Amitava Raychaudhuri - Academia.edu (original) (raw)

Drafts by Amitava Raychaudhuri

We explore the consequences of promoting bilinear R-parity violation, usually formulated in the m... more We explore the consequences of promoting bilinear R-parity violation, usually formulated in the minimal supersymmetric standard model framework, to a supersymmetric SU(5) grand unified theory. We observe that the limits on proton decay and neutrino mass place tight constraints on the bilinear SU(5) R-parity violating interactions of the colour triplet and SU(2) L doublet types respectively, creating a different doublet-triplet issue. The new mass-term-type parameters are both required to be small compared to the their expected order – the GUT scale. This cannot be resolved by an extension of the usual fine-tuning in the symmetry breaking scalar sector, which keeps the doublet sector light at the cost of pushing the triplet to the GUT-scale, and is an obstacle for R-parity violation in SU(5).

Papers by Amitava Raychaudhuri

Physical review, Dec 15, 1978

The N-quantum approximation (NQA) is examined in the light of its application to the bound state ... more The N-quantum approximation (NQA) is examined in the light of its application to the bound state of two scalar particles with scalar exchange. Bound-state wave functions are obtained as expansion coefficients in a truncated Haag expansion. An integral equation satisfied by the wave function is derived from the equations of motion for the Heisenberg fields and the NQA expansions. In the nonrelativistic limit the equation is shown to properly reduce to the SchrMinger equation. The equation is simplified by two difFerent methods and then solved numerically. The results are compared with other calculations.

Journal of High Energy Physics, 2018

A model with three scalar doublets can be conveniently accommodated within an A4 symmetric framew... more A model with three scalar doublets can be conveniently accommodated within an A4 symmetric framework. The A4 symmetry permits only a restricted form for the scalar potential. We show that for the global minima of this potential alignment follows as a natural consequence. We also verify that in every case positivity and unitarity constraints are satisfactorily met.

Physical review, Dec 27, 2016

We develop a seesaw model for neutrino masses and mixing with an S3 × Z3 symmetry. It involves an... more We develop a seesaw model for neutrino masses and mixing with an S3 × Z3 symmetry. It involves an interplay of Type-I and Type-II seesaw contributions of which the former is subdominant. The S3 × Z3 quantum numbers of the fermion and scalar fields are chosen such that the Type-II seesaw generates a mass matrix which incorporates the atmospheric mass splitting and sets θ 23 = π/4. The solar splitting and θ 13 are absent, while the third mixing angle can achieve any value, θ 0 12. Specific choices of θ 0 12 are of interest, e.g., 35.3 • (tribimaximal), 45.0 • (bimaximal), 31.7 • (golden ratio), and 0 • (no solar mixing). The role of the Type-I seesaw is to nudge all the above into the range indicated by the data. The model results in novel interrelationships between these quantities due to their common origin, making it readily falsifiable. For example, normal (inverted) ordering is associated with θ 23 in the first (second) octant. CP-violation is controlled by phases in the righthanded neutrino Majorana mass matrix, M νR. In their absence, only normal ordering is admissible. When M νR is complex the Dirac CP-phase, δ, can be large, i.e., ∼ ±π/2, and inverted ordering is also allowed. The preliminary results from T2K and NOVA which favour normal ordering and δ ∼ −π/2 are indicative, in this model, of a lightest neutrino mass of 0.05 eV or more.

$Research paper thumbnail of A reappraisal of constraints on <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msup><mi>Z</mi><mo mathvariant="normal" lspace="0em" rspace="0em">′</mo></msup></mrow><annotation encoding="application/x-tex">Z^{\prime}</annotation></semantics></math>Z′ models from unitarity and direct searches at the LHC$

We reexamine the ubiquitous U(1) extension of the Standard Model (SM), with a new neutral gauge b... more We reexamine the ubiquitous U(1) extension of the Standard Model (SM), with a new neutral gauge boson (Z), in a truly model-independent approach. No new fermions, except for three right-handed neutrinos, are added. We use the current LHC Drell-Yan data to put modelindependent constraints on the Z parameter space, defined by M Z , the Z-Z mixing angle (α z) and the extra U(1) effective gauge coupling (g x), which absorb all model dependence. Additional constraints are imposed from unitarity and ν µ-e scattering. However, limits extracted from direct searches turn out to be the most stringent. * Speaker.

Modern Physics Letters A, Oct 20, 1991

We have studied the bounds on mixing angles of fermions with their exotic partners which may stem... more We have studied the bounds on mixing angles of fermions with their exotic partners which may stem from different possibilities of new physics. The tree level effects of mixing have been taken care of by a modification of the effective vector and axial-vector couplings of Z to the fermions. The radiative corrections arising from new physics of exotic fermions are assumed to be negligible; as a result the ρ parameter and the effective sin 2 θw are calculated within the framework of the Standard Model. Mixing angles have been treated as free parameters during simultaneous fits to the combined data of cross-sections and lepton asymmetries from the four LEP experiments which have collected over 550,000 Z0 decays in 1990. Fitted values of mixing angles and the upper bounds at 90% C. L. are discussed.

Physics Letters B, Apr 1, 2011

An SO(10) model where the 10 H and 120 H representations are used for generating fermion masses i... more An SO(10) model where the 10 H and 120 H representations are used for generating fermion masses is quite predictive, though due to the absence of SU (2) L,R triplet/singlet fields it cannot give rise to neutrino masses through the usual type-I or type-II seesaw mechanisms. In this paper for neutrino masses we propose an extension of such an SO(10) model by adding fermions in the adjoint representation (45 F) and a symmetry breaking scalar 16 H. The 16 H couples the adjoint fermions to the standard fermions in 16 F and induces neutrino masses through the 'double seesaw' mechanism. In order to enhance the predictivity of the model we impose µ − τ flavour symmetry on the Yukawa matrices for 10 H and 16 H whereas for the 120 H it is assumed to be antisymmetric. We discuss the conditions that the mass matrices must obey so that the model can reproduce the tri-bimaximal mixing pattern.

Second in a series of international workshops in high energy physics, WHEPP II deals with frontli... more Second in a series of international workshops in high energy physics, WHEPP II deals with frontline areas of particle phenomenolgy with an eye to new physics with planned accelerators. Among the topics discussed are collider physics and structure function; B physics, hadronic matrix elements and lattice results; new particle search and model building, LEP results and radiative corrections to electro-weak processes; and baryon number violation in electro-weak processes.

Journal of Physics G, Jun 1, 1994

... Comments on 'Virtual effects of squark-gluino coupling on Z decays into bb'... more ... Comments on 'Virtual effects of squark-gluino coupling on Z decays into bb' Gautam Bhattacharyya and Amitava Raychaudhuri Department of Pure Physics, University of Calcutta, 92 Acharya Prafulla Chandra Road, Calcutta 700 009, India Received 18 October 1993 Abstract. ...

Nuclear physics, Jun 1, 2014

In universal extra-dimensional models a conserved Z 2 parity stabilizes the lightest Kaluza-Klein... more In universal extra-dimensional models a conserved Z 2 parity stabilizes the lightest Kaluza-Klein particle, a darkmatter candidate. Boundary-localized kinetic terms, in general, do not preserve this symmetry. We examine, in the presence of such terms, the single production of Kaluza-Klein excitations of the neutral electroweak gauge bosons and their decay to zero-mode fermion-antifermion pairs. We explore how experiments at the Large Hadron Collider constrain the boundary-localized kinetic terms for different compactification radii.

Physical review, Jul 19, 2000

The standard formulation of the Left-Right symmetric model involves scalars transforming as a tri... more 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 5σ 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 5σ discovery limit of the singly-charged mode extends to 240 GeV for an integrated luminosity of 100 fb −1. At the Tevatron, with an integrated luminosity of 25 fb −1 , 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.

Physical review, Mar 1, 1998

The Standard Model of electroweak interactions has one scalar doublet. The minimal extension of t... more 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 = 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 2jets + E / 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 gluongluon fusion and subsequent detection. We compare the signals with the expected backgrounds.