Particle theory

Abstract:

We study the deconfinement phase transition in SU(N) gauge theories for N=2,3,4,6,8. The transition is first order for N ≥ 3, with the strength increasing as N increases. We extrapolate Tc/σ to the continuum limit for each N, and observe a rapid approach to the large N limit. As N increases the phase transition becomes clear-cut on smaller spatial volumes, indicating the absence of (non-singular) finite volume corrections at N = ∞ - reminiscent of large N reduction. The observed rapid increase of the inter-phase surface tension with N may indicate that for N = ∞ the deconfinement transition cannot, in practise, occur. © 2004 Published by Elsevier B.V.

Abstract:

Observations of cosmic rays with energies above similar to 4 x 10(10) GeV have inspired several speculative suggestions concerning their origin. The crucial question is whether or not the spectrum exhibits the expected 'GZK cutoff' at this energy-concerning which there are presently contradictory results. If there is indeed a cutoff, then the sources are cosmologically distant and rather exotic in nature. If there is no cutoff then new physics is required.