Dynamical soft-wall AdS/QCD

We present a solution of the five-dimensional gravity-dilaton-tachyon equations of motion with a pure AdS5 metric and a quadratic dilaton and linear tachyon in conformal coordinates. This leads to an infrared soft-wall model where the dilaton profile gives rise to linear Regge trajectories for the four-dimensional mass spectrum of the dual gauge theory. Even though our approach is phenomenological the scalar fields resemble the dilaton and the closed string tachyon of a noncritical string theory. Interestingly, the linear tachyon has the correct profile to imply that chiral symmetry is not restored for highly excited states. Our solution thus provides a dynamical bottom-up model of linear confinement in holographic QCD.