Enhanced chiral logarithms in partially quenched QCD

I discuss the properties of pions in ``partially quenched'' theories, i.e. those in which the valence and sea quark masses, $m_V$ and $m_S$, are different. I point out that for lattice fermions which retain some chiral symmetry on the lattice, e.g. staggered fermions, the leading order prediction of the chiral expansion is that the mass of the pion depends only on $m_V$, and is independent of $m_S$. This surprising result is shown to receive corrections from loop effects which are of relative size $m_S \ln m_V$, and which thus diverge when the valence quark mass vanishes. Using partially quenched chiral perturbation theory, I calculate the full one-loop correction to the mass and decay constant of pions composed of two non-degenerate quarks, and suggest various combinations for which the prediction is independent of the unknown coefficients of the analytic terms in the chiral Lagrangian. These results can also be tested with Wilson fermions if one uses a non-perturbative definition of the quark mass.Comment: 14 pages, 3 figures, uses psfig. Typos in eqs (18)-(20) corrected (alpha_4 is replaced by alpha_4/2

Quantization of Fayet-Iliopoulos Parameters in Supergravity

In this short note we discuss quantization of the Fayet-Iliopoulos parameter in supergravity theories. We argue that in supergravity, the Fayet-Iliopoulos parameter determines a lift of the group action to a line bundle, and such lifts are quantized. Just as D-terms in rigid N=1 supersymmetry are interpreted in terms of moment maps and symplectic reductions, we argue that in supergravity the quantization of the Fayet-Iliopoulos parameter has a natural understanding in terms of linearizations in geometric invariant theory (GIT) quotients, the algebro-geometric version of symplectic quotients.Comment: 21 pages, utarticle class; v2: typos and tex issue fixe

Introduction to the new usability

This paper introduces the motivation for and concept of the "new usability" and positions it against existing approaches to usability. It is argued that the contexts of emerging products and systems mean that traditional approaches to usability engineering and evaluation are likely to prove inappropriate to the needs of "digital consumers." The paper briefly reviews the contributions to this special issue in terms of their relation to the idea of the "new usability" and their individual approaches to dealing with contemporary usability issues. This helps provide a background to the "new usability" research agenda, and the paper ends by posing what are argued to be the central challenges facing the area and those which lie at the heart of the proposed research agenda

Linear stability of planar premixed flames: reactive Navier-Stokes equations with finite activation energy and arbitrary Lewis number

A numerical shooting method for performing linear stability analyses of travelling waves is described and applied to the problem of freely propagating planar premixed flames. Previous linear stability analyses of premixed flames either employ high activation temperature asymptotics or have been performed numerically with finite activation temperature, but either for unit Lewis numbers (which ignores thermal-diffusive effects) or in the limit of small heat release (which ignores hydrodynamic effects). In this paper the full reactive Navier-Stokes equations are used with arbitrary values of the parameters (activation temperature, Lewis number, heat of reaction, Prandtl number), for which both thermal-diffusive and hydrodynamic effects on the instability, and their interactions, are taken into account. Comparisons are made with previous asymptotic and numerical results. For Lewis numbers very close to or above unity, for which hydrodynamic effects caused by thermal expansion are the dominant destablizing mechanism, it is shown that slowly varying flame analyses give qualitatively good but quantitatively poor predictions, and also that the stability is insensitive to the activation temperature. However, for Lewis numbers sufficiently below unity for which thermal-diffusive effects play a major role, the stability of the flame becomes very sensitive to the activation temperature. Indeed, unphysically high activation temperatures are required for the high activation temperature analysis to give quantitatively good predictions at such low Lewis numbers. It is also shown that state-insensitive viscosity has a small destabilizing effect on the cellular instability at low Lewis numbers

Hadronic Electromagnetic Properties at Finite Lattice Spacing

Electromagnetic properties of the octet mesons as well as the octet and decuplet baryons are augmented in quenched and partially quenched chiral perturbation theory to include O(a) corrections due to lattice discretization. We present the results for the SU(3) flavor group in the isospin limit as well as the results for SU(2) flavor with non-degenerate quarks. These corrections will be useful for extrapolation of lattice calculations using Wilson valence and sea quarks, as well as calculations using Wilson sea quarks and Ginsparg-Wilson valence quarks.Comment: 19 pages, 0 figures, RevTeX

Thermodynamics of lattice QCD with 3 flavours of colour-sextet quarks

We have been studying QCD with 2 flavours of colour-sextet quarks to distinguish whether it is QCD-like or conformal. For comparison we are now studying QCD with 3 flavours of colour-sextet quarks, which is believed to be conformal in the chiral limit. Here we present the results of simulations of lattice QCD with 3 colour-sextet quarks at finite temperatures on lattices of temporal extent $N_t=4$ and 6, with masses small enough to yield access to the chiral limit. As for the 2-flavour case, we find well-separated deconfinement and chiral-symmetry restoration transitions, both of which move to appreciably weaker couplings as $N_t$ is increased from 4 to 6. If this theory is conformal, we would expect there to be a bulk chiral transition at a fixed coupling. For this reason we conclude that for $N_t=4$ and 6, the chiral and hence the deconfinement transitions are in the strong-coupling domain where the theory is essentially quenched. The similarity between the behaviours of the 2 and 3 flavour theories suggested that the $N_t=4$ and 6 transitions for the 2-flavour theory also lie in the strong-coupling domain. The phase structure of both theories is very similar.Comment: 17 pages Latex(Revtex), 7 postscript figure

Are men funnier than women, or do we just think they are?

Despite the widely held view that men are funnier than women, research supporting this view is inconsistent. Instead, the view that men are funnier than women may be a stereotype rather than a reflection of real differences in humor. Considering a previously found source memory bias in the attribution of funnier captions to men and less funny captions to women, this stereotype may be working to further perpetuate this mistaken belief. The current study aims to investigate this possible stereotype and further investigate an attribution bias arising from this stereotype. Two-hundred and twenty-eight participants from three countries (Britain, Canada, and Australia) rated the funniness of male and female-authored cartoon captions while blind to the gender of the caption authors. Participants were then asked to guess the gender of the caption authors and were also asked which gender they believe to be the funniest. Participants both male and female believed men are the funniest gender. However, this belief was not reflected in their ratings of the funniness of the cartoon captions. Support was found for a bias in attributing male authorship to the funniest cartoon captions, and female authorship to the least funny cartoon captions. This bias cannot not be attributed to source memory. It was suggested this stereotype may be self-fulfilling in nature and additional mechanisms maintaining this stereotype are proposed

Chiral Perturbation Theory for the Quenched Approximation of QCD

[This version is a minor revision of a previously submitted preprint. Only references have been changed.] We describe a technique for constructing the effective chiral theory for quenched QCD. The effective theory which results is a lagrangian one, with a graded symmetry group which mixes Goldstone bosons and fermions, and with a definite (though slightly peculiar) set of Feynman rules. The straightforward application of these rules gives automatic cancellation of diagrams which would arise from virtual quark loops. The techniques are used to calculate chiral logarithms in $f_K/f_\pi$, $m_\pi$, $m_K$, and the ratio of $\langle{\bar s}s\rangle$ to $\langle{\bar u}u\rangle$. The leading finite-volume corrections to these quantities are also computed. Problems for future study are described.Comment: 14 page

Partial Flavor Symmetry Restoration for Chiral Staggered Fermions

We study the leading discretization errors for staggered fermions by first constructing the continuum effective Lagrangian including terms of O(a^2), and then constructing the corresponding effective chiral Lagrangian. The terms of O(a^2) in the continuum effective Lagrangian completely break the SU(4) flavor symmetry down to the discrete subgroup respected by the lattice theory. We find, however, that the O(a^2) terms in the potential of the chiral Lagrangian maintain an SO(4) subgroup of SU(4). It follows that the leading discretization errors in the pion masses are SO(4) symmetric, implying three degeneracies within the seven lattice irreducible representations. These predictions hold also for perturbatively improved versions of the action. These degeneracies are observed, to a surprising degree of accuracy, in existing data. We argue that the SO(4) symmetry does not extend to the masses and interactions of other hadrons (vector mesons, baryons, etc), nor to higher order in a^2. We show how it is possible that, for physical quark masses of O(a^2), the new SO(4) symmetry can be spontaneously broken, leading to a staggered analogue of the Aoki-phase of Wilson fermions. This does not, however, appear to happen for presently studied versions of the staggered action.Comment: 26 pages, 2 figures (using psfig). Version to appear in PRD (clarifications added to introduction and section 6; typos corrected; references updated

Hadron Masses from the Valence Approximation to Lattice QCD

We evaluate pseudoscalar, vector, spin 1/2 and spin 3/2 baryon masses predicted by lattice QCD with Wilson quarks in the valence (quenched) approximation for a range of different values of lattice spacing, lattice volume and quark mass. Extrapolating these results to physical quark mass, then to zero lattice spacing and infinite volume we obtain values for eight mass ratios. We also determine the zero lattice spacing, infinite volume limit of an alternate set of five quantities found without extrapolation in quark mass. Both sets of predictions differ from the corresponding observed values by amounts consistent with the predicted quantities' statistical uncertainties.Comment: 108 pages of Latex, including 50 PostScript figures, tarred, compressed and uuencoded. IBM-HET-94-3. (The first version of this posting exceeded the size limit. I squeezed the second version in by dropping out the figues. This version gets the figures in but has to be run through Latex and dvips.