Interpreting the 95 GeV di-photon and di-tau Excesses in the Georgi-Machacek Model

Abstract

We revisit the 95~GeV $\gamma \gamma$ and $\tau \tau$ excesses in the Georgi--Machacek model using a combined fit to a single light $CP$-even custodial singlet $H$. Using the one-loop renormalization group-improved effective potential and positive-definiteness conditions for vacuum stability, together with perturbative unitarity, electroweak precision tests, $B$-physics, and Higgs data, we identify a narrow but viable parameter region. In the allowed region ${\mu }_{\gamma \gamma }$ approaches the experimental central value, while ${\mu }_{\tau \tau }$ reaches only $\sim 0.5$ (about $1.4\sigma$ below the CMS central value) and remains within the $2\sigma$ interval - a good description of the di-photon excess but only a partial accommodation of the di-tau excess. The scenario predicts characteristic patterns in the singlet mixing and triplet vacuum expectation values and is highly testable at the HL-LHC and future lepton colliders via precision ${\kappa }_V$ measurements and direct exotic searches.

31 pages, 6 figures, 1 table. published version