Robi Peschanski

Boost-invariant early time dynamics from AdS/CFT

Boost-invariant dynamics of a strongly-coupled conformal plasma is studied in the regime of early proper-time using the AdS/CFT correspondence. It is shown, in contrast with the late-time expansion, that a scaling solution does not exist. The boundary dynamics in this regime depends on initial conditions encoded in the bulk behavior of a Fefferman-Graham metric coefficient at initial proper-time. The relation between the early-time expansion of the energy density and initial conditions in the bulk of AdS is provided. As a general result it is proven that a singularity of some metric coefficient in Fefferman-Graham frame exists at all times. Requiring that this singularity at ? = 0 is a mere coordinate singularity without the curvature blow-up gives constraints on the possible boundary dynamics. Using a simple Pade resummation for solutions satisfying the regularity constraint, the features of a transition to local equilibrium, and thus to the hydrodynamical late-time regime, have been observed. The impact of this study on the problem of thermalization is discussed.

Exclusive vector meson production at HERA from QCD with saturation

Following recent predictions that the geometric scaling properties of deep inelastic scattering data in inclusive

Entropy flow of a perfect fluid in (1+1) hydrodynamics

{\ensuremath{\gamma}}^{*}p

Systematics of geometric scaling

collisions are expected also in exclusive diffractive processes, we investigate the diffractive production of vector mesons. Using analytic results in the framework of the Balitsky-Kovchegov (BK) equation at nonzero momentum transfer, we extend to the nonforward amplitude a QCD-inspired forward saturation model including charm, following the theoretical predictions for the momentum transfer dependence of the saturation scale. We obtain a good fit to the available HERA data and make predictions for deeply virtual Compton scattering measurements.

Consequences of strong fluctuations on high-energy QCD evolution

Using the formalism of the Khalatnikov potential, we derive exact general formulae for the entropy flow dS/dy, where y is the rapidity, as a function of temperature for the (1+1) relativistic hydrodynamics of a perfect fluid. We study in particular flows dominated by a sufficiently long hydrodynamic evolution, and provide an explicit analytical solution for dS/dy. We discuss the theoretical implications of our general formulae and some phenomenological applications for heavy-ion collisions.

Traveling waves and geometric scaling at nonzero momentum transfer

Abstract Using all available data on the deep-inelastic cross-sections at HERA at x ⩽ 10 −2 , we look for geometric scaling of the form σ γ ∗ p ( τ ) where the scaling variable τ behaves alternatively like log Q 2 − λ Y , as in the original definition, or log Q 2 − λ Y , which is suggested by the asymptotic properties of the Balitsky–Kovchegov (BK) equation with running QCD coupling constant. A “Quality Factor” (QF) is defined, quantifying the phenomenological validity of the scaling and the uncertainty on the intercept λ . Both choices have a good QF, showing that the second choice is as valid as the first one, predicted for fixed coupling constant. A comparison between the QCD asymptotic predictions and data is made and the QF analysis shows that the agreement can be reached, provided going beyond leading logarithmic accuracy for the BK equation.

Sensitivity to the standard model Higgs boson in exclusive double diffraction

We investigate the behavior of the QCD evolution towards high energy, in the diffusive approximation, in the limit where the fluctuation contribution is large. Our solution for the equivalent stochastic Fisher equation predicts the amplitude as well as the whole set of correlators in the strong-noise limit. The speed of the front and the diffusion coefficient are obtained. We analyze the consequences on high-energy evolution in QCD.

Diffractive χ production at the Tevatron and the LHC

Abstract We extend the search for traveling-wave asymptotic solutions of the nonlinear Balitsky–Kovchegov (BK) saturation equation to non-forward dipole–target amplitudes. Making use of conformal invariant properties of the Balitsky–Fadin–Kuraev–Lipatov (BFKL) kernel, we exhibit traveling-wave solutions in momentum space in the region where the momentum transfer q is smaller than the characteristic scale Q of the projectile. We prove geometric scaling in the variable Q / q Ω s ( Y ) , where Ω s ( Y ) has the same energy dependence as in the forward analysis space. Consequences for phenomenology are drawn.

High Energy Bounds on Soft N=4 SYM Amplitudes from AdS/CFT

We use a Monte Carlo implementation of recently developed models of double diffraction to assess the sensitivity of the LHC experiments to standard model Higgs bosons produced in exclusive double diffraction. The signal is difficult to extract, due to experimental limitations related to the first level trigger, and to contamination by inclusive double diffractive background. Assuming these difficulties can be overcome, the expected signal-to-background ratio is presented as a function of the experimental resolution on the missing mass. With a missing mass resolution of 2 GeV, a signal-to-background ratio of about 0.5 is obtained; a resolution of 1 GeV brings a signal to background ratio of 1. This result is lower than previous estimates, and the discrepancy is explained.

A Global analysis of inclusive diffractive cross sections at HERA

Abstract We present predictions for the diffractive production of χ mesons in the central rapidity region usually covered by collider detectors. The predicted cross sections are based on the Bialas–Landshoff formalism for both exclusive and inclusive productions and make use of the DPEMC Monte Carlo simulation adapted with kinematics appropriate for small-mass diffractive production. We compare generator-level results with a CDF measurement for exclusive χ production, and study background and other scenarios including the contribution of inclusive χ production. The results agree with the Tevatron data and are extrapolated, highlighting the exclusive χ c 0 production at LHC energies. A possible new measurement at the Tevatron using the DO forward detectors is investigated, taking advantage of the dominance of exclusive production for high enough diffractive mass fraction.