Out-of-equilibrium photon production from disoriented chiral condensates

Abstract

We study the production of photons through the non-equilibrium relaxation of a disoriented chiral condensate. We propose that to search for nonequilibrium photons in the direct photon measurements of heavy-ion collisions can be a potential test of the formation of disoriented chiral condensates.

Photon production from non-equilibrium disoriented chiral condensates in a longitudinal expansion: A theoretic framework

“…Later, the authors in Ref. [11] have taken into account another dominant contribution that also involves the dynamics of π 0 due to the decay of the vector meson through the electromagnetic vertex. They have found that for large initial amplitudes of the π 0 mean field the photon production is enhanced by parametric amplification, resulting in a distinct energy distribution of the produced photons.…”

Photon production from non-equilibrium disoriented chiral condensates in a spherical expansion

“…Later, the authors in Ref. [11] have taken into account another dominant contribution that also involves the dynamics of π 0 due to the decay of the vector meson through the electromagnetic vertex. Although the corresponding dimensionless effective coupling involving the vector meson is quite perturbatively small, for the large amplitude oscillations of the π 0 mean field, the contribution to the photon production is of the same order of magnitude as the anomalous interaction.…”

“…where V is identified as the ω meson, and the coupling λ V is obtained from the ω → π 0 γ decay width [16]. This effective action has been obtained by two of us [11] in the study of out-of-equilibrium photon production from DCC domains by taking the rapid "quench" phase transition scenario. Here we will consider the similar non-equilibrium phenomena taking account of the hydrodynamical expansion.…”

“…3 reveal the dramatically different features as compared with the results in Refs. [9,11], where the authors have considered the similar non-equilibrium phenomena in the temperature quenching scenario without convoluting the photon production rate with the plasma expansion, and shown that prominent peaks appear in the photon spectrum locating at resonant momenta of the parametric amplification determined by the frequency of the π 0 oscillations. Since the measured emitted photons are chosen with the momentum along the ẑ direction and the plasma expansion is along the radial direction, the Doppler effect would cause the emitted photons either blue-shifted if the photon comes from the place where the direction of its momentum is along with that of the expansion at that place, or red-shifted if the direction of its momentum is opposite to that of the expansion.…”

“…3, the Doppler effect leads to smoothing out the resonant peaks found in Refs. [9,11]. In addition, one can also estimate the corresponding boost factor arising from the background expansion effect.…”