MMT Survey for Intervening MgII Absorption

We present the results from a spectroscopic survey for intervening MgII absorption in the spectra of 381 background QSOs conducted at the Multiple Mirror Telescope. This survey complements our earlier SDSS EDR MgII survey, extending our results to lower redshift ($z \simeq 0.15$) and weaker MgII $\lambda2796$ rest equivalent width ($W_0^{\lambda2796} \simeq 0.1$\AA). We confirm two major results from that survey: the transition in the $W_0^{\lambda2796}$ distribution at $W_0^{\lambda2796} \approx 0.3$\AA, and the $W_0^{\lambda2796}$-dependent evolution of the incidence of systems. The nature of $\partial^2N/\partial z \partial W_0^{\lambda2796}$ is consistent with the idea that multiple physically-distinct components/processes contribute to the incidence of MgII absorption systems in a $W_0$-dependent manner and evolve at different rates. A significant decrease in the total proper absorption cross section is detected in our MMT data for systems as weak as 1.0 \AA $\le W_0^{\lambda2796} < 1.5$\AA at $z\lesssim 0.4$. We discuss this $W_0$-dependent evolution in the context of the evolution of galaxy structures, processes including superwinds and interactions, and damped-Ly$\alpha$ absorbers. We also consider the possibility that the observed redshift and $W_0^{\lambda2796}$ dependence of the incidence of absorption in spectroscopic surveys for low-ion/neutral gas results from the effects of dust-induced extinction.Comment: 16 pages, 7 figures, accepted for publication in The Astrophysical Journa

Strong Absorption-line Systems at Low Redshift: MgII and Damped Lyman Alpha

We detail a powerful indirect method for the study of damped Lyman alpha systems (DLAs) at low redshift. We increase the probability of finding a low-redshift DLA to nearly 50% by targeting QSOs that are known to have strong low-redshift MgII and FeII absorption lines in their spectra. We are using Sloan Digital Sky Survey QSO spectra complemented by a survey we are conducting at the MMT to study the metal-line systems. The Hubble Space Telescope is being used to confirm low-redshift DLAs. In addition, we are imaging low-redshift DLA galaxies with several ground-based telescopes to directly study their environments.Comment: 6 pages, 4 figures. To appear in the proceedings for "The IGM/Galaxy Connection" conference held in Boulder, Colorado, August 8-10, 200

Probing the deviation from maximal mixing of atmospheric neutrinos

Pioneering atmospheric muon neutrino experiments have demonstrated the near-maximal magnitude of the flavor mixing angle $\theta_{23}$. But the precise value of the deviation $D \equiv 1/2 - \sin^2 \theta_{23}$ from maximality (if nonzero) needs to be known, being of great interest -- especially to builders of neutrino mass and mixing models. We quantitatively investigate in a three generation framework the feasibility of determining $D$ in a statistically significant manner from studies of the atmospheric $\nu_\mu,\bar\nu_\mu$ survival probability including both vacuum oscillations and matter effects. We show how this determination will be sharpened by considering the up-down ratios of observed $\nu_\mu$- and $\bar\nu_\mu$-induced events and the differences of these ratios in specified energy and zenith angle bins. We consider 1 Megaton year of exposure to a magnetized iron calorimeter such as the proposed INO detector ICAL, taking into account both energy and zenith angle resolution functions. The sensitivity of such an exposure and the dependence of the determination of $D$ on the concerned oscillation parameters are discussed in detail. The vital use of matter effects in fixing the octant of $\theta_{23}$ is highlighted.Comment: Version to appear in PR

Non-classical photon pair generation in atomic vapours

A scheme for the generation of non-classical pairs of photons in atomic vapours is proposed. The scheme exploits the fact that the cross correlation of the emission of photons from the extreme transitions of a four-level cascade system shows anti-bunching which has not been reported earlier and which is unlike the case of the three level cascade emission which shows bunching. The Cauchy-Schwarz inequality which is the ratio of cross-correlation to the auto correlation function in this case is estimated to be $10^3-10^6$ for controllable time delay, and is one to four orders of magnitude larger compared to previous experiments. The choice of Doppler free geometry in addition to the fact that at three photon resonance the excitation/deexcitation processes occur in a very narrow frequency band, ensures cleaner signals.Comment: 18 pages, 7 figure

Confusing Sterile Neutrinos with Deviation from Tribimaximal Mixing at Neutrino Telescopes

We expound the impact of extra sterile species on the ultra high energy neutrino fluxes in neutrino telescopes. We use three types of well-known flux ratios and compare the values of these flux ratios in presence of sterile neutrinos, with those predicted by deviation from the tribimaximal mixing scheme. We show that in the upcoming neutrino telescopes, its easy to confuse between the signature of sterile neutrinos with that of the deviation from tribimaximal mixing. We also show that if the measured flux ratios acquire a value well outside the range predicted by the standard scenario with three active neutrinos only, it might be possible to tell the presence of extra sterile neutrinos by observing ultra high energy neutrinos in future neutrino telescopes.Comment: 22 pages, version to appear in Phys. Rev.