Thermal correlator at null infinity

Abstract: We study the thermal Carrollian correlators at null infinity in the real-time formalism. We derive the Feynman rules to calculate these correlators in the position space. We compute the bulk-to-bulk, bulk-to boundary and boundary-to-boundary propagators for massless scalar theory. Due to the doubling of the fields degrees of freedom, the number of each propagator is quadrupled. The bulk-to-boundary propagators have the form of (extended) Bose-Einstein distribution in the position space. Utilizing the contour integral of the propagators, we can transform the Feynman rules to momentum space. Interestingly, the external lines and the amplitude in the momentum space depend on the contour while Carrollian correlators in the position space are independent of the contour. We show how to compute four point correlators at finite temperature. The tree level correlators can be written as the summation of Barnes zeta functions and reduce to the ones in the zero temperature limit.