Asymmetry distributions and mass effects in dijet events at a polarized HERA

The asymmetry distributions for several kinematic variables are considered for finding a systematic way to maximize the signal for the extraction of the polarized gluon density. The relevance of mass effects for the corresponding dijet cross section is discussed and the different approximations for including mass effects are compared. We also compare via the programs Pepsi and Mepjet two different Monte Carlo (MC) approaches for simulating the expected signal in the dijet asymmetry at a polarized HERA.Comment: 18 pages, LaTeX, minor stylistic changes for Z.Phys.

Note on Moufang-Noether currents

The derivative Noether currents generated by continuous Moufang tranformations are constructed and their equal-time commutators are found. The corresponding charge algebra turns out to be a birepresentation of the tangent Mal'ltsev algebra of an analytic Moufang loop.Comment: LaTeX2e, 6 pages, no figures, presented on "The XVth International Colloquium on Integrable Systems and Quantum Symmetries, Prague, 15-17 June, 2006

Reduced sigma-model on AdS_5 x S^5: one-loop scattering amplitudes

We compute one-loop S-matrix in the reduced sigma-model which describes AdS_5 x S^5 string theory in the near-flat-space limit. The result agrees with the corresponding limit of the S-matrix in the full sigma-model, which demonstrates the consistency of the reduction at the quantum level.Comment: 9 pages, 1 figure; v2: reference added; v3: misprint in (3.6) corrected; v4: typo in (3.4) corrected; v5: new form of the actio

Transient absorption and reshaping of ultrafast XUV light by laser-dressed helium

We present a theoretical study of transient absorption and reshaping of extreme ultraviolet (XUV) pulses by helium atoms dressed with a moderately strong infrared (IR) laser field. We formulate the atomic response using both the frequency-dependent absorption cross section and a time-frequency approach based on the time-dependent dipole induced by the light fields. The latter approach can be used in cases when an ultrafast dressing pulse induces transient effects, and/or when the atom exchanges energy with multiple frequency components of the XUV field. We first characterize the dressed atom response by calculating the frequency-dependent absorption cross section for XUV energies between 20 and 24 eV for several dressing wavelengths between 400 and 2000 nm and intensities up to 10^12 W/cm^2. We find that for dressing wavelengths near 1600 nm, there is an Autler-Townes splitting of the 1s ---> 2p transition that can potentially lead to transparency for absorption of XUV light tuned to this transition. We study the effect of this XUV transparency in a macroscopic helium gas by incorporating the time-frequency approach into a solution of the coupled Maxwell-Schr\"odinger equations. We find rich temporal reshaping dynamics when a 61 fs XUV pulse resonant with the 1s ---> 2p transition propagates through a helium gas dressed by an 11 fs, 1600 nm laser pulse.Comment: 13 pages, 8 figures, 1 table, RevTeX4, revise

Generalized Parton Distributions in Full Lattice QCD

We present recent results on generalized parton distributions from dynamical lattice QCD calculations. Our set of twelve different combinations of couplings and quark masses allows for a preliminary study of the pion mass dependence of the transverse nucleon structure.Comment: 8 pages, 5 figures; Talk presented by Ph.H. at Light-Cone 2004, Amsterdam, 16 - 20 Augus

A lattice study of the strangeness content of the nucleon

We determine the quark contributions to the nucleon spin Delta s, Delta u and Delta d as well as their contributions to the nucleon mass, the sigma-terms. This is done by computing both, the quark line connected and disconnected contributions to the respective matrix elements, using the non-perturbatively improved Sheikholeslami-Wohlert Wilson Fermionic action. We simulate n_F=2 mass degenerate sea quarks with a pion mass of about 285 MeV and a lattice spacing a = 0.073 fm. The renormalization of the matrix elements involves mixing between contributions from different quark flavours. The pion-nucleon sigma-term is extrapolated to physical quark masses exploiting the sea quark mass dependence of the nucleon mass. We obtain the renormalized value sigma_{piN}=38(12) MeV at the physical point and the strangeness fraction f_{Ts}=sigma_s/m_N=0.012(14)(+10-3) at our larger than physical sea quark mass. For the strangeness contribution to the nucleon spin we obtain in the MSbar scheme at the renormalization scale of 2.71 GeV Delta s = -0.020(10)(2).Comment: 7 pages, 3 figures, Invited Talk at the 33rd Erice School on Nuclear Physics, Erice, 16-24 September 2011, Ital

Singlet VA \tilde V correlator within the instanton vacuum model

The correlator of singlet axial-vector and vector currents in the external electromagnetic field is studied within the instanton liquid model of QCD vacuum. In the chiral limit we calculate the longitudinal w_L^0 and transversal w_T^0 with respect to axial-vector index invariant amplitudes at arbitrary momentum transfer q. It is demonstrated how the anomalous longitudinal part of the correlator is renormalized at low momenta due to the presence of the U_A(1) anomaly.Comment: 9 pages, 4 figure