Improved Holographic Models for QCD

by Elias Kiritsis (Ecole Polytechnique, Paris, and Heraklion Univ, Greece)

Tuesday 28 Aug 2007, 14:00 → 15:30 Europe/Zurich

TH Theory Conference Room (CERN)

Holographic approaches to QCD in five dimensions are explored using input both from the putative non-critical string theory as well as QCD. It is argued that a gravity theory in five dimensions coupled to a dilaton and an axion may capture the important qualitative features of pure QCD. A part of the higher $\a'$-corrections are resummed into a dilaton potential. The potential is shown to be in one-to-one correspondence with the exact $\beta$-function of QCD, and its knowledge determines the full structure of the vacuum solution. The geometry near the UV boundary is that of AdS$_5$ with logarithmic corrections reflecting the asymptotic freedom of QCD. The IR confining geometries are classified and analyzed. They all end in a ``good" (repulsive) singularity in the IR where the 't Hooft coupling is driven to infinity. The glueball spectra are gaped and discrete, and they favorably compare to the lattice data. Quite generally, confinement and discrete spectra imply each other. Asymptotically linear glueball masses can also be achieved. Asymptotic mass ratios of various glueballs with different spin also turn out to be universal. Mesons dynamics is implemented via space filling $D_4-\bar D_4$ brane pairs. The associated tachyon dynamics is analyzed and chiral symmetry breaking is shown. The dynamics of the RR axion is analyzed, and the non-perturbative running of the QCD $\theta$-angle is obtained. It is shown to always vanish in the IR.