Poonam Mehta

Mass Hierarchy Determination via future Atmospheric Neutrino Detectors

We study the problem of determination of the sign of {delta}m{sub 31}{sup 2}, or the neutrino mass hierarchy, through observations of atmospheric neutrinos in future detectors. We consider two proposed detector types: (a) Megaton sized water Cerenkov detectors, which can measure the event rates of {nu}{sub {mu}}+{nu}{sub {mu}} and {nu}{sub e}+{nu}{sub e} and (b) 100 kton sized magnetized iron detectors, which can measure the event rates of {nu}{sub {mu}} and {nu}{sub {mu}}. For energies and path lengths relevant to atmospheric neutrinos, these rates obtain significant matter contributions from P{sub {mu}}{sub e}, P{sub {mu}}{sub {mu}} and P{sub ee}, leading to an appreciable sensitivity to the hierarchy. We do a binned {chi}{sup 2} analysis of simulated data in these two types of detectors which includes the effect of smearing in neutrino energy and direction and incorporates detector efficiencies and relevant statistical, theoretical and systematic errors. We also marginalize the {chi}{sup 2} over the allowed ranges of neutrino parameters in order to accurately account for their uncertainties. Finally, we compare the performance of both types of detectors vis a vis the hierarchy determination.

Atmospheric neutrinos as a probe of CPT and Lorentz violation

Abstract We show that atmospheric neutrinos can provide a sensitive and robust probe of CPT violation (CPTV). We perform realistic event-rate calculations and study the variations of the ratio of total muon to antimuon survival rates with L / E and L ( L ≡ baseline length, E ≡ neutrino energy) in a detector capable of identifying the muon charge. We demonstrate that measurements of these ratios when coupled with the significant L and E range which characterizes the atmospheric neutrino spectrum provides a method of both detecting the presence of such violations and putting bounds on them which compare very favorably with those possible from a future neutrino factory.

Testing nonstandard neutrino matter interactions in atmospheric neutrino propagation

We study the eects of non-standard interactions on the oscillation pattern of atmospheric neutrinos. We use neutrino oscillograms as our main tool to infer the role of non-standard interactions (NSI) parameters at the probability level in the energy range, E 2 [1; 20] GeV and zenith angle range, cos 2 [ 1; 0]. We compute the event rates for atmospheric neutrino events in presence of NSI parameters in the energy range E2 [1; 10] GeV for two dierent detector congurations - a magnetized iron calorimeter and an unmagnetized liquid

Topological phase in two flavor neutrino oscillations

We show that the phase appearing in neutrino flavor oscillation formulae has a geometric and topological contribution. We identify a topological phase appearing in the two flavor neutrino oscillation formula using Pancharatnams prescription of quantum collapses between nonorthogonal states. Such quantum collapses appear naturally in the expression for appearance and survival probabilities of neutrinos. Our analysis applies to neutrinos propagating in vacuum or through matter. For the minimal case of two flavors with CP conservation, our study shows for the first time that there is a geometric interpretation of the neutrino oscillation formulae for the detection probability of neutrino species.

Large matter effects in nu(mu) ---> nu(tau) oscillations

We show that matter effects change the numu-->nutau oscillation probability by as much as 70% for certain ranges of energies and path lengths. Consequently, the numu-->nutau survival probability also undergoes large changes. A proper understanding of numu survival rates must consider matter effects in Pmutau as well as Pmue. We comment on (a) how these matter effects may be observed and the sign of Delta31 determined in atmospheric neutrino measurements and at neutrino factories, and (b) how they lead to heightened sensitivity for small theta13.

Signals of R -parity violating supersymmetry in neutrino scattering at muon storage rings

Neutrino oscillation signals at muon storage rings can be faked by supersymmetric (SUSY) interactions in an R-parity violating scenario. We investigate the \ensuremath{\tau}-appearance signals for both long-baseline and near-site experiments, and conclude that the latter is of great use in distinguishing between oscillation and SUSY effects. On the other hand, for a wide and phenomenologically consistent choice of parameters, SUSY can cause a manifold increase in the event rate for wrong-sign muons at a long-baseline setting, thereby providing us with signatures of new physics.

Interplay of energy dependent astrophysical neutrino flavor ratios and new physics effects

We discuss the importance of flavor ratio measurements in neutrino telescopes, such as by measuring the ratio between muon tracks to cascades, for the purpose of extracting new physics signals encountered by astrophysical neutrinos during propagation from the source to the detector. The detected flavor ratios not only carry the energy information of specific new physics scenarios which alter the transition probabilities in distinctive ways, but also the energy dependent flavor composition at the source. In the present work, we discuss the interplay of these two energy dependent effects and identify which new physics scenarios can be distinguished from the detected flavor ratios as a function of astrophysical parameters. We use a recently developed self-consistent neutrino production model as our toy model to generate energy dependent source flavor ratios and discuss (invisible) neutrino decay and quantum decoherence as specific new physics examples. Furthermore, we identify potentially interesting classes of sources on the Hillas plot for the purpose of new physics searches. We find that sources with substantial magnetic fields 103 GaussB106 Gauss, such as Active Galactic Nuclei (AGN) cores, white dwarfs, or maybe gamma-ray bursts, have, in principle, the best discrimination power for the considered new physics scenarios, whereas AGN jets, which typically perform as pion beam sources, can only discriminate few sub cases in the new physics effects. The optimal parameter region somewhat depends on the class of new physics effect considered.

Classical light analogue of the non-local Aharonov-Bohm effect

We demonstrate the existence of a non-local geometric phase in the intensity-intensity correlations of classical incoherent light, that is not seen in the lower-order correlations. This two-photon Pancharatnam phase was observed and modulated in a Mach-Zehnder interferometer. Using acousto-optic interaction, independent phase noise was introduced to light in the two arms of the interferometer to create two independent incoherent classical sources from laser light. The experiment is the classical optical analogue of the multi-particle Aharonov-Bohm effect. As the trajectory of light over the Poincare sphere introduces a phase shift observable only in the intensity-intensity correlation, it provides a means of deflecting the two-photon wavefront, while having no effect on single photons.

Can we probe intrinsic CP and T violations and nonunitarity at long baseline accelerator experiments

One of the fundamental parameters entering neutrino oscillation framework is the leptonic CP phase

Large Matter Effects in

\delta_{13}