Anatomy of the real Higgs triplet model

A bstract In this article, we examine the Standard Model extended by a Y = 0 real Higgs triplet, the ∆SM. It contains a CP -even neutral Higgs (∆ 0 ) and two charged Higgs bosons (∆ ± ), which are quasi-degenerate in mass. We first study the theoretical constraints from vacuum stability and perturbative unitarity and then calculate the Higgs decays, including the loop-induced modes such as di-photons ( γγ ) and Zγ . In the limit of a small mixing between the SM Higgs and ∆ 0 , the latter decays dominantly to WW and can have a sizable branching ratio to di-photon. The model predicts a positive definite shift in the W mass, which is compatible with the current global electroweak fit. At the Large Hadron Collider, it leads to a ( i ) stau-like signature from pp → ∆ + ∆ − → $$ {\tau}^{+}{\tau}^{-}\nu \overline{\nu} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>τ</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>τ</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> , ( ii ) multi-lepton final states from pp → γ * → ∆ + ∆ − → W + W − ZZ and pp → W * → ∆ ± ∆ 0 → W ± ZW + W − as well as ( iii ) associated di-photon production from pp → W * → ∆ ± (∆ 0 → γγ ). Concerning ( i ), the reinterpretation of the recent supersymmetric tau partner search by ATLAS and CMS excludes $$ {m}_{\Delta ^{\pm }} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>m</mml:mi> <mml:msup> <mml:mtext>∆</mml:mtext> <mml:mo>±</mml:mo> </mml:msup> </mml:msub> </mml:math> &lt; 110 GeV at 95% CL. From ( ii ), some of the signal regions of multi-lepton searches lead to bounds close to the predicted cross-section, but electroweak scale masses are still allowed. For ( iii ), the recast of the associated di-photon searches by ATLAS and a combined log-likelihood fit of signal and background to data find that out of the 25 signal regions, 10 provide relevant limits on Br(∆ 0 → γγ ) at the per cent level. Interestingly, 6 signal regions show weaker than expected limits at around 152 GeV, leading to a preference for a non-zero di-photon branching ratio of about (0.7 ± 0.2)%.