arXiv subjects
Publications and source records attributed to Debasish Majumdar.
We investigate the deviation from tribimaximal mixing value and the reach of $θ_{13}$ using neutrino factory at CERN and ICAL detector at INO.
The unparticle is proposed by Georgi as a conceptual new physics beyond the standard model to describe the low energy sector of a nontrivial scale invariant sector of an effective theory. We consider the neutrino decay in unparticle scenario and investigate the effect of such decay for the case of ultra high energy neutrinos from GRB. The effect on the detection yield of these neutrinos are also probed for a kilometer scale ice-Cerenkov detector.
We investigate deviation from the tri-bimaximal mixing in the case of ultra high energy neutrino using ICECUBE detector. We consider the ratio of No. of muon tracks to the shower generated due to eletrons and hadrons. Our analysis shows for tri-bimaximal mixing the ratio comes out around 4.05. Keeping $θ_12$ and $θ_23$ fixed at tri-bimaximal value, we have varied the angle $θ_{13}$ = $3^o$, $6^o$, $9^o$ and the value of the ratio gradually decreases. The variation of ratio lies 8% to 18% from the tri-bimaximal mixing value.
The cosmological observations coupled with theoretical calculations suggest the existence of enormous amount of unseen and unknown matter or dark matter in the universe. The evidence of their existence, the possible candidates and their possible direct detections are discussed.
The possibility to verify the pseudo-Dirac nature of neutrinos is investigated here via the detection of ultra high energy neutrinos from distant cosmological objects like GRBs. The very long baseline and the energy range from $\sim$ TeV to $\sim$ EeV for such neutrinos invokes the likelihood to probe very small pseude-Dirac splittings. The expected secondary muons from such neutrinos that can be detected by a kilometer scale detector such as ICECUBE is calculated. The pseudo-Dirac nature, if exists, will show a considerable departure from flavour oscillation scenario in the total yield of the secondary muons induced by such neutrinos.
We demonstrate that `Bimaximal + Democratic' type neutrino mass matrix can accommodate the deviation of $θ_\odot$ from its maximal value which referred in the literature as `quark-lepton complementarity' along with the other present day neutrino experimental results, namely, atmospheric, CHOOZ, neutrinoless double beta decay ($ββ_{0ν}$) and result obtained from WMAP experiment. We define a function $χ_p$ in terms of solar and atmospheric neutrino mass squared differences and solar neutrino mixing angle (obtained from different experiments and our proposed texture). The masses and mixing angles are expressed in terms of three parameters in our proposed texture. The allowed region of the texture parameters is obtained through minimization of the above function. The proposed texture crucially depends on the value of the experimental results of $ββ_{0ν}$ experiment among all other above mentioned experiments. If, in future, $ββ_{0ν}$ experiments, namely, MOON, EXO, GENIUS shift the lower bound on $ $ at the higher side by one order, the present texture will be ruled out.
We have considered neutralino to be the lightest supersymmetric particle (LSP) in the framework of minimal Anomaly Mediated Supersymmetric (mAMSB) model. We have studied variation of neutralino mass with the supersymmetric parameters. Considering these neutralinos to be the candidates for weakly interacting massive particle (WIMP) or cold dark matter (CDM), we have calculated the neutralino nucleon scalar cross-sections and compared them with DAMA-NaI neutralino direct detection search results. From this study we observe that the mAMSB model results cannot explain the allowed region in WIMP mass and WIMP-nucleon scalar cross-section space obtained from annual modulation signature in DAMA-NaI experiment.
In view of recent neutrino experimental results such as SNO, Super-Kamiokande (SK), CHOOZ and neutrinoless double beta decay $(ββ_{0ν})$, we consider a texture of neutrino mass matrix which contains three parameters in order to explain those neutrino experimental results. We have first fitted parameters in a model independent way with solar and atmospheric neutrino mass squared differences and solar neutrino mixing angle which satisfy LMA solution. The maximal value of atmospheric neutrino mixing angle comes out naturally in the present texture. Most interestingly, fitted parameters of the neutrino mass matrix considered here also marginally satisfy recent limit on effective Majorana neutrino mass obtained from neutrinoless double beta decay experiment. We further demonstrate an explicit model which gives rise to the texture investigated by considering an $SU(2)_L\times U(1)_Y$ gauge group with two extra real scalar singlets and discrete $Z_2\times Z_3$ symmetry. Majorana neutrino masses are generated through higher dimensional operators at the scale $M$. We have estimated the scales at which singlets get VEV's and M by comparing with the best fitted results obtained in the present work.
We consider the lightest Kaluza-Klein particle at N=1 mode (LKP) of universal extra dimension to be the candidate for Dark Matter and predict the detection rates for such particles for Germenium and NaI detectors. We have also calculated the nature of annual modulation for the signals in these two types of detectors for LKP Dark Matter. The rates with different values of speed of solar system in the Galactic rest frame are also evaluated.
The half lives are calculated for the process of $β^\pm$ decay and electron capture for nuclei in mass range $\sim$ 65 - 100 relevant for the core of a massive star at late burning stage of steller evolution that leads to supernova explosion. The rates of electron capture process are also computed for nuclei relevant during presupernova stage of massive stars. These half lives and rates are calculated by expressing $β^\pm$ Gamow-Teller decay strengths in terms of smoothed bivariate strength densities. These strength densities are constructed in the framework of spectral averaging theory for two body nuclear Hamiltonian in a large nuclear shell model space. The method has a natural extension to weak interaction rates for r and rp-processes.
We re-examine MSW solutions of the solar neutrino problem in a two flavor scenario taking (a) the results on total rates and the electron energy spectrum from the 1117-day SuperKamiokande (SK) data and (b) those on total rates from the Chlorine and Gallium experiments. We find that the SMA solution gives the best fit to the total rates data from the different experiments. One new feature of our analysis is the use of the moments of the SK electron spectrum in a $χ^2$ analysis. The best-fit to the moments is broadly in agreement with that obtained from a direct fit to the spectrum data and prefers a $Δm^2$ comparable to the SMA fit to the rates but the required mixing angle is larger. In the combined rate and spectrum analysis, apart from varying the normalization of the $^8$B flux as a free parameter and determining its best-fit value we also obtain the best-fit parameters when correlations between the rates and the spectrum data are included and the normalization of the $^8$B flux held fixed at its SSM value. We observe that the correlations between the rates and spectrum data are important and the goodness of fit worsens when these are included. In either case, the best-fit lies in the LMA region.
Violation of the Equivalence Principle (VEP) can lead to neutrino oscillation through the non-diagonal coupling of neutrino flavor eigenstates with the gravitational field. The neutrino energy dependence of this oscillation probability is different from that of the usual mass-mixing neutrino oscillations. In this work we explore, in detail, the viability of the VEP hypothesis as a solution to the solar neutrino problem in a two generation scenario with both the active and sterile neutrino alternatives, choosing these states to be massless. To obtain the best-fit values of the oscillation parameters we perform a chi square analysis for the total rates of solar neutrinos seen at the Chlorine (Homestake), Gallium (Gallex and SAGE), Kamiokande, and SuperKamiokande (SK) experiments. We find that the goodness of these fits is never satisfactory. It markedly improves, especially for VEP transformation to sterile neutrinos, if the Chlorine result is excluded from the analysis. The 1117-day SK data for recoil electron spectrum are also examined for signals of VEP oscillations. For these fits, we consider variations of the Standard Solar Model by allowing the absolute normalizations of the 8B and hep neutrinos to vary. Here the fits are quite good but the best fit values of the parameters are rather different from those from the total rates fits. A combined fit to the total rates and recoil electron spectrum data is also performed. We present the 90% confidence limit contours for all the three analyses mentioned above. The best-fit parameters obtained from the recoil electron spectrum and the combined analysis of rate and spectrum are used to predict the charge current and scattering electron spectrum at SNO.
We re-examine the neutrino decay solution to the solar neutrino problem in the light of the SuperKamiokande (SK) data. For the decay solution the SK spectrum data by its own can provide a fit comparable to the fit obtained from the MSW solution. However when one combines the results from the total rates of the $^{37}{Cl}$ and $^{71}{Ga}$ experiments the fit becomes much poorer.
We re-examine vacuum oscillation solutions of the solar neutrino problem taking (a) the results on total rates, electron energy spectrum, and the seasonal variations from the 708 day SuperKamiokande data and (b) those on total rates from the Chlorine and Gallium experiments. Best fit values for the mixing angle and mass splitting are found for oscillations to sequential and sterile neutrinos and the 90% C.L. allowed regions are determined.
The SuperKamiokande collaboration has presented results on the observation of solar neutrinos. The Sudbury Neutrino Observatory (SNO) is also expected to go on-line in the near future. We propose several new variables, insensitive to the absolute flux of the initial solar neutrino beam, which probe the shape of the observed spectrum at these experiments and can sensitively signal neutrino oscillations. One class of such variables involves normalised moments of the distributions recorded at the two facilities while another variable, specific to SNO, depends on the integrated charged and neutral current signals. The utility of these variables in the context of supernova neutrinos, both from the collapse epoch and the post-bounce era, is also emphasised. It is shown that, notwithstanding the imprecise nature of the information about the initial neutrino spectra from a supernova, oscillations can be detected using these variables and it will be possible to distinguish between the alternatives of oscillation to a sequential neutrino {\em vis-a-vis} that to a sterile neutrino.
Results for solar neutrino detection from the SuperKamiokande collaboration have been presented recently while those from the Sudbury Neutrino Observatory are expected in the near future. These experiments are sensitive to the 8B neutrinos from the sun, the shape of whose spectrum is well-known but the normalisation is less certain. We propose several variables, insensitive to the absolute flux of the incident beam, which probe the shape of the observed spectrum and can sensitively signal neutrino oscillations. They provide methods to extract the neutrino mixing angle and mass splitting from the data and also to distinguish oscillation to sequential neutrinos from those to a sterile neutrino.
Neutrinos and antineutrinos of all three flavours are emitted during the post bounce phase of a core collapse supernova with $\numu/\nutau (\anumu/\anutau)$ having average energies more than that of $\nue(\anue)$. They can be detected by the new earth bound detector like SNO and Super-Kamiokande which are sensitive to neutrinos of all three flavours. In this letter we consider the effect of flavour oscillations on the neutrino flux and their expected number of events at the detector. We do a three-generation analysis and for the mass and mixing schemes we first consider the threefold maximal mixing model consistent with the solar and the atmospheric neutrino data and next a scenario with one $Δm^2 \sim 10^{-11} eV^2$ (solar range) and the other $Δm^2 \sim 10^{-18} eV^2$, for which the oscillation length is of the order of the supernova distance. In both these scenarios there are no matter effects in the resultant neutrino spectrum and one is concerned with vacuum oscillations. We find that though neutrino oscillations result in a depletion in the number of $\nue$ and $\anue$ coming from the supernova, the actual signals at the detectors are appreciable enhanced.
Neutrinos emitted during stellar core collapse leading to a supernova are primarily of the electron neutrino type at source which may undergo oscillation between flavor eigenstates during propagation to an earth-bound detector. Although the number of neutrinos emitted during the pre-bounce collapse phase is much smaller than that emitted in the post-bounce phase (in which all flavors of neutrinos are emitted), a nearby supernova event may nevertheless register a substantial number of detections from the pre-bounce phase at SuperKamiokande (SK) and the Sudbury Neutrino Observatory (SNO). The calorimetric measurement of the supernova neutrino fluence from this stage via the charge current and neutral current detection channels in SNO and the corresponding distortion of detected spectrum in SK over the no-oscillation spectrum, can probe information about neutrino mass difference and mixing which are illustrated here in terms of two- and three-flavor oscillation models.