Particle theory

Abstract:

We derive constraints on the relic abundance of a generic particle of mass ∼ 1-1014 TeV which decays into neutrinos at cosmological epochs, using data from the Fréjus and IMB nucleon decay detectors and the Fly's Eye air-shower array. The lifetime of such unstable particles which may constitute the dark matter today is bounded to be greater than ∼ 1014-1018 yr, depending on the mass. For lifetimes shorter than the age of the universe, neutrino energy losses due to scattering and the expansion redshift become important and set limits to the ability of neutrino observatories to probe the early universe. © 1993.

Abstract:

We investigate the crumpling transition on crystalline random surfaces with extrinsic curvature on lattices up to $64^2$. Our data are consistent with a second order phase transition and we find correlation length critical exponent $\nu=0.89\pm 0.07$. The specific heat exponent, $\alpha=0.2\pm 0.15$, is in much better agreement with hyperscaling than hitherto. The long distance behaviour of tangent-tangent correlation functions confirms that the so-called Hausdorff dimension is $d_H=\infty$ throughout the crumpled phase.

Abstract:

The U(1) Villain model is simulated in three and four dimensions. We locate monopoles using both the conventional DeGrand-Toussaint prescription and the exact prescription as provided by the model itself. The two monopole gases thus obtained are compared, in particular with respect to their confining and percolation properties. In this way we investigate to how strong a coupling the conventional definition of lattice monopoles remains reliable. We show that in the interesting range of "intermediate" couplings (β0.3) the difference between the two monopole gases can be very well reproduced by a random distribution of dipoles (which possesses trivial long-distance properties). This suggests that the DeGrand-Toussaint prescription can indeed be meaningfully used in studies of, for example, the U(1) phase transition and the monopole mechanism for non-Abelian confinement. © 1993 The American Physical Society.