Holographic Walking from Tachyon DBI

TL;DR

This paper uses holography to model conformal phase transitions relevant to QCD and technicolor, analyzing the spectrum and phase transitions of tachyonic scalar fields in AdS spacetime.

Contribution

It introduces a holographic model with a tachyonic scalar field in AdS, resembling hard and soft wall QCD models, and studies their spectra and finite temperature phase transitions.

Findings

Hard wall models exhibit a linear spectrum m_n ~ n.

Soft wall models show a spectrum m_n ~ n^eta with 0<eta extless{}=1/2.

Phase transitions can be first or second order depending on potential behavior.

Abstract

We use holography to study Conformal Phase Transitions, which are believed to be realized in four dimensional QCD and play an important role in walking technicolor models of electroweak symmetry breaking. At strong coupling they can be modeled by the non-linear dynamics of a tachyonic scalar field with mass close to the Breitenlohner-Freedman bound in anti de Sitter spacetime. Taking the action for this field to have a Tachyon-Dirac-Born-Infeld form gives rise to models that resemble hard and soft wall AdS/QCD, with a dynamically generated wall. For hard wall models, the highly excited spectrum has the KK form m_n ~ n; in the soft wall case we exhibit potentials with m_n ~ n^\alpha, 0<\alpha\leq1/2. We investigate the finite temperature phase structure and find first or second order symmetry restoration transitions, depending on the behavior of the potential near the origin of field space.