Nuclear Theory·nucl-th

Friday·August 3, 2018

10 papers—4 primary·6 cross-listed

05
Long-term GRMHD Simulations of Neutron Star Merger Accretion Disks: Implications for Electromagnetic Counterparts
Rodrigo Fernández🇨🇦 · Alexander Tchekhovskoy🇺🇸 · Eliot Quataert🇺🇸 · Francois Foucart🇺🇸 · Daniel Kasen🇺🇸
We investigate the long-term evolution of black hole accretion disks formed in neutron star mergers. These disks expel matter that contributes to an $r$ -process kilonova, and can produce relativistic jets powering short gamma-ray bursts. Here we report the results of a three-dimensional, general-relativistic magnetohydrodynamic (GRMHD) simulation of such a disk which is evolved for long enough ( $\sim 9$ s, or $\sim 6 \times 1 0^{5} r_{g} / c$ ) to achieve completion of mass ejection far from the disk. Our model starts with a poloidal field, and fully resolves the most unstable mode of the magnetorotational instability. We parameterize the dominant microphysics and neutrino cooling effects, and compare with axisymmetric hydrodynamic models with shear viscosity. The GRMHD model ejects mass in two ways: a prompt MHD-mediated outflow and a late-time, thermally-driven wind once the disk becomes advective. The total amount of unbound mass ejected ( $0.013 M_{⊙}$ , or $≃ 40%$ of the initial torus mass) is twice as much as in hydrodynamic models, with higher average velocity ( $0.1 c$ ) and a broad electron fraction distribution with a lower average value ( $0.16$ ). Scaling the ejected fractions to a disk mass of $\sim 0.1 M_{⊙}$ can account for the red kilonova from GW170817 but underpredicts the blue component. About $\sim 1 0^{- 3} M_{⊙}$ of material should undergo neutron freezout and could produce a bright kilonova precursor in the first few hours after the merger. With our idealized initial magnetic field configuration, we obtain a robust jet and sufficient ejecta with Lorentz factor $\sim 1 - 10$ to (over)produce the non-thermal emission from GW1708107.
↳ astro-ph.HEastro-ph.SRgr-qcnucl-thMNRAS(2019)·290 citations
06
Transition radiation as a probe of chiral anomaly
Xu-Guang Huang🇨🇳 · Kirill Tuchin🇺🇸
A fast charged particle crossing the boundary between the chiral matter and vacuum radiates the transition radiation. Its most remarkable features --- the resonant behavior at a certain emission angle and the circular polarization of the spectrum --- depend on the parameters of the chiral anomaly in a particular material/matter. The chiral transition radiation can be used to investigate the chiral anomaly in such diverse media as the quark-gluon plasma, the Weyl semimetals, and the axionic dark matter.
↳ hep-phcond-mat.mes-hallnucl-thPRL(2018)·20 citations
07
Initial correlations of the Glasma energy-momentum tensor
Javier L. Albacete🇪🇸 · Pablo Guerrero-Rodríguez🇪🇸 · Cyrille Marquet🇫🇷
We present an analytical calculation of the covariance of the energy-momentum tensor associated to the gluon field produced in ultra-relativistic heavy ion collisions at early times, the Glasma. This object involves the two-point and single-point correlators of the energy-momentum tensor ( $⟨ T^{μν} (x_{⊥}) T^{σ ρ} (y_{⊥})⟩$ and $⟨ T^{μν} (x_{⊥})⟩$ , respectively) at proper time $τ = 0^{+}$ . Our approach is based on the Color Glass Condensate effective theory, which allows us to map the fluctuations of the valence color sources in the colliding nuclei to those of the energy-momentum tensor of the produced gluon fields via the solution of the classical equations of motion in the presence of external currents. The color sources in the two colliding nuclei are characterized by Gaussian correlations, albeit in more generality than in the McLerran-Venugopalan model, allowing for non-trivial impact parameter and transverse dependence of the two-point correlator. We compare our results to those obtained under the Glasma Graph approximation, finding agreement in the limit of short transverse separations. However, important differences arise at larger transverse separations, where our result displays a slower fall-off than the Glasma Graph result ( $r^{- 2}$ vs $r^{- 4}$ power-law decay), indicating that the color screening of the correlations in the transverse plane occurs at distances larger than $1/ Q_{s}$ by a logarithmic factor sensitive to the infrared. In the Glasma flux tube picture, this implies that the color domains are larger than originally estimated.
↳ hep-phnucl-thJHEP(2019)·34 citations
08
$p_{t}$ - dependence of the flow coefficients for pp collisions in the color string scenario. Monte-Carlo simulations
M.A. Braun🇷🇺 · C. Pajares🇪🇸
In the color string picture with fusion and percolation the dependence of the flow coefficients $v_{n}$ on the transverse momentum is studied for pp collisions the LHC energy respectively. Monte-Carlo simulations are used to locate simple strings and their fused clusters. The results favorably agree with the CMS data in the region $0.2 \leq p_{t} \leq 3.$ GeV/c appropriate for the string scenario.
↳ hep-phnucl-thEPJA(2018)·5 citations
09
Electron-photon deep inelastic scattering at small x in holographic QCD
Akira Watanabe🇨🇳 · Hsiang-nan Li🇹🇼
We study the electron-photon deep inelastic scattering at small Bjorken variable x in the framework of holographic QCD, employing the Pomeron exchange to describe the involved strong interaction. With the Brower-Polchinski-Strassler-Tan Pomeron exchange kernel and appropriate wave functions for the incident and target particles, which are defined in the five-dimensional AdS space, we obtain the photon structure functions. It is shown that our predictions agree with the experimental data measured at LEP and with those derived from a known parameterization of the photon parton distribution functions.
↳ hep-phnucl-thPoS(2018)·0 citations
10
Semi-inclusive back-to-back production of a hadron pair and a single hadron in $e^{+} e^{-}$ annihilation
Hrayr H. Matevosyan🇦🇺 · Aram Kotzinian🇦🇲 · Anthony W. Thomas🇦🇺
Inclusive hadron production in $e^{+} e^{-}$ annihilation has long been used to study both single hadron fragmentation functions (FF) and dihadron fragmentation functions (DiFF). In particular, the polarized DiFFs can be accessed in electron-positron annihilation by measuring azimuthal correlations between two back-to-back pairs of hadrons in the center of mass system, where the relevant structure functions can be expressed as convolutions of two (polarized) DiFFs. Here we explore the advantages of measuring the inclusive back-to-back production of a single hadron on one side against a hadron pair on the opposite side of the detector in two jet events. The leading twist cross section for this process contains convolutions of the corresponding single hadron FFs on one side and the DiFFs for the hadron pair on the other side, which furnishes several interesting new opportunities. A measurement of the unpolarized cross section with a number of different types of observed hadrons will help in untangling the quark flavor dependence of the unpolarized DiFFs, when the results are analyzed together with the inclusive measurements of dihadron pairs, such as those recently performed by the $BELLE$ collaboration. Even more interesting, with a polarized hyperon on one side we can study the quark spin-dependent DiFFs of an unpolarized hadron pair on the other side. This, in turn, will allow us to test the universality of the spin-dependent DiFFs entering the cross sections of electron-positron annihilation and semi-inclusive deep inelastic scattering processes.
↳ hep-phhep-exnucl-thJHEP(2018)·10 citations

Affiliations

first authorsco-authorsvia INSPIRE

Long-term GRMHD Simulations of Neutron Star Merger Accretion Disks: Implications for Electromagnetic Counterparts

Transition radiation as a probe of chiral anomaly

Initial correlations of the Glasma energy-momentum tensor

pt​- dependence of the flow coefficients for pp collisions in the color string scenario. Monte-Carlo simulations

Electron-photon deep inelastic scattering at small x in holographic QCD

Semi-inclusive back-to-back production of a hadron pair and a single hadron in e+e− annihilation

Affiliations

$p_{t}$ - dependence of the flow coefficients for pp collisions in the color string scenario. Monte-Carlo simulations

Semi-inclusive back-to-back production of a hadron pair and a single hadron in $e^{+} e^{-}$ annihilation