Gravitons in multiply warped scenarios: At 750 GeV and beyond

Abstract

The search for extra dimensions has so far yielded no positive results at the LHC. Along with the discovery of a 125 GeV Higgs boson, this implies a moderate degree of fine tuning in the parameter space of the Randall-Sundrum model. Within a 6-dimensional warped compactification scenario, with its own interesting phenomenological consequences, the parameters associated with the additional spatial direction can be used to eliminate the need for fine tuning. We examine the constraints on this model due to the 8TeV LHC data and survey the parameter space that could be probed at the 14 TeV run of the LHC. We also identify the region of parameter space that is consistent with the recently reported excess in the diphoton channel in the 13 TeV data. Finally, as an alternative explanation for the observed excess, we discuss a scenario with brane-localized Einstein-Hilbert terms with Standard Model fields in the bulk. IntroductionThe warped geometry model proposed by Randall and Sundrum (RS) [1] is one of the many models in the literature that offer a resolution of the well-known naturalness problem. This model is particularly promising because (i) it resolves the gauge hierarchy problem with large extra dimensions); (ii) the modulus of the extra dimension can be stabilized to a desired value by well-understood mechanisms, e.g. the one due to Goldberger and Wise [2], and (iii) a similar warped solution can be obtained from a more fundamental theory like string theory where extra dimensions appear naturally [3]. As a result, several search strategies at the LHC were designed specifically [4, 5,6, 7, 8] to detect signatures of these warped extra dimensions through the decays of Kaluza-Klein (KK) excitations of the graviton which appear at the TeV scale in this model. The results, so far, have been negative, with the ATLAS Collaboration [9] setting a lower bounds of 2.66 (1.41) TeV on the mass of the lightest KK excitation of the graviton for a coupling of k 5 /M P l = 0.1 (0.01). The limits obtained by the CMS Collaboration are similar [5]. This result, together with the very restrictive nature of the RS model,

Stabilization of moduli in spacetime with nested warping and the UED

“…In Fig.1, we display V eff (k) for a fixed value of the mass parameter µ (equivalently, m). As is obvious, depending on the ratio v 2 /v 1 , minima exist for 0.1 < ∼ k < ∼ 0.6, the range that is of particular interest not only to explain the non-observation (so far) of the KK-graviton at the LHC [18,19], but also for scenarios wherein the SM fields are extended in to the bulk [20,21]. What is particularly encouraging is that such minima arise for very natural values of the parameters and are not overly sensitive to their precise values.…”

“…Consequently, the graviton production rates are further suppressed and the scenario easily survives the current bounds from the LHC [18,19]. On the other hand, while the allowed parameter space of the model is still quite extensive, it can be probed well in the current run of LHC.…”

Universal extra dimensions and the graviton portal to dark matter

“…Furthermore, the large coupling enhancement that allowed for the RSgravitons to be extensively produced at the LHC, is now tempered to a significant degree [27]. Consequently, the production rates are suppressed and the scenario easily survives the current bounds [27,28]. The brane potentials are determined by the junction conditions.…”

Precision tools and models to narrow in on the 750 GeV diphoton resonance

“…on-shell (3.28) then for one dominant particle p in the loop, we can estimate the uncertainty as 29) where the factor of 1 or 1/2 assumes that the couplings C p p do not depend upon the mass m p (but the prefactor in r p therefore does). For most values of m p the loop functions are slowly changing (only peaking around τ p = 1) so we will have a proportional uncertainty in the result of .…”

“…This possibility would be favoured by a large width of the resonance, as first indications seem to suggest. Another possibility is to interpret the signal in the context of extra-dimensional models [5,9,29,30,48,84,125,141,203,225,312], with the resonance being a scalar, a graviton, a dilaton, or a radion, depending on the scenario. However, some of these interpretations are in tension with the non-observation of this resonance in other channels.…”