Bi-large neutrino mixing and the Cabibbo angle

Recent measurements of the neutrino mixing angles cast doubt on the validity of the so-far popular tri-bimaximal mixing ansatz. We propose a parametrization for the neutrino mixing matrix where the reactor angle seeds the large solar and atmospheric mixing angles, equal to each other in first approximation. We suggest such bi-large mixing pattern as a model building standard, realized when the leading order value of the reactor angle equals the Cabibbo angle.Comment: 4 pages, 2 figs. v2: matches version appearing in Phys.Rev.D, rapid communication

Constraining nonstandard neutrino-quark interactions with solar, reactor and accelerator data

We present a reanalysis of nonstandard neutrino-down-quark interactions of electron and tau neutrinos using solar, reactor and accelerator data. In addition updating the analysis by including new solar data from SNO phase III and Borexino, as well as new KamLAND data and solar fluxes, a key role is played in our analysis by the combination of these results with the CHARM data. The latter allows us to better constrain the axial and axial-vector electron and tau-neutrino nonstandard interaction parameters characterizing the deviations from the Standard Model predictions.Comment: 11 pages, 6 figures, 2 tables, typo corrected in Figure 2, version published in Phys. Rev.

Exact relativistic beta decay endpoint spectrum

The exact relativistic form for the beta decay endpoint spectrum is derived and presented in a simple factorized form. We show that our exact formula can be well approximated to yield the endpoint form used in the fit method of the KATRIN collaboration. We also discuss the three neutrino case and how information from neutrino oscillation experiments may be useful in analyzing future beta decay endpoint experiments.Comment: 12 pages, 3 figure

Low-energy neutrino-electron scattering as a Standard Model probe: the potential of LENA as case study

Several proposals for studying neutrinos with large detectors are currently under discussion. We suggest that they could provide a precise measurement of the electroweak mixing angle as well as a probe for new physics, such as non-standard neutrino interactions (NSI), and the electroweak gauge structure. We illustrate this explicitly for the case of the LENA proposal, either with an artificial radioactive source or by using the solar neutrino flux

A_4-based neutrino masses with Majoron decaying dark matter

We propose an A_4 flavor-symmetric SU(3)xSU(2)xU(1) seesaw model where lepton number is broken spontaneously. A consistent two-zero texture pattern of neutrino masses and mixing emerges from the interplay of type-I and type-II seesaw contributions, with important phenomenological predictions. We show that, if the Majoron becomes massive, such seesaw scenario provides a viable candidate for decaying dark matter, consistent with cosmic microwave background lifetime constraints that follow from current WMAP observations. We also calculate the sub-leading one-loop-induced decay into photons which leads to a mono-energetic emission line that may be observed in future X-ray missions such as Xenia.Comment: 16 pages, 6 eps figures. Minor corrections. To appear in Phys. Rev.

Where we are on θ13\theta_{13}: addendum to "Global neutrino data and recent reactor fluxes: status of three-flavour oscillation parameters"

In this addendum to arXiv:1103.0734 we consider the recent results from long-baseline $\nu_\mu\to\nu_e$ searches at the T2K and MINOS experiments and investigate their implications for the mixing angle $\theta_{13}$ and the leptonic Dirac CP phase $\delta$. By combining the $2.5\sigma$ indication for a non-zero value of $\theta_{13}$ coming from T2K data with global neutrino oscillation data we obtain a significance for $\theta_{13} > 0$ of about $3\sigma$ with best fit points $\sin^2\theta_{13} = 0.013(0.016)$ for normal (inverted) neutrino mass ordering. These results depend somewhat on assumptions concerning the analysis of reactor neutrino data.Comment: 5 pages, 2 figures and 1 tabl

Two-parameter neutrino mass matrices with two texture zeros

We reanalyse Majorana-neutrino mass matrices M_nu with two texture zeros, by searching for viable hybrid textures in which the non-zero matrix elements of M_nu have simple ratios. Referring to the classification scheme of Frampton, Glashow and Marfatia, we find that the mass matrix denoted by A1 allows the ratios (M_nu)_{mu mu} : (Mnu)_{tau tau} = 1:1 and (M_nu)_{e tau} : (Mnu)_{mu tau} = 1:2. There are analogous ratios for texture A2. With these two hybrid textures, one obtains, for instance, good agreement with the data if one computes the three mixing angles in terms of the experimentally determined mass-squared differences Delta m^2_21 and Delta m^2_31. We could not find viable hybrid textures based on mass matrices different from those of cases A1 and A2.Comment: 10 pages, no figures, minor changes, some references adde

Nature of 4FGL J1838.2+3223: a flaring `spider' pulsar candidate

An unidentified $\gamma$-ray source 4FGL J1838.2+3223 has been proposed as a pulsar candidate. We present optical time-series multi-band photometry of its likely optical companion obtained with the 2.1-m telescope of Observatorio Astron\'omico Nacional San Pedro M\'artir, Mexico. The observations and the data from the Zwicky Transient Facility revealed the source brightness variability with a period of $\approx$4.02 h likely associated with the orbital motion of the binary system. The folded light curves have a single sine-like peak per period with an amplitude of about three magnitude accompanied by fast sporadic flares up to one magnitude level. We reproduce them modelling the companion heating by the pulsar. As a result, the companion side facing the pulsar is strongly heated up to 11300$\pm$400 K, while the temperature of its back side is only 2300$\pm$700 K. It has a mass of 0.10$\pm$0.05 ${\rm M}_\odot$ and underfills its Roche lobe with a filling factor of $0.60^{+0.10}_{-0.06}$. This implies that 4FGL J1838.2+3223 likely belongs to the `spider' pulsar family. The estimated distance of $\approx$3.1 kpc is compatible with Gaia results. We detect a flare from the source in X-rays and ultraviolet using Swift archival data and another one in X-rays with the eROSITA all-sky survey. Both flares have X-ray luminosity of $\sim$10$^{34}$ erg s$^{-1}$ which is two orders of magnitude higher than the upper limit in quiescence obtained from eROSITA assuming spectral shape typical for spider pulsars. If the spider interpretation is correct, these flares are among the strongest flares observed from non-accreting spider pulsars.Comment: 10 pages, 11 figures, accepted for publication in Monthly Notices of the Royal Astronomical Societ

Fermion masses, leptogenesis and supersymmetric SO (10) unification

Current neutrino oscillation data indicate the existence of two large lepton mixing angles, while Kobayashi-Maskawa matrix elements are all small. Here we show how supersymmetric SO(10) with extra chiral singlets can easily reconcile large lepton mixing angles with small quark mixing angles within the framework of the successful Fritzsch ansatz. Moreover, we show how this is fully consistent with the thermal leptogenesis scenario, avoiding the so-called gravitino problem. A sizable asymmetry can be generated at scales as low as possible within the leptogenesis mechanism. We present our results in terms of the leptonic CP violation parameter that characterizes neutrino oscillations