Chiral vortical effect: Black-hole versus flat-space derivation

The chiral vortical effect (CVE) was derived first for massless fermions, within the framework of thermal quantum field theory. Recently, a dual description of the CVE, as related to the radiation from the horizon of a rotating black hole was suggested. Generalizing the latter approach to the case of photons, we encounter a crucial factor-of-2 difference from the predictions based on the thermal field theory. To elucidate the reason for this discrepancy, we turn to the limit of large spin $S$ of the massless particles. Within the gravitational approach, the CVE grows as ${S}^{3}$, while the flat-space relations result in a dependence which is linear in $S$. We also discuss briefly an alternative formulation of the presumed duality between the statistical and gravitational approaches.