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Soft-contribution to thermal photon emission from chiral QCD medium

Nilanjan Chaudhuri, Sourav Duari, Pradip Roy, Sourav Sarkar

TL;DR

This work addresses soft thermal photon emission from a chirally imbalanced quark–gluon plasma by employing a hard thermal loop framework with a dressed quark propagator. The authors derive the photon polarization function in the presence of a finite axial chemical potential $\mu_5$, revealing a splitting of $L$ and $R$ quasiparticle modes into distinct thermal masses and plasmino branches. The imaginary part of the retarded photon self-energy is computed with an infrared separation scale $k_c$, yielding a compact soft rate that includes additional terms proportional to $\mu^2$ and $\mu_5^2$, and shows an enhanced photon emission in the presence of chiral imbalance. The results connect to known limits when $\mu_5\to0$ or $\mu\to0$ and suggest that chiral dynamics can noticeably affect photon spectra, motivating further studies with hard contributions and realistic space-time evolution.

Abstract

We evaluate the thermal photon emission rate from a chirally asymmetric quark gluon plasma using the Hard Thermal Loop approximation. The quasiparticle and plasmino modes prevalent at finite temperature split into L and R-modes in the presence of chiral imbalance and are found to disperse differently acquiring different thermal masses. The soft contribution to the thermal photon emission rate obtained from the retarded self-energy is found to contain additional terms proportional to the square of the quark and chiral chemical potentials which is found to cause an enhancement to thermal photon emission in the presence of chiral imbalance.

Soft-contribution to thermal photon emission from chiral QCD medium

TL;DR

This work addresses soft thermal photon emission from a chirally imbalanced quark–gluon plasma by employing a hard thermal loop framework with a dressed quark propagator. The authors derive the photon polarization function in the presence of a finite axial chemical potential , revealing a splitting of and quasiparticle modes into distinct thermal masses and plasmino branches. The imaginary part of the retarded photon self-energy is computed with an infrared separation scale , yielding a compact soft rate that includes additional terms proportional to and , and shows an enhanced photon emission in the presence of chiral imbalance. The results connect to known limits when or and suggest that chiral dynamics can noticeably affect photon spectra, motivating further studies with hard contributions and realistic space-time evolution.

Abstract

We evaluate the thermal photon emission rate from a chirally asymmetric quark gluon plasma using the Hard Thermal Loop approximation. The quasiparticle and plasmino modes prevalent at finite temperature split into L and R-modes in the presence of chiral imbalance and are found to disperse differently acquiring different thermal masses. The soft contribution to the thermal photon emission rate obtained from the retarded self-energy is found to contain additional terms proportional to the square of the quark and chiral chemical potentials which is found to cause an enhancement to thermal photon emission in the presence of chiral imbalance.

Paper Structure

This paper contains 8 sections, 23 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Setup
  3. Photon self energy in chirally imbalanced medium
  4. Spectral representation of quark propagator
  5. Calculation of in-medium photon polarization function at finite $\mu_5$
  6. Imaginary part of the retarded photon self-energy
  7. Soft contribution to the photon rate
  8. Summary

Figures (4)

  • Figure 1: The one-loop photon self-energy is evaluated in the HTL approximation. The internal fermion line with a black blob represents the soft quark propagator dressed with HTL resummation, while the line without the blob denotes the bare hard quark propagator.
  • Figure 2: Dispersion of $L$ and $R$-mode for different values of $\mu_5$ at $T=200$ MeV and $\mu = 150$ MeV.
  • Figure 3: The photon production rate as a function of photon energy at $T$= 200 MeV and $\alpha_s = 0.3$. (a) $\mu= 200$ MeV, $\mu_5 = 200$ MeV and (b) $\mu= 300$ MeV, $\mu_5= 300$ MeV
  • Figure 4: The photon production rate as a function of $\mu_5$ for different values of photon energy at (a) $T= 200$ MeV and (b) $T= 300$ MeV in absence of $\mu$.