We propose a physically motivated parametrization for the unpolarized generalized parton distributions. At zero value of the skewness variable, ζ, the parametrization is constrained by simultaneously fitting the experimental data on both the nucleon elastic form factors and the deep inelastic structure functions. A rich phenomenology can be addressed based on this parametrization. In particular, we track the behavior of the average: i) interparton distances as a function of the momentum fraction, X, ii) X as a function of the four-momentum transfer, t; iii) the intrinsic transverse momentum k ⊥ as a function of X. We discuss the extension of our parametrization to ζ = 0 where additional constraints are provided by higher moments of the generalized parton distributions obtained from ab initio lattice QCD calculations.

Exclusive o electroproduction from nucleons is suggested for extracting the tensor charge and other quantities related to transversity from experimental data. This process isolates C-parity odd and chiral-odd combinations of t-channel exchange quantum numbers. In a hadronic picture it connects the meson production amplitudes to C-odd Regge exchanges with final state interactions. In a description based on partonic degrees of freedom, the helicity structure for this C-odd process relates to the quark helicity flip, or chiral-odd generalized parton distributions. This differs markedly from deeply virtual Compton scattering, and both vector meson and charged electroproduction, where the axial charge can enter the amplitudes. Contrarily, the tensor charge enters the o process. The connection through the helicity description of the process to both the partonic and hadronic perspectives is studied and exploited in model calculations to indicate how the tensor charge and other transversity parameters can be related to cross section and spin asymmetry measurements over a broad range of kinematics.

First passage in a stochastic process may be influenced by the presence of an external confining potential, as well as "stochastic resetting" in which the process is repeatedly reset back to its initial position. Here we study the interplay between these two strategies, for a diffusing particle in an onedimensional trapping potential V (x), being randomly reset at a constant rate r. Stochastic resetting has been of great interest as it is known to provide an 'optimal rate' (r * ) at which the mean first passage time is a minimum. On the other hand an attractive potential also assists in first capture process. Interestingly, we find that for a sufficiently strong external potential, the advantageous optimal resetting rate vanishes (i.e. r * → 0). We derive a condition for this optimal resetting rate vanishing transition, which is continuous. We study this problem for various functional forms of V (x), some analytically, and the rest numerically. We find that the optimal rate r * vanishes with the deviation from critical strength of the potential as a power law with an exponent β which appears to be universal. PACS number(s): 05.40.-a,02.50.-r,02.50.Ey

In an effort to clarify the significance of the recent observation of long-range topological charge coherence in QCD gauge configurations, we study the local topological charge distributions in twodimensional CP Nÿ1 sigma models, using the overlap Dirac operator to construct the lattice topological charge. We find long-range sign coherence of topological charge along extended one-dimensional structures in two-dimensional spacetime. We discuss the connection between the long-range topological structure found in CP Nÿ1 and the observed sign coherence along three-dimensional sheets in fourdimensional QCD gauge configurations. In both cases, coherent regions of topological charge form along membranelike surfaces of codimension one. We show that the Monte Carlo results, for both twodimensional and four-dimensional gauge theory, support a view of topological charge fluctuations suggested by Lüscher and Witten. In this framework, the observed membranes are associated with boundaries between ''k-vacua,'' characterized by an effective local value of which jumps by 2 across the boundary.

We propose a physically motivated parametrization for the unpolarized generalized parton distributions, H and E, valid at both zero and non-zero values of the skewness variable, ζ. Our approach follows a previous detailed study of the ζ = 0 case where H and E were determined using constraints from simultaneous fits of the experimental data on both the nucleon elastic form factors and the deep inelastic structure functions in the non singlet sector. Additional constraints at ζ = 0 are provided by lattice calculations of the higher moments of generalized parton distributions. We illustrate a method for extracting generalized parton distributions from lattice moments based on a reconstruction using sets of orthogonal polynomials. The inclusion in our fit of data on Deeply Virtual Compton Scattering is also discussed. Our method provides a step towards an extraction of generalized distributions based on a global fit of the available data within the given set of constraints.