Sphaleron bound in some nonstandard cosmology scenarios

TL;DR

This paper explores how nonstandard cosmological scenarios, including scalar fields and extra dimensions, can influence the sphaleron bound and electroweak baryogenesis, potentially relaxing constraints on new physics models.

Contribution

It analyzes the impact of modified expansion histories on the sphaleron bound within two different nonstandard cosmology frameworks, providing new bounds and viability conditions.

Findings

Modified expansion history can raise the cutoff scale for Higgs operators from 860 GeV to 1 TeV.

In Randall-Sundrum models, the five-dimensional Planck scale constraints can be alleviated by nonstandard cosmology.

Non-interacting scalar fields can make certain models compatible with the sphaleron bound.

Abstract

In the first scenario, we revise the upper bound of the cutoff scale of the dimension-six potential Higgs operator required for a successful electroweak baryogenesis in the case of a modified expansion history caused by the existence of a non-interacting scalar field at the time phase transition happens. The upper bound 860 GeV of the cutoff scale in the conventional case can be improved to 1 TeV in the modified expansion case under certain conditions. In the second scenario, we consider the Randall-Sundrum type II model. We show that the lower bound of the five-dimensional Planck scale in this model, which is determined from the validity of Newtonian gravitational potential at small distance, turns out to be crucial in eliminating this model as a viable candidate to satisfy the sphaleron bound; however, again modifying the expansion history by including a non-interacting scalar field at the electroweak scale can then make this model satisfy the sphaleron bound with a certain parameter space.