Abstract
There is a renewed interest in constraining the sum of the masses of the three neutrino flavours by using cosmological measurements. Solar, atmospheric, reactor and accelerator neutrino experiments have confirmed neutrino oscillations, implying that neutrinos have non-zero mass, but without pinning down their absolute masses. While it has been established that the effect of light neutrinos on the evolution of cosmic structure is small, the upper limits derived from a large-scale structure could help significantly to constrain the absolute scale of the neutrino masses. It is also important to know the sum of neutrino masses as it is degenerate with the values of other cosmological parameters, e.g. the amplitude of fluctuations and the primordial spectral index. A summary of the cosmological neutrino mass limits is given. Current results from cosmology set an upper limit on the sum of the neutrino masses at ∼1 eV, somewhat dependent on the datasets used in the analyses and assumed priors on cosmological parameters. It is important to emphasize that the total neutrino mass (‘hot dark matter’) is derived by assuming that the other components in the universe are baryons, cold dark matter and dark energy. We assessed the impact of neutrino masses on the matter power spectrum, the cosmic microwave background, peculiar velocities and gravitational lensing. We also discuss possible methods to improve the mass upper limits by an order of magnitude.
Highlights
The connection between neutrino masses and cosmic structure formation was realised in the 1970’s by Zeldovich and others, but for a long time cosmologists were mostly interested in neutrino masses in the ∼ 10 eV range, i.e. massive enough to make up all of the dark matter
After WMAP, there is a further tendency towards stronger upper limits, reflecting the dual role of the cosmic microwave background (CMB) and large-scale structure in constraining neutrino masses: the matter power spectrum is most sensitive to the ratio Ων/Ωm, but one needs good constraints on pre-WMAP None pre-WMAP pre-WMAP WMAP+CBI+ACBAR WMAP+Wang comp
Even when taking the uncertainties in the properties of dark energy into account, the combination of weak lensing tomography and high-precision CMB experiments may reach sensitivities down to the lower bound of 0.06 eV on the sum of the neutrino masses set by the current oscillation data [68]
Summary
The connection between neutrino masses and cosmic structure formation was realised in the 1970’s by Zeldovich and others, but for a long time cosmologists were mostly interested in neutrino masses in the ∼ 10 eV range, i.e. massive enough to make up all of the dark matter. The downfall of the top-down ‘hot dark matter’ scenario of structure formation, and the fact that no evidence for neutrino masses existed before Super-Kamiokande detected oscillations of atmospheric neutrinos in 1998, explains why there was very little continuous interest in this sub-field. For the effective neutrino mass scale involved in neutrino less double beta decay a range 0.1-0.9 eV has been inferred from the claimed detection of this process [16, 17].
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