Nonperturbative Quark Sea Asymmetries

The effects of nonperturbatively generated ``quark sea'' have been investigated to determine the flavor structure of the octet baryons. The chiral constituent quark model ($\chi$CQM), which is known to provide a satisfactory explanation of the proton spin and related issues in the nonperturbative regime, is able to explain the qualitative generation of the requisite amount of quark sea. The importance of quark sea has been studied at different values of the Bjorken scaling variable $x$ by including it phenomenologically in the sea quark distribution functions. The results for the quark sea asymmetries like $\bar d(x)-\bar u(x)$, $\bar d(x)/\bar u(x)$ and Gottfried integral for the octet baryons strengthen the significance of quark sea at lower values of $x$.Comment: 9 pages. Presented at the Gribov-80 Memorial Workshop on Quantum Chromodynamics and Beyond held at ICTP, Trieste in May 2010. (To appear in the World Scientific Proceedings

Single Transverse Spin Asymmetries in Semi-inclusive Deep Inelastic Scattering in a Spin-1 Diquark Model

The observed results for the azimuthal single spin asymmetries (SSAs) of the proton, measured in the semi-inclusive deep inelastic scattering (SIDIS), can be explained by the final-state interaction (FSI) from the gluon exchange between the outgoing quark and the target spectator system. SSAs require a phase difference between two amplitudes coupling the target with opposite spins to the same final state. We have used the model of light front wave functions (LFWFs) consisting of a spin-$\frac{1}{2}$ system as a composite of a spin-$\frac{1}{2}$ fermion and a spin-1 vector boson to estimate the SSAs. The implications of such a model have been investigated in detail by considering different coupling constants. The FSIs also produce a complex phase which can be included in the LFWFs to calculate the Sivers and Boer-Mulders distribution functions of the nucleon.Comment: 23 pages, 4 figures. To appear in Eur. Phys. J.

Wigner distributions and GTMDs in a proton using light-front quark-diquark model

We investigate the Wigner distributions and generalized transverse momentum-dependent distributions (GTMDs) for $u$ and $d$ quarks in the proton by using light-front quark-diquark model. We consider the contribution of scalar and axial-vector diquark having spin-0 and spin-1 respectively. We take different polarization configurations of quark and proton to calculate the Wigner distributions. The Wigner distributions are studied in the impact-parameter space, momentum space and mixed space for $u$ and $d$ quarks in the proton. We also study the relation of GTMDs with longitudinal momentum fraction carried by the active quark $x$ for different values of $\zeta$ (skewness) which is defined as the longitudinal momentum transferred to the proton. Further, we study the GTMDs in the relation with $x$ for zero skewness $(\zeta=0)$ at different values of quark transverse momentum $\textbf{p}_\perp$ as well as at different values of total momentum transferred to the proton ${\bf \Delta}_\perp$.Comment: 40 pages, 17 figures. To appear in Nucl. Phys.