Phenomenology of the Flavor-Asymmetry in the Light-Quark Sea of the Nucleon

A phenomenological ansatz for the flavor-asymmetry of the light sea distributions of the nucleon, based on the Pauli exclusion principle, is proposed. This ansatz is compatible with the measured flavor-asymmetry of the unpolarized sea distributions, $\bar{d}>\bar{u}$, of the nucleon. A prediction for the corresponding polarized flavor-asymmetry is presented and shown to agree with predictions of (chiral quark--soliton) models which successfully reproduced the flavor-asymmetry of the unpolarized sea.Comment: 5 pages, LaTeX, 2 figures, uses epsfi

The Photon Structure Function at Small-x

It is shown that recent small-x measurements of the photon structure function F_2^{\gamma}(x,Q^2) by the LEP-OPAL collaboration are consistent with parameter-free QCD predictions at all presently accessible values of Q^2.Comment: 7 pages, LaTeX, 2 figure

Extraction of Polarized Gluon Distributions from Large-pt Light Hadron Pair Production

We propose a new formula for extracting the polarized gluon distribution from the large-$p_T$ light hadron pair production for semi-inclusive processes in polarized deep inelastic scattering. In general, a large-$p_T$ hadron pair is produced via photon-gluon fusion(PGF) and QCD Compton at the lowest order of QCD. The PGF gives us a direct information on $\Delta g$ in the nucleon, while QCD Compton becomes background to the signal process for extracting $\Delta g$. We show that the contribution from this background, i.e. the QCD Compton process, can be removed by using symmetry relation among fragmentation functions and taking an appropriate combination of various light hadron pair production processes, and thus the double spin asymmetry can be described in terms of $\Delta g/g$ alone.Comment: 14 pages 3 EPS figures Late

Has the QCD RG-Improved Parton Content of Virtual Photons been Observed?

It is demonstrated that present $e^+e^-$ and DIS ep data on the structure of the virtual photon can be understood entirely in terms of the standard `naive' quark--parton model box approach. Thus the QCD renormalization group (RG) improved parton distributions of virtual photons, in particular their gluonic component, have not yet been observed. The appropriate kinematical regions for their future observation are pointed out as well as suitable measurements which may demonstrate their relevance.Comment: 24 pages, LaTeX, 5 figure

New proton polarized structure functions in charged current processes at HERA

Estimates for longitudinal spin asymmetries which single out new polarized nucleon structure functions in deeply inelastic charged current interactions at HERA energies are given, exploiting their interpretation in terms of polarized quark distributions. These asymmetries turn out to be large and allow a measurement of the new polarized structure functions $g_1^{W}$ and $g_5^{W}$, which would add valuable tests and information on the spin content of quarks inside a polarized proton. We also show that single spin asymmetries in neutral current interactions are very small.Comment: LaTeX, 8 pages, 6 figure

On dynamically generated parton distribution functions and their properties

The idea of ``dynamically'' generated parton distribution functions, based on regular initial conditions at low momentum scale, is reanalyzed with particular emphasize paid to its compatibility with the factorization mechanism. Basic consequences of this approach are discussed and compared to those of the conventional approach, employing singular initial distribution functions.Comment: 15 pages, Latex, 5 figures in PS format attache

Heavy Quark Initiated Contributions to Deep Inelastic Structure Functions

We present O(alpha_s^1) corrections to deep inelastic scattering amplitudes on massive quarks obtained within the scheme of Aivazis, Collins, Olness and Tung (ACOT). After identifying the correct subtraction term the convergence of these contributions towards the analogous coefficient functions for massless quarks, obtained within the modified minimal subtraction scheme (MSbar), is demonstrated. Furthermore, the quantitative relevance of the contributions to neutral current (NC) and charged current (CC) structure functions is investigated for several choices of the factorization scale.Comment: 29 pages, 6 figures; uses epsfig.sty, amssymb.sty, axodraw.sty; minor changes for publication in Phys. Rev.

Appearance of quark-hadron duality in the Rein-Sehgal model

Quark-hadron duality in neutrino-nucleon reactions is investigated under the assumption that cross sections in the resonance region are given by the Rein-Sehgal model. The quantitative analysis of the duality is done by means of appropriate integrals of the structure functions in the Nachtmann variable. We conclude that with the definition of the resonance region $W\in (M+m_{\pi}, 2$ GeV) the duality holds for neutrino-proton reaction $F_2$ structure function for $Q^2\in (0.5, 3)$ GeV$^2$ and it is absent for neutrino-neutron reaction.Comment: 4 pages, 7 figures, presented at NuInt05 conference, Okayama, Sept. 26-29, 200

Spin Asymmetries in Squark and Gluino Production at Polarized Hadron Colliders

We study the production cross sections for squarks and gluinos in collision of longitudinally polarized hadrons. The corresponding polarized partonic cross sections are computed in leading order supersymmetric QCD. The resulting asymmetries are evaluated for the polarized proton collider RHIC, as well as for hypothetical polarized options of the Tevatron and the LHC. These asymmetries turn out to be sizable over a wide range of supersymmetric particle masses, thus potentially opening a window to detailed sparticle spectroscopy at future polarized hadron colliders.Comment: 25 pages, LaTeX, typos correcte

Semi-inclusive Lambda_c^+ Leptoproductions and Polarized Gluon Distributions

In order to extract the behavior and magnitude of the spin-dependent gluon distribution, we propose a semi-inclusive $\Lambda_c^+$ production using unpolarized lepton beams and polarized proton targets. The correlation between the target proton spin and the spin of $\Lambda_c^+$ produced in the target fragmentation region might be very effective for testing various models of polarized gluons.Comment: 9 pages + 4 Postscript figures(2 PS files), LaTe