958 research outputs found
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
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
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 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
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
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