We study pion condensation at zero temperature in a hard-wall holographic
model of hadrons with isospin chemical potential. We find that the transition
from the hadronic phase to the pion condensate phase is first order except in a
certain limit of model parameters. Our analysis suggests that immediately
across the phase boundary the condensate acts as a stiff medium approaching the
Zel'dovich limit of equal energy density and pressure.Comment: 19 pages, 7 eps figure
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.
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