Bound states and deconfinement from Romans supergravity with magnetic flux

TL;DR

This paper uses gauge-gravity duality to analyze bound states in a family of strongly coupled, confining 4D field theories via Romans supergravity, revealing a phase transition and scalar spectrum behavior.

Contribution

It provides a detailed holographic study of bound states and phase transitions in non-supersymmetric confining theories with magnetic flux using Romans supergravity.

Findings

Identified a first-order deconfinement phase transition triggered by magnetic flux.

Found two light scalar particles with suppressed, nearly degenerate masses.

Observed scalar mixing and mass suppression near the phase transition.

Abstract

We apply the dictionary of gauge-gravity dualities to study the spectrum of bound states in a special one-parameter family of strongly coupled, confining field theories in four dimensions. The top-down, holographic gravity dual description of this class of theories has been identified recently. It consists of non-supersymmetric regular background solutions of Romans half-maximal supergravity theory in six dimensions, in the presence of a non-trivial Abelian magnetic flux along a compactified direction of the geometry. A zero-temperature, deconfinement, first-order phase transition appears at one end of this branch of solutions. It is triggered by the strength of the flux, setting an upper bound on the magnitude of the magnetic flux that can be supported by the geometry. We compute the spectrum of fluctuations of the background fields in the gravity description, that correspond to field-theory bound states. Two scalar particles are the lightest in the spectrum, their masses being suppressed and almost degenerate across the whole parameter space. Away from the transition, the heaviest between these two particles is identified as a dilaton, the pseudo-Nambu-Goldstone boson associated with scale invariance. It couples to the trace of the stress-energy tensor of the dual field theory, while the lightest scalar does not. In the range of parameter space closest to the extremum of the one-parameter family, near the first-order phase transition, a region with large curvature appears at the end of space of the geometry of the solutions. In this range, the two scalars mix non-trivially, and their masses are parametrically suppressed, in respect to the other bound states.