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Emission of linearly polarized photons in a strongly coupled magnetized plasma from the gauge/gravity correspondence

Daniel Ávila, Tonantzin Monroy, Francisco Nettel, Leonardo Patiño

TL;DR

This work addresses how a strongly coupled magnetized plasma emits photons with definite polarization. Using a holographic setup based on a 5D truncation of type IIB supergravity with a background magnetic field, the authors compute the photon production rate from linearized gravitational and gauge-field perturbations, relating it to the boundary spectral density $\chi_{\mu\nu}$ of the EM current. A topological constraint $F\wedge F=0$ together with backreaction drives all but one polarization channel to vanish for propagation at any angle $\vartheta\neq 0$, yielding strictly linear polarization in the plane of the reaction. The result provides a robust holographic prediction for photon polarization in a strongly coupled magnetized plasma, clarifying the role of the Chern-Simons/topological term and highlighting limitations to QCD-like applicability and potential extensions to massive flavors.

Abstract

We use holographic methods to show that photons emitted by a strongly coupled plasma subject to a magnetic field are linearly polarized regardless of their four-momentum, except when they propagate along the field direction. The gravitational dual is constructed using a 5D truncation of 10-dimensional type IIB supergravity, and includes a scalar field in addition to the constant magnetic one. In terms of the geometry of the collision experiment that we model, our statement is that any photon produced there has to be in its only polarization state parallel to the reaction plane.

Emission of linearly polarized photons in a strongly coupled magnetized plasma from the gauge/gravity correspondence

TL;DR

This work addresses how a strongly coupled magnetized plasma emits photons with definite polarization. Using a holographic setup based on a 5D truncation of type IIB supergravity with a background magnetic field, the authors compute the photon production rate from linearized gravitational and gauge-field perturbations, relating it to the boundary spectral density of the EM current. A topological constraint together with backreaction drives all but one polarization channel to vanish for propagation at any angle , yielding strictly linear polarization in the plane of the reaction. The result provides a robust holographic prediction for photon polarization in a strongly coupled magnetized plasma, clarifying the role of the Chern-Simons/topological term and highlighting limitations to QCD-like applicability and potential extensions to massive flavors.

Abstract

We use holographic methods to show that photons emitted by a strongly coupled plasma subject to a magnetic field are linearly polarized regardless of their four-momentum, except when they propagate along the field direction. The gravitational dual is constructed using a 5D truncation of 10-dimensional type IIB supergravity, and includes a scalar field in addition to the constant magnetic one. In terms of the geometry of the collision experiment that we model, our statement is that any photon produced there has to be in its only polarization state parallel to the reaction plane.

Paper Structure

This paper contains 6 sections, 38 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Photon production in a strongly coupled magnetized plasma
  3. Gravitational dual setup
  4. Holographic photon production
  5. Linearly polarized photons
  6. Discussion and final remarks

Figures (1)

  • Figure 1: In this figure the spatial parts of the photon momentum $\vec{k}$ and of the polarization vectors $\vec{\epsilon}_{(1)}$ and $\vec{\epsilon}_{(2)}$ are shown. The magnetic field $\vec{B}$ points perpendicular to the reaction plane, which is depicted as a disk in the $xy$-plane. Because of the rotational symmetry around the $z$-direction, the photon momentum can be chosen to lie in the $xz$-plane without loss of generality. Our result shows that any photon produced within the plasma has to be in its only polarization state parallel to the reaction plane.