Nuclear Theory·nucl-th

Tuesday·July 9, 2019

14 papers—8 primary·6 cross-listed

09
Effective Coupling Constant of Plasmons
Margaret E. Carrington🇨🇦 · Stanislaw Mrowczynski🇵🇱
We study an ultrarelativistic QED plasma in thermal equilibrium. Plasmons - photon collective excitations - are postulated to correspond not to poles of the retarded photon propagator but to poles of the propagator multiplied by the fine structure constant. This product is an invariant of the renormalization group that is independent of an arbitrarily chosen renormalization scale. In addition, our proposal is physically motivated since one needs to scatter a charged particle off a plasma system to probe its spectrum of collective excitations. We present a detailed calculation of the QED running coupling constant at finite temperature using the Keldysh-Schwinger representation of the real-time formalism. We discuss the issue of how to choose the renormalization scale and show that the temperature is a natural choice which prevents the breakdown of perturbation theory through the generation of potentially large logarithmic terms. Our method could be applied to anisotropic systems where the choice of the renormalization scale is less clear, and could have important consequences for the study of collective modes.
↳ hep-phhep-thnucl-thPRD(2019)·4 citations
10
Cross sections for 2-to-3 meson-meson scattering
Wan-Xia Li🇨🇳 · Xiao-Ming Xu🇨🇳 · H. J. Weber🇺🇸
We study 2-to-3 meson-meson scattering based on the process that a gluon is created from a constituent quark or antiquark and subsequently the gluon creates a quark-antiquark pair. The transition potential for the process is derived in QCD. Eight Feynman diagrams at tree level are involved in the 2-to-3 meson-meson scattering. Starting from the $S$ -matrix element, we derive the unpolarized cross section from the eight transition amplitudes corresponding to the eight Feynman diagrams. The transition amplitudes contain color, spin, and flavor matrix elements. The 2-to-3 meson-meson scattering includes $π π \to π K K ˉ$ , $π K \to π π K$ , $π K \to K K K ˉ$ , $K K \to π K K$ , and $K K ˉ \to π K K ˉ$ . Cross sections for the reactions are calculated. The cross sections depend on temperature obviously, and the cross section for $π K \to π π K$ for total isospin $I = 3/2$ at zero temperature is compared to experimental data. By comparison with inelastic 2-to-2 meson-meson scattering, we find that 2-to-3 meson-meson scattering may be as important as inelastic 2-to-2 meson-meson scattering.
↳ hep-phnucl-thPRD(2020)·2 citations
11
$N π$ -excited state contamination in nucleon 3-point functions using ChPT
Oliver Bar🇩🇪
The $N π$ -state contribution to nucleon 3-pt functions involving the pseudoscalar density $P (x)$ and the time component $A_{4} (x)$ of the axial vector current are computed to LO in ChPT. In case of the latter the $N π$ contribution is O( $M_{N}$ ) enhanced compared to the single-nucleon ground state contribution. In addition, a relative sign in two terms of the $N π$ contribution leads an almost linear dependence on the operator insertion time, as it is observed in lattice data. In case of the pseudoscalar density the $N π$ contribution is strongly dependent on the momentum transfer, leading to a distortion of the pseudoscalar nucleon form factor. Finally, the $N π$ state contamination in the form factors result in a violation of the generalized Goldberger-Treiman relation as observed in various lattice calculations.
↳ hep-latnucl-thPoS(2019)·8 citations
12
Theory of elastic neutrino-electron scattering
Oleksandr Tomalak🇺🇸 · Richard J Hill🇺🇸
Theoretical predictions for elastic neutrino-electron scattering have no hadronic or nuclear uncertainties at leading order making this process an important tool for normalizing neutrino flux. However, the process is subject to large radiative corrections that differ according to experimental conditions. In this paper, we collect new and existing results for total and differential cross sections accompanied by radiation of one photon, $ν e \to ν e (γ)$ . We perform calculations within the Fermi effective theory and provide analytic expressions for the electron energy spectrum and for the total electromagnetic energy spectrum as well as for double- and triple-differential cross sections with respect to electron energy, electron angle, photon energy, and photon angle. We discuss illustrative applications to accelerator-based neutrino experiments and provide the most precise up-to-date values of neutrino-electron scattering cross sections. We present an analysis of theoretical error, which is dominated by the $\sim 0.2 - 0.4%$ uncertainty of the hadronic correction. We also discuss how searches for new physics can be affected by radiative corrections.
↳ hep-phhep-exnucl-exnucl-thPRD(2020)·78 citations
13
Mapping collinear in-medium parton splittings
Fabio Dominguez🇪🇸 · Jose Guilherme Milhano🇵🇹 · Carlos A. Salgado🇪🇸 · Konrad Tywoniuk🇳🇴 · Victor Vila🇪🇸
We map the spectrum of $1 \to 2$ parton splittings inside a medium characterized by a transport coefficient $q^$ onto the kinematical Lund plane, taking into account the finite formation time of the process. We discuss the distinct regimes arising in this map for in-medium splittings, pointing out the close correspondence to a semi-classical description in the limit of hard, collinear radiation with short formation times. Although we disregard any modifications of the original parton kinematics in course of the propagation through the medium, subtle modifications to the radiation pattern compared to the vacuum baseline can be traced back to the physics of color decoherence and accumulated interactions in the medium. We provide theoretical support to vacuum-like emissions inside the medium by delimiting the regions of phase space where it is dominant, identifying also the relevant time-scales involved. The observed modifications are shown to be quite general for any dipole created in the medium.
↳ hep-phnucl-thEPJC(2020)·57 citations
14
Effect of non-eikonal corrections on azimuthal asymmetries in the Color Glass Condensate
Pedro Agostini🇪🇸 · Tolga Altinoluk🇵🇱 · Néstor Armesto🇪🇸
We analyse the azimuthal structure of two gluon correlations in the Color Glass Condensate including those effects that result from relaxing the shockwave approximation for the target. Working in the Glasma graph approach suitable for collisions between dilute systems, we compute numerically the azimuthal distributions and show that both even and odd harmonics appear. We study their dependence on model parameters, energy of the collision, pseudorapidity and transverse momentum of the produced particles, and length of the target. While the contribution from non-eikonal corrections vanishes with increasing collision energy and becomes negligible at the energies of the Large Hadron Collider, it is found to be sizeable up to top energies at the Relativistic Heavy Ion Collider.
↳ hep-phnucl-thEPJC(2019)·44 citations

Affiliations

first authorsco-authorsvia INSPIRE

Effective Coupling Constant of Plasmons

Cross sections for 2-to-3 meson-meson scattering

Nπ-excited state contamination in nucleon 3-point functions using ChPT

Theory of elastic neutrino-electron scattering

Mapping collinear in-medium parton splittings

Effect of non-eikonal corrections on azimuthal asymmetries in the Color Glass Condensate

Affiliations

$N π$ -excited state contamination in nucleon 3-point functions using ChPT