Particle theory

Abstract:

We propose a model of TeV-scale resonant leptogenesis based upon recent models of the generation of light neutrino masses from supersymmetry-breaking effects with TeV-scale right-handed (rhd) neutrinos, Ni The model leads to large cosmological lepton asymmetries via the resonant behaviour of the one-loop self-energy contribution to Ni decay. Our model addresses the primary problems of previous phenomenological studies of low-energy leptogenesis: a rational for TeV-scale rhd neutrinos with small Yukawa couplings so that the out-of equilibrium condition for Ni decay is satisfied; the origin of the tiny, but non-zero mass splitting required between at least two Ni masses; and the necessary non-trivial breaking of flavour symmetries in the rhd neutrino sector. The low mass-scale of the rhd neutrinos and their superpartners, and the TeV-scale A-terms automatically contained within the model offer opportunities for partial direct experimental tests of this leptogenesis mechanism at future colliders. © SISSA/ISAS 2004.

Abstract:

We reiterate that there is no evidence that BL Lacs are sources of ultrahigh energy cosmic rays.

Abstract:

A critical review is given of the current status of cosmological nucleosynthesis. In the framework of the standard model with 3 types of relativistic neutrinos, the baryon-to-photon ratio, \eta, corresponding to the inferred primordial abundances of helium-4 and lithium-7 is presently ~2 \sigma below the value implied by the abundance of deuterium. The latter value is also coincident with the independent determination of \eta from WMAP observations of CMB anisotropy. However taking systematic uncertainties in the abundance estimates into account, there is overall concordance in the range \eta = (3.4 - 6.9) x 10^{-10} @ 95% c.l. corresponding to a cosmological baryon density \Omega_B h^2 = 0.012 - 0.025. If the above discrepancy is due to a neutrino chemical potential, then upto 7.1 effective neutrino species are allowed by nucleosynthesis. Other constraints on new physics are briefly discussed.