Cosmological phase transitions without high-temperature expansions

Cosmological first-order phase transitions play a central role in scenarios of baryogenesis and can generate gravitational-wave signals accessible to next-generation detectors. Accurate theoretical predictions, however, are limited by the breakdown of conventional high-temperature expansions and the difficulty of evaluating massive multi-loop thermal sum-integrals. In this talk, I will present a new perturbative framework that computes the full four-dimensional resummed thermal effective potential without relying on high-T approximations. The method systematically separates hard and soft momentum scales and treats them within a single, locally finite expression. Massive sum-integrals are evaluated using a finite-temperature generalization of Loop–Tree Duality that enables direct numerical integration in momentum space. Applied to a scalar–Yukawa model, the framework shows that strong phase transitions—particularly those relevant for gravitational-wave phenomenology—can be reliably described beyond the traditional 3d EFT regime, opening the door to precision predictions in a wide range of BSM theories.