Phenomenology and Cosmology of an Electroweak Pseudo-Dilaton and Electroweak Baryons

TL;DR

This paper explores the phenomenology and cosmology of a pseudo-dilaton arising in strongly-interacting electroweak models, analyzing its experimental constraints, potential role as dark matter, and implications for the electroweak phase transition.

Contribution

It introduces a low-energy effective theory with Skyrmion solutions representing electroweak baryons, and examines their cosmological and experimental implications.

Findings

Pseudo-dilaton couplings differ from Standard Model Higgs by fixed factors.

Electroweak phase transition may be first-order, affecting baryogenesis.

Electroweak baryons could contribute to dark matter, with detectable scattering cross sections.

Abstract

In many strongly-interacting models of electroweak symmetry breaking the lowest-lying observable particle is a pseudo-Goldstone boson of approximate scale symmetry, the pseudo-dilaton. Its interactions with Standard Model particles can be described using a low-energy effective nonlinear chiral Lagrangian supplemented by terms that restore approximate scale symmetry, yielding couplings of the pseudo-dilaton that differ from those of a Standard Model Higgs boson by fixed factors. We review the experimental constraints on such a pseudo-dilaton in light of new data from the LHC and elsewhere. The effective nonlinear chiral Lagrangian has Skyrmion solutions that may be identified with the `electroweak baryons' of the underlying strongly-interacting theory, whose nature may be revealed by the properties of the Skyrmions. We discuss the finite-temperature electroweak phase transition in the low-energy effective theory, finding that the possibility of a first-order electroweak phase transition is resurrected. We discuss the evolution of the Universe during this transition and derive an order-of-magnitude lower limit on the abundance of electroweak baryons in the absence of a cosmological asymmetry, which suggests that such an asymmetry would be necessary if the electroweak baryons are to provide the cosmological density of dark matter. We revisit estimates of the corresponding spin-independent dark matter scattering cross section, with a view to direct detection experiments.