New CMBR data and the cosmic neutrino background

New precision Cosmic Microwave Background Radiation (CMBR) anisotropy data are beginning to constrain physics beyond the standard model, for example in the form of additional light particle species. These constraints are complementary to what can be obtained from big bang nucleosynthesis (BBN) considerations because they apply to much later times. We derive a constraint on the equivalent number of neutrino species, N_\nu, from the presently available data. Specifically we analyse two different CMBR data sets to test the robustness of our results. Analyzing only CMBR data yields an upper bound of N_\nu < 17 (95% confidence). Adding large scale structure (LSS) data from the PSC-z survey tightens the upper bound slightly. However, the addition of LSS data gives a non-trivial {\it lower} bound of N_\nu > 1.5/2.5 (95% confidence) for the two data sets. This is the first independent indication of the presence of the cosmological neutrino background which is predicted by the standard model, and seen in big bang nucleosynthesis. The value $N_\nu = 0$ is disfavoured at 3\sigma and 4\sigma for the two data sets respectively.Comment: 5 pages, 3 figure

Decay-Produced Neutrino Hot Dark Matter

We investigate different types of neutrino hot dark matter with respect to structure formation and anisotropies in the cosmic microwave background radiation (CMBR). The possibility of neutrino hot dark matter produced through the decay of a heavier neutrino by the process nu_H -> nu_L + phi, where phi is a scalar particle, is discussed in detail. This type of dark matter can possibly be distinguished observationally from the standard neutrino dark matter by using new CMBR data from the upcoming satellite missions MAP and PLANCK.Comment: To appear in Phys. Rev. Letter

Cosmological Constraints on Neutrino Masses and Mixings

The bounds on neutrino masses and mixing that follows from the data on light element abundances, large scale structure formation, and angular fluctuations of cosmic microwave background radiation are analyzed. The role of neutrino oscillations in BBN and the bounds on cosmological lepton asymmetry are discussed.Comment: Talk presented at the NOON 2003 workshop, February 10-14, 2003, Kanazawa, Japan (to be published in the Proceedings), 10 page

New constraints on neutrino physics from Boomerang data

We have performed a likelihood analysis of the recent data on the Cosmic Microwave Background Radiation (CMBR) anisotropy taken by the Boomerang experiment. We find that this data places a strong upper bound on the radiation density present at recombination. Expressed in terms of the equivalent number of neutrino species the $2\sigma$ bound is N_nu < 13, and the standard model prediction, N_nu = 3.04, is completely consistent the the data. This bound is complementary to the one found from Big Bang nucleosynthesis considerations in that it applies to any type of radiation, i.e. it is not flavour sensitive. It also applies to the universe at a much later epoch, and as such places severe limits on scenarios with decaying neutrinos. The bound also yields a firm upper limit on the lepton asymmetry in the universe.Comment: 4 pages, 2 postscript figures, matches version to appear in PR

Probing neutrino decays with the cosmic microwave background

We investigate in detail the possibility of constraining neutrino decays with data from the cosmic microwave background radiation (CMBR). Two generic decays are considered \nu_H -> \nu_L \phi and \nu_H -> \nu_L \nu_L_bar \nu_L. We have solved the momentum dependent Boltzmann equation in order to account for possible relativistic decays. Doing this we estimate that any neutrino with mass m > 1 eV decaying before the present should be detectable with future CMBR data. Combining this result with other results on stable neutrinos, any neutrino mass of the order 1 eV should be detectable.Comment: 8 pages, 4 figures, to appear in Phys. Rev.

Ultrahigh Energy Cosmic Rays from Topological Defects --- Cosmic Strings, Monopoles, Necklaces, and All That

The topological defect scenario of origin of the observed highest energy cosmic rays is reviewed. Under a variety of circumstances, topological defects formed in the early Universe can be sources of very massive particles in the Universe today. The decay products of these massive particles may be responsible for the observed highest energy cosmic ray particles above $10^{20}$ eV. Some massive particle production processes involving cosmic strings and magnetic monopoles are discussed. We also discuss the implications of results of certain recent numerical simulations of evolution of cosmic strings. These results (which remain to be confirmed by independent simulations) seem to show that massive particle production may be a generic feature of cosmic strings, which would make cosmic strings an inevitable source of extremely high energy cosmic rays with potentially detectable flux. At the same time, cosmic strings are severely constrained by the observed cosmic ray flux above $10^{20}$ eV, if massive particle radiation is the dominant energy loss mechanism for cosmic strings.Comment: Latex, 27 pages, including 1 ps fig. Invited talk given at the Workshop on ``Observing the Highest Energy Particles ($> 10^{20}$ eV) from Space'', College Park, Maryland, USA, November 13 -- 15, 1997, to be published in the proceedings (AIP

The History of Astrophysics in Antarctica

We examine the historical development of astrophysical science in Antarctica from the early 20th century until today. We find three temporally overlapping eras, each having a rather distinct beginning. These are the astrogeological era of meteorite discovery, the high energy era of particle detectors, and the photon astronomy era of microwave, sub--mm and infrared telescopes, sidelined by a few niche experiments at optical wavelengths. The favourable atmospheric and geophysical conditions are briefly examined, followed by an account of the major experiments and a summary of their results.Comment: 29 pages, 10 figures, 1 table Submitted to PASA in April 200