We revisit the hard thermal loop (HTL) self-energy of gravitons in thermal backgrounds, motivated by recent studies that suggest a negative mass correction for superhorizon tensor modes via the radiation exchange mechanism in the real-time formalism. While conventional calculations using the imaginary-time formalism predict a positive plasmon mass shift, we reconsider the kinetic theory approach and demonstrate that, when consistently matched to the plasma energy-momentum tensor, it reproduces the negative mass shift obtained in the radiation exchange framework.
In this talk, I present a consistent connection between kinetic theory and quantum field-theoretic treatments of thermal gravitons in cosmology.
