisions