495 research outputs found
Axion hot dark matter bounds
We derive cosmological limits on two-component hot dark matter consisting of
neutrinos and axions. We restrict the large-scale structure data to the safely
linear regime, excluding the Lyman-alpha forest. We derive Bayesian credible
regions in the two-parameter space consisting of m_a and sum(m_nu).
Marginalizing over sum(m_nu) provides m_a<1.02 eV (95% CL). In the absence of
axions the same data and methods give sum(m_nu)< 0.63 eV (95% CL).Comment: Contribution to Proc. 4th Patras Workshop on Axions, WIMPs and WISPs
(18-21 June 2008, DESY
Observational bounds on the cosmic radiation density
We consider the inference of the cosmic radiation density, traditionally
parameterised as the effective number of neutrino species N_eff, from precision
cosmological data. Paying particular attention to systematic effects, notably
scale-dependent biasing in the galaxy power spectrum, we find no evidence for a
significant deviation of N_eff from the standard value of N_eff^0=3.046 in any
combination of cosmological data sets, in contrast to some recent conclusions
of other authors. The combination of all available data in the linear regime
prefers, in the context of a ``vanilla+N_eff'' cosmological model,
1.1<N_eff<4.8 (95% C.L.) with a best-fit value of 2.6. Adding data at smaller
scales, notably the Lyman-alpha forest, we find 2.2<N_eff<5.8 (95% C.L.) with
3.8 as the best fit. Inclusion of the Lyman-alpha data shifts the preferred
N_eff upwards because the sigma_8 value derived from the SDSS Lyman-alpha data
is inconsistent with that inferred from CMB. In an extended cosmological model
that includes a nonzero mass for N_eff neutrino flavours, a running scalar
spectral index and a w parameter for the dark energy, we find 0.8<N_eff<6.1
(95% C.L.) with 3.0 as the best fit.Comment: 23 pages, 3 figures, uses iopart.cls; v2: 1 new figure, references
added, matches published versio
Observing trans-Planckian ripples in the primordial power spectrum with future large scale structure probes
We revisit the issue of ripples in the primordial power spectra caused by
trans-Planckian physics, and the potential for their detection by future
cosmological probes. We find that for reasonably large values of the first
slow-roll parameter epsilon (> 0.001), a positive detection of trans-Planckian
ripples can be made even if the amplitude is as low as 10^-4. Data from the
Large Synoptic Survey Telescope (LSST) and the proposed future 21 cm survey
with the Fast Fourier Transform Telescope (FFTT) will be particularly useful in
this regard. If the scale of inflation is close to its present upper bound, a
scale of new physics as high as 0.2 M_Planck could lead to observable
signatures.Comment: 20 pages, 3 figures, uses iopart.cls; v2: 21 pages, added references,
to appear in JCA
Neutrino mass from future high redshift galaxy surveys: sensitivity and detection threshold
We calculate the sensitivity of future cosmic microwave background probes and large scale structure measurements from galaxy redshift surveys to the neutrino mass. We find that, for minimal models with few parameters, a measurement of the matter power spectrum over a large range of redshifts has more constraining power than a single measurement at low redshifts. However, this improvement in sensitivity does not extend to larger models. We also quantify how the non-Gaussian nature of the posterior distribution function with respect to the individual cosmological parameter influences such quantities as the sensitivity and the detection threshold. For realistic assumptions about future large scale structure data, the minimum detectable neutrino mass at 95 % C.L. is about 0.05 eV in the context of a minimal 8-parameter cosmological model. In a more general model framework, however, the detection threshold can increase by as much as a factor of three
Cosmological constraints on neutrino plus axion hot dark matter
We use observations of the cosmological large-scale structure to derive
limits on two-component hot dark matter consisting of mass-degenerate neutrinos
and hadronic axions, both components having velocity dispersions corresponding
to their respective decoupling temperatures. We restrict the data samples to
the safely linear regime, in particular excluding the Lyman-alpha forest. Using
standard Bayesian inference techniques we derive credible regions in the
two-parameter space of m_a and sum(m_nu). Marginalising over sum(m_nu) provides
m_a < 1.2 eV (95% C.L.). In the absence of axions the same data and methods
give sum(m_nu) < 0.65 eV (95% C.L.). We also derive limits on m_a for a range
of axion-pion couplings up to one order of magnitude larger or smaller than the
hadronic value.Comment: 13 pages, 2 figures, uses iopart.cl
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.
Cosmological constraints on neutrino plus axion hot dark matter: Update after WMAP-5
We update our previous constraints on two-component hot dark matter (axions
and neutrinos), including the recent WMAP 5-year data release. Marginalising
over sum m_nu provides m_a < 1.02 eV (95% C.L.) for the axion mass. In the
absence of axions we find sum m_nu < 0.63 eV (95% C.L.).Comment: 4 pages, 1 figure, uses iopart.cls; v2 matches published versio
Self-induced conversion in dense neutrino gases: Pendulum in flavour space
Neutrino-neutrino interactions can lead to collective flavour conversion effects in supernovae and in the early universe. We demonstrate that the case of "bipolar" oscillations, where a dense gas of neutrinos and antineutrinos in equal numbers completely converts from one flavour to another even if the mixing angle is small, is equivalent to a pendulum in flavour space. Bipolar flavour conversion corresponds to the swinging of the pendulum, which begins in an unstable upright position (the initial flavour), and passes through momentarily the vertically downward position (the other flavour) in the course of its motion. The time scale to complete one cycle of oscillation depends logarithmically on the vacuum mixing angle. Likewise, the presence of an ordinary medium can be shown analytically to contribute to a logarithmic increase in the bipolar conversion period. We further find that a more complex (and realistic) system of unequal numbers of neutrinos and antineutrinos is analogous to a spinning top subject to a torque. This analogy easily explains that such a system can oscillate in both the bipolar or the synchronised mode, depending on the neutrino density and the size of the neutrino-antineutrino asymmetry. Our simple model applies to isotropic and "single-angle" systems, as well as systems in which the matrix of neutrino-neutrino couplings possesses certain symmetries that prevent kinematical decoherence between the individual neutrino modes. In more general cases, however, and especially in the case of neutrinos emitted from a supernova core, these symmetries are not necessarily manifest. As a result, quick decoherence in flavour space, rather than collective bipolar oscillations, for both the normal and inverted mass hierarchies may in fact be the generic behaviour of dense neutrino gases
Neutrino Physics: Open Theoretical Questions
We know that neutrino mass and mixing provide a window to physics beyond the
Standard Model. Now this window is open, at least partly. And the questions
are: what do we see, which kind of new physics, and how far "beyond"? I
summarize the present knowledge of neutrino mass and mixing, and then formulate
the main open questions. Following the bottom-up approach, properties of the
neutrino mass matrix are considered. Then different possible ways to uncover
the underlying physics are discussed. Some results along the line of: see-saw,
GUT and SUSY GUT are reviewed.Comment: 17 pages, latex, 12 figures. Talk given at the XXI International
Symposium on Lepton and Photon Interactions at High Energies, ``Lepton Photon
2003", August 11-16, 2003 - Fermilab, Batavia, IL US
Using BBN in cosmological parameter extraction from CMB: a forecast for Planck
Data from future high-precision Cosmic Microwave Background (CMB)
measurements will be sensitive to the primordial Helium abundance . At the
same time, this parameter can be predicted from Big Bang Nucleosynthesis (BBN)
as a function of the baryon and radiation densities, as well as a neutrino
chemical potential. We suggest to use this information to impose a
self-consistent BBN prior on and determine its impact on parameter
inference from simulated Planck data. We find that this approach can
significantly improve bounds on cosmological parameters compared to an analysis
which treats as a free parameter, if the neutrino chemical potential is
taken to vanish. We demonstrate that fixing the Helium fraction to an arbitrary
value can seriously bias parameter estimates. Under the assumption of
degenerate BBN (i.e., letting the neutrino chemical potential vary), the
BBN prior's constraining power is somewhat weakened, but nevertheless allows us
to constrain with an accuracy that rivals bounds inferred from present
data on light element abundances.Comment: 14 pages, 4 figures; v2: minor changes, matches published versio
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