The negative results in the search for Kaluza-Klein graviton modes at the LHC, when confronted with the discovery of the Higgs, has been construed to have severely limited the efficacy of the Randall-Sundrum model as an explanation of the hierarchy problem. We show, though, that the presence of multiple warping offers a natural resolution of this conundrum through modifications in both the graviton spectrum and their couplings to the Standard Model fields.Comment: 16 pages, 6 figure

The lack of evidence for a TeV-mass graviton has been construed as constricting the Randall-Sundrum model. However, a doubly-warped generalization naturally avoids such restrictions. We develop, here, the formalism for extension of the Standard Model gauge bosons and fermions into such a six-dimensional bulk. Apart from ameliorating the usual problems such as flavour-changing neutral currents, this model admits two very distinct phases, with their own unique phenomenologies.

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,

The absence, so far, of any graviton signatures at the LHC imposes severe constraints on the Randall-Sundrum scenario. Although a generalization to higher dimensions with nested warpings has been shown to avoid these constraints, apart from incorporating several other phenomenologically interesting features, moduli stabilization in such models has been an open question. We demonstrate here how both the moduli involved can be stabilized, employing slightly different mechanisms for the two branches of the theory. This also offers a dynamical mechanism to generate and stabilize the scale for the Universal Extra Dimensions, another long-standing issue.Comment: 22 pages, 3 figure

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