Hyperscaling violation and Electroweak Symmetry Breaking

TL;DR

This paper explores holographic models with hyperscaling violation to understand electroweak symmetry breaking, analyzing scalar and vector spectra, and deriving bounds on resonance masses from precision electroweak constraints.

Contribution

It introduces a bottom-up holographic model with hyperscaling violation and studies its implications for the spectrum of composite states and electroweak precision parameters.

Findings

Existence of a parametrically light scalar state under certain conditions

Mass bounds on spin-1 resonances from electroweak precision tests

Techni-rho mesons are constrained to be heavier than several TeV

Abstract

We consider a class of simplified models of dynamical electroweak symmetry breaking built in terms of their five-dimensional weakly-coupled gravity duals, in the spirit of bottom-up holography. The sigma-model consists of two abelian gauge bosons and one real, non-charged scalar field coupled to gravity in five dimensions. The scalar potential is a simple exponential function of the scalar field. The background metric resulting from solving the classical equations of motion exhibits hyperscaling violation, at least at asymptotically large values of the radial direction. We study the spectrum of scalar composite states of the putative dual field theory by fluctuating the sigma-model scalars and gravity, and discuss in which cases we find a parametrically light scalar state in the spectrum. We model the spontaneous breaking of the (weakly coupled) gauge symmetry to the diagonal subgroup by the choice of IR boundary conditions. We compute the mass spectrum of spin-1 states, and the precision electroweak parameter S as a function of the hyperscaling coefficient. We find a general bound on the mass of the lightest spin-1 resonance, by requiring that the indirect bounds on the precision parameters be satisfied, that implies that precision electroweak physics excludes the possibility of a techni-rho meson with mass lighter than several TeV.