Browsing by Author "Vaidya, Rishikesh"

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B--> X_s + gamma in Supersymmetry without R-parity
(ARXIV, 2004-11) Vaidya, Rishikesh
We present a systematic analysis of the decay B--> X_s + gamma at the leading log within the framework of Supersymmetry without R-parity. We point out some new contributions in the form of bilinear-trilinear combination of R-parity violating (RPV) couplings that are enhanced by large tanbeta. We also improve by a few orders of magnitude, bounds on several combinations of R-parity violating parameters
Bi-maximal mixing and bilinear R violation
(Elsevier, 2002-09) Vaidya, Rishikesh
We perform a general analytic study of feasibility of obtaining a combined explanation for the deficits in the solar and the atmospheric neutrino fluxes with two large mixing angles in supersymmetric model with bilinear R parity violations. The required hierarchy among the solar and atmospheric neutrino mass scales follows in this framework in the presence of an approximate Higgs–slepton universality at the weak scale. The solar mixing angle is shown to be related to non-universality in slepton mass terms specifically to differences in soft parameters of the first two leptonic generations. It is shown that this flavour universality violation should be as strong as the Higgs–slepton universality violation if solar neutrino mixing angle is to be large. The standard supergravity models with universal boundary conditions at a high scale lead to the required Higgs–slepton universality violations but the predicted violation of flavour universality among the first two generations is much smaller than required. This model therefore cannot provide an explanation of large solar neutrino mixing angle unless some universality violations in soft supersymmetry breaking parameters are introduced at a high scale itself.
Constraining R Violation from Anomalous Abelian Family Symmetry
(ARXIV, 2002-03) Vaidya, Rishikesh
The patterns of R violation resulting from imposition of a gauged U(1) horizontal symmetry, on the minimal supersymmetric standard model are systematically analyzed. We concentrate on a class of models with integer U(1) charges chosen to reproduce the quark masses and mixings as well as charged lepton masses exactly or approximately. The U(1) charges are further restricted from the requirement that very large bilinear lepton number violating terms should not be allowed in the super-potential. It is shown that all the trilinear λ′ijk and all but at most two trilinear λijk couplings vanish or are enormously suppressed.
CP-violation in the mass matrix of heavy neutrinos
(Elsevier, 1998-12) Vaidya, Rishikesh
We discuss the question of CP-violation in the effective Hamiltonian approach in models of leptogenesis through heavy right handed neutrino decays. We first formulate the problem in four component notation and then point out that before the heavy neutrinos have decayed away, the universe becomes CP-asymmetric in the heavy neutrinos. However, the lepton asymmetry generated after they completely decay are independent of this asymmetry.
Flavor changing Higgs decays in supersymmetry with minimal flavor violation
(Elsevier, 2007-03) Vaidya, Rishikesh
We study the flavor changing neutral current decays of the MSSM Higgs bosons into strange and bottom quarks. We focus on a scenario of minimum flavor violation here, namely only that induced by the CKM matrix. Taking into account constraint from , δρ as well as experimental constraints on the MSSM spectrum, we show that the branching ratio of and combined, for Φ being either one of the CP even Higgs states, can reach the order for large , large μ, and large . The result illustrates the significance of minimal flavor violation scenario which can induce competitive branching fraction for flavor changing Higgs decays. This can be compared with the previous studies where similar branching fraction has been reported, but with additional sources of flavor violations in squark mass matrices. We also discuss some basic features of the flavor violating decays in the generic case.
Neutrino anomalies in a gauge mediated model with trilinear R violation
(APS, 2002-02) Vaidya, Rishikesh
The structure of neutrino masses and mixing resulting from trilinear R violating interactions is studied in the presence of gauge mediated supersymmetry breaking. Neutrino masses arise in this model at the tree level through the renormalization-group-induced vacuum expectation values of the sneutrinos and also through direct contribution at one loop. The relative importance of these contributions is determined by the values of the strong- and weak-coupling constants. In the case of purely λ′ couplings, the tree contribution dominates over the one-loop diagram. In this case, one simultaneously obtains atmospheric neutrino oscillations and quasivacuum oscillations of the solar neutrinos if all the λ′ couplings are assumed to be of similar magnitudes. If R parity violation arises from the trilinear λ couplings, then the loop-induced contribution dominates over the tree level. One cannot simultaneously explain the solar and atmospheric deficit in this case if all the λ couplings are of similar magnitude. This, however, becomes possible with hierarchical λ and we give a specific example of this.
Quark Loop Contribution to Neutron EDM from R-parity Violation
(ARXIV, 2005-05) Vaidya, Rishikesh
We present a detailed analysis together with numerical calculations on one-loop contributions to the neutron electric dipole moment from supersymmetry without R parity, focusing on the quark-scalar loop contributions. Complete formulas are given for the various contributions through the quark dipole operators. Analytical expressions illustrating the explicit role of the R-parity violating parameters are given following perturbative diagonalization of mass-squared matrices for the scalars. Dominant contributions come from the combinations B∗iλ′ij1 for which we obtain robust bounds. Even if the R-parity violating couplings are real, CKM phase does induce RPV contribution and for some cases such a contribution is as strong as contribution from phases in the R-parity violating couplings. Hence, we have bounds directly on |B∗ił′ij1| even if the parameters are all real.
Quark loop contributions to neutron, deuteron, and mercury electric dipole moments from supersymmetry without R parity
(APS, 2007-07) Vaidya, Rishikesh
We present a detailed analysis together with numerical calculations on one-loop contributions to the neutron, deuteron, and mercury electric dipole moment from supersymmetry without R parity, focusing on the quark-scalar loop contributions. Being proportional to top Yukawa and top mass, such contributions are often large, and since these are proportional to hitherto unconstrained combinations of bilinear and trilinear R-parity violating (RPV) parameters, they are all the more interesting. Complete formulas are given for the various contributions through the quark dipole operators including the contribution from the color dipole operator. The contribution from the color dipole operator is found to be a similar order in magnitude when compared to the electric dipole operator and should be included in any consistent analysis. Analytical expressions illustrating the explicit role of the R-parity violating parameters are given following perturbative diagonalization of mass-squared matrices for the scalars. Dominant contributions come from the combinations B∗iλ′ij1 for which we obtain robust bounds. It turns out that neutron and deuteron electric dipole moments (EDMs) receive much stronger contributions than the mercury EDM and any null result at the future deuteron EDM experiment or Los Alamos neutron EDM experiment can lead to extraordinary constraints on RPV parameter space. Even if R-parity violating couplings are real, Cabibbo-Kobayashi-Maskawa (CKM) phase does induce RPV contribution and for some cases such a contribution is as strong as the contribution from phases in the R-parity violating couplings. Hence, we have bounds directly on |B∗iλ′ij1| even if the RPV parameters are all real. Interestingly, even if slepton mass and/or μ0 is as high as 1 TeV, it still leads to neutron EDM that is an order of magnitude larger than the sensitivity at the Los Alamos experiment. Since the results are not much sensitive to tanβ, our constraints will survive even if other observables tighten the constraints on tanβ
Radiative B decays in supersymmetry without R parity
(APS, 2005-03) Vaidya, Rishikesh
We present a systematic analysis of all the contributions at the leading log order to the branching ratio of the inclusive radiative decay B→Xs+γ in the framework of supersymmetry without R parity. The relevant set of four-quark operators involved in QCD running are extended from six (within the standard model and the minimal supersymmetric standard model) to 24, with also many new contributions to the Wilson coefficients of (chromo)magnetic penguins for either chiral structure. We present complete analytical results here without any a priori assumptions on the form of R-parity violation. Mass-eigenstate expressions are given; hence the results are free from the commonly adopted mass-insertion approximation. In the numerical analysis, we focus here only on the influence of the trilinear λ′ijk couplings and report on the possibility of a few orders of magnitude improvement for the bounds on a few combinations of the λ′ couplings. Our study shows that the Wilson coefficients of the current-current operators due to R-parity violation dominate over the direct contributions to the penguins. However, the interplay of various contributions is complicated due to the QCD corrections which we elaborate here
Radiative B decays in Supersymmetry without R-parity
(ARXIV, 2004-11) Vaidya, Rishikesh
We present a systematic analysis of all the contributions at the leading log order to the branching ratio of the inclusive radiative B decay, B --> X_s + gamma in the framework of supersymmetry without R-parity. The relevant set of four-quark operators involved in QCD running are extended from 6 (within SM and MSSM) to 24, with also many new contributions to the Wilson coefficients of (chromo)magnetic penguins for either chiral structure. We present complete analytical results here without any a priori assumptions on the form of R-parity violation. Mass eigenstate expressions are given, hence the results are free from the commonly adopted mass-insertion approximation. In the numerical analysis, we focus here only on the influence of the trilinear lambda-prime couplings and report on the possibility of a few orders of magnitude improvement for the bounds on a few combinations of the lambda-prime couplings. Our study shows that the Wilson coefficients of the current-current operators due to R-parity violation dominate over the direct contributions to the penguins. However, the inter-play of various contributions is complicated due to the QCD corrections which we elaborate here.
Some novel contributions to radiative B decays in supersymmetry without R parity
(APS, 2005-07) Vaidya, Rishikesh
We present a systematic analysis at the leading log order of the influence of combination of bilinear and trilinear R parity violating couplings on the decay b→s+γ. Such contributions have never been explored in the context of b→s+γ decay. We show that influence of charged-slepton-Higgs mixing mediated loops can dominate the SM and MSSM contributions and hence can provide strong bounds on the combination of bilinear-trilinear R parity violating couplings. Such contributions also are enhanced by large tanβ. With substantially extended basis of operators (28 operators), we provide illustrative analytical formulas of the major contributions to complement our complete numerical results which demonstrate the importance of QCD running effects.
Tanbeta enhanced contributions to b--> s gamma in SUSY without R-parity
(ARXIV, 2004-11) Vaidya, Rishikesh
We present a systematic analysis of the decay b --> s gamma at the leading log within the framework of Supersymmetry without R-parity. We point out some new contributions in the form of bilinear-trilinear combination of R-parity violating (RPV) couplings that are enhanced by large tanbeta. We also improve by a few orders of magnitude, bounds on several combinations of RPV parameters.
U(1) symmetry and R parity violation
(APS, 2000-10) Vaidya, Rishikesh
The patterns of R violation resulting from the imposition of a gauged U(1) horizontal symmetry on the minimal supersymmetric standard model are systematically analyzed. We concentrate on a class of models with integer U(1) charges chosen to reproduce the quark masses and mixings as well as charged lepton masses exactly or approximately. The U(1) charges are further restricted by the requirement that very large bilinear lepton number violating terms should not be allowed in the superpotential. It is shown that this leads to severely constrained patterns of trilinear interactions. Specifically, the only choice compatible with phenomenological restrictions is the one in which all the trilinear λ′ijk and all but at most two trilinear λijk couplings vanish or are enormously suppressed. The U(1) symmetry can allow the effective generation of bilinear lepton number violating parameters through terms in the Kähler potential. The resulting models are identified and the structure of neutrino masses in some of these is briefly discussed.
Working group report: Beyond the standard model
(IAS, 2003) Vaidya, Rishikesh
The working group on Beyond the StandardModel concentrated on identifying interesting physics issues in models of ‘new physics’ which go beyond the standard model. There were two aspects to this activity. One was to familiarise participants with the areas, for which the expertise available among the participants was very useful. The other aspect involved is the identification and formulation of research problems out of these issues, with the ultimate aim of building fruitful collaborations. In view of the range of current interest in the high energy physics community, this working group was organised according to the following focal themes:
Working group report: Collider Physics
(Springer, 2006-10) Vaidya, Rishikesh
This is summary of the activities of the working group on collider physics in the IXth Workshop on High Energy Physics Phenomenology (WHEPP-9) held at the Institute of Physics, Bhubaneswar, India in January 2006. Some of the work subsequently done on these problems by the subgroups formed during the workshop is included in this report.
Working group report: Flavor physics and model building
(Springer, 2006-11) Vaidya, Rishikesh
This is the report of flavor physics and model building working group at WHEPP-9. While activites in flavor physics have been mainly focused on B-physics, those in model building have been primarily devoted to neutrino physics. We present summary of working group discussions carried out during the workshop in the above fields, and also briefly review the progress made in some projects subsequently.
Working group report: High energy and collider physics
(Springer, 2004-12) Vaidya, Rishikesh
This is a summary of the projects undertaken by the working group I on high energy and collider physics.
Working group report: Low energy and flavour physics
(Springer, 2004-12) Vaidya, Rishikesh
This is a report of the low energy and flavour physics working group at WHEPP-8, held at the Indian Institute of Technology, Mumbai, India, during 5–16 January 2004.