Cosmological bounds on sub-MeV mass axions

Axions with mass greater than 0.7 eV are excluded by cosmological precision data because they provide too much hot dark matter. While for masses above 20 eV the axion lifetime drops below the age of the universe, we show that the cosmological exclusion range can be extended from 0.7 eV till 300 keV, primarily by the cosmic deuterium abundance: axion decays would strongly modify the baryon-to-photon ratio at BBN relative to the one at CMB decoupling. Additional arguments include neutrino dilution relative to photons by axion decays and spectral CMB distortions. Our new cosmological constraints complement stellar-evolution limits and laboratory bounds.Comment: 19 pages, 10 figure

Cosmological neutrino bounds for non-cosmologists

I briefly review cosmological bounds on neutrino masses and the underlying gravitational physics at a level appropriate for readers outside the field of cosmology. For the case of three massive neutrinos with standard model freezeout, the current 95% upper limit on the sum of their masses is 0.42 eV. I summarize the basic physical mechanism making matter clustering such a sensitive probe of massive neutrinos. I discuss the prospects of doing still better in coming years using tools such as lensing tomography, approaching a sensitivity around 0.03 eV. Since the lower bound from atmospheric neutrino oscillations is around 0.05 eV, upcoming cosmological measurements should detect neutrino mass if the technical and fiscal challenges can be met.Comment: 4 pages, 2 figs, in "Neutrino Physics", Proceedings of Nobel Symposium 129, eds., L Bergstrom, O. Botner, P. Carlson, P. O. Hulth, and T. Ohlsso

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.

Neutrino and axion hot dark matter bounds after WMAP-7

We update cosmological hot dark matter constraints on neutrinos and hadronic axions. Our most restrictive limits use 7-year data from the Wilkinson Microwave Anisotropy Probe for the cosmic microwave background anisotropies, the halo power spectrum (HPS) from the 7th data release of the Sloan Digital Sky Survey, and the Hubble constant from Hubble Space Telescope observations. We find 95% C.L. upper limits of \sum m_\nu<0.44 eV (no axions), m_a<0.91 eV (assuming \sum m_\nu=0), and \sum m_\nu<0.41 eV and m_a<0.72 eV for two hot dark matter components after marginalising over the respective other mass. CMB data alone yield \sum m_\nu<1.19 eV (no axions), while for axions the HPS is crucial for deriving m_a constraints. This difference can be traced to the fact that for a given hot dark matter fraction axions are much more massive than neutrinos.Comment: 9 pages, 3 figures, uses iopart.cls; v2: one additional figure, references added, version accepted by JCA

Recent Results of non-accelarator-based neutrino experiments

Recent results of non-accelerator-based experiments, including those of solar, atmospheric, and reactor neutrinos oscillations, neutrinoless double-beta decays, and neutrino magnetic moments, are reviewed. Future projects and their respective prospects are summarized.Comment: V.2, minor changes with one more reference added. Plenary talk given at the "32nd International Conference on High Energy Physics", Aug. 16-22, 2004, Beijing, P.R. Chin

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

Cosmological mass limits on neutrinos, axions, and other light particles

The small-scale power spectrum of the cosmological matter distribution together with other cosmological data provides a sensitive measure of the hot dark matter fraction, leading to restrictive neutrino mass limits. We extend this argument to generic cases of low-mass thermal relics. We vary the cosmic epoch of thermal decoupling, the radiation content of the universe, and the new particle's spin degrees of freedom. Our treatment covers various scenarios of active plus sterile neutrinos or axion-like particles. For three degenerate massive neutrinos, we reproduce the well-known limit of m_nu < 0.34 eV. In a 3+1 scenario of 3 massless and 1 fully thermalized sterile neutrino we find m_nu < 1.0 eV. Thermally produced QCD axions must obey m_a < 3.0 eV, superseding limits from a direct telescope search, but leaving room for solar eV-mass axions to be discovered by the CAST experiment.Comment: 15 pages, 6 figures, matches version in JCA

Angular Signatures of Annihilating Dark Matter in the Cosmic Gamma-Ray Background

The extragalactic cosmic gamma-ray background (CGB) is an interesting channel to look for signatures of dark matter annihilation. In particular, besides the imprint in the energy spectrum, peculiar anisotropy patterns are expected compared to the case of a pure astrophysical origin of the CGB. We take into account the uncertainties in the dark matter clustering properties on sub-galactic scales, deriving two possible anisotropy scenarios. A clear dark matter angular signature is achieved when the annihilation signal receives only a moderate contribution from sub-galactic clumps and/or cuspy haloes. Experimentally, if galactic foregrounds systematics are efficiently kept under control, the angular differences are detectable with the forthcoming GLAST observatory, provided that the annihilation signal contributes to the CGB for a fraction >10-20%. If, instead, sub-galactic structures have a more prominent role, the astrophysical and dark matter anisotropies become degenerate, correspondingly diluting the DM signature. As complementary observables we also introduce the cross-correlation between surveys of galaxies and the CGB and the cross-correlation between different energy bands of the CGB and we find that they provide a further sensitive tool to detect the dark matter angular signatures.Comment: 13 pages, 8 figures; improved discussion; matches published versio