Scalar decays to γγ , Zγ , and Wγ in the Georgi-Machacek model

Abstract

We compute the decay widths for the neutral and singly-charged Higgs bosons in the Georgi-Machacek model into the final states γγ, Zγ, and W γ. These decays are most phenomenologically interesting for the fermiophobic custodial fiveplet states H 0 5 and H ± 5 when their masses are below threshold for decays into W W , ZZ, or W Z. We study the allowed branching ratios into these final states using scans over the allowed parameter space, and show how the model can be constrained by LEP searches for a fermiophobic Higgs boson decaying to two photons. The calculation involves evaluating one-loop diagrams in which the loop contains particles with two different masses, some of which do not appear in the existing literature. We give results for these diagrams in a form convenient for numerical implementation using the LoopTools package.1 Heterogeneous diagrams contributing to neutral Higgs boson decays to Zγ involving fermions and vector bosons in the loops have been computed in Refs.[57] and [58], respectively. These contributions do not appear in the GM model.

Light (and darkness) from a light hidden Higgs

“…In the low mass region of the diphoton search window considered here, various limits on charged Higgs bosons from LEP in principle apply, but these can be evaded if the charged Higgs is fermiophobic [25,27,74,75]. The same is true for indirect constraints such as b → sγ [76].…”

“…These suppressions require O(1 − 50%) level cancelations between the W boson loop and other contributions. Though this implies a certain level of tuning, it can happen and in particular in models containing doubly charged particles [27]. This also illustrates the importance of extending diphoton searches to as low a mass as possible [41] since masses below 65 GeV are not ruled out by Tevatron four photon searches [36] in the degenerate (custodial) limit.…”

“…However, the presence of doubly charged scalars in the model allows for larger destructive interference with W boson loops which can lead to a suppressed effective coupling to photons. These cancellations have also been shown [27] to open up the possibility of avoiding stringent LEP diphoton search constraints (when s θ 0.1) for masses below ∼ 110 GeV. One could also simply add an additional stable neutral particle giving a potential dark matter candidate [93] and opening up an invisible decay channel.…”

“…many recent studies [27,67,71,71,76,77,[88][89][90][91][92][93][94][95][96]. In minimal versions [76,86], there is no neutral LSP which could open up an invisible decay channel to avoid diphoton constraints.…”

“…Thus, even for masses well below the 125 GeV Higgs boson, many limits which typically apply to extended Higgs sectors, can be evaded. 2 However, as shown in past [30][31][32][33][34][35] as well as more recent studies, diphoton [15,27] and multiphoton [29] searches can put robust constraints on these light, but otherwise difficult to detect Higgs bosons. This is especially true when combined with the universal Drell-Yan Higgs pair production mechanism [15,36] which dominates for small exotic Higgs VEV.…”