55 pages, 9 figures, no major changes, references added, a comment added to sec 3.1, typos correctedThe standard model Higgs sector, extended by one weak gauge triplet of scalar fields with a very small vacuum expectation value, is a very promising setting to account for neutrino masses through the so-called type II seesaw mechanism. In this paper we consider the general renormalizable doublet/triplet Higgs potential of this model. We perform a detailed study of its main dynamical features that depend on five dimensionless couplings and two mass parameters after spontaneous symmetry breaking, and highlight the implications for the Higgs phenomenology. In particular, we determine (i) the complete set of tree-level unitarity constraints on the couplings of the potential and (ii) the exact tree-level boundedness from below constraints on these couplings, valid for all directions. When combined, these constraints delineate precisely the theoretically allowed parameter space domain within our perturbative approximation. Among the seven physical Higgs states of this model, the mass of the lighter (heavier) CPeven state h(0) (H-0) will always satisfy a theoretical upper (lower) bound that is reached for a critical value mu(c) of mu (the mass parameter controlling triple couplings among the doublet/triplet Higgses). Saturating the unitarity bounds, we find an upper bound m(h)(0) < O(0.7-1 TeV), while the upper bound for the remaining Higgses lies in the range of several tens of TeV. However, the actual masses can be much lighter. We identify two regimes corresponding to mu greater than or similar to mu(c) and mu less than or similar to mu(c). In the first regime the Higgs sector is typically very heavy, and only h(0) that becomes SM-like could be accessible to the LHC. In contrast, in the second regime, somewhat overlooked in the literature, most of the Higgs sector is light. In particular, the heaviest state H-0 becomes SM-like, the lighter states being the CPodd Higgs, the (doubly) charged Higgses, and a decoupled h(0), possibly leading to a distinctive phenomenology at the colliders

Abstract:We study the two photon decay channel of the Standard Model-like component of the CP-even Higgs bosons present in the type II Seesaw Model. The corresponding cross-section is found to be significantly enhanced in parts of the parameter space, due to the (doubly-)charged Higgs bosons' (H ±± )H ± virtual contributions, while all the other Higgs decay channels remain Standard Model(SM)-like. In other parts of the parameter space H ±± (and H ± ) interfere destructively, reducing the two photon branching ratio tremendously below the SM prediction. Such properties allow to account for any excess such as the one reported by ATLAS/CMS at ≈ 125 GeV if confirmed by future data; if not, for the fact that a SM-like Higgs exclusion in the diphoton channel around 114-115 GeV as reported by ATLAS, does not contradict a SM-like Higgs at LEP(!), and at any rate, for the fact that ATLAS/CMS exclusion limits put stringent lower bounds on the H ±± mass, particularly in the parameter space regions where the direct limits from same-sign leptonic decays of H ±± do not apply.

In this paper we consider a minimal extension to the standard model by a scalar triplet field with hypercharge Y = 2. This model relies on the seesaw mechanism which provides a consistent explication of neutrino mass generation. We show from naturalness considerations that the Veltman condition is modified by virtue of the additional scalar charged states and that quadratic divergencies at one loop can be driven to zero within the allowed space parameter of the model, the latter is severely constrained by unitarity, boundedness from below and is consistent with the di-photon Higgs decay data of LHC. Furthermore, we analyse the naturalness condition effects to the masses of heavy Higgs bosons H 0 , A 0 , H ± and H ±± , providing a drastic reduction of the ranges of variation of m H ± and m H ±± with an upper bounds at 288 and 351 GeV respectively, while predicting an almost degeneracy for the other neutral Higgs bosons H 0 , A 0 at about 207 GeV.

Using the most recent results of CMS and ATLAS, we study the Higgs decays to γγ and Zγ in the scenario where the two CP even Higgs predicted by the type II seesaw model (HTM) are close to mass degenerate with a mass near 125 GeV. We analyse the effects of the Higgs potential parameters constrained by the full set of perturbative unitarity, boundedness from below (BFB) as well as from precision electroweak measurements on these decay modes. Our analysis demonstrates that the observed excess in the diphoton Higgs decay channel can be interpreted in our scenario within a delineated region controlled by λ 1 and λ 4 coupling. We also find a deviation in the Higgs decay to Zγ with respect to the Standard Model prediction and the largest enhancement is found for a ratio R Zγ of the order 1.6. Furthermore we show that consistency with current ATLAS data on the diphoton decay channel favours a light doubly charged Higgs with mass in the range 92 − 180 GeV. Finally, we find that the γγ and Zγ Higgs decay modes are generally correlated and the magnitude of correlation is sensitive to the sign of the λ 1 parameter.

In this paper, we investigate the Higgs Triplet Model with hypercharge Y Δ = 0 (HTM0), an extension of the Standard model, caracterized by a more involved scalar spectrum consisting of two CP even Higgs h 0 , H 0 and two charged Higgs bosons H ± . We first show that the parameter space of HTM0, usually delimited by combined constraints originating from unitarity and BFB as well as experimental limits from LEP and LHC, is severely reduced when the modified Veltman conditions at one loop are also imposed. Then, we perform an rigorous analysis of Higgs decays either when h 0 is the SM-like or when the heaviest neutral Higgs H 0 is identified to the observed 125 GeV Higgs boson at LHC. In these scenarios, we perform an extensive parameter scan, in the lower part of the scalar mass spectrum, with a particular focus on the Higgs to Higgs decay modes H 0 → h 0 h 0 , H ± H ∓ leading predominantly to invisible Higgs decays. Finally, we also study the scenario where h 0 , H 0 are mass degenerate. We thus find that consistency with LHC signal strengths favours a light charged Higgs with a mass about 176-178 GeV. Our analysis shows that the diphoton Higgs decay mode and H → Z γ are not always positively correlated as claimed in a previous study. Anti-correlation is rather seen in the scenario where h is SM like, while correlation is sensitive to the sign of the potential parameter λ when H is identified to 125 GeV observed Higgs.