Prof Subir Sarkar

Abstract:

Two ground-based experiments have recently independently detected TeV $\gamma$-rays from the direction of the Galactic center. The observations made by the VERITAS and CANGAROO collaborations are unexpected, although not impossible to interpret in terms of astrophysical sources. Here we examine in detail whether the observed $\gamma$-rays may arise from the more exotic alternative of annihilations of dark matter particles clustered in the center of the Galaxy.

Abstract:

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

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.