On the glueball spectrum of walking backgrounds from wrapped-D5 gravity duals

TL;DR

This paper calculates the glueball mass spectrum in strongly-coupled theories with walking behavior using supergravity duals, revealing a light scalar glueball whose physicality depends on the background's UV properties.

Contribution

It provides a rigorous analysis of the glueball spectrum in wrapped-D5 supergravity backgrounds, improving previous methods by including precise boundary conditions and consistent truncation.

Findings

Both backgrounds exhibit a light scalar glueball.

In one background, the scalar is a physical state.

In the other, the spectrum depends on an unphysical UV cutoff.

Abstract

We compute the mass spectrum of glueball excitations of a special class of strongly-coupled field theories via their type-IIB supergravity dual. We focus on two subclasses of backgrounds, which have different UV-asymptotics, but both of which exhibit walking behavior, in the weak sense that the gauge coupling of the dual field theory exhibits a quasi-constant behavior at strong coupling over a range of energies, before diverging in the deep IR. We improve on earlier calculations, by making use of the fully rigorous treatment of the 5-dimensional consistent truncation, including the rigorous form of the boundary conditions. In both cases there is a parametrically light scalar glueball. In the first case, this is a physical state, while in the second case this result is unphysical, since the presence of higher-order operators in the dual field theory makes the whole (physical) spectrum depend explicitly on a (unphysical) UV-cutoff scale.