Rare few-body decays of the Standard Model Higgs boson

TL;DR

This paper surveys rare and exclusive few-body decays of the Standard Model Higgs boson, providing theoretical branching ratios, experimental limits, and new decay channels to guide future research and experimental searches.

Contribution

It compiles and estimates branching fractions for about 70 unobserved Higgs decay channels, including 20 newly computed for the first time, aiding future experimental and theoretical efforts.

Findings

Collected theoretical branching ratios for rare Higgs decays.

Estimated experimental limits and bounds for HL-LHC.

Identified 20 new decay channels for ultrarare Higgs decays.

Abstract

We present a survey of rare and exclusive few-body decays of the standard model (SM) Higgs boson, defined as those into two to four final particles with branching fractions $\mathcal{B}\lesssim 10^{-5}$. Studies of such decays can be exploited to constrain Yukawa couplings of quarks and leptons, probe flavour-changing Higgs decays, estimate backgrounds for exotic Higgs decays into beyond-SM particles, and/or confirm quantum chromodynamics factorization with small nonperturbative corrections. We collect the theoretical $\mathcal{B}$ values for about 70 unobserved Higgs rare decay channels, indicating their current experimental limits, and estimating their expected bounds in p-p collisions at the HL-LHC. Among those, we include 20 new decay channels computed for the first time for ultrarare Higgs boson decays into photons and/or neutrinos, radiative quark-flavour-changing exclusive decays, and radiative decays into leptonium states. This survey can help guide and prioritize upcoming experimental and theoretical studies of unobserved Higgs boson decays.