The mass varying neutrino scenario is a model that successfully explains the origin of dark energy while at the same time solves the coincidence problem. The model is, however, heavily constrained by its stability towards the formation of neutrino bound states when the neutrinos become nonrelativistic. We discuss these constraints and find that natural, adiabatic, stable models with the right amount of dark energy today do not exist. Secondly, we explain why using the lightest neutrino, which is still relativistic, as an explanation for dark energy does not work because of a feedback mechanism from the heavier neutrinos.
We discuss constraints on the effective number of neutrino species Nnu from recent cosmological observations such as CMB, LSS, BBN, including our own analysis which uses the WMAP and the Luminous Red Galaxy power spectrum data. We also discuss their implications on some non-standard cosmological scenarios such as the low (MeV-scale) reheating temperature scenario and the scenario with decaying particles between BBN and structure formation.
Concern about systematic uncertainty in the $^4$He abundance as well as the chemical evolution of $^3$He leads us to re-examine this important limit. It is shown that with conservative assumptions no more than the equivalent of 4 massless neutrino species are allowed. Even with the most extreme estimates of the astrophysical uncertainties a meaningful limit still exists, less than 5 massless neutrino species, and illustrates the robustness of this argument. A definitive measurement of the deuterium abundance in high-redshift hydrogen clouds should soon sharpen the limit.
We discuss how much we can probe the effective number of neutrino species N_nu with cosmic microwave background alone. Using the data of WMAP, ACBAR, CBI and BOOMERANG experiments, we obtain a constraint on the effective number of neutrino species as 0.96< N_nu <7.94 at 95% C.L. for a power-law LCDM flat universe model. The limit is improved to be 1.39 < N_nu < 6.38 at 95% C.L. if we assume that the baryon density, N_nu and the helium abundance are related by the big bang nucleosynthesis theory. We also provide a forecast for the PLANCK experiment using a Markov chain Monte Carlo approach. In …
We derive constraint on the effective number of neutrino species N_nu from the cosmic microwave background power spectrum of the WMAP and galaxy clustering power spectrum of the SDSS luminous red galaxies (LRGs). Using these two latest data sets of CMB and galaxy clustering alone, we obtain the limit 0.9 < N_nu < 8.2 (95% C.L.) for the power-law LambdaCDM flat universe, with no external prior. The lower limit corresponds to the lower bound on the reheating temperature of the universe T_R > 2 MeV.
The MiniBooNE results have still not been able to comprehensively rule out the oscillation interpretation of the LSND experiment. So far the so-called short baseline experiments with energy in the MeV range and baseline of few meters have been probing the existence of sterile neutrinos. We show how signatures of these extra sterile states could be obtained in TeV energy range atmospheric neutrinos travelling distances of thousands of kilometers. Atmospheric neutrinos in the TeV range would be detected by the upcoming neutrino telescopes. Of course vacuum oscillations of these neutrinos would b…
A review of the neutrino conversion and oscillations among the two neutrino species (active and sterile) induced by strong twisting magnetic field is presented and implications to neutrinos in neutron star, supernova, the Sun and interstellar galactic media are discussed. The ``cross-boundary effect" (CBE) (i.e., a possible conversion of one half of neutrinos of the bunch from active into sterile specie) at the surface of neutron star is also studied for a realistic neutron star structure.
We have performed a thorough analysis of the constraints which can be put on neutrino parameters from cosmological observations, most notably those from the WMAP satellite and the 2dF galaxy survey. For this data we find an upper limit on the sum of active neutrino mass eigenstates of \sum m_nu < 1.0 eV (95% conf.), but this limit is dependent on priors. We find that the WMAP and 2dF data alone cannot rule out the evidence from neutrinoless double beta decay reported by the Heidelberg-Moscow experiment. In terms of the relativistic energy density in neutrinos or other weakly interacting specie…
Cosmological limits on neutrino masses are softened, by more than a factor 2, if Cold Dark Matter (CDM) and Dark Energy (DE) are coupled. In turn, a neutrino mass yielding $Ω_ν$ up to $\sim0.20$ allows coupling levels $β\simeq 0.15, $ or more, already easing the coincidence problem. The coupling, in fact, displaces both $P(k)$ and $C_l$ spectra in a fashion opposite to neutrino mass. Estimates are obtained through a Fisher--matrix technique.
We investigate the cosmological effects of a neutrino interaction with cold dark matter. We postulate a neutrino that interacts with a ``neutrino interacting dark matter'' (NIDM) particle with an elastic-scattering cross section that either decreases with temperature as $T^2$ or remains constant with temperature. The neutrino--dark-matter interaction results in a neutrino--dark-matter fluid with pressure, and this pressure results in diffusion-damped oscillations in the matter power spectrum, analogous to the acoustic oscillations in the baryon-photon fluid. We discuss the bounds from the Sloa…
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.
I point out that the sterile neutrinos suggested as candidates of "cool" Dark Matter will decay through their mixing with light neutrinos. This leads to an upper bound of about 200 keV on the mass of the sterile neutrinos, but might facilitate their detection.
We examine how constraints can be placed on the neutrino component of dark matter by an accurate measurement of neutrinoless double beta ($0νββ$) decay and the solar oscillation amplitude. We comment on the alleged evidence for $0νββ$ decay.
The significance of light massive neutrinos as hot dark matter is outlined. The power of neutrino oscillation experiments with respect to detect such neutrinos in the eV-region is discussed. Present hints for neutrino oscillations in solar, atmospheric and LSND data are reviewed as well as future experiments and their potential.
Cosmology at present provides the nominally strongest constraint on the masses of standard model neutrinos. However, this constraint extremely dependent on the nature of the dark energy component of the Universe. When the dark energy equation of state parameter is taken as a free (but constant) parameter, the neutrino mass bound is sum m_nu < 1.48 eV (95% C.L.), compared with sum m_nu < 0.65 eV (95% C.L.) in the standard model where the dark energy is in the form of a cosmological constant. This has important consequences for future experiments aimed at the direct measurement of neutrino masse…
We investigate an extension of the Minimal Standard Model by right-handed neutrinos (the $ν$MSM) to incorporate neutrino masses consistent with oscillation experiments. Within this theory, the only candidates for dark matter particles are sterile right-handed neutrinos with masses of a few keV. Requiring that these neutrinos explain entirely the (warm) dark matter, we find that their number is at least three. We show that, in the minimal choice of three sterile neutrinos, the mass of the lightest active neutrino is smaller than ${\cal O}(10^{-5})$ eV, which excludes the degenerate mass spectra…
We propose that right-handed neutrinos are very long-lived dark matter. The long lifetime is realized by the separation of the wavefunction of right-handed neutrinos and that of other fermions in an extra dimension. Such long-lived and superheavy dark matter can naturally explain observed ultra high energy cosmic rays above the GZK cutoff (5 * 10^{19} eV) and huge amounts of cold dark matter simultaneously. Furthermore, the exponentially suppressed Yukawa couplings of right-handed neutrinos leads to the high predictablilty on the mass parameter of the neutrinoless double beta decay, as all the…
We propose a model for neutrino masses that simultaneously results in a new dark matter candidate, the right-handed neutrino. We derive the dark matter abundance in this model, show how the hierarchy of neutrino masses is obtained, and verify that the model is compatible with existing experimental results. The model provides an economical method of unifying two seemingly separate puzzles in contemporary particle physics and cosmology.
Extremely high energy (up to 10**(22) eV) cosmic neutrino beams initiate high energy particle cascades in the background of relic neutrinos from the Big Bang. We perform numerical calculations to show that such cascades could contribute more than 10% to the observed cosmic ray flux above 10**(19) eV if neutrinos have masses in the electron volt range. The required intensity of primary neutrinos could be consistent with astrophysical models for their production if the maximum neutrino energy reaches to 10**(22) eV and the massive neutrino dark matter is locally clustered. Future observations of…
Principle of neutralino dark matter detection with neutrino telescopes and predictions are reviewed. The future Antares detector is described. Prospection in the CMSSM is exposed including comparison with experiment sensitivities of both neutrino indirect detection and direct detection experiments. Results in other frameworks are shortly surveyed. Models with a non negligible neutralino higgsino fraction are promising for neutrino telescopes detection.
We present a supersymmetric model of dark energy from Mass Varying Neutrinos which is stable against radiative corrections to masses and couplings, and free of dynamical instabilities. This is the only such model of dark energy involving fields with significant couplings to any standard model particle. We briefly discuss consequences for neutrino oscillations and solar neutrinos.
Dark matter annihilations in the Sun to neutrino-antineutrino pairs have striking signatures in neutrino detectors such as IceCube and KM3. We make a model independent study of the signals after propagation of the neutrinos from the center of the Sun to the Earth. A large spin-dependent DM capture cross section in the Sun make the discovery prospects robust.
We calculate the time delays of neutrinos emitted in gamma ray bursts due to the effects of neutrino mass and quantum gravity using a time dependent Hubble constant which can significantly change the naive results presented hitherto in the literature for large redshifts, and gives some sensitivity to the details of dark energy. We show that the effects of neutrino mass, quantum gravity and dark energy may be disentangled by using low energy neutrinos to study neutrino mass, high energy neutrinos to study quantum gravity, and large redshifts to study dark energy. From low energy neutrinos one m…
In this brief report we consider couplings of the dark energy scalar, such as Quintessence to the neutrinos and discuss its implications in studies on the neutrino mass limits from Baryogenesis. During the evolution of the dark energy scalar, the neutrino masses vary, consequently the bounds on the neutrino masses we have here differ from those obtained before.
An interesting dynamical model for dark energy which does not require extremely light scalar fields such as quintessence, and at the same time explains the (near-) coincidence between the neutrino and dark energy densities is the model of dark energy coupled to mass varying neutrinos (MaVaNs). Despite the attractions of this model, we show that, generically, this model contains a catastrophic instability which occurs when neutrinos become non-relativistic. As a result of this instability, as neutrinos become non-relativistic, they condense into neutrino nuggets which redshift away similar to c…
We show that the vacuum condensate due to neutrino mixing in quantum field theory (QFT) contributes to the dark energy budget of the universe which gives rise to the accelerated behavior of cosmic flow. The mechanism of neutrino mixing is therefore a possible candidate to contribute to the cosmological dark energy.
In this paper we discuss light neutrino dipole moments, computed in the neutrino-mass extended standard model (SM), as a possible source for neutrino condensates which may cause cosmological constant observed today.
