The Electroweak Phase Transition: A Collider Target

TL;DR

This paper explores how a first order electroweak phase transition, unlike the crossover in the Standard Model, could be detectable at future colliders and has implications for cosmology and gravitational waves.

Contribution

It provides generic, quantitative criteria linking new physics parameters to the possibility of a first order electroweak phase transition observable at colliders.

Findings

New particles involved cannot be too heavy or weakly interacting.

Quantitative expectations for masses and couplings are derived.

Implications for collider phenomenology of non-standard EWSB history.

Abstract

Determining the thermal history of electroweak symmetry breaking (EWSB) is an important challenge for particle physics and cosmology. Lattice simulations indicate that EWSB in the Standard Model (SM) occurs through a crossover transition, while the presence of new physics beyond the SM could alter this thermal history. The occurrence of a first order EWSB transition would be particularly interesting, providing the needed pre-conditions for generation of the cosmic matter-antimatter asymmetry and sources for potentially observable gravitational radiation. I provide simple, generic arguments that if such an alternate thermal history exists, the new particles involved cannot be too heavy with respect to the SM electroweak temperature, nor can they interact too feebly with the SM Higgs boson. These arguments do not rely on the decoupling limit. I derive corresponding quantitative expectations for masses and interaction strengths which imply that their effects could in principle be observed (or ruled out) by prospective next generation high energy colliders. The simple, generic arguments provide a quantitative, parametric understanding of results obtained in a wide range of explicit model studies; relate them explicitly to the electroweak temperature; and delineate broad contours of collider phenomenology pertaining to a non-standard history of EWSB.