Minimal Extension of the Standard Model Scalar Sector

TL;DR

The paper analyzes a minimal extension of the Standard Model that adds a real singlet scalar S mixing with the Higgs. It concentrates on the regime where the lighter scalar h_- is mostly singlet and light, and the heavier state h_+ is SM-like but can decay to h_- h_- if kinematically allowed, suppressing standard Higgs decay channels by a common factor. It derives the parameter dependence on the mixing angle, masses, and the h_+→h_-h_- branching, and discusses experimental constraints from LEP and B decays that bound the mixing and lifetimes. The work highlights distinctive collider signatures, including Higgs decays to pairs of light scalars and unusual multi-fermion final states, with production rates modulated by sin^2 θ and the h_- mass, motivating targeted searches at the LHC.

Abstract

The minimal extension of the scalar sector of the standard model contains an additional real scalar field with no gauge quantum numbers. Such a field does not couple to the quarks and leptons directly but rather through its mixing with the standard model Higgs field. We examine the phenomenology of this model focusing on the region of parameter space where the new scalar particle is significantly lighter than the usual Higgs scalar and has small mixing with it. In this region of parameter space most of the properties of the additional scalar particle are independent of the details of the scalar potential. Furthermore the properties of the scalar that is mostly the standard model Higgs can be drastically modified since its dominant branching ratio may be to a pair of the new lighter scalars.

Figures (2)

• Figure 1: The suppression factor $f$ discussed in the text.
• Figure 2: The branching ratios of the light $h_-$ scalar particle.