#### Riccardo Torre (CERN & INFN, Genova)

## 5D Linear Dilaton: structure and phenomenology

Abstract

I will review some recent progress in the study of extra-dimensional solutions to the hierarchy problem that do not admit an interpretation in terms of a dual Conformal Field Theory (CFT). One geometry singles out as an alternative to Randall-Sundrum (RS) solutions, which is referred to in the literature as Linear Dilaton, and more recently, Clockwork. The extra dimensional geometry is generated by a bulk scalar (dilaton) with a linear profile and has been extensively discussed in the context of Little String Theory, a 6D version of string theory without gravity. In this talk I will take a bottom up approach on this geometry, construct the 5D effective field theory and its corresponding 4D one. I will discuss the existence of the Linear Dilaton background, the mechanism of radius stabilization and to what extent this can be considered as a natural solution to the hierarchy problem. The model provides very interesting phenomenology, which is crucially different than the usual phenomenology of extra-dimensions. In fact, the spectrum features a mass gap typical of warped extra dimensions (like RS) followed by a nearly continuum of Kaluza-Klein modes typical of large extra dimensions. This peculiar spectrum opens up the possibility of new analysis techniques, based on the Fourier transform of the invariant mass spectrum, for instance in the di-photon channel. I will discuss the main signatures and phenomenological implications of this model.