Collins Fragmentation and the Single Transverse Spin Asymmetry

We study the Collins mechanism for the single transverse spin asymmetry in the collinear factorization approach. The correspondent twist-three fragmentation function is identified. We show that the Collins function calculated in this approach is universal. We further examine its contribution to the single transverse spin asymmetry of semi-inclusive hadron production in deep inelastic scattering and demonstrate that the transverse momentum dependent and twist-three collinear approaches are consistent in the intermediate transverse momentum region where both apply.Comment: 10 pages, 2 figure

Structured variable selection and estimation

In linear regression problems with related predictors, it is desirable to do variable selection and estimation by maintaining the hierarchical or structural relationships among predictors. In this paper we propose non-negative garrote methods that can naturally incorporate such relationships defined through effect heredity principles or marginality principles. We show that the methods are very easy to compute and enjoy nice theoretical properties. We also show that the methods can be easily extended to deal with more general regression problems such as generalized linear models. Simulations and real examples are used to illustrate the merits of the proposed methods.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS254 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

On Primordial Perturbations of Test Scalar Fields

The primordial perturbations of test scalar fields not affecting the evolution of background may be very interesting since they can be transferred to the curvature perturbations by some mechanisms, and thus under certain condition can be responsible for the structure formation of observable universe. In this brief report we study the primordial perturbations of test scalar fields in various (super)accelerated expanding backgrounds.Comment: 4 pages, no figures, clarifications and refs. added, typos corrected, to publish in PR

Moduli and K\"ahler potential in fermionic strings

We study the problem of identifying the moduli fields in fermionic four-dimensional string models. We deform a free-fermionic model by introducing exactly marginal operators in the form of Abelian Thirring interactions on the world-sheet, and show that their couplings correspond to the untwisted moduli fields. We study the consequences of this method for simple free-fermionic models which correspond to $Z_2\times Z_2$ orbifolds and obtain their moduli space and K\"ahler potential by symmetry arguments and by direct calculation of string scattering amplitudes. We then generalize our analysis to more complicated fermionic structures which arise in constructions of realistic models corresponding to asymmetric orbifolds, and obtain the moduli space and K\"ahler potential for this case. Finally we extend our analysis to the untwisted matter sector and derive expressions for the full K\"ahler potential to be used in phenomenological applications, and the target space duality transformations of the corresponding untwisted matter fields.Comment: 27pp Latex text, no figs, CERN-TH.7259/94, CTP-TAMU-14/94 and ACT-06/9

Hadronic Dijet Imbalance and Transverse-Momentum Dependent Parton Distributions

We compare several recent theoretical studies of the single transverse spin asymmetry in dijet-correlations at hadron colliders. We show that the results of these studies are all consistent. To establish this, we investigate in particular the two-gluon exchange contributions to the relevant initial and final state interactions in the context of a simplifying model. Overall, the results confirm that the dijet imbalance obeys at best a non-standard or "generalized" transverse-momentum-dependent factorization.Comment: 13 pages, 3 figure

Deep-subwavelength features of photonic skyrmions in a confined electromagnetic field with orbital angular momentum

In magnetic materials, skyrmions are nanoscale regions where the orientation of electron spin changes in a vortex-type manner. Here we show that spin-orbit coupling in a focused vector beam results in a skyrmion-like photonic spin distribution of the excited waveguided fields. While diffraction limits the spatial size of intensity distributions, the direction of the field, defining photonic spin, is not subject to this limitation. We demonstrate that the skyrmion spin structure varies on the deep-subwavelength scales down to 1/60 of light wavelength, which corresponds to about 10 nanometre lengthscale. The application of photonic skyrmions may range from high-resolution imaging and precision metrology to quantum technologies and data storage where the spin structure of the field, not its intensity, can be applied to achieve deep-subwavelength optical patterns