Marko Djurić

String-gauge dual description of deep inelastic scattering at small-x

The AdS/CFT correspondence in principle gives a new approach to deep inelastic scattering as formulated by Polchinski and Strassler. Subsequently Brower, Polchinski, Strassler and Tan (BPST) computed the strong coupling kernel for the vacuum (or Pomeron) contribution to total cross sections. By identifying deep inelastic scattering with virtual photon total cross section, this allows a self consistent description at small-x where the dominant contribution is the vacuum exchange process. Here we formulate this contribution and compare it with HERA small-x DIS scattering data. We find that the BPST kernel along with a very simple local approximation to the proton and current “wave functions” gives a remarkably good fit not only at large Q2 dominated by conformal symmetry but also extends to small Q2, supplemented by a hard-wall cut-off of the AdS in the IR. We suggest that this is a useful phenomenological parametrization with implications for other diffractive processes, such as double diffractive Higgs production.

Odderon in gauge/string duality

At high energies, elastic hadronic cross sections, such as pp, p, π±p, are dominated by vacuum exchange, which in leading order of the 1/Nc expansion has been identified as the BFKL Pomeron or its strong AdS dual the closed string Reggeized graviton [1]. However the difference of particle anti-particle cross sections are given by a so-called Odderon, carrying C = -1 vacuum quantum numbers identified in weak coupling with odd numbers of exchanged gluons. Here we show that in the dual description the Odderon is the Reggeized Kalb-Ramond field (Bμν) in the Neveu-Schwartz sector of closed string theory. To first order in strong coupling, the high energy contribution of the Odderon is evaluated for = 4 Super Yang-Mills by a generalization of the gravity dual analysis for the Pomeron in ref. [1]. The consequences of confinement on the Odderon are estimated in the confining QCD-like AdS5 hardwall model of Polchinski and Strassler [2].

Diffractive Higgs Production by AdS Pomeron Fusion

A bstractThe double diffractive Higgs production at central rapidity is formulated in terms of the fusion of two AdS gravitons/Pomerons first introduced by Brower, Polchinski, Strassler and Tan in elastic scattering. Here we propose a simple self-consistent holographic framework intended to provide new phenomenologically compelling estimates of diffractive cross sections at the LHC. As a first step, we evaluate the lowest order two Pomeron fusion diagram, fixing the overall normalization. The important suppression factor due to multiple Pomeron exchange (the “survival probability”) is presented in the eikonal approximation but its evaluation is left to future phenomenological analysis.

Strong Coupling Expansion for the Conformal Pomeron/Odderon Trajectories

A bstractFrom the perspective of AdS/CFT the Pomeron is identified with a Reggeized Graviton, while the Odderons correspond to Reggeized anti-symmetric AdS5 Kalb-Ramond tensor-fields. In this paper, we consider the strong coupling expansion of the dimension of the leading twist operators dual to these Regge trajectories, Δ(j), to determine its analytic continuation in j beyond the diffusion limit. In particular, we compute the strong coupling expansion of the intercept to order λ−3, where λ is the t’Hooft coupling, for both the Pomeron, which is C = +1 crossing-even, and the “Odderons”, which are the leading C = −1 crossing-odd Regge singularities. We discuss the spectral curves of the class of single-trace operators to which these string modes couple.

Vector meson production at low x from gauge/gravity duality

A bstractWe use gauge/gravity duality to study vector meson (J/Ψ, ρ0, Ω, Φ) production in electron-proton scattering, in the limit of high center of mass energy at fixed momentum transfer, corresponding to the limit of low Bjorken x, where the process is dominated by pomeron exchange. Our approach considers the pomeron at strong coupling, described by the graviton Regge trajectory in AdS space with a hard-wall to mimic confinement effects. Both the proton and vector mesons are described by simple holographic wave functions in AdS. This model agrees with HERA H1 data with a χ2 per degree of freedom below one on total cross-sections, and below two on differential cross-sections, confirming the success of previous studies that model low x DIS and DVCS using gauge/gravity duality.

Deeply virtual Compton scattering from gauge/gravity duality

We use gauge/gravity duality to study deeply virtual Compton scattering (DVCS) in the limit of high center of mass energy at fixed momentum transfer, corresponding to the limit of low Bjorken x, where the process is dominated by the exchange of the pomeron. At strong coupling, the pomeron is described as the graviton Regge trajectory in AdS space, with a hard wall to mimic confinement effects. This model agrees with HERA data in a large kinematical range. The behavior of the DVCS cross section for very high energies, inside saturation, can be explained by a simple AdS black disk model. In a restricted kinematical window, this model agrees with HERA data as well.

Soft Pomeron in Holographic QCD

We study the graviton Regge trajectory in Holographic QCD as a model for high energy scattering processes dominated by soft pomeron exchange. This is done by considering spin J fields from the closed string sector that are dual to glueball states of even spin and parity. In particular, we construct a model that governs the analytic continuation of the spin J field equation to the region of real J < 2, which includes the scattering domain of negative Maldelstam variable t. The model leads to approximately linear Regge trajectories and is compatible with the measured values of 1.08 for the intercept and 0.25 GeV

Saturation and Confinement: Analyticity, Unitarity and AdS/CFT Correspondence

^{-2}

Holographic Approach to Deep Inelastic Scattering at Small-x at High Energy

for the slope of the soft pomeron. The intercept of the secondary pomeron trajectory is in the same region of the subleading trajectories, made of mesons, proposed by Donnachie and Landshoff, and should therefore be taken into account.

Holographic double diffraction of Higgs and the AdS/CFT graviton/Pomeron

In