B-Mesons on the Transverse Lattice

We present results from a first study of $B$-mesons that is based on a transverse lattice formulation of light-front QCD. The shape of the Isgur-Wise form factor is in very good agreement with experimental data. However, the calculations yield rather large values for $f_B$ and $\bar{\Lambda}$ compared to contemporary calculations based on other techniques.Comment: invited talk given at CSSM workshop on `Lattice Hadron Physics', Cairns, July 2001 and at ECT* workshop on `Light-cone Physics: Particles and String', Trento, Sept. 200

Quark Correlations and Single Spin Asymmetries

We analyze the Sivers asymmetry in light-cone gauge. The average transverse momentum of the quark distribution is related to the correlation between the quark distribution and the transverse component of the gauge field at $x^-\pm \infty$. We then use finiteness conditions for the light-cone Hamiltonian to relate the transverse gauge field at $x^-=\pm \infty$ to the color density integrated over $x^-$. This result allows us to relate the average transverse momentum of the active quark to color charge correlations in the transverse plane.Comment: 8 pages, 1 figur

Some Inequalities for the Generalized Parton Distribution E(x,0,t)

We discuss some constraints on the $x$ and $t$-dependence of $E(x,0,t)$ that arise from positivity bounds in the impact parameter representation. In addition, we show that $E(x,0,0)$ for the nucleon vanishes for $x\to 1$ at least as rapidly as $(1-x)^4$. Finally we provide an inequality that limits the contribution from $E$ to the angular momentum sum rule.Comment: 3 page

Nucleon spin densities in a light-front constituent quark model

The first moment of longitudinal and transverse spin densities of quarks in the nucleon are calculated in a light-front constituent quark model for the different cases of quark and nucleon polarization. Significant distortions are found for the transverse spin densities. In particular the Sivers function is predicted with opposite sign for up and down quarks and the Boer-Mulders function is predicted large and negative for both up and down quarks, in agreement with lattice calculations. Quite a different spin distribution is obtained for up and down quarks in the cases of quarks and proton transversely or longitudinally polarized in the same direction.Comment: one reference added; to be published in Phys. Lett.

Impact Parameter Space Interpretation for Generalized Parton Distributions

The Fourier transform of generalized parton distribution functions at xi=0 describes the distribution of partons in the transverse plane. The physical significance of these impact parameter dependent parton distribution functions is discussed. In particular, it is shown that they satisfy positivity constraints which justify their physical interpretation as a probability density. The generalized parton distribution H is related to the impact parameter distribution of unpolarized quarks for an unpolarized nucleon, H-tilde is related to the distribution of longitudinally polarized quarks in a longitudinally polarized nucleon, and $E$ is related to the distortion of the unpolarized quark distribution in the transverse plane when the nucleon has transverse polarization.Comment: addtl. corrections, 34 page

Generalized Parton Distributions for large xx

The $t$-dependence of generalized parton distrbutions for $x\to 1$ is discussed. We argue that constituent quark models, where the $t$-dependence for $x\to 1$ is through the product $(1-x)t$, are inconsistent. Instead we suggest a leading dependence in terms of $(1-x)^n t$, where $n\geq 2$, for $x\to 1$.Comment: 4 pages, revte

Chromodynamic Lensing and Transverse Single Spin Asymmetries

We illustrate how an axial asymmetry in impact parameter dependent parton distributions can give rise to an axial asymmetry for the transverse momentum of the leading quark in the photo-production of hadrons. The effect is related to the asymmetry originating from the Wilson-line phase factor in gauge invariant Sivers distributions. The single spin asymmetry arising from the asymmetry of the impact parameter dependent parton distributions is shown to exhibit a pure $\sin \phi$ dependence.Comment: 6 page