Investigating two-loop effects for first-order electroweak phase transitions

TL;DR

This study uses advanced two-loop calculations to analyze electroweak phase transitions in an extended Standard Model, revealing more precise conditions for strong first-order transitions and implications for collider experiments.

Contribution

It provides the first comprehensive two-loop effective potential analysis of electroweak phase transitions in the real-singlet extended Standard Model, improving thermodynamic accuracy.

Findings

Two-loop corrections narrow the parameter space for strong transitions.

Critical temperatures are significantly reduced at two-loop order.

Transitions with singlet discontinuity are notably stronger at two-loop level.

Abstract

We study first-order electroweak phase transitions in the real-singlet extended Standard Model, for which non-zero mixing between the Higgs and the singlet can efficiently strengthen the transitions. We perform large-scale parameter space scans of the model using two-loop effective potential at next-to-next-to leading order in the high-temperature expansion, greatly improving description of phase transition thermodynamics over existing one-loop studies. We find that 1) two-loop corrections to the effective potential lead to narrower regions of strong first-order transitions and significantly smaller critical temperatures, 2) transitions involving a discontinuity in the singlet expectation value are significantly stronger at two-loop order, 3) high-temperature expansion is accurate for a wide range of parameter space that allows strong transitions, although it is less reliable for the very strongest transitions. These findings suggest revisiting past studies that connect the possibility of a first-order electroweak phase transition with future collider phenomenology.