U_A(1) Problems and Gluon Topology - Anomalous Symmetry in QCD

Many of the distinctive and subtle features of the dynamics in the $U_A(1)$ channel in QCD can be related to gluon topology, more precisely to the topological susceptibility $\chi(k^2) = i\int d^4x~e^{ikx}$, where Q = {\a_s\over8\pi} {\rm tr} G_{\m\n} \tilde G^{\m\n} is the gluon topological charge density. The link is the $U_A(1)$ axial (ABJ) anomaly. In this lecture, we describe the anomalous $U_A(1)$ chiral Ward identities in a functional formalism and show how two apparently unrelated `$U_A(1)$ problems' -- the mass of the $\eta'$ and the violation of the Ellis-Jaffe sum rule in polarised deep-inelastic scattering -- can be explained in terms of the gluon topological susceptibility. They are related through a $U_A(1)$ extension of the Goldberger-Treiman formula, which is derived here for QCD with both massless and massive quarks.Comment: Lecture at 1998 Zuoz Summer School, `Hidden Symmetries and Higgs Phenomena'. 22 pages, plain TeX, 2 ps or eps figure

η′→γγ\eta'\to\gamma\gamma and the topological susceptibility

The radiative decays \eta'(\eta)\rta\gamma\gamma are discussed. The modifications of the conventional PCAC formulae due to the gluonic contribution to the flavour singlet axial anomaly are given. The decay constants satisfy a modified Dashen formula which generalises the Witten--Veneziano formula for the mass of the $\eta'$. It is shown how the topological susceptibility in QCD with massive, dynamical quarks may be extracted from measurements of \eta'(\eta)\rta\gamma\gamma.Comment: 4 pages, LaTeX, uses espcrc2.sty. To appear in Proceedings, QCD99 Montpellie

The Proton-Spin Crisis: another ABJ anomaly?

Contents: 1. Introduction; 2. The First Moment Sum Rule for $g_1^p$; 3. The Parton Model and the `Proton Spin'; 4. The CPV Method and Topological Charge Screening; 5. Experiment; 6. Semi-Inclusive Polarised DIS.Comment: Lecture at the International School of Subnuclear Physics, `From the Planck Length to the Hubble Radius', Erice, 1998. 22 pages, plain TeX, 2ps or eps figure

When to make the sensory social: Registering in copresent openings

This article provides the first detailed empirical analysis of naturally-occurring videorecorded openings during which participants make the sensory social through the action of registering – calling joint attention to a selected, publicly perceivable referent so others shift their sensory attention to it. Examining sequence-initial actions that register referents for which a participant is regarded as responsible, this study elucidates a systematic preference organization which observably guides when and how people initiate registering sequences sensitive to both referent ownership and referent value. Analysis shows how choosing to register an owned referent puts involved participants’ face, affiliation, and social relationship on the line

When to Make the Sensory Social: Registering in Face-to-Face Openings

This article analyzes naturally occurring video-recorded openings during which participants make the sensory social through the action of registering—calling joint attention to a selected, publicly perceiv- able referent so others shift their sensory attention to it. It examines sequence-initial actions that register referents for which a participant is regarded as responsible. Findings demonstrate a systematic preference organization which observably guides when and how people initiate registering sequences sensitive to ownership of, and displayed stance toward, the target referent. Analysis shows how registering an owned referent achieves intersubjectivity and puts involved participants’ face, affiliation, and social relationship on the line. A video abstract is available at https://youtu.be/rNL70vawG3

Being a Good Parent in Parent-Teacher Conferences

This research advances our understanding of what constitutes a good parent in the course of actual social interaction. Examining video-recorded naturally occurring parent-teacher conferences, this article shows that, while teachers deliver student-praising utterances, parents may display that they are gaining knowledge; but when teachers’ actions adumbrate student-criticizing utterances, parents systematically display prior knowledge. This article elucidates the details of how teachers and parents tacitly collaborate to enable parents to express student-troubles first, demonstrating that parents display competence -- appropriate involvement with children’s schooling -- by asserting their prior knowledge of, and/or claiming/describing their efforts to remedy, student-troubles. People (have to) display competence generically in interaction. By explicating how parents display competence, this article offers insights for several areas of communication research

The Refractive Index of Curved Spacetime: the Fate of Causality in QED

It has been known for a long time that vacuum polarization in QED leads to a superluminal low-frequency phase velocity for light propagating in curved spacetime. Assuming the validity of the Kramers-Kronig dispersion relation, this would imply a superluminal wavefront velocity and the violation of causality. Here, we calculate for the first time the full frequency dependence of the refractive index using world-line sigma model techniques together with the Penrose plane wave limit of spacetime in the neighbourhood of a null geodesic. We find that the high-frequency limit of the phase velocity (i.e. the wavefront velocity) is always equal to c and causality is assured. However, the Kramers-Kronig dispersion relation is violated due to a non-analyticity of the refractive index in the upper-half complex plane, whose origin may be traced to the generic focusing property of null geodesic congruences and the existence of conjugate points. This puts into question the issue of micro-causality, i.e. the vanishing of commutators of field operators at spacelike separated points, in local quantum field theory in curved spacetime.Comment: 43 pages, 19 figures, JHEP3, conclusions respecting microcausality modifie

`Superluminal' Photon Propagation in QED in Curved Spacetime is Dispersive and Causal

It is now well-known that vacuum polarisation in QED can lead to superluminal low-frequency phase velocities for photons propagating in curved spacetimes. In a series of papers, we have shown that this quantum phenomenon is dispersive and have calculated the full frequency dependence of the refractive index, explaining in detail how causality is preserved and various familiar results from quantum field theory such as the Kramers-Kronig dispersion relation and the optical theorem are realised in curved spacetime. These results have been criticised in a recent paper by Akhoury and Dolgov arXiv:1003.6110 [hep-th], who assert that photon propagation is neither dispersive nor necessarily causal. In this note, we point out a series of errors in their work which have led to this false conclusion.Comment: 11 page