Upper limit on the cosmic gamma-ray burst rate from high energy diffuse neutrino background
We derive upper limits on the ratio f{sub GRB/CCSN}(z){identical_to}R{sub GRB}(z)/R{sub CCSN}(z){identical_to}f{sub GRB/CCSN}(0)(1+z){sup {alpha}}, the ratio of the rate, R{sub GRB}, of long-duration gamma-ray bursts (GRBs) to the rate, R{sub CCSN}, of core-collapse supernovae (CCSNe) in the Universe (z being the cosmological redshift and {), by using the upper limit on the diffuse TeV-PeV neutrino background given by the AMANDA-II experiment in the South Pole, under the assumption that GRBs are sources of TeV-PeV neutrinos produced from decay of charged pions produced in p{gamma} interaction of protons accelerated to ultrahigh energies at internal shocks within GRB jets. For the assumed ''concordance model'' of cosmic star formation rate, R{sub SF}, with R{sub CCSN}(z){proportional_to}R{sub SF}(z), our conservative upper limits are f{sub GRB/CCSN}(0){ =}1, already more restrictive than) the current upper limit on this ratio inferred from other astronomical considerations, thus providing a useful independent probe of and constraint on the CCSN-GRB connection. Nondetection of a diffuse TeV-PeV neutrino background by the upcoming IceCube detector in the South Pole after three years of operation, for example, will bring down the upper limit on f{sub GRB/CCSN}(0)more » to below a few x10{sup -5} level, while a detection will confirm the hypothesis of proton acceleration to ultrahigh energies in GRBs and will potentially also yield the true rate of occurrence of these events in the Universe.« less

title: Observing supernova neutrino light curve in future dark matter detectors
abstract: The possibility of observing supernova (SN) neutrinos through the process of coherent elastic neutrino-nucleus scattering (CENNS) in future ton scale detectors designed primarily for direct detection of dark matter is investigated. In particular, we focus on the possibility of distinguishing the various phases of the SN neutrino emission. The neutrino emission rates from the recent long term Basel/Darmstadt simulations are used to calculate the expected event rates. The recent state-of-the-art SN simulations predict closer fluxes among different neutrino flavors and lower average energies compared to the earlier simulation models. We find that our estimated total event rates are typically a factor of two lower than those predicted using older simulation models. We further find that, with optimistic assumptions on the detector's time resolution (~ 10 ms) and energy threshold (~ 0.1 keV), the neutrinos associated with the accretion phase of the SN can in principle be demarcated out with, for example, a 10-ton Xe detector, although distinguishing the neutrinos associated with the neutronization burst phase of the explosion would typically require several tens of ton detectors. We also comment on the possibility of studying the properties of non-electron flavor neutrinos from the CENNS of SN neutrinos.

title: On the Observability of Collective Flavor Oscillations in Diffuse Supernova Neutrino Background
abstract: Collective flavor oscillations are known to bring multiple splits in the supernova (SN) neutrino and antineutrino spectra. These spectral splits depend not only on the mass hierarchy of the neutrinos but also on the initial relative flux composition. Observation of spectral splits in a future galactic supernova signal is expected to throw light on the mass hierarchy pattern of the neutrinos. However, since the Diffuse Supernova Neutrino Background (DSNB) comprises of a superposition of neutrino fluxes from all past supernovae, and since different supernovae are expected to have slightly different initial fluxes, it is pertinent to check if the hierarchy dependent signature of collective oscillations can survive this averaging of the flux spectra. Since the actual distribution of SN with initial relative flux spectra of the neutrinos and antineutrinos is unknown, we assume a log-normal distribution for them. We study the dependence of the hierarchy sensitivity to the mean and variance of the log-normal distribution function. We find that the hierarchy sensitivity depends crucially on the mean value of the relative initial luminosity. The effect of the width is to reduce the hierarchy sensitivity for all values of the mean initial relative luminosity. We find that in the very small mixing angle ( θ 13 ) limit considering only statistical errors even for very moderate values of variance, there is almost no detectable hierarchy sensitivity if the mean relative luminosities of ν e and ν ¯ e are greater than 1.

title: Stringent constraint on neutrino Lorentz-invariance violation from the two IceCube PeV neutrinos
abstract: LAPTh,  As a consequence, particles may not travel at the universal speed of light. Inparticular, superluminal extragalactic neutrinos would rapidly lose energy via the bremssthralung ofelectron-positron pairs (ν → ν e

title: Constraining scalar singlet dark matter with CDMS, XENON and DAMA and prediction for direct detection rates
abstract: We consider a simplest extension of the Standard Model (SM) through the incorporation of a real scalar singlet and an additional discrete Z2 symmetry. The model admits the neutral scalar singlet to be stable and thus, a viable component of dark matter. We explore the parameter space of the model keeping in view the constraints arise from different dark matter direct detection experiments through WIMP -nucleon scattering. First of all, we have utilised the data obtained from CDMS, XENON-10 and XENON-100 collaborations. We further constraint the parameter space from the DAMA collaboration results (both with and without channelling) and CoGeNT collaboration results. Throughout our analysis, the constraint arises due to the observed relic density of dark matter reported by WMAP experiment, is also incorporated. Utilising all those constraints, on the model parameter space, we calculate the event rates and the annual variation of event rates in the context of a Liquid Argon Detector experiment.

title: Optimised sensitivity to leptonic CP violation from spectral information: the LBNO case at 2300 km baseline
abstract: One of the main goals of the Long Baseline Neutrino Observatory (LBNO) is to study the $L/E$ behaviour (spectral information) of the electron neutrino and antineutrino appearance probabilities, in order to determine the unknown CP-violation phase $\delta_{CP}$ and discover CP-violation in the leptonic sector. The result is based on the measurement of the appearance probabilities in a broad range of energies, covering t he 1st and 2nd oscillation maxima, at a very long baseline of 2300 km. The sensitivity of the experiment can be maximised by optimising the energy spectra of the neutrino and anti-neutrino fluxes. Such an optimisation requires exploring an extended range of parameters describing in details the geometries and properties of the primary protons, hadron target and focusing elements in the neutrino beam line. In this paper we present a numerical solution that leads to an optimised energy spectra and study its impact on the sensitivity of LBNO to discover leptonic CP violation. In the optimised flux both 1st and 2nd oscillation maxima play an important role in the CP sensitivity. The studies also show that this configuration is less sensitive to systematic errors (e.g. on the total event rates) than an experiment which mainly relies on the neutrino-antineutrino asymmetry at the 1st maximum to determine the existence of CP-violation.

title: DOMAIN WALL IN LYRA GEOMETRY
abstract: In this paper we have discussed two models of domain walls within the framework of Lyra geometry. An exact solution is obtained for a thick non static domain wall. The space time is non singular both in its spatial and temporal behavior and the gravitational field experienced by a test particle is attractive. It is found that these exists no particle horizon in our case. Also we have presented a spherical domain wall with nonvanishing stress components in the direction perpendicular to the plane of the wall. The gravitational field of the domain wall is shown to be attractive in nature.

title: Geometry of the thermodynamics of the black holes in Hořava-Lifshitz gravity
abstract: Recently, a non-relativistic renormalizable theory of gravity has been proposed by Hořava. This theory is essentially a field theoretic model for a UV complete theory of gravity and it reduces to Einstein’s general relativity at large distances. Subsequently, Cai and his collaborators have obtained black hole solution in this gravity theory and studied the thermodynamic properties of the black hole solutions. In present work, we investigate the geometric thermodynamics of the above black hole solutions and examine the possibilities of any phase transition.

title: Particle production and universal thermodynamics
abstract: In the present work, particle creation mechanism has been employed to the Universe as a thermodynamical system. The Universe is considered to be a spatially flat FRW model and cosmic fluid is chosen as a perfect fluid with a barotropic equation of state—$$p=(\gamma -1)\rho $$p=(γ-1)ρ. By proper choice of the particle creation rate, expressions for the entropy and temperature have been determined at various stages of evolution of the Universe. Finally, using the deceleration parameter q as a function of the redshift parameter z based on recent observations, the particle creation rate has been evaluated and its variation at different epochs have been shown graphically.

title: Higher-dimensional Bianchi-V model in Brans-Dicke theory and inflation
abstract: This paper deals with the question whether an inflationary scenario is possible for the higher-dimensional Bianchi-V model in Brans-Dicke theory with a perfect fluid. Exact analytic solutions have been evaluated with a barotropic equation of state. These solutions have been analyzed and some of them have shown the properties of the inflationary scenario.

title: Non-standard interaction in neutrino oscillations and recent Daya Bay, T2K experiments
abstract: We study the possible constraints on non-standard interaction(NSIs) in a model independent way by considering the recent results from T2K and Daya Bay neutrino oscillations experiments. Using perturbation method we present generic formulas (suitable for T2K baseline and for large $\theta_{13}$ as evident from Daya Bay) for the probability of oscillation for $\nu_\mu \rightarrow \nu_e$, taking into account NSIs at source ($\epsilon^s$), detector ($\epsilon^d$) and during propagation ($\epsilon^m$) of neutrinos through matter. Two separate cases of perturbation with small (slightly large) NSI ($\epsilon_{\alpha\beta}^m \sim 0.03(0.18)$) are discussed in detail. Using various possible presently allowed NSI values we reanalyze numerically the $\theta_{13} - \delta$ allowed region given by recent T2K experimental data. We obtain model independent constraints on NSIs in the $\delta-\epsilon_{\alpha\beta}^m$ plane using the $\theta_{13}$ value as measured by Daya Bay, where $\delta$ is the CP violating phase. Depending on $\delta$ values significant constraints on $\epsilon_{e\tau}$ and $\epsilon_{\tau\tau}$, in particular, are possible for both hierarchies of neutrino masses. Corresponding to T2K's 66% confidence level result, the constraints on $\epsilon_{\tau\tau}$ is shown to be independent of any $\delta$ value.