Open EFT treatment of Inflation with Thermal Initial Conditions

Investigating the thermal inflationary model, we introduce stochastic effects, incorporating a cutoff parameter $\sigma$ which distinguishes between quantum and classical modes. Testing the model against Planck 2018 data, we observe a preference for a non-zero $\sigma$ at least at 68\% C.L., suggesting the classicalization of most modes and providing a theoretical foundation for the quantum to classical transition. As a result of introducing the stochastic effects, we find that the solution to the large-scale power deficit requires a lower comoving temperature of inflaton.