Holographic Walking Technicolor from D-branes

TL;DR

This paper explores a holographic model of dynamical electroweak symmetry breaking using D-branes in a walking gauge theory background, calculating the S parameter and meson properties with improved accuracy over previous models.

Contribution

It develops a detailed holographic model with explicit calculations of the S parameter and meson spectra, showing better approximation of the full S value from low-lying states.

Findings

The S parameter is positive and smaller than in QCD-like models.

Explicit meson masses and decay constants are computed.

Summing contributions of low-lying states approximates the full S value well.

Abstract

We investigate a model of dynamical electroweak symmetry breaking via a dual gravitational description. The gravity dual is obtained by embedding a D7 - anti-D7 pair of branes into a type IIB background that is dual to a walking gauge theory. We develop further a previous study of this model. In particular, we show that there is a nontrivial relation that needs to be satisfied in order for axial-vector modes to exist. Furthermore, we compute explicitly the electroweak S parameter. The result is positive-definite and, as was to be expected, much smaller than in earlier QCD-like D-brane constructions. We also find the masses and decay constants of the vector and axial-vector mesons in this model. This allows us to obtain another estimate for S by summing the contributions of the discrete states. It is noteworthy that, in contrast to previous holographic studies, the sum of the first several lowest-lying states does give a very good approximation to the full answer.