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arXiv · 2503.08659

On new physics off the Z peak in $H \rightarrow \ell^+\ell^- γ$

Aliaksei Kachanovich·Jean Kimus·Steven Lowette·Michel H. G. Tytgat
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Abstract

Motivated by a small but intriguing excess observed in the decay mode $ H\rightarrow \ell^+\ell^- γ$ reported by both the ATLAS and CMS collaborations, we explore the possibility that new physics contributes directly to the effective $ H \ell \overline{\ell} γ$ coupling rather than modifying the $ Z $ peak. Concretely, we consider a dimension-8 operator that could arise from new particles via box diagrams. Such non-resonant contribution may provide an alternative origin for current or future excesses. We examine how experimental cuts may distinguish between possible modifications of the $ Z $ peak and non-resonant contributions. The currently measured excess requires that the new physics scale is relatively low $( Λ_R \sim v $). However, we show that it may remain within current experimental bounds. In particular, we illustrate this using a simplified model, motivated by the dark matter problem, and discuss its other experimental constraints.

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Aliaksei Kachanovich, Jean Kimus, Steven Lowette, Michel H. G. Tytgat. 2025-04-07. On new physics off the Z peak in $H \rightarrow \ell^+\ell^- γ$. https://arxiv.org/abs/2503.08659

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