Resonant top pair searches at the LHC: a window to electroweak phase transition

TL;DR

This paper investigates the potential of the HL-LHC to detect signals of a strong first-order electroweak phase transition in the type-I 2HDM, focusing on resonant top-quark pair production as a promising signature.

Contribution

It introduces the top-quark pair final state in Higgstrahlung processes as the most sensitive probe for SFOEWPT at the HL-LHC, comparing it with other search channels and gravitational wave signals.

Findings

Top-quark pair final state offers the highest sensitivity for SFOEWPT detection.

Higgstrahlung searches complement other collider and gravitational wave probes.

Resonant top pair production could be a key signature at the HL-LHC.

Abstract

The dynamics of electroweak phase transition could have profound consequences for particle physics and cosmology. We study the prospects for the HL-LHC to probe the strong first-order electroweak phase transition (SFOEWPT) regime in the type-I 2HDM. We focus on the Higgstrahlung channel $pp\to ZH/A$ with a resonant top-quark pair final state $H/A\to t\bar t$. We find that the top-quark pair final state renders the largest sensitivity to the SFOEWPT regime, in comparison to the other Higgstrahlung searches already performed by ATLAS and CMS, that focus on the $H/A\to bb$ and $H\to WW$ final states. We also derive the complementarity of the Higgstrahlung searches with other relevant classes of searches at the HL-LHC and compare them with the gravitational wave sensitivity at LISA.