$h\to {\rm Y}\gamma$ Decay: Smoking Gun Signature of Wrong-Sign $hb\bar{b}$ Coupling

Abstract

We perform a model-independent study of new physics effects in the Higgs decay $h\to {\rm Y}\gamma$, focusing on scenarios that spoil the accidental cancellation between the direct and indirect amplitudes. After imposing all existing constraints from Higgs production and decay measurements, we find that a wrong-sign $hb\bar{b}$ coupling is the only viable scenario capable of enhancing the $h\to {\rm Y}\gamma$ decay width by nearly two orders of magnitude. Therefore, an observation of a significantly enhanced $h\to {\rm Y}\gamma$ rate at the LHC or future colliders would provide unambiguous evidence for a wrong-sign $hb\bar{b}$ coupling, directly pointing to the presence of an extended Higgs sector.

36 pages, 29 figures, 12 tables. Minor comments added in the main text and figures updated. Matches version published in PRD

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