Improved soft-wall model with a negative dilaton

TL;DR

This paper modifies the soft-wall AdS/QCD model by changing the dilaton sign to better implement confinement and chiral symmetry breaking, resulting in realistic meson spectra and eliminating unphysical states.

Contribution

It introduces a negative dilaton in the soft-wall model, leading to improved IR behavior and consistent meson spectra, especially regarding chiral symmetry and the elimination of unphysical states.

Findings

The scalar field approaches a constant in the IR, avoiding divergence.

The model guarantees Regge trajectories for mesons.

Unphysical massless states in the vector channel can be removed.

Abstract

I propose to change the sign of the dilaton in the infrared~(IR) soft-wall AdS/QCD model, in order to implement confinement. The deformed model exhibits interesting properties, especially in describing chiral symmetry breaking. The expectation value of the scalar field $X$, which determines the quark mass and condensate, approaches a constant in the IR limit, rather than blows up in the original model. In contrast to the estimate in Ref. \cite{Shifman:2007xn}, this kind of solution will not lead to chiral symmetry restoration for highly-excited states, due to the property of the harmonic-oscillator equation. Instead, it will guarantee the Regge behavior of the axial meson spectrum, and also the pseudoscalar mesons. The value of the condensate can be fixed by requiring that the pion be massless in the chiral limit, but only under some approximation in the present model. We also find that, by relaxing the IR boundary conditions, the unphysical massless state in the vector channel can be eliminated.