arXiv subjects

Biswarup Mukhopadhyaya

Publications and source records attributed to Biswarup Mukhopadhyaya.

At least 181 records · Page 10Linked to original sources

arXiv1999

Neutrino mass patterns, R-parity violating supersymmetry and associated phenomenology

Motivated by the recent SuperKamiokande results on atmospheric neutrinos, we incorporate massive neutrinos, with large angle oscillation between the second and third generations, in a theory with R-parity violating supersymmetry. The general features of such a theory are briefly reviewed. We emphasize its testability through the observation of comparable numbers of muons and taus, produced together with the W-boson, in decays of the lightest neutralino. A distinctly measurable decay gap is another remarkable feature of such a scenario.

hep-ph↗

arXiv1999

Constraining an R-parity violating supersymmetric theory from the SuperKamiokande data on atmospheric neutrinos

The constraints on an R-parity violating supersymmetric theory arising from the recent SuperKamiokande results on atmospheric neutrinos are studied, with special reference to a scenario with bilinear R-parity violating terms. Considering both the fermionic and scalar sectors, we find that a large area of the parameter space is allowed, in terms of both the lepton-number violating entries in the superpotential and the soft R-violating terms in the scalar potential, and that no fine-tuning is required. However, the need to avoid flavour changing neutral currents puts additional restrictions on the theory, requiring either the R-violating terms in the superpotential to be smaller than the R-conserving ones, or a hierarchy in the R-violating parameters for different lepton flavours in the superpotential.

hep-ph↗

arXiv1999

Tau-neutrino Appearance Searches using Neutrino Beams from Muon Storage Rings

We study the possibilities offered by muon storage rings for tau-neutrino appearance experiments due to nu_mu to nu_tau and nu_e to nu_tau oscillations. Tau event rates for such experiments are first discussed with a view to examining their variation prior to the inclusion of experimental cuts, in order to better understand how baselines, beam energies, forward peaking of decay neutrinos with increasing energies and average fluxes intercepted by detectors of various sizes can affect their optimization. Subsequently, event rates implementing cuts are computed for hadronic and wrong-sign lepton decay modes and used to plot 90% C.L. contours for the parameters that can be explored in such experiments. The expected scaling of the contours with energy and baseline is discussed. The results show that even for modest muon beam energies, convincing coverage of the Super Kamiokande parameters is possible. In addition, very significant enlargement of present-day bounds on the mass and mixing parameters of all types of neutrino oscillations is guaranteed by such searches.

hep-ph↗

arXiv1998

A geometrical interpretation of parity violation in gravity with torsion

In a space-time with torsion, the action for the gravitational field can be extended with a parity-violating piece. We show how to obtain such a piece from geometry itself, by suitably modifying the affine connection so as to include a pseudo-tensorial part. A consistent method is thus suggested for incorporating parity-violation in the Lagrangians of all matter fields with spin in a space-time background with torsion.

hep-th↗

arXiv1998

Correlation between neutrino oscillations and collider signals of supersymmetry in an R-parity violating model

Motivated by the recent Super-Kamiokande results on atmospheric neutrinos, we incorporate massive neutrinos, with large angle oscillation between the second and third generations, in a scenario with R-parity violating supersymmetry. We emphasize the testability of such models through the observation of comparable numbers of muons and taus, produced together with the W-boson, in decays of the lightest neutralino. A distinctly measurable decay gap is another remarkable feature of such a scenario.

hep-ph↗

arXiv1998

Semileptonic charm decay as a test for the spectator model in the $B_c$-meson

The $b$ and the $c$ quark compete with each other in decays of the $B_c$-meson. We emphasize the need of obtaining reliable signals of $c \to s$ in order to assess the merits of the spectator approximation in calculating the relative strengths of the two types of decays. This, we argue, can be done by considering the decay $B_c \to B_s (B_s^*) l \bar{ν_l}$, followed by semileptonic decays of the $B_s$. We suggest looking for like-sign dileptons together with a $D_s$ at the BTeV or LHC-B experiments, and show that such signals can be made background-free by suitable event selection.

hep-ph↗

arXiv1998

Filtering Out Signals of Gauge-Mediated Supersymmetry Breaking: Can We Always Eliminate Conventional Supersymmetric Effects ?

We investigate the signal $γγ$ + missing energy in a high-energy linear $e^+e^-$ collider, with a view to differentiating between gauge-mediated supersymmetry breaking and the conventional supersymmetric models. Prima facie, there is considerable chance of confusion between the two scenarios if the assumption of gaugino mass unification is relaxed. We show that the use of polarized electron beams enables one to distinguish between the two schemes in most cases. There are some regions in the parameter space where this idea does not work, and we suggest some additional methods of distinction. We also perform an analysis of some signals in the gauge-mediated model, coming from the pair production of the second-lightest neutralino.

hep-ph↗

arXiv1998

Observing Doubly Charged Higgs Bosons in Photon-Photon Collisions

We discuss the possibility of observing doubly charged Higgs bosons in $γγ$ collisions. We find that one can increase the range of observability close to the kinematic limit by a judicious choice of the polarisations of the initial $e^-/ e^+$ beams as well as the initial laser beam photons which are made to back-scatter from the former. We also note that, in a large region of parameter space, the generally used lepton number violating decay mode is dominated by the decay into a singly charged Higgs and a real or virtual $W$-boson, giving rise to a large number of fermions in the final state. This can qualitatively alter the strategy for discovering doubly-charged scalars.

hep-ph↗

arXiv1997

Testing Gauge-Gravitino Coupling in Gauge-Mediated Supersymmetry Breaking Through Single Photon Events

We show that the process $e^+e^- \to γ+$ missing energy, arising from the pair production of neutralinos, can probe the $γ-\tildeγ- \gravitino$ as well as the $Z-\tilde Z-\gravitino$ couplings in Gauge Mediated Supersymmetry Breaking models. This enables one to study the mutual relationship of the Goldstino couplings of the different gauginos, a feature whose testability has not been emphasized so far. The Standard Model backgrounds get suppresed with the use of a right polarized electron beam. The energy and angular distribution of the emitted photon can distinguish such models from the minimal supersymmetric theory and its variants.

hep-ph↗

arXiv1997

Gauge-Mediated Supersymmetry Breaking Signals in an Electron-Photon Collider

We show the usefulness of an $e^-γ$ collider with backscattered laser photons in unveiling the signatures of Gauge-Mediated Supersymmetry Breaking models, with a right selectron as the next LSP. We also show how the signal can be distinguished from the Standard Model background as well as from signals of minimal supersymmetry.

hep-ph↗

arXiv1997

Some Implications of a Supersymmetric Model with R-Parity Breaking Bilinear Interactions

We investigate a supersymmetric scenario where R-parity is explicitly broken through a term bilinear in the lepton and Higgs superfields in the superpotential. We show that keeping such a term alone can lead to trilinear interactions, similar to those that are parametrized by $λ$-and $λ'$ in the literature, involving the physical fields. The upper limits of such interactions are predictable from the constraints on the parameter space imposed by the lepton masses and the neutrino mass limits. It is observed that thus the resulting trilinear interactions are restricted to values that are smaller than the existing bounds on most of the $λ$-and $λ'$-parameters. Some phenomenological consequences of such a scenario are discussed.

hep-ph↗

arXiv1996

Probing Gauge-Mediated Supersymmetry Breaking Through Polarized Electron Beams in an $e^+e^-$ Collider

Using the facts that in Gauge-Mediated Supersymmetry Breaking schemes, masses of the right and the left sfermions can differ widely, and the gravitino is the Lightest Supersymmetric Particle, we show that it is possible to obtain unambiguous signatures of such schemes in a high energy $e^+e^-$ collider if one looks at the asymmetries in the cross-sections for certain final states with left-and right-polarized beams.

hep-ph↗

arXiv1996

Supersymmetry and the spontaneous breaking of a U(1) gauge factor

We investigate a supersymmetric theory with an extra U(1) gauge symmetry surviving down to low energies. The extra U(1) is assumed to originate from an E$_6$ grand unified theory (GUT). We show that if one assumes universal soft supersymmetry breaking scalar masses at the GUT scale, and requires the mass of the additional U(1) gauge boson to satisfy phenomenological bounds, then the conditions for electroweak symmetry breaking will provide stringent restrictions on the allowed parameter space of such a theory. We also determine the masses of standard as well as exotic sfermions and find that it is possible for the latter to be lighter than the former. An interesting specific observation is that a light stop is difficult to accommodate with an extra U(1) gauge symmetry.

hep-ph↗

arXiv1996

Unusual Charged Higgs Signals at LEP-2

We have made a detailed study of the signals produced at LEP-2 from charged scalar bosons whose dominant decay channels are into four fermions. The event rates as well as kinematics of the final states are discussed when such scalars are either pair-produced or are generated through a tree-level interaction involving a charged scalar, the W and the Z. The backgrounds in both cases are discussed. We also suggest the possibility of reconstructing the mass of such a scalar at LEP-2.

hep-ph↗

arXiv1996

Distinctive Signals of spontaneous R-parity breaking at LEP-II

We consider the signals of pair-produced charginos in an $e^{+}e^{-}$ collider, in a scenario where R-parity is spontaneously broken. The possibility of lepton-chargino mixing, together with the presence of a Majoron, opens up the two-body decay channel of a chargino into a tau and a Majoron. We have studied the regions where this is the dominant decay of a chargino, and have shown that over a large region of the parameter space the ensuing signals, namely tau-pairs with missing-$p_T$, may rise well above standard model backgrounds at LEP-II. Such signals can also enable one to distinguish between spontaneous and explicit R-parity breaking.

hep-ph↗

arXiv1995

Some Signals for a Light Neutralino

If a light gaugino sector exists in the supersymmetric standard model then the mass of lightest neutralino may be of the order of 1 GeV or less. As a consequence of neutral flavor violation in supersymmetric theories $B_s$-meson may decay into a pair of lightest neutralinos in such a case. It is found that the parameter space for such light neutralinos can be appreciably constrained by looking for such decays. We also show how a rare B-decays ($B \longrightarrow K(K^{*}) + invisible$ channels) can help us in probing a light neutralino in B-factories in a reasonably model- independent manner. Finally, we observe that that the decay of a tau-lepton into a muon and a pair of light neutralinos can cause a violation of weak universality which is larger in magnitude than that from any source known so far.

hep-ph↗

arXiv1995

Tau-Universality Violation with Light Neutralinos

In a supersymmetric model with the lightest supersymmetric particle (LSP) $χ$ in the range of a few hundred MeV's, the decay $τ{\longrightarrow} μχχ$ is going to be allowed. We investigate the departure from tau-universality caused by this decay. It is found that the universality violation in this way can be greater than both non-universal electroweak radiative corrections and supersymmetric one-loop corrections over a considerable region of the parameter space allowed by experiments so far. Thus it suggests a method of constraining the parameter space with light LSP's using data from tau-factories.

hep-ph↗

arXiv1995

A General Higgs Sector: Constraints and Phenomenology

We have investigated some phenomenological aspects of an $SU(2)\times U(1)$ scenario where scalars belonging to arbitrary representations of $SU(2)$ are involved in electroweak symmetry breaking. The resulting interaction terms are derived. Some constraints are obtained on the arbitrary scalar sector from the requirement of tree-level unitarity in longitudinal gauge boson scattering. We also show that, in cases where the scalars ensure $ρ=1$ at tree-level, useful restrictions on their parameter space follow from precision measurements of the $Zb\bar b$ vertex. Finally, some salient features about the production of such Higgs bosons in $e^+e^-$ collision are discussed.

hep-ph↗