XXVI DAE-BRNS High Energy Physics Symposium 2024

Anatomy of the Real Higgs Triplet Model

Not scheduled

20m

Swatantrata Bhavan, Banaras Hindu University, Varanasi

Oral Higgs physics

Speaker

Siddharth Prasad Maharathy (Institute of Physics)

Description

We examine the $Y=0$ real Higgs triplet model. In addition to the SM Higgs, it contains a $CP$-even neutral Higgs (${\mathrm{\Delta }}^0$) and two charged Higgs bosons (${\mathrm{\Delta }}^{\pm }$), which are quasi-degenerate in mass. We first study the theoretical constraints from vacuum stability and perturbative unitarity and then calculate the decay widths of ${\mathrm{\Delta }}^0$ and ${\mathrm{\Delta }}^{\pm }$, including the loop-induced modes $\gamma \gamma$ and $Z\gamma$. In the limit of a small mixing between the SM Higgs and ${\mathrm{\Delta }}^0$, the latter decays dominantly to $WW$ and can have a sizable branching ratio to photons. The model predicts a positive definite shift in the $W$ mass, which is in agreement with the current global electroweak fit. At the LHC, it leads to a $(i)$ stau-like signature from $pp\to {\mathrm{\Delta }}^{+}{\mathrm{\Delta }}^{-}\to {\tau }^{+}{\tau }^{-}\nu \overline{\nu }$, $(ii)$ multi-lepton final states from $pp\to {\gamma }^{\ast }\to {\mathrm{\Delta }}^{+}{\mathrm{\Delta }}^{-}\to W^{+}{W}^{-}ZZ$ and $pp\to W^{\ast }\to {\mathrm{\Delta }}^{\pm }{\mathrm{\Delta }}^0\to W^{\pm }Z{W}^{+}{W}^{-}$ as well as $(iii)$ associated di-photon production from $pp\to W^{\ast }\to {\mathrm{\Delta }}^{\pm }({\mathrm{\Delta }}^0\to \gamma \gamma )$. Concerning $(i)$, the reinterpretation of the recent stau search by ATLAS and CMS excludes $m_{{\mathrm{\Delta }}^{\pm }}<110$\,GeV at 95\% CL. From $(ii)$, some of the signal regions of multilepton searches lead to bounds close to the prediction cross-section, but electroweak scale masses are still allowed. For $(iii)$, the recast of the associated di-photon searches by ATLAS by performing a combined log-likelihood fit of signal and background to data finds that out of the 23 signal regions provided by ATLAS, 8 provide relevant limits on Br$({\mathrm{\Delta }}^0\to \gamma \gamma )$ at the per cent level. Interestingly, 6 signal regions show excesses at around 152\,GeV, leading to a non-zero di-photon decay rate with $\approx 4\sigma$ significance.