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Steven D. Bass

Publications and source records attributed to Steven D. Bass.

62 records · Page 4Linked to original sources
arXiv2001

Spin structure in non-forward partons

Renormalisation induces anomalous contributions in light-cone correlation functions. We discuss the role of the axial anomaly and gluon topology in non-forward parton distributions noting that non-forward matrix elements of the gluonic Chern-Simons current K_μ are not gauge-invariant even in perturbation theory. The axial anomaly means that one has to be careful how to interpret information from hard exclusive reactions about the orbital angular-momentum carried by the proton's internal constituents.

hep-ph↗
arXiv2000

g_1 at low x and low Q^2 with Polarized ep Colliders

Measurements of g_1 at low x and low Q^2 are expected to provide a sensitive probe of the transition from Regge to perturbative QCD dynamics, offering a new testing ground for models of small x physics. We discuss the potential of polarized ep colliders (Polarized HERA and eRHIC) to investigate this physics --- varying Q^2 between 0.01 and 1 GeV^2 --- and to constrain the high-energy part of the Drell-Hearn-Gerasimov sum-rule for polarized photoproduction.

hep-ph↗
arXiv2000

Axial U(1) dynamics in eta and eta' photoproduction

We discuss the sensitivity of eta and eta' photoproduction near threshold to the gluonic OZI breaking parameters in the U_A(1)-extended effective chiral Lagrangian for low-energy QCD. Our coupled-channels analysis hints at a strong correlation between the gluon-induced contributions to the eta' mass and the low-energy pp -> pp eta' reaction and the near-threshold behaviour of the gamma p -> eta p cross-section.

hep-ph↗
arXiv2000

Proton spin structure and the low-energy pp -> pp eta' reaction

Gluonic degrees of freedom induce a contact term in the effective chiral Lagrangian description of the low-energy pp -> pp eta' reaction. The strength of this contact term is, in part, related to the amount of spin carried by polarised gluons in a polarised proton.

hep-ph↗
arXiv1999

Gluons and the eta' nucleon coupling constant

We derive the effective chiral Lagrangian for low energy eta--nucleon and eta'--nucleon interactions and show that gluonic degrees of freedom, via the axial anomaly, induce a contact term in the pp -> pp eta and pp -> pp eta' reactions. We then discuss the consequences for the extraction of g_{eta'NN} from experimental data.

hep-ph↗
arXiv1999

Constituent Quarks and g_1

We review the theory and present status of the proton spin problem with emphasis on the transition between current quarks and constituent quarks in QCD.

hep-ph↗
arXiv1998

The Spin Structure of a Polarized Photon

We show that the first moment of the spin-dependent structure function $g_1^γ(x,Q^2)$ of a real photon vanishes independent of the momentum transfer $Q^2$ it is probed with. This result is non-perturbative: it holds to all orders in perturbation theory in abelian and non-abelian gauge theory and at every twist.

hep-ph↗