Presence Of Massive Neutrinos Research Articles

Weighing neutrinos using high redshift galaxy luminosity functions

Laboratory experiments measuring neutrino oscillations, indicate small mass differences between different mass eigenstates of neutrinos. The absolute mass scale is however not determined, with at present the strongest upper limits coming from astronomical observations rather than terrestrial experiments. The presence of massive neutrinos suppresses the growth of perturbations below a characteristic mass scale, thereby leading to a decreased abundance of collapsed dark matter halos. Here we show that this effect can significantly alter the predicted luminosity function (LF) of high redshift galaxies. In particular we demonstrate that a stringent constraint on the neutrino mass can be obtained using the well measured galaxy LF and our semi-analytic structure formation models. Combining the constraints from the Wilkinson Microwave Anisotropy Probe 7 year (WMAP7) data with the LF data at z = 4, we get a limit on the sum of the masses of 3 degenerate neutrinos \Sigma m_\nu < 0.52 eV at the 95 % CL. The additional constraints using the prior on Hubble constant strengthens this limit to \Sigma m_\nu < 0.29 eV at the 95 % CL. This neutrino mass limit is a factor of order 4 improvement compared to the constraint based on the WMAP7 data alone, and as stringent as known limits based on other astronomical observations. As different astronomical measurements may suffer from different set of biases, the method presented here provides a complementary probe of \Sigma m_\nu . We suggest that repeating this exercise on well measured luminosity functions over different redshift ranges can provide independent and tighter constraints on \Sigma m_\nu .

Quantum flavor oscillations extended to the Dirac theory

AbstractFlavor oscillations by itself and its coupling with chiral oscillations and/or spin‐flipping are the most relevant quantum phenomena of neutrino physics. This report deals with the quantum theory of flavor oscillations in vacuum, extended to fermionic particles in the several subtle aspects of the first quantization and second quantization theories. At first, the basic controversies regarding quantum‐mechanical derivations of the flavor conversion formulas are reviewed based on the internal wave packet (IWP) framework. In this scenario, the use of the Dirac equation is required for a satisfactory evolution of fermionic mass‐eigenstates since in the standard treatment of oscillations the mass‐eigenstates are implicitly assumed to be scalars and, consequently, the spinorial form of neutrino wave functions is not included in the calculations. Within first quantized theories, besides flavor oscillations, chiral oscillations automatically appear when we set the dynamic equations for a fermionic Dirac‐type particle. It is also observed that there is no constraint between chiral oscillations, when it takes place in vacuum, and the process of spin‐flipping related to the helicity quantum number, which does not take place in vacuum. The left‐handed chiral nature of created and detected neutrinos can be implemented in the first quantized Dirac theory in presence of mixing; the probability loss due to the changing of initially left‐handed neutrinos to the undetected right‐handed neutrinos can be obtained in analytic form. These modifications introduce correction factors proportional to mν2/Eν2 that are very difficult to be quantified by the current phenomenological analysis. All these effects can also be identified when the non‐minimal coupling with an external (electro)magnetic field in the neutrino interacting Lagrangian is taken into account. In the context of a causal relativistic theory of a free particle, one of the two effects should be present in flavor oscillations: (a) rapid oscillations or (b) initial flavor violation. Concerning second quantized approaches, a simple second quantized treatment exhibits a tiny but inevitable initial flavor violation without the possibility of rapid oscillations. Such effect is a consequence of an intrinsically indefinite but approximately well defined neutrino flavor. Within a realistic calculation in pion decay, including the quantum field treatment of the creation process with finite decay width, it is possible to quantify such violation. The violation effects are shown to be much larger than loop induced lepton flavor violation processes, already present in the standard model in the presence of massive neutrinos with mixing. For the implicitly assumed fermionic nature of the Dirac theory, the conclusions of this report lead to lessons concerning flavor mixing, chiral oscillations, interference between positive and negative frequency components of Dirac equation solutions, and the field formulation of quantum oscillations.

PERTURBATIONS OF DARK MATTER GRAVITY

Until recently the study of the gravitational field of dark matter was primarily concerned with its local effects on the motion of stars in galaxies and galaxy clusters. On the other hand, the WMAP experiment has shown that the gravitational field produced by dark matter amplifies the higher acoustic modes of the CMBR power spectrum, more intensely than the gravitational field of baryons. Such a wide range of experimental evidences from cosmology to local gravity suggests the necessity of a comprehensive analysis of the dark matter gravitational field per se, regardless of any other attributes that dark matter may eventually possess. In this paper we introduce and apply Nash's theory of perturbative geometry to the study of the dark matter gravitational field alone, in a higher-dimensional framework. It is shown that the dark matter gravitational perturbations in the early universe can be explained by the extrinsic curvature of the standard cosmology. Together with the estimated presence of massive neutrinos, such geometric perturbation is compatible not only with the observed power spectrum in the WMAP experiment but also with the most recent data on the accelerated expansion of the universe. It is possible that the same structure formation exists locally, such as in the cases of young galaxies or in cluster collisions. In most other cases it seems to have ceased when the extrinsic curvature becomes negligible, leading to Einstein's equations in four dimensions. The slow motion of stars in galaxies and the motion of plasma substructures in nearly colliding clusters are calculated with the geodesic equation for a slowly moving object in a gravitational field of arbitrary strength.

WMAP dark matter constraints onb−τ Yukawa unification with massive neutrinos

We revisit the WMAP dark matter constraints on Yukawa Unification in the presence of massive neutrinos. The large lepton mixing indicated by the data may modify the predictions for the bottom quark mass, enabling Yukawa unification also for large $\tan\beta$, and for positive $\mu$ that was previously disfavoured. As a result, the allowed parameter space for neutralino dark matter increases for positive $\mu$, particularly for areas with resonant enhancement of the neutralino relic density. On the contrary, a negative $\mu$ is not easily compatible with large lepton mixing and Dirac neutrino Yukawa couplings, and the WMAP allowed parameter space is in this case strongly constrained.

Higher order corrections to the large scale matter power spectrum in the presence ofmassive neutrinos

We present the first systematic derivation of the one-loop correctionto the large scale matter power spectrum in a mixed cold+ hot dark matter cosmology with subdominant massive neutrino hot dark matter.Starting with the equations of motion for the density and velocity fields, we deriveperturbative solutions to these quantities and construct recursion relations forthe interaction kernels, noting and justifying all approximations along theway. We find interaction kernels similar to those for a cold dark matter onlyuniverse, but with additional dependences on the neutrino energy density fractionfν and the linear growth functions of the incoming wavevectors. Compared with thefν = 0 case, the one-loop corrected matter power spectrum for a mixed dark mattercosmology exhibits a decrease in small scale power exceeding the canonical∼8fν suppression predicted by linear theory, a feature also seen in multi-componentN-body simulations.

Neutrino mass effects on vector and tensor CMB anisotropies in the presence of a primordial magnetic field

If a primordial magnetic field (PMF) is present during photon decoupling and afterward, a finite neutrino mass can affect all modes of the CMB. In this work, we expand on earlier studies of the scalar mode effects by constructing the vector and tensor-mode equations in the presence of massive neutrinos and a PMF. We compute the power spectrum of the various modes in an illustrative example and find that the neutrino mass can significantly affect the vector and tensor modes when a PMF exists, while the effects are negligible for no PMF. The most prominent result of the present analysis is the behavior of the EE (grad-like polarization power spectrum) component of the tensor mode at low multipoles. For massive neutrinos the EE mode can become comparable to the observed primary anisotropy. Therefore, if and when the EE mode power spectrum is measured at low multipoles the possibility exists to place a strong constraint on the sum of the neutrino masses.

Neutrino mass, dark energy, and the linear growth factor

We study the degeneracies between neutrino mass and dark energy as they manifest themselves in cosmological observations. In contradiction to a popular formula in the literature, the suppression of the matter power spectrum caused by massive neutrinos is not just a function of the ratio of neutrino to total mass densities ${f}_{\ensuremath{\nu}}={\ensuremath{\Omega}}_{\ensuremath{\nu}}/{\ensuremath{\Omega}}_{m}$, but also each of the densities independently. We also present a fitting formula for the logarithmic growth factor of perturbations in a flat universe, $f(z,k;{f}_{\ensuremath{\nu}},w,{\ensuremath{\Omega}}_{\mathrm{DE}})\ensuremath{\approx}[1\ensuremath{-}A(k){\ensuremath{\Omega}}_{\mathrm{DE}}{f}_{\ensuremath{\nu}}+B(k){f}_{\ensuremath{\nu}}^{2}\ensuremath{-}C(k){f}_{\ensuremath{\nu}}^{3}]{\ensuremath{\Omega}}_{m}^{\ensuremath{\alpha}}(z)$, where $\ensuremath{\alpha}$ depends on the dark energy equation of state parameter $w$. We then discuss cosmological probes where the $f$ factor directly appears: peculiar velocities, redshift distortion, and the integrated Sachs-Wolfe effect. We also modify the approximation of Eisenstein and Hu [Astrophys. J. 511, 5 (1999)] for the power spectrum of fluctuations in the presence of massive neutrinos and provide a revised code [http://www.star.ucl.ac.uk/~lahav/nu_matter_power.f].

Nonlinear cosmological matter power spectrum with massive neutrinos: The halo model

Measurements of the linear power spectrum of galaxies have placed tight constraints on neutrino masses. We extend the framework of the halo model of cosmological nonlinear matter clustering to include the effect of massive neutrino infall into cold dark matter (CDM) halos. The magnitude of the effect of neutrino clustering for three degenerate mass neutrinos with ${m}_{{\ensuremath{\nu}}_{i}}=0.9\text{ }\mathrm{e}\mathrm{V}$ is of order $\ensuremath{\sim}1%$, within the potential sensitivity of upcoming weak lensing surveys. In order to use these measurements to further constrain---or eventually detect---neutrino masses, accurate theoretical predictions of the nonlinear power spectrum in the presence of massive neutrinos will be needed, likely only possible through high-resolution multiple particle (neutrino, CDM and baryon) simulations.

General theory of weak processes involving neutrinos. II. Pure leptonic decays

We present a general theory of leptonic decays which consistently incorporates possibility of nonzero neutrino masses and associated lepton mixing. We calculate differential decay distribution $\frac{{d}^{2}\ensuremath{\Gamma}}{d{E}_{b}d}$ $cos\ensuremath{\theta}$ and ${l}_{b}$ polarization for the decay ${l}_{a}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\mathrm{la}}{l}_{b}{\overline{\ensuremath{\nu}}}_{\mathrm{lb}}$, i.e., in general incoherent sum of decays ${l}_{a}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{i}{l}_{b}{\overline{\ensuremath{\nu}}}_{j}$ into all allowed mass eigenstates ${\ensuremath{\nu}}_{i}$ and ${\overline{\ensuremath{\nu}}}_{j}$. Expressions are also given for average quantities $〈cos\ensuremath{\theta}〉({E}_{b})$, $〈cos\ensuremath{\theta}〉$ (integrated over ${E}_{b}$), $〈{E}_{b}〉(\ensuremath{\theta})$, and $〈{E}_{b}〉$ for individual ($i$,$j$) decay modes and observed sum. The total rate for massive-neutrino modes is calculated for relevant experimental cases. These results are applied to analyze what observable characteristics of massive neutrinos and lepton mixing would be in leptonic ${l}_{a}$ decay. We show that $\frac{d\ensuremath{\Gamma}}{d{E}_{b}}$ would in general contain kinks at intermediate energies and carry out a search for these in existing $\ensuremath{\mu}$ and $\ensuremath{\tau}$ decay data. We further show that conventional determination of Lorentz structure of weak leptonic couplings via measurement of spectral parameters $\ensuremath{\rho}$, $\ensuremath{\eta}$, $\ensuremath{\xi}$, and $\ensuremath{\delta}$ is not applicable in presence of massive neutrinos and lepton mixing; a deviation of observed parameters (with radiative corrections extracted) from their conventional $V\ensuremath{-}A$ values could be caused either by non-($V\ensuremath{-}A$) Lorentz structure or by massive-neutrino decay modes and lepton mixing. Thus, past measurements of spectral parameters yield information only on combined effects of underlying Lorentz structure of couplings and on possible neutrino masses and mixing, but not on either of these in isolation. The appropriate generalized formalism for analysis of Lorentz structure in leptonic decays is given, and a quantitative study is performed of effects of neutrino masses and mixing on spectral parameters. We propose methods to distinguish between these effects and those due to possible non-($V\ensuremath{-}A$) Lorentz structure; these methods can be applied in a reanalysis of old $\ensuremath{\mu}$ and $\ensuremath{\tau}$ decay data, and can serve as part of a generalized framework for analysis of forthcoming data. Within context of standard electroweak theory we apply our results to existing data to obtain new upper bounds on possible contributions of massive neutrino modes. Finally, we determine optimal ways in which, and corresponding sensitivity with which, forthcoming experiments on $\ensuremath{\mu}$ and $\ensuremath{\tau}$ decay can search for massive neutrinos and lepton mixing.