Mesons in Gauge/Gravity Duals - A Review

TL;DR

This review discusses recent advances in understanding mesons through gauge/gravity duality, focusing on string theory models that describe strongly coupled confining gauge theories and their phenomenological implications.

Contribution

It provides a comprehensive overview of top-down string theory models for mesons, including new unpublished results and comparisons with lattice QCD and phenomenological approaches.

Findings

Gravity duals can model chiral symmetry breaking.

Finite temperature effects on mesons are described.

Comparison with lattice results validates models.

Abstract

We review recent progress in studying mesons within gauge/gravity duality, in the context of adding flavour degrees of freedom to generalizations of the AdS/CFT correspondence. Our main focus is on the `top-down approach' of considering models constructed within string theory. We explain the string-theoretical constructions in detail, aiming at non-specialists. These give rise to a new way of describing strongly coupled confining large N gauge gauge theories similar to large N QCD. In particular, we consider gravity dual descriptions of spontaneous chiral symmetry breaking, and compare with lattice results. A further topic covered is the behaviour of flavour bound states in finite temperature field theories dual to a gravity background involving a black hole. We also describe the `bottom up' phenomenological approach to mesons within AdS/QCD. -- Some previously unpublished results are also included.