Particle theory

Abstract:

We discuss some aspects of the hadron spectrum with two flavors of Kogut-Susskind dynamical quarks at 6/g2 = 5.6 and amq = 0.01 and 0.025, using both Kogut-Susskind and Wilson valence quarks. Our high statistics simulations allow us to study systematic errors. Among the problematic features of our results are a dip in the pion effective mass which we ascribe to replicating the lattice in the time direction and large finite size effects in the baryon masses. We also compare the full QCD results to a quenched simulation at similar lattice spacing and quark masses to test whether the effects of dynamical fermions can be absorbed into renormalization of the lattice parameters. © 1991.

Abstract:

I focus on three topics in my review of pure gauge theories. Firstly, how close are we to solving the continuum theory. Secondly, cooling and confinement. Thirdly, the status of lattice topology. © 1991.

Abstract:

We present results from a study of hadron thermodynamics with Wilson quarks. The crossover curve between the high and low temperature phases is determined as a function of the gauge coupling and hopping parameter on 83 × 4 lattices. Meson masses are calculated along the crossover curve, and screening lengths are determined in the vicinity of it on 83 × 16 and 82 × 16 × 4 lattices, respectively. © 1991.

Abstract:

We discuss the implications of the recent measurement of a 17 keV mass component in the electron neutrino sector. Such a heavy state must decay in order to be compatible with cosmology; this requires states additional to those of the standard model. The most likely candidates are either majorons, allowing the decay into massless weakly interacting scalars, or single neutrinos, allowing the decay via the Z into light neutrinos. We show that in the latter case there is a lower bound on the lifetime in conflict with the cosmological constraints on this decay channel and on the photon plus neutrino decay channel which is also present. The extensions of the standard model needed to reduce the lifetime are considered. We analyze the mass matrix, playing particular regard to the singlet neutrino case, and discuss how it might be extended to explain the solar neutrino deficit. © 1991.

Abstract:

We investigate some basic aspects of topological fluctuations in lattice QCD, in the version with two colours and four light flavours; and we do so in both the confining, chiral symmetry broken phase and in the non-confining, chirally symmetric phase. This latter phase is found to ccut not only high temperatures, just as in the pure gauge system, but also in small spatial volumes, which is unlike the pure gauge case. We derive the way the topological susceptibility should vary with quark mass at small quark masses. We find that the calculated topological susceptibility decerases to zero with the quark mass, with the theretically expected powers except - in the symmetric phase - at the very smallest values of the quark mass. We demonstrate that this anomalous behaviour can be understood as arising from the fact that the lattice topological "zero modes" are in fact sufficiently far from being zero. We also show, in the chirally symmetric phase, that, just as expected, the average distance between instantons and anti-instantons decreases with decreasing quark mass. We finish with a new and more precise estimate of the location of the finite-temperature transition in SU(2) with four light flavours. © 1991.