Nonstandard Higgs Boson Decays

TL;DR

The paper investigates how a light SM-like Higgs can remain consistent with precision electroweak data and LEP constraints if it decays predominantly into non-SM, hidden-sector states. It develops the NMSSM as a concrete framework in which h -> a1 a1 decays dominate, alleviating fine-tuning and aligning with a Higgs mass around 100 GeV, while offering distinctive collider signatures such as h -> 4f, displaced vertices, and missing energy. The authors survey LEP search results, B-factory probes, and LHC implications, emphasizing that many nonstandard decay topologies evade standard Higgs searches and require expanded strategies across detectors, including LHCb for displaced vertices. They argue that nonstandard decays can both obscure Higgs discovery at the LHC and provide crucial windows into new sectors, illustrating the need for complementary facilities like linear colliders to fully resolve the Higgs and its connections to beyond-Standard-Model physics.

Abstract

This review summarizes the motivations for and phenomenological consequences of nonstandard Higgs boson decays, with emphasis on final states containing a pair of non-Standard-Model particles that subsequently decay to Standard Model particles. Typically these non-Standard-Model particles are part of a ``hidden'' sector, for example a pair of neutral Higgs bosons or a pair of unstable neutralinos. We emphasize that such decays allow for a Higgs substantially below the Standard Model Higgs LEP limit of 114 GeV. This in turn means that the ``fine-tuning'' problems of many Beyond the Standard Model (BSM) theories, in particular supersymmetric models, can be eliminated while achieving excellent consistency with precision electroweak data which favor a Higgs boson with mass below $100\gev$ and standard $WW$, $ZZ$, and top couplings.