Two-loop Radiative Corrections to Neutrino Masses in SU(3)L×U(1)NSU(3)_L \times U(1)_N Gauge Models

We have constructed two $SU(3)_L \times U(1)_N$ gauge models with the $L^\prime = L_e-L_\mu-L_\tau$ symmetry, which accommodate tiny neutrino masses generated by one-loop and two-loop radiative effects. The heavy neutral leptons and heavy charged leptons are employed to specify the lepton triplets in $SU(3)_L$, respectively, accompanied by ($\phi^0$, $\phi^-$, $h^+$) and ($\phi^+$, $\phi^0$, $h^+$), where $\phi$ stands for the standard Higgs scalar and $h^+$ is a key ingredient for radiative mechanisms. From our numerical calculations, we find that both our models are relevant to yield the VO solution to the solar neutrino problem.Comment: Talk at Post Summer Institute 2000 on Neutrino Physics, August 21-24, 2000, Fuji-Yoshida, Japa

Comment on Neutrino Masses and Oscillations in an SU(3)L×U(1)NSU(3)_L \times U(1)_N Model with Radiative Mechanism

We discussed how neutrino masses and oscillations are radiatively generated in an $SU(3)_L$ $\times$ $U(1)_N$ gauge model with a symmetry based on $L_e-L_\mu-L_\tau$ ($\equiv$$L^\prime$). The model is characterized by lepton triplets $\psi^i=(\nu^i,\ell^{-i},E^{-i})$, where $E^{-i}$ are negatively charged heavy leptons, an $SU(3)_L$ triplet Higgs scalar $\xi$ and a singlet Higgs scalar $k^{++}$. These Higgs scalars can be interpreted as a Zee's and Zee-Babu's scalar for radiative mechanisms. We demonstrated that the mass hierarchy of $\Delta m_{atm}^2$ $\gg$ $\Delta m_\odot^2$ arise as a consequence of the dynamical hierarchy between $L^\prime$-conserving one-loop effects and $L^\prime$-violating two-loop effects, and our model is relevant to yield quasivacuum solution for solar neutrino problem.Comment: 6 Pages, Latex2e, RevTex macr

Scotogenic dark matter and single-zero textures of the neutrino mass matrix

The scotogenic model can simultaneously account for the presence of dark matter and the origin of neutrino masses. We assume that the flavor neutrino mass matrix has one zero element and Yukawa matrix elements are real in the scotogenic model. It turns out that only one pattern of the flavor neutrino mass matrix in the one-zero-texture scheme within the scotogenic model is viable with the observed neutrino oscillation data, the relic abundance of the dark matter, and the upper limit of the branching ratio of the $\mu \rightarrow e \gamma$ process.Comment: 8 pages, 6 figures, references added, Accepted for publication in Physical Review

Clockwork origin of neutrino mixings

The clockwork mechanism provides a natural way to obtain hierarchical masses and couplings in a theory. We propose a clockwork model that has nine clockwork generations. In this model, the candidates of the origin of the neutrino mixings are nine Yukawa mass matrix elements $Y^{a\beta}$ that connect neutrinos and clockwork fermions, nine clockwork mass ratios $q_{a\beta}$, and nine numbers of clockwork fermions $n_{a\beta}$, where $a, \beta=1,2,3$. Assuming $|Y^{a\beta}|=1$, the neutrino mixings originate from the pure clockwork sector. We show that the observed neutrino mixings are exactly obtained from a clockwork model in the case of the $q_{a\beta}$ origin scenario. In the $n_{a\beta}$ origin scenario, the correct order of magnitude of the observed neutrino mixings is obtained from a clockwork model.Comment: 9 pages, 4 figures. Accepted for publication in Physical Review

Neutrino Oscillations Induced by Two-loop Radiative Effects

Phenomena of neutrino oscillations are discussed on the basis of two-loop radiative neutrino mechanism. Neutrino mixings are experimentally suggested to be maximal in both atmospheric and solar neutrino oscillations. By using $L_e - L_\mu - L_\tau$ ($\equiv L^\prime$)-conservation, which, however, only ensures the maximal solar neutrino mixing, we find that two-loop radiative mechanism dynamically generates the maximal atmospheric neutrino mixing and that the estimate of $\Delta m^2_\odot/\Delta m^2_{atm} \sim\epsilon m_e/m_\tau$ explains $\Delta m^2_\odot/\Delta m^2_{atm} \ll 1$ because of $m_e/m_\tau \ll 1$, where $\epsilon$ measures the breaking of the $L^\prime$-conservation. Together with $\Delta m^2_{atm} \approx 3\times 10^{-3}$ eV$^2$, this estimate yields $\Delta m^2_\odot \sim 10^{-7}$ eV$^2$ for $\epsilon \sim 0.1$, which corresponds to the LOW solution to the solar neutrino problem. Neutrino mass scale is given by $(16\pi^2)^{-2} m_em_\tau /M$ ($M \sim$ 1 TeV), which is of order 0.01 eV.Comment: 10 pages,6 figures,Talk given at the Post Summer Institute 2000 on Neutrino Physics, August 21-24, 2000, Fuji-Yoshida, Yamanashi, Japa

Fermi-Boltzmann statistics of neutrinos and relativistic effective degrees of freedom

We investigate the effect of the presence of non-pure fermionic neutrinos on the relativistic effective degrees of freedom in the early universe. The statistics of neutrinos is transformed continuously from Fermi-Dirac to Maxwell-Boltzmann statistics. We find that the relativistic degrees of freedom decreases with the deviation from pure Fermi-Dirac statistics of neutrinos if there are constant and large lepton asymmetries. Additionally, we confirm that the change of the statistics of neutrinos from Fermi-Dirac to Maxwell-Boltzmann is not sufficient to cover the excess of the effective number of neutrinos.Comment: 15 pages, 5 figures, version to appear in Modern Physics Letters

Asymmetric dark matter and effective number of neutrinos

We study the effect of the MeV-scale asymmetric dark matter annihilation on the effective number of neutrinos $N_{\rm eff}$ at the epoch of the big bang nucleosynthesis. If the asymmetric dark matter $\chi$ couples more strongly to the neutrinos $\nu$ than to the photons $\gamma$ and electrons $e^-$, $\Gamma_{\chi\gamma, \chi e} \ll \Gamma_{\chi\nu}$, or $\Gamma_{\chi\gamma, \chi e} \gg \Gamma_{\chi\nu}$, the lower mass limit on the asymmetric dark matter is about $18$ MeV for $N_{\rm eff}\simeq 3.0$.Comment: 13 pages, 14 figures, version accepted for publication in Physical Review

Seesaw model and two zero flavor neutrino texture

In the two zero flavor neutrino mass matrix scheme with nonvanishing Majorana effective mass $M_{ee}$ for the neutrino less double beta decay, four textures are compatible with observed data. We obtain the complete list of the possible textures of four zero Dirac neutrino mass matrix $m_D$ in the seesaw mechanism providing these four flavor neutrino textures. Explicit analytical analysis of $m_D$ turns out to provide the relation of $m_D \propto \sqrt{M_{ee}}$.Comment: 14 pages, 1 figure, version accepted for publication in International Journal of Modern Physics

Maximal CP Violation in Flavor Neutrino Masses

Since flavor neutrino masses $M_{\mu\mu,\tau\tau,\mu\tau}$ can be expressed in terms of $M_{ee,e\mu,e\tau}$, mutual dependence among $M_{\mu\mu,\tau\tau,\mu\tau}$ is derived by imposing some constraints on $M_{ee,e\mu,e\tau}$. For appropriately imposed constraints on $M_{ee,e\mu,e\tau}$, we show a texture of neutrino mass matrix giving rise to maximal CP violation. When the atmospheric neutrino mixing is also maximal, we discuss various specific textures of neutrino mass matrices including the texture with $M_{\tau\tau}=M^\ast_{\mu\mu}$ derived as the simplest solution to the constraint of $M_{\tau\tau}-M_{\mu\mu}$=imaginary, which is required by the constraint of $M_{e\mu}\cos\theta_{23}-M_{e\tau}\sin\theta_{23}$=real for $\cos 2\theta_{23}=0$. It is found that Majorana CP violation depends on the phase of $M_{ee}$.Comment: 12 pages, no figure. version accepted for publication in International Journal of Modern Physics

Characterizing Earth-like Planets Using a Combination of High-Dispersion Spectroscopy and High-Contrast Instruments: Doppler-shifted Water and Oxygen Lines

Future radial velocity, astrometric, and direct-imaging surveys will find nearby Earth-sized planets within the habitable zone in the near future. How can we search for water and oxygen in those nontransiting planets? We show that a combination of high-dispersion spectroscopic and coronagraphic techniques is a promising technique to detect molecular lines imprinted in the scattered light of Earth-like planets (ELPs). In this method, the planetary signals are spectroscopically separated from telluric absorption by using the Doppler shift. Assuming a long observing campaign (a 10-day exposure) using a high-dispersion spectrometer (R=50,000) with speckle suppression on a 30-m telescope, we simulate the spectra from ELPs around M dwarfs (whose stellar effective temperature is 2750-3750 K) at 5 pc. Performing a cross-correlation analysis with the spectral template of the molecular lines, we find that raw contrasts of $10^{-4}$ and $10^{-5}$ (using Y, J, and H bands) are required to detect water vapor at the 3 $\sigma$ and 16 $\sigma$ levels, respectively, for $T_\star$=3000 K. The raw contrast of $10^{-5}$ is required for a 6 $\sigma$ detection of the oxygen 1.27 $\mu$m band. We also examine possible systematics, incomplete speckle subtraction, and the correction for telluric lines. When those are not perfect, a telluric water signal appears in the cross-correlation function. However, we find the planetary signal is separated from that resulting from the velocity difference. We also find that the intrinsic water lines in the Phoenix spectra are too weak to affect the results for water detection. We conclude that a combination of high-dispersion spectroscopy and high-contrast instruments can be a powerful means to characterize ELPs in the extremely large telescope era.Comment: 36 pages, 13 figures, 3 tables, additional consideration of targets and discussions about systematic