Nonlinear Boundary Dynamics and Chiral Symmetry in Holographic QCD

TL;DR

This paper explores nonlinear boundary dynamics in holographic QCD models, showing they are essential for accurate chiral symmetry breaking descriptions and that classical calculations remain reliable despite improvements.

Contribution

It introduces nonlinear boundary conditions in holographic QCD to better capture chiral symmetry breaking, linking them to Sturm-Liouville systems and demonstrating their impact on observables.

Findings

Nonlinear boundary conditions are necessary for correct chiral symmetry breaking.

Classical calculations remain accurate with the improved boundary conditions.

Observables insensitive to the chiral limit are only slightly affected.

Abstract

In a hard-wall model of holographic QCD, we find that nonlinear boundary dynamics are required in order to maintain the correct pattern of explicit and spontaneous chiral symmetry breaking beyond leading order in the pion fields. With the help of a field redefinition, we relate the requisite nonlinear boundary conditions to a standard Sturm-Liouville system. Observables insensitive to the chiral limit receive only small corrections in the improved description, and classical calculations in the hard-wall model remain surprisingly accurate.