Kinetic mixing between a Higgs and a nearly degenerate Dark scalar: oscillations and displaced vertices

TL;DR

This paper investigates the dynamical effects of kinetic mixing between a nearly degenerate Dark scalar and the Higgs, revealing oscillations, interference, and displaced vertices as potential experimental signatures.

Contribution

It provides a detailed analysis of the kinetic mixing dynamics, including the derivation of an effective non-hermitian Hamiltonian and the prediction of observable displaced vertices.

Findings

Kinetic mixing causes Higgs-Dark scalar oscillations similar to meson mixing.

Degeneracy enhances the kinetic coupling, affecting decay lifetimes.

Displaced vertices emerge as potential experimental signals.

Abstract

Extensions beyond the Standard Model allow for a gauge singlet scalar to be kinetically coupled with the Higgs. We consider kinetic mixing between a Dark scalar gauge singlet \emph{nearly degenerate} with the Higgs, focusing on the \emph{dynamical} aspects of the mixing phenomena. The renormalization program is carried out by obtaining the one-loop effective action which yields an effective non-hermitian Hamiltonian to study the dynamics of mixing. The scalar Higgs becomes a coherent superposition of the mass eigenstates, thus kinetic mixing leads to oscillations and common decay channels in striking similarity with neutral meson mixing. Near degeneracy yields an \emph{enhancement} of the kinetic coupling. For small kinetic mixing we find that the mass eigenstates feature different lifetimes which result in a wide separation of time scales of evolution along with important coherence aspects from Dark scalar-Higgs interference. The wide separation of scales is manifest as displaced decay vertices which could potentially be a telltale experimental signal of kinetic mixing.