Triangular Seminar Elias Kiritsis (Ecole Polytechnique, CPHT)
Various holographic approaches to QCD in five dimensions are explored using input both from the perturbative five-dimensional 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 YM theory. A part of the effects of higher a'-corrections is 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 AdS5 with logarithmic corrections reflecting the asymptotic freedom of QCD. The IR confining geometries are classified and analyzed. Near the singularity the 't Hooft coupling is driven to infinity. The glueball spectra are gapped 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. Meson dynamics is implemented via space filling D4-anti D4 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. The finite temperature structure is also analyzed and phase diagram is studied. Our preliminary results show a first order deconfining transition to a QGP phase with a transition temperature in agreement with lattice data.