Nonlinear realisation of chiral symmetry breaking in holographic soft wall models

We investigate nonlinear extensions of the holographic soft wall model proposed by Karch, Katz, Son and Stephanov [1] with a positive quadratic dilaton. We consider a Higgs-like potential for the tachyonic field that brings a more natural realisation of chiral symmetry breaking in the infrared regime. Utilising the AdS/CFT dictionary and holographic renormalisation we find the chiral condensate as a function of the quark mass. The nonlinearity of the Higgs potential leads to a nonlinear relation between the chiral condensate and the quark mass. Solving the effective Schr\"odinger equations for the field perturbations we estimate meson masses and decay constants and evaluate their dependence on the quark mass. In the axial sector we find an interesting behaviour for the decay constants as the quark mass increases. We also investigate the effect of a 5d running mass for the tachyonic field. We conclude that nonlinear soft wall models with a positive quadratic dilaton do not provide spontaneous symmetry breaking in the chiral limit.