Tau Neutrinos Underground: Signals of νμ→ντ\nu_\mu \to \nu_\tau Oscillations with Extragalactic Neutrinos

The appearance of high energy tau neutrinos due to $\nu_\mu \to \nu_\tau$ oscillations of extragalactic neutrinos can be observed by measuring the neutrino induced upward hadronic and electromagnetic showers and upward muons. We evaluate quantitatively the tau neutrino regeneration in the Earth for a variety of extragalactic neutrino fluxes. Charged-current interactions of the upward tau neutrinos below and in the detector, and the subsequent tau decay create muons or hadronic and electromagnetic showers. The background for these events are muon neutrino and electron neutrino charged-current and neutral-current interactions, where in addition to extragalactic neutrinos, we consider atmospheric neutrinos. We find significant signal to background ratios for the hadronic/electromagnetic showers with energies above 10 TeV to 100 TeV initiated by the extragalactic neutrinos. We show that the tau neutrinos from point sources also have the potential for discovery above a 1 TeV threshold. A kilometer-size neutrino telescope has a very good chance of detecting the appearance of tau neutrinos when both muon and hadronic/electromagnetic showers are detected.Comment: section added and two new figs; accepted for publication in Physical Review

Discovery of two new Galactic candidate luminous blue variables with Wide-field Infrared Survey Explorer

We report the discovery of two new Galactic candidate luminous blue variable (LBV) stars via detection of circular shells (typical of confirmed and candidate LBVs) and follow‐up spectroscopy of their central stars. The shells were detected at 22 μm in the archival data of the Mid‐Infrared All Sky Survey carried out with the Wide‐field Infrared Survey Explorer (WISE). Follow‐up optical spectroscopy of the central stars of the shells conducted with the renewed Southern African Large Telescope (SALT) showed that their spectra are very similar to those of the well‐known LBVs P Cygni and AG Car, and the recently discovered candidate LBV MN112, which implies the LBV classification for these stars as well. The LBV classification of both stars is supported by detection of their significant photometric variability: one of them brightened in the R and I bands by 0.68 ± 0.10 and 0.61 ± 0.04 mag, respectively, during the last 13–18 years, while the second one (known as Hen 3‐1383) varies its B, V, R, I and Ks brightnesses by ≃0.5–0.9 mag on time‐scales from 10 d to decades. We also found significant changes in the spectrum of Hen 3‐1383 on a time‐scale of ≃3 months, which provides additional support for the LBV classification of this star. Further spectrophotometric monitoring of both stars is required to firmly prove their LBV status. We discuss a connection between the location of massive stars in the field and their fast rotation, and suggest that the LBV activity of the newly discovered candidate LBVs might be directly related to their possible runaway status