Different escape modes in two-photon double ionization of helium

The quadrupole channel of two-photon double ionization of He exhibits two distinctly different modes of correlated motion of the photoelectron pair. The mode associated with the center-of-mass motion favors a large total momentum which is maximazed at a parallel emission. However, the mode associated with the relative motion favors an antiparallel emission. This difference is manifested in a profoundly different width of the angular correlation functions corresponding to the center-of-mass and relative motion modes.Comment: 4 pages, 3 figure

Incoherent quantum feedback control of collective light scattering by Bose-Einstein condensates

It is well known that in the presence of a ring cavity the light scattering from a uniform atomic ensemble can become unstable resulting in the collective atomic recoil lasing. This is the result of a positive feedback due to the cavity. We propose to add an additional electronic feedback loop based on the photodetection of the scattered light. The advantage is a great flexibility in choosing the feedback algorithm, since manipulations with electric signals are very well developed. In this paper we address the application of such a feedback to atoms in the Bose-Einstein condensed state and explore the quantum noise due to the incoherent feedback action. We show that although the feedback based on the photodetection does not change the local stability of the initial uniform distribution with respect to small disturbances, it reduces the region of attraction of the uniform equilibrium. The feedback-induced nonlinearity enables quantum fluctuations to bring the system out of the stability region and cause an exponential growth even if the uniform state is globally stable without the feedback. Using numerical solution of the feedback master equation we show that there is no feedback-induced noise in the quadratures of the excited atomic and light modes. The feedback loop, however, introduces additional noise into the number of quanta of these modes. Importantly, the feedback opens an opportunity to position the modulated BEC inside a cavity as well as tune the phase of scattered light. This can find applications in precision measurements and quantum simulations.Comment: 7 pages, 7 figure

Diffractive jets production in pp-collisions

We consider the exclusive diffractive dissociation of a proton into three jets with large transverse momenta in the double-logarithmic approximation of perturbative QCD. This process is sensitive to the proton unintegrated gluon distribution at small x and to the proton light-cone distribution amplitudes. According to our estimates, an observation of such processes in the early runs at LHC is feasible for jet transverse momenta of the order of 5 GeV.Comment: Presented at International Workshop on Diffraction in High-Energy Physics, La Londe-les-Maures, France, September 9 - 14, 200

NLO Evolution of Color Dipoles in N = 4 SYM

The small-$x_B$ deep inelastic scattering in the saturation region is governed by the non-linear evolution of Wilson-line operators. In the leading logarithmic approximation it is given by the BK equation for the evolution of color dipoles. I discuss recent calculation of the next-to-leading order evolution of color dipoles in QCD and ${\cal N}=4$ SYM.Comment: 4 pages, Prepared for the International Workshop on Diffraction in High-Energy Physics in La Londe-les-Maures, France, 9-14 September 200

Nonlinear Regge Trajectories in Theory and Practice

The problems related to nonlinear behavior of Regge trajectories (RT) and their renormalization group invariance are discussed.Comment: The extended version of the talk at the International Workshop Diffraction-2008 (La Londe-les-Maures, France, September 9 - 14, 2008

Exclusive quasielastic production of dijets at hadronic colliders

We critically re-examine the calculation of central production of dijets in quasi-elastic hadronic collisions. We find that the process is not dominated by the perturbative contribution, and discuss several sources of uncertainties in the calculation.Comment: 4 pages, talk given at Diffraction-2008, La Londe-les-Maures, France, 9-14 Sept 200

Elastic positronium-atom scattering using the stochastic variational method

The stochastic variational method is used in conjunction with stabilization ideas to compute the low energy phase shifts and scattering lengths for positronium-atom scattering. Results are obtained for the Ps-H, Ps-Li+, Ps-He, and Ps-Ps systems. The Ps-H scattering lengths are probably accurate to better than 5% and are the most accurate so far computed. The results for Ps-Li+ and Ps-Ps scattering represent the first published scattering lengths for these systems. The positive scattering length for completely spin-aligned (3)Ps-(3)Ps scattering, namely 2.95a(o), is particularly significant since it demonstrates the feasibility of forming a stable Bose-Einstein condensate of (3)Ps atoms

Studying the Sivers function by model calculations

A formalism is presented to evaluate the Sivers function in constituent quark models. A non-relativistic reduction of the scheme is performed and applied to the Isgur-Karl model. The sign for the $u$ and $d$ flavor contributions that we obtained turns out to be opposite. The Burkardt Sum Rule is fulfilled to a large extent. After the estimate of the QCD evolution of the results from the momentum scale of the model to the experimental one, a reasonable agreement with the available data is obtained.Comment: To appear in the proceedings of Diffraction 2008: International Workshop On Diffraction In High Energy Physics, 9-14 Sep 2008, La Londe-les-Maures, France. Misprints corrected, reference adde

Prompt photon hadroproduction in the k_T-factorization approach

We study the production of prompt photons at high energy in the framework of the k_T-factorization approach. The amplitude for production of a single photon associated with quark pair in the fusion of two off-shell gluons is calculated. Theoretical results are compared with the Tevatron data.Comment: 4 pages, 3 figures, to be published in the Proceedings of Workshop "Diffraction 2008", La Londe-les-Maures, France, Sept. 9-14, 200

QCD and total cross-sections: photons and hadrons

In this contribution, we discuss a total cross-section model which can be applied to both photon and purely hadronic processes. We find that the model can reproduce photo-production cross-sections, as well as extrapolations of gamma* p processes to gamma p using vector meson dominance models, with minimal modifications from the proton case.Comment: 5 pages, 1 figure, to be published in Proceedings of Diffraction 2008, September 9-14 2008, Marseille, Franc