arXiv subjects

Amitava Raychaudhuri

Publications and source records attributed to Amitava Raychaudhuri.

At least 73 records · Page 4Linked to original sources

arXiv2001

Solar Neutrino Rates, Spectrum, and its Moments : an MSW Analysis in the Light of Super-Kamiokande Results

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.

hep-ph↗

arXiv2001

Solar neutrino results and Violation of the Equivalence Principle: An analysis of the existing data and predictions for SNO

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.

hep-ph↗

arXiv2000

Cosmological constraints on R-parity violation from neutrino decay

If the neutrino mass is non-zero, as hinted by several experiments, then R-parity-violating supersymmetric Yukawa couplings can drive a heavy neutrino decay into lighter states. The heavy neutrino may either decay radiatively into a lighter neutrino, or it may decay into three light neutrinos through a Z-mediated penguin. For a given mass of the decaying neutrino, we calculate its lifetime for the various modes, each mode requiring certain pairs of R-parity-violating couplings be non-zero. We then check whether the calculated lifetimes fall in zones allowed or excluded by cosmological requirements. For the latter case, we derive stringent new constraints on the corresponding products of R-parity-violating couplings for given values of the decaying neutrino mass.

hep-ph↗

arXiv2000

Mass bounds for Triplet Scalars of the Left-Right symmetric model and their future detection prospects

The standard formulation of the Left-Right symmetric model involves scalars transforming as a triplet under SU(2)L. This multiplet contains particles which are uncharged, singly-charged, and doubly-charged. We derive a bound on the uncharged scalar mass of 55.4 GeV using results from LEP-II and find that a range upto 110 GeV may be explored at the NLC at the 5sigma level. We also discuss search strategies for the singly- and doubly-charged scalars at the Tevatron and the LHC. Possible Standard Model backgrounds for the relevant modes are estimated and compared with the signal. At the LHC, the prospects of detecting the doubly-charged scalar are bright up to a mass of 850 GeV while the 5sigma discovery limit of the singly-charged mode extends to 240 GeV for an integrated luminosity of 100 inverse fb. At the Tevatron, with an integrated luminosity of 25 inverse fb, the doubly-charged state can be detected if its mass is less than 275 GeV while the reach for the singly charged scalar is 140 GeV.

hep-ph↗

arXiv1999

Vacuum Oscillation solutions of the Solar Neutrino Problem : A status Report

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.

hep-ph↗

arXiv1999

R-parity-violating trilinear couplings and recent neutrino data

The nontrivial structure of the neutrino mass matrix, suggested by the recent Super-Kamiokande results and data from other neutrino experiments, can be reproduced in R-parity-violating supersymmetric theories. This requires sets of products of R-parity-violating trilinear couplings to take appropriately chosen values. It is shown that the existing constraints on these couplings are satisfied by these choices.

hep-ph↗

arXiv1999

New Variables For Neutrino Oscillation Diagnostics at Superkamiokande and the Sudbury Neutrino Observatory

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.

hep-ph↗

arXiv1998

Solar Neutrino Oscillation Diagnostics at Superkamiokande and Sno

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.

hep-ph↗

arXiv1998

Oscillation Effects On Neutrinos From The Early Phase Of a Nearby Supernova

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.

astro-ph↗

arXiv1998

New constraints on R-parity violation from K and B systems

We have derived new upper limits on several products (two at a time) of lepton number violating $λ'$-type couplings from the consideration of $ΔS = 2$ and $ΔB = 2$ box graphs. Each box contains one scalar lepton and one W-boson or one charged-Higgs-boson as internal lines. Most of these bounds are more stringent than previously obtained. Some of these product couplings drive $K_L$ (and some other $B_d$) decays to two charged leptons at enhanced rates. Some of them can explain the rare $K^+ \to π^+ ν\barν$ event recently observed at BNL.

hep-ph↗

arXiv1997

Excited States of 71Ge above the Neutron Emission Threshold and Solar Neutrino Capture rates for Ga Detectors

In Gallium detectors for solar neutrinos, the capture rate due to Gamow-Teller transitions to excited states of 71Ge beyond the neutron emission threshold is usually neglected. We make a model calculation to estimate its effect and find that this yields an additional contribution which may be as much as 0.4 SNU, even larger than that from the Isobaric Analog State in 71Ge reached by Fermi transitions, which is normally included in the standard predictions.

astro-ph↗

arXiv1997

Next to Minimal Higgs : Mass Bounds and Search Prospects

The Standard Model of electroweak interactions has one scalar doublet. The minimal extension of this sector is effected by adding a neutral, singlet scalar field. Depending on whether the singlet field has a non-zero vacuum expectation value, x, or not, the scenario has quite distinctive predictions. In particular, x unequal to 0 produces a mixing between the usual SU(2) doublet and the singlet, giving rise to two physical states and a goldstone boson with non-vanishing coupling to these. Presence of this coupling modifies the 2 jets + missing energy signal of the Bjorken process at LEP. We update the bounds on the Higgs mass using the LEP-1 data. We then explore, using parton-level Monte Carlo event generators, the production of these scalars at the LHC via gluon-gluon fusion and subsequent detection. We compare the signals with the expected backgrounds.

hep-ph↗

arXiv1996

Unification and Model Building, Astroparticle Physics and Neutrinos

This report summarises the work done during the Workshop on High Energy Physics Phenomenology 4 (S.N.Bose National Centre for Basic Sciences, Calcutta, India, Jan 2-14,1996) in Working Groups IV (Unification and Model Building) and V (Astroparticle Physics and Neutrinos).

hep-ph↗

arXiv1995

Searching $R$-parity-violating supersymmetry in semileptonic $B$-decays

If $R$-parity is broken and the photino, although unstable, does not decay within the detector, then in new semileptonic $B$-decay modes a light ($\sim$ 2--3 GeV) photino can be produced carrying missing energy. However, the photino, being massive, arranges a different kinematical configuration for the visible decay products as compared to a standard semileptonic event where the neutrino carries the missing energy. We study the above kinematic distributions in an attempt to explore the above scenario.

hep-ph↗

arXiv1995

Constraining the charged Higgs mass in the left--right symmetric model from $b \to s γ$

In the context of the left--right symmetric model, the decay $b \rightarrow s γ$ receives contributions from the gauge interactions mediated mainly by the $W_L$, through $W_L$--$W_R$ mixing and also from the Yukawa interactions of the charged and the neutral (flavour-changing) scalars (the latter type of Yukawa interaction has been overlooked in the previous literature). Following the recent CLEO measurement of the inclusive $b \rightarrow s γ$ process and the measurement of the top-quark mass by the CDF and D0 collaborations, the parameter space of the left--right symmetric model is more squeezed than before.

hep-ph↗

arXiv1995

Singlet-Higgs-Boson Signals at Hadron Colliders

Many extensions of the Standard Model include $SU(2)_L \times U(1)_Y$ singlet higgs bosons, $h^0$, and also vectorlike fermions which couple to it. The production and detection possibilities of such singlet neutral scalars at hadron colliders are considered for different scenarios of vectorlike fermions. We find that for some values of masses and couplings, detection at the CERN Large Hadron Collider (LHC) appears to be a distinct possibility, while at the Fermilab Tevatron upgrade the $h^0$ might be observed only in very favourable circumstances.

hep-ph↗

arXiv1995

Accelerator, reactor and atmospheric neutrino data: a three flavour oscillation analysis

We perform a three flavour analysis of the atmospheric, accelerator and reactor neutrino data from the Kamiokande, LSND and Bugey experiments respectively. Choosing the values of ${Δ{m}}^2$ obtained from two flavour fits of the first two experiments, the allowed ranges of the three generation mixing angles are determined. The accelerator experiments CHORUS and NOMAD are found to be most sensitive to regions of the allowed parameter space which correspond to genuine three generation solutions for the atmospheric neutrino anomaly.

hep-ph↗

arXiv1995

Resonant neutrino oscillations and shock revival in type-II supernovae

The role of matter enhanced resonant neutrino oscillations in reviving a stalled shock in a type-II supernova through delayed neutrino heating is investigated. The extent of neutrino heating is estimated for the allowed possibility of complete flavour conversion self-consistently with the changes in nuclear equilibrium. The average internal energy per nucleon is substantially increased indicating the possiblty of a robust explosion.

hep-ph↗