Atmospheric Neutrinos and the Oscillations Bonanza

New observations with atmospheric neutrinos from the underground experiments SuperKamiokande, Soudan 2, and MACRO, together with earlier results from Kamiokande and IMB, are reviewed. The most recent observations reconfirm aspects of atmospheric flavor content and of zenith angle distributions which appear anomalous in the context of null oscillations. The anomalous trends, exhibited with high statistics in both sub-GeV and multi-GeV data of the SuperKamiokande water Cherenkov experiment, occur also in event samples recorded by the tracking calorimeters. The data are well-described by disappearence of nu_mu flavor neutrinos arising in oscillations with dominant two-state mixing, for which there exists a parameter region allowed by all experiments. In a new analysis by SuperKamiokande, nu_mu -> nu_tau is favored over nu_mu -> nu_s as the dominant oscillation based upon absence of oscillation suppression from matter effects at high energies. The possibility for sub-dominant nu_mu -> nu_e oscillations in atmospheric neutrinos which arises with three-flavor mixing, is reviewed, and intriguing possibilities for amplification of this oscillation by terrestrial matter-induced resonances are discussed. Developments and future measurements which will enhance our knowledge of the atmospheric neutrino fluxes are briefly noted.Comment: Plenary talk at the XIX Int. Symposium on Lepton and Photon Interactions at High Energies, Stanford, Aug. 1999, 28 pages, 16 figures; added a reference for section 1

Aristotle on virtue: a response to Thomas Hurka

I defend Aristotle's account of the motivations of the virtuous agent from criticisms made by Thomas Hurka

Boundary of Nuclear Physics and QCD

Recent progress in lattice QCD, combined with the imminent advent of a new generation of dedicated supercomputers and advances in chiral extrapolation mean that the next few years will bring quite novel insights into hadron structure. We review some of the recent highlights in this field, the questions which might be addressed and the experiments which may be expected to stretch that understanding to its limits. Only with a sound understanding of hadron structure can one hope to explore the fundamental issue of how that structure may change at finite density (or temperature). We explore potential future insights from lattice QCD into the phenomenon of nuclear saturation and a very important hint from recent data of a change in the structure of a bound nucleon.Comment: Invited talk presented at INPC2001, Berkeley, August 200

The spin structure function of the neutron

The neutron spin structure function, $g_{1n}$, has been of considerable interest recently in connection with the Bjorken sum rule and the proton spin crisis. Work on this problem has concentrated on measurements at low-$x$. We recall the important, non-perturbative physics to be learnt by going instead to larger values of $x$ and especially from a determination of the place where the expected sign change occurs. Of course, in order to obtain neutron data one must use nuclear targets and apply appropriate corrections. In this regard, we review recent progress concerning the various nuclear corrections that must be applied to measurements on polarised $^3$He.Comment: Invited presentation at the Workshop on the Spin Structure of the Proton and Polarized Collider Physics, ECT* Trento, July 23-28, 200

Against requirements of rationality

Are inferences, theoretical and practical, subject to requirements of rationality? If so, are these of the form 'if … ought …' or 'ought … if …'? If the latter, how are we to understand the 'if'? It seems that, in all cases, we get unintuitive implications (often involving bootstrapping) if 'ought' connotes having reason. It is difficult to formulate such requirements, and obscure what they explain. There might also be a requirement forbidding self-contradiction (not that one's current beliefs can be consciously contradictory). It is a good question whether self-contradiction constitutes, or evidences, irrationality; but talk of a rational requirement causes trouble

Are Plato’s soul-parts psychological subjects?

It is well-known that Plato’s Republic introduces a tripartition of the incarnate human soul; yet quite how to interpret his ‘parts’ (a term, meros, that is neither recurrent nor emphatic)1 is debated. On a strong reading, they are psychological subjects – much as we take ourselves to be, but homunculi, not homines. On a weak reading, they are something less paradoxical: aspects of ourselves, identified by characteristic mental states, dispositional and occurrent, that tend to come into conflict. Christopher Bobonich supports the strong reading in his Plato’s Utopia Recast: His Later Ethics and Politics (2002). In his The Brute Within: Appetitive Desire in Plato and Aristotle (2006), Hendrik Lorenz agrees with Bobonich that the parts of the soul are ‘the subjects or bearers of psychological states’ (23). Any ascription to my Mental Conflict (1995) of the opposed, weak view needs qualification: my Plato is highly ambivalent (56-7).2 But my intention here is less to defend an earlier self – though I predict failing to escape it – than to reconsider tripartition in the Republic in the light of Bobonich’s virtuosity and Lorenz’s lucidity. They persuade me of the inexhaustibility of the text, notably within Book 4 from 436 to 439. About these pages we may indeed disagree: they find them decisive in favour of their view, as I don’t. When Socrates remarks, ‘Let us have our understanding still more precise, lest as we proceed we become involved in dispute’ (436c8-9), he was not anticipating the dissensions of interpreters

Cosmological backreaction in higher-derivative gravity expansions

We calculate a general effective stress-energy tensor induced by cosmological inhomogeneity in effective theories of gravity where the action is Taylor-expandable in the Riemann tensor and covariant derivatives of the Riemann tensor. This is of interest as an effective fluid that might provide an alternative to the cosmological constant, but it also applies to gravitational waves. We use an adaptation of Green and Wald's weak-averaging framework, which averages over perturbations in the field equation where the perturbation length scales are small compared to the averaging scale. In this adaptation, the length scale of the effective theory, $1/M$, is also taken to be small compared with the averaging scale. This ensures that the perturbation length scales remain in fixed proportion to the length scale of the effective theory as the cosmological averaging scale is taken to be large. We find that backreaction from higher-derivative terms in the effective action can continue to be important in the late universe, given a source of sufficiently high-frequency metric perturbations. This backreaction might also provide a window on exotic particle physics in the far ultraviolet.Comment: 27 pages, 2 references added, minor clarifications made, comments added to introduction and discussion, some details moved to appendice