Nuclear Theory·nucl-th

Friday·March 15, 2019

8 papers—4 primary·4 cross-listed

05
The tidal deformability of an anisotropic compact star: Implications of GW170817
Bhaskar Biswas · Sukanta Bose
We use gravitational wave (GW) and electromagnetic (EM) observations of GW170817 to constrain the extent of pressure anisotropy in it. While it is quite likely that the pressure inside a neutron star is mostly isotropic, certain physical processes or characteristics, such as phase transitions in nuclear matter or the presence of strong magnetic fields, can introduce pressure anisotropy. In this work, we show that anisotropic pressure in neutron stars can reduce their tidal deformability substantially. For the anisotropy-pressure model of Bowers and Liang and a couple of relativistic EOSs -- DDH $δ$ and GM1 -- we demonstrate that this reduction in spherical neutron stars with masses in the range of 1 to 2 $M_{⊙}$ can be 23% to 46%. This suggests that certain EOSs that are ruled out by GW170817 observations, under assumptions of pressure isotropy, can become viable if the stars had a significant enough anisotropic pressure component, but do not violate causality. We also show how the inference of the star radius can be used to rule out certain EOSs (such as GM1), even for high anisotropic pressure, because their radii are larger than what the observations find.
↳ gr-qcastro-ph.HEnucl-thPRD(2019)·100 citations
06
Constraining compact star properties with nuclear saturation parameters
Jia Jie Li (ITP, Frankfurt)🇩🇪 · Armen Sedrakian (FIAS)🇩🇪
A set of hadronic equations of state (EoSs) derived from relativistic density functional theory and constrained by terrestrial experiments, astrophysical observations, in particular by the GW170817 event, and chiral effective field theory ( $χ$ EFT) of neutron matter is used to explore the sensitivity of the EoS parameterization on the few nuclear matter characteristics defined at the saturation density. We find that the gross properties of compact stars are most sensitive to the isoscalar skewness coefficient $Q_{sat}$ and the isovector slope coefficient $L_{sym}$ around saturation density, since the higher order coefficients, such as $K_{sym}$ , are fixed by our model. More specifically, (i) among these $Q_{sat}$ is the dominant parameter controlling both the maximum mass and the radii of compact stars while $L_{sym}$ is constrained somewhat by $χ$ EFT of neutron matter; (ii) massive enough ( $M \sim 2.0 M_{⊙})$ compact stars featuring both hyperons and $Δ$ resonances can be obtained if the value of $Q_{sat}$ is large enough; (iii) the emergence of $Δ$ 's reduces the radius of a canonical mass ( $M \sim 1.4 M_{⊙})$ compact star thus easing the tension between the predictions of the relativistic density functionals and the inferences from the X-ray observation of nearby isolated neutron stars.
↳ astro-ph.HEnucl-thPRC(2019)·53 citations
07
Photon induced processes in semi-central nucleus-nucleus collisions
Antoni Szczurek🇵🇱
We calculate total and differential cross sections for $J / ψ$ photoproduction in ultrarelativistic lead-lead collisions at the LHC energy $s_{N N} = 2.76$ TeV. We use a simple model based on vector dominance picture and multiple scattering of the hadronic ( $c c ˉ$ ) state in a cold nucleus. In our analysis we use Glauber formulae for calculating $σ_{t o t, J / ψ P b}$ which is a building block of our model. For semi-central collisions a modification of the photon flux is necessary. We discuss how to effectively correct photon fluxes for geometry effects. We try to estimate the cross sections for different centrality bins and for $J / ψ$ mesons emitted in forward rapidity range ( $2.5 < y < 4$ ) corresponding to the ALICE experimental results. We discuss similar analysis for dilepton production in ultrarelativistic heavy-ion collisions at very low pair transverse momenta, $P_{T} \leq 0.15$ \,GeV. We investigate the interplay of thermal radiation with photon annihilation processes, $γ γ \to l^{+} l^{-}$ , due to the coherent electromagnetic fields of the colliding nuclei. For the thermal radiation, we employ the emission from the QGP and hadronic phases with in-medium vector spectral functions. We first verify that the combination of photon fusion, thermal radiation and final-state hadron decays gives a fair description of the low- $P_{T}$ invariant-mass as well as $P_{T}$ distributions as measured recently by the STAR collaboration in $s_{N N}$ =200\,GeV Au+Au collisions for different centralities. The coherent contribution dominates in peripheral collisions, while thermal radiation shows a significantly stronger increase with centrality. We also provide predictions for the ALICE experiment at the LHC. The resulting excitation function reveals a nontrivial interplay of photoproduction and thermal radiation.
↳ hep-phnucl-thActa Phys.Polon.B(2019)·0 citations
08
Discovery potential of multi-ton xenon detectors in neutrino electromagnetic properties
Chung-Chun Hsieh🇹🇼 · Lakhwinder Singh🇹🇼 · Chih-Pan Wu🇹🇼 · Jiunn-Wei Chen🇹🇼 · Hsin-Chang Chi🇹🇼 · C.-P. Liu🇹🇼 · Mukesh K. Pandey🇹🇼 · Henry T. Wong🇹🇼
Next-generation xenon detectors with multi-ton-year exposure are powerful direct probes of dark matter candidates, in particular the favorite weakly-interacting massive particles. Coupled with the features of low thresholds and backgrounds, they are also excellent telescopes of solar neutrinos. In this paper, we study the discovery potential of ton-scale xenon detectors in electromagnetic moments of solar neutrinos. Relevant neutrino-atom scattering processes are calculated by applying a state-of-the-arts atomic many-body method--relativistic random phase approximation (RRPA). Limits on these moments are derived from existing data and estimated with future experiment specifications. With one ton-year exposure, XENON-1T can improve the effective milli-charge constraint by a factor two. With LZ and DARWIN, the projected improvement on the solar neutrino effective milli-charge(magnetic moment) is around 7(2) times smaller than the current bound. If LZ can keep the same background level and push the electron recoil threshold to 0.5 keV, the projected improvement on milli-charge(magnetic moment) is about 10(3) times smaller than the current bound.
↳ hep-phhep-exnucl-exnucl-thPRD(2019)·35 citations

Affiliations

first authorsco-authorsvia INSPIRE

The tidal deformability of an anisotropic compact star: Implications of GW170817

Constraining compact star properties with nuclear saturation parameters

Photon induced processes in semi-central nucleus-nucleus collisions

Discovery potential of multi-ton xenon detectors in neutrino electromagnetic properties

Affiliations