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S. D. Bass

Publications and source records attributed to S. D. Bass.

28 records · Page 2Linked to original sources
arXiv1996

The role of the pion cloud in the interpretation of the valence light-cone wavefunction of the nucleon

The pion cloud renormalises the light-cone wavefunction of the nucleon which is measured in hard, exclusive photon-nucleon reactions. We discuss the leading twist contributions to high-energy exclusive reactions taking into account both the pion cloud and perturbative QCD physics. The nucleon's electromagnetic form-factor at high $Q^2$ is proportional to the bare nucleon probability $Z$ and the cross-sections for hard (real at large angle or deeply virtual) Compton scattering are proportional to $Z^2$. Our present knowledge of the pion-nucleon system is consistent with $Z = 0.7 \pm 0.2$. If we apply just perturbative QCD to extract a light-cone wavefunction directly from these hard exclusive cross-sections, then the light-cone wavefunction that we extract measures the three valence quarks partially screened by the pion cloud of the nucleon. We discuss how this pion cloud renormalisation effect might be understood at the quark level in terms of the (in-)stability of the perturbative Dirac vacuum in low energy QCD.

hep-ph↗
arXiv1996

Sea polarisation and the Drell-Hearn-Gerasimov sum-rule(s)

The Drell-Hearn-Gerasimov sum-rule is really two sum-rules: one for each of the valence and the sea/glue contributions to the nucleon wavefunction. The convergence of these sum-rules follows from the Froissart bound for spin dependent processes in QCD and is necessary for the consistency of the constituent quark model of low energy QCD. Some challenges for future polarised photoproduction experiments, for example at ELFE, are discussed.

hep-ph↗
arXiv1996

A New Hypothesis on the Origin of the Three Generations

We suggest that the Standard Model may undergo a supercritical transition near the Landau scale, where the U(1) gauge boson couples to the left and right handed states of any given fermion with different charges. This scenario naturally gives rise to three generations of fermion, corresponding to the three critical scales for the right-right, right-left and left-left fermion interactions going supercritical, as well as CP violation in the quark sector.

hep-ph↗
arXiv1994

Gribov Confinement and Chiral Perturbation Theory

I discuss the chiral dynamics of Gribov's theory of confinement. At a critical coupling $α_s^c$ the light quark vacuum undergoes a series of phase transitions which should be taken into account in the application of chiral perturbation theory. The Gribov theory offers a simple explanation of the value of the pion nucleon sigma term without need to invoke a large strange quark component in the nucleon.

nucl-th↗
arXiv1994

The trace anomaly and the parton model

The trace anomaly is relevant to the renormalisation of the unpolarised parton distributions. The role of the trace anomaly in F_2 is compared with the axial anomaly in g_1.

hep-ph↗
arXiv1994

Confinement and the Pion Nucleon Sigma Term

Gribov's theory of confinement offers a simple explanaton of the value of the pion nucleon sigma term. There is no need to invoke a large strange quark component in the nucleon.

hep-ph↗
arXiv1993

The Spin Structure of the Nucleon

We provide an introduction to the ideas of spin-dependent deep-inelastic scattering. Recent experimental results are summarised and possible explanations related to the axial anomaly presented. Further experiments that could greatly clarify the situation are also described.

hep-ph↗
arXiv1993

Gauge symmetry and the EMC spin effect

We emphasise the EMC spin effect as a problem of symmetry and discuss the renormalisation of the $C=+1$ axial tensor operators. This involves the generalisation of the Adler-Bell-Jackiw anomaly to each of these operators. We find that the contribution of the axial anomaly to the spin dependent structure function $g_1 (x, Q^2)$ scales at $O(α_s)$. This means that the anomaly can be a large $x$ effect in $g_1$. Finally we discuss the jet signature of the anomaly.

hep-ph↗