Particle theory

Abstract:

We reiterate that there is no evidence that BL Lacs are sources of ultrahigh energy cosmic rays. © 2004 The American Physical Society.

Abstract:

We study the time evolution of freely rolling moduli in the context of M-theory on a G2 manifold. This free evolution approximates the correct dynamics of the system at sufficiently large values of the moduli when effects from non-perturbative potentials and flux are negligible. Moduli fall into two classes, namely bulk moduli and blow-up moduli. We obtain a number of non-trivial solutions for the time-evolution of these moduli. As a generic feature, we find the blow-up moduli always expand asymptotically at early and late time. © SISSA/ISAS 2004.

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.