Mixed Higgs–radion states at the LHC – a detailed study

Abstract

Light radions constitute one of the few surviving possibilities for observable new particle states at the sub-TeV level which arise in models with extra spacetime dimensions. It is already known that the 125 GeV state discovered at CERN is unlikely to be a pure radion state, since its decays resemble those of the Standard Model Higgs boson too closely. However, due to experimental errors in the measured decay widths, the possibility still remains that it could be a mixture of the radion with one (or more) Higgs states. We use the existing LHC data at 8 and 13 TeV to make a thorough investigation of this possibility. Not surprisingly, it turns out that this model is already constrained quite effectively by direct LHC searches for an additional scalar heavier than 125 GeV. We then make a detailed study of the so-called 'conformal point', where this heavy state practically decouples from (most of) the Standard Model fields. Some projections for the future are also included.

Rapid holographic phase transition with brane-localized curvature

“…The principle decay modes of the radion are to W + W − , ZZ and hh, with the ZZ → 4l channel being the most constraining. Ignoring the Higgs-radion mixing, the results in [32] reveal that the bounds on Λ r range from ∼ 10 TeV for m r = 200 GeV to ∼ 4 TeV for m r = 1 TeV. Therefore with the radion mass below 1 TeV we would expect Λ r = Zµ − 4 TeV.…”

“…With the standard model residing on the TeV brane, the radion phenomenology depends only on two parameters; the mass and the effective interaction scale. Much work has already been done, using results from LHC searches, to put experimental constraints on these two parameters [31][32][33]. Note that our discussion so far is particularly simple in that we do not consider a possible non-minimal coupling of the Higgs to the Ricci scalar, which should in principle be present.…”

“…To estimate the constraints on Λ r and m r we can use the results from Ref. [32]. The principle decay modes of the radion are to W + W − , ZZ and hh, with the ZZ → 4l channel being the most constraining.…”

“…Again using the results from Ref. [32] (Figure 9) we can estimate that when ξ hR takes the value associated with this conformal point, the experimental bound on Λ r is of order 1 TeV for radion masses in the range 0.2 − 1 TeV. A dedicated study of the radion phenomenology with a larger range of radion masses and including both the brane curvature and the curvature-Higgs mixing is required in order to obtain a complete and accurate account of the bounds on the model considered in this paper; however, this is beyond the scope of our present discussion.…”

Radion-Higgs mixing in 2HDMs

“…After diagonalization the physical fields become mixtures of the original non-mixed radion and Higgs boson. The phenomenological consequences of a non-zero mixing ξ = 0 have been studied extensively in the literature [22,[25][26][27][28][29][30][31][32][33][34][35][36].…”