******** CTCD/NTHU HEP Seminar ********

Speaker : Dr. Amitayus Banik (Chungbuk National University)

Title ：Consistent Thermal Resummation and Phase Transitions with 2PI
Methods

Time ：12:30-13:30, Thursday, 2026/5/7

Place ：R521, 5F, General Building II, Nat'l Tsing Hua Univ.

Host ： Prof. Kingman Cheung (NTHU) & Prof. Norihiro Iizuka (NTHU)

Abstract:
We apply the two-particle irreducible (2PI) formalism as a framework for
consistent thermal resummation in studies of cosmological phase
transitions (PTs). Considering a model with two real scalar fields, we
work within the Hartree approximation and renormalise the 2PI effective
action using an on-shell scheme, while introducing a connection to
physical parameters. This yields the Hartree-resummed finite-temperature
effective potential, which treats high- and low-temperature corrections
on an equal footing, thereby avoiding the limitations of conventional
methods based on the high-temperature approximation. With this
potential, we study PTs within the model, computing the PT parameters
(temperature, duration, and strength of the transition). We find that
stronger PTs are predicted using 2PI methods, compared to those observed
using resummation schemes widely employed in the literature. Finally,
using these PT parameters, we evaluate the gravitational wave spectrum
generated from first-order PTs, demonstrating the impact of the choice
of resummation scheme on the spectrum.
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