Dynamic AdS/QCD: A holographic approach to asymptotically free gauge theories

Abstract

Dynamic AdS/QCD is a bottom-up model inspired from top-down, probe-brane extensions to the renowned AdS/CFT correspondence. The AdS/CFT correspondence states that there is an equivalence in the physics describing an N = 4 super-Yang-Mills gauge theory and that pertaining to a type IIB superstring theory on an AdS5S5 background. Moreover, the duality between the two theories in a particular limit requires that the gauge theory be strongly coupled when the superstring theory is weakly coupled. From this, we have a tool for studying strongly coupled gauge theories in a physically equivalent gravitational description. Using the AdS/CFT correspondence as a springboard, relationships between more complex superstring constructions on varying backgrounds have been studied to push the dual gauge theory to be more like those of QCD. In this thesis, we use one such bottom-up model, Dynamic AdS/QCD, to probe the behaviours of strongly coupled, asymptotically free gauge theories, including QCD.We show that the model correctly describes the hyperscaling relations of quark masses and the condensate, the behaviours expected of the scalar, vector and axial meson spectra in theories with infrared fixed points and how the condensate is affected by temperature and magnetic field in such theories. We finally go on to show that it is possible to describe QCD-like theories with a Lorentz-symmetry breaking vacuum, e.g. a striped condensate, and follow up with the cosmological ramifications of such a proposal and conclude that outside of a totally disconnected dark sector, this behaviour is highly constrained.

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