Light and Heavy Hadrons in AdS/QCD

Abstract

We discuss light and heavy hadrons in a holographic soft-wall AdS/QCD model. This approach is based on an action which describes hadron structure with broken conformal and chiral invariance and incorporates confinement through the presence of a background dilaton field. According to the gauge/gravity duality the five-dimensional boson and fermion fields propagating in AdS space are dual to four-dimensional fields leaving on the surface of AdS sphere, which correspond to hadrons. In this picture hadronic wave functions — basics blocks of hadronic properties — are dual to the profiles of AdS fields in the fifth (holographic) dimension, which is identified with scale variable. As applications we consider properties of light and heavy hadrons from unified point of view: mass spectrum, form factors, decay rates and parton distributions. Based on the gauge/gravity duality [1], a class of AdS/QCD approaches which model QCD by using methods of extra-dimensional field theories formulated in anti-de Sitter (AdS) space, was recently successfully developed for describing the phenomenology of hadronic properties (for a recent review see e.g. [2]). One of the popular formalisms of this kind is the “soft-wall” model [3]-[6] which uses a soft infrared (IR) cuto in the fifth dimension. This pro cedure can be introduced in the following ways: i) as a background field (dilaton) in the overall exponential of the action (“dilaton” soft-wall model), ii) in the warping factor of the AdS metric (“metric” soft-wall model), iii) in the eective potential of the action. In Ref. [5] we showed that these three ways of proceeding are equivalent to each other via a redefinition of the bulk fields and by inclusion of extra eective potentials in the action. In our opinion, the ”dil aton” form of the soft-wall model is more convenient in performing the calculations. In this paper we consider such type of soft-wall AdS/QCD approach. We report the applications of our approach to the properties of light and heavy hadrons. In particular, we present results for hadronic mass spectra, coupling constants and form factors [4]-[6].