LHC: Standard Higgs and hidden Higgs

Abstract

Interpretations of Higgs searches critically involve production cross sections and decay probabilities for different analysis channels. Mixing effects can reduce production rates, while invisible decays can reduce decay probabilities. Both effects may transparently be quantified in Higgs systems where a visible Higgs boson is mixed with a hidden sector Higgs boson. Recent experimental exclusion bounds can be re-interpreted in this context as a sign for non-standard Higgs properties. Should a light Higgs boson be discovered, then our analysis will quantify how closely it may coincide with the Standard Model. [5, 6], so that each experiment alone has about the same sensitivity as the combination in the low mass region, raising the low-mass bound of the Higgs from the LEP2 limit [7] of 114.4 GeV to 115.5/115 GeV and leading to an exclusion of the mass from 131 GeV/127 GeV to 453 GeV/600 GeV by ATLAS/CMS, respectively. Bounds as low as fractions R ≤ 0.3 have been set on the production cross sections with respect to the Standard Model [SM] for some of the masses probed. Given the far reaching consequences, the question arises naturally to what extent Higgs bosons, in slightly generalized scenarios, may still exist in this mass region.On the other hand, a gap from about 130 GeV down to the low-mass limit of about 115 GeV is left, presently, in which a SM-type Higgs signal can be expected to either rise up or plunge in the near future [5, 6]. When a Higgs boson will indeed be discovered in this mass range, the standard-hidden Higgs scenario allows to quantify how well the global properties of the particle coincide with the predictions of the Standard Model.Both these questions have been addressed [8,9] at the theoretical level in a standard-hidden Higgs scenario. The present sequel will include the recent LHC results on the Higgs sector in the analysis. The ground for the fundamental idea to use the Higgs boson as a portal to a novel hidden sector in nature has been laid for general model structures in Ref. [11]. Phenomenological implications [12] can then be studied in specific frameworks like hidden valleys [13]. Other than the Higgs portal there exist two additional portal-type interactions in a renormalizable theory, namely kinetic U (1) mixing [14] and mixing with sterile neutrinos [15].The experimentally observed rates depend on the Higgs production cross sections and the decay branching ratios [16]. In scenarios in which the standard Higgs boson is mixed with another Higgs boson, originating from a hidden sector for instance, the production cross sections are reduced universally by the mixing parameter and, in addition, the visible branching ratios may be lowered by decays into invisible channels induced by mixing. Throughout this paper we will consider the minimal Standard Model Higgs sector as the activator of the visible Higgs boson [17], but the same arguments trivially hold for extended visible Higgs sectors, for example in supersymmetry or other extensions to the Standard Model [18]. In the early theoret...

The Higgs mass and the scale of new physics

“…In our simple model we couple the additional scalar to the Standard Model through a Higgs portal [72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91] added to the effective potential of eq. (2.6),…”

Probing for invisible Higgs decays with global fits

“…This is the case we explore in detail throughout section 2. We briefly discuss and summarize the prospects for global fits to uncover Br inv in broader scenarios in section 3 where the effective couplings of the Higgs to the SM fields deviate from their SM values due to the Higgs being a pseudo-Goldstone boson or due 1 For other model independent approaches to Higgs couplings determination see [11][12][13].…”

“…First, consider the case of fixing or marginalizing over one of the parameters (a, c, Br inv ), 12 to examine the robustness of our global fit results when Br inv = 0 is assumed, as in ref. [10].…”

“…It is interesting that this is another example where the breaking of the approximate c ↔ −c symmetry in the parameter space has a physical consequence. If (relative) excesses in the signal strengths of h → γγ became statistically significant with a larger data set, coincident 12 In the remainder of the paper we will always choose the value m h = 124 GeV as we have shown that the fit results are not strongly dependent (considering current errors) on the chosen mass (when varied in the range 124-126 GeV). Figure 6.…”

“…Recent papers have investigated the potential of a 7 TeV collider in direct searches for an invisible Higgs boson [12,[53][54][55][56]. The invisible branching ratio of a 125 GeV Higgs boson produced in weak boson fusion with SM strength can be constrained down to ∼ 40% at √ s = 7 TeV and L = 20 fb −1 [54].…”