Deep inelastic structure functions from supergravity at small x

Deep inelastic structure functions can be calculated from supergravity when the Bjorken parameter $x$ satisfies $x > 1/\sqrt{gN}$. We consider a gauge theory with very large 't Hooft coupling $gN$ in order to investigate the region $x << 1$. In this case the center of mass energy is large enough to increase the number of hadronic constituents of the final state. We calculate the structure functions in terms of the number of final hadronic constituents. At small $x$ we find a scaling law similar to geometric scaling but with $\gamma_s = 0.5$ and $\lambda = 1$.Comment: In V1 we assumed the transversality of the 4-d hadronic tensor but considered a non conserved 5-d current that spoils this property. In this V2 we define a modified conserved 5-d current that solves this problem and preserves our previous results for the structure functions. We also clarify the meaning of our final hadronic state. 14 pgs., 1 latex fi

On a Holographic Model for Confinement/Deconfinement

We study the thermodynamics of the hard wall model, which consists in the introduction of an infrared cut-off in asymptotically AdS spaces. This is a toy model for confining backgrounds in the context of the gauge/gravity correspondence. We use holographic renormalization and reproduce the existence of a Hawking Page phase transition recently discussed by Herzog. We also show that the entropy jumps from $N^0$ to $N^2$, which reinforces the interpretation of this transition as the gravity dual of confinement/deconfinement. We also show that similar results hold for the phenomenologically motivated soft wall model, underlining the potential universality of our analysis.Comment: 14 pages. V2: We included a new section discussing the soft wall model and new references. V3: We clarified some points and updated the references. Results unchanged. Version published in PR