Screening the Higgs portal

TL;DR

This paper investigates how mixing between a light scalar and the Higgs field can screen fifth forces mediated by Higgs portal interactions, revealing conditions where naive approximations fail and implications for relaxion models.

Contribution

It demonstrates the importance of considering dynamical scalar fields and their mixing with the Higgs in screening fifth forces, highlighting scenarios where common approximations break down.

Findings

Screening of fifth forces depends on scalar-Higgs mixing and object size.

Naive integration out of scalar fields can fail near mass matrix degeneracies.

Implications for relaxion models with nearly massless scalars.

Abstract

Light scalar fields that couple to matter through the Higgs portal mediate long range fifth forces. We show how the mixing of a light scalar with the Higgs field can lead to this fifth force being screened around macroscopic objects. This behaviour can only be seen by considering both scalar fields as dynamical, and is missed if the mixing between the Higgs field and the scalar field is not taken into account. We explain under which conditions the naive "integrating out" procedure fails, i.e. when the mass matrix of the Higgs-scalars system has a nearly vanishing mass eigenvalue. The resulting flat direction in field space can be lifted at the quadratic order in the presence of matter and the resulting fifth force mediated by the Higgs portal can be screened either when the gravitating objects are large enough or their surface Newton potential exceeds a threshold. Finally we discuss the implications of these results for nearly massless relaxion models.