Gradient Correction to Photon Emission Rate at Strong Coupling

Abstract

We compute the correction to the photon emission rate in first order of shear components of fluid velocity gradients, ${\sigma }_{ij}$, in near-equilibrium hydrodynamic plasma at strong coupling regime, using the real-time Schwinger-Keldysh formalism in AdS/CFT correspondence. Our result is an integral of an analytic expression. We observe that the gradient correction to the photon emission rate at strong coupling is about 0.3 - 0.4 times of the equilibrium rate in units of ${\sigma }_{ij}/T$.

Comments: 28 pages, 9 figures; references added; more discussion about the phenomenological importance of the gradient correction added in the Discussion section, published in PRD