Supernova neutrinos: production, propagation and oscillations

I shall review some of the recent results concerning the astrophysics of a core collapse supernova (SN) and neutrino oscillations. Neutrinos play an important role in the SN explosion, and they also carry most of the energy of the collapse. The energy spectra of neutrinos and antineutrinos arriving at the Earth incorporate information on the primary neutrino fluxes as well as the neutrino mixing scenario. The analysis of neutrino propagation through the matter of the supernova and the Earth, combined with the observation of a neutrino burst from a galactic SN, enables us to put limits on the mixing angle $\theta_{13}$ and identify whether the mass hierarchy is normal or inverted. The neutrino burst also acts as an early warning signal for the optical observation, and in addition allows us to have a peek at the shock wave while still inside the SN mantle.Comment: 8 pages, uses espcrc2.sty (Nucl. Phys. B). Talk given at Neutrino 2004, Pari

Test of T violation in neutral B decays

T violation should be tested independently of CP violation. Besides K system, B meson decays provide another good place to study T violation. In the Standard Model, T violation in $B^0 \rightleftharpoons \bar{B^0}$ oscillation is expected to be small. The angular distribution of $B\to VV$ decay permits one to extract the T-odd correlation. In the absence of final state interaction, T violation in $B\to J/\psi(l^+ l^-) K^*(K_S\pi^0)$ decay can reach $4-7$ via $B^0-\bar{B^0}$ mixing.Comment: Latex, 11 pages, revised version will appear in PL

Self-Calibration of Neutrino Detectors using characteristic Backgrounds

We introduce the possibility to use characteristic natural neutrino backgrounds, such as Geoneutrinos (\bar{\nu}_e) or solar neutrinos (\nu_e), with known spectral shape for the energy calibration of future neutrino detectors, e.g. Large Liquid Scintillator Detectors. This "CalEffect" could be used without the need to apply any modifications to the experiment in all situations where one has a suitable background with sufficient statistics. After deriving the effect analytically using \chi^2 statistics, we show that it is only tiny for reactor neutrino experiments, but can be applicable in other situations. As an example, we present its impact on the identification of the wiggles in the power spectrum of supernova neutrinos caused by Earth matter effects. The Self-Calibration Effect could be used for cross checking other calibration methods and to resolve systematical effects in the primary neutrino interaction processes, in particular in the low energy cross sections.Comment: 6 pages, 4 figure

No-go for exactly degenerate neutrinos at high scale?

We show in a model independent manner that, if the magnitudes of Majorana masses of neutrinos are exactly equal at some high scale, the radiative corrections cannot reproduce the observed masses and mixing spectrum at the low scale, irrespective of the Majorana phases or the mixing angles at the high scale.Comment: 12 pages ReVTeX, A few typos corrected in the 2nd versio

2540 km: Bimagic baseline for neutrino oscillation parameters

We show that a source-to-detector distance of 2540 km offers multiple advantages for a low energy neutrino factory with a detector that can identify muon charge. At this baseline, for any neutrino hierarchy, the wrong-sign muon signal is almost independent of CP violation and $\theta_{13}$ in certain energy ranges. This reduces the uncertainties due to these parameters and allows the identification of the hierarchy in a clean way. In addition, part of the muon spectrum is also sensitive to the CP violating phase and $\theta_{13}$, so that the same setup can be used to probe these parameters as well.Comment: 4 pages, 4 figures, Revtex4. Text modified. Version to appear in PR

Combining LSND and Atmospheric Anomalies in a Three-Neutrino Picture

We investigate the three-neutrino mixing scheme for solving the atmospheric and LSND anomalies. We find the region in the parameter space that provides a good fit to the LSND and the SK atmospheric data, taking into account the CHOOZ constraint. We demonstrate that the goodness of this fit is comparable to that of the conventional fit to the solar and atmospheric data. Large values of the LSND angle are favoured and $\sin^2(2\theta_{\rm LSND})$ can be as high as 0.1. This can have important effects on the atmospheric electron neutrino ratios as well as on down-going multi-GeV muon neutrino ratios. We examine the possibility of distinguishing this scheme from the conventional one at the long baseline experiments. We find that the number of electron neutrino events observed at the CERN to Gran Sasso experiment may lead us to identify the scheme, and hence the mass pattern of neutrinos

Measurement of the Lifetime Difference of BdB_d Mesons: Possible and Worthwhile?

We estimate the decay width difference $\Delta Gamma_d / \Gamma_d$ in the $B_d$ system including $1/m_b$ contributions and next-to-leading order QCD corrections, and find it to be around 0.3%. We explicitly show that the time measurements of an untagged $B_d$ decaying to a single final state isotropically can only be sensitive to quadratic terms in $\Delta Gamma_d / \Gamma_d$, and hence the use of at least two different final states is desired. We discuss such pairs of candidate decay channels for the final states and explore the feasibility of a $\Delta Gamma_d / \Gamma_d$ measurement through them. The measurement of this width difference is essential for an accurate measurement of $\sin(2\beta)$ at the LHC. The nonzero width difference may also be used to identify new physics effects and to resolve a twofold discrete ambiguity in the $B_d$-$\bar{B}_d$ mixing phase. We also derive an upper bound on the value of $\Delta Gamma_d / \Gamma_d$ in the presence of new physics, and point out some differences in the phenomenology of width differences in the $B_s$ and $B_d$ systems.Comment: latex, 31 pages, revised versio

Low-rank and Sparse Soft Targets to Learn Better DNN Acoustic Models

Conventional deep neural networks (DNN) for speech acoustic modeling rely on Gaussian mixture models (GMM) and hidden Markov model (HMM) to obtain binary class labels as the targets for DNN training. Subword classes in speech recognition systems correspond to context-dependent tied states or senones. The present work addresses some limitations of GMM-HMM senone alignments for DNN training. We hypothesize that the senone probabilities obtained from a DNN trained with binary labels can provide more accurate targets to learn better acoustic models. However, DNN outputs bear inaccuracies which are exhibited as high dimensional unstructured noise, whereas the informative components are structured and low-dimensional. We exploit principle component analysis (PCA) and sparse coding to characterize the senone subspaces. Enhanced probabilities obtained from low-rank and sparse reconstructions are used as soft-targets for DNN acoustic modeling, that also enables training with untranscribed data. Experiments conducted on AMI corpus shows 4.6% relative reduction in word error rate