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Amitava Raychaudhuri

Publications and source records attributed to Amitava Raychaudhuri.

At least 37 records · Page 2Linked to original sources
arXiv2011

Light neutrinos from massless texture and below TeV seesaw scale

We present general conditions on Dirac and Majorana mass terms under which a type-I seesaw mechanism can lead to three exactly massless neutrinos at the tree level. We depict several examples where the conditions are satisfied and relate some of them to an underlying U(1) symmetry. We show that higher order corrections may generate the small observed masses and this may be achieved even when the heavy Majorana neutrinos are at the electroweak scale or a little higher.

hep-ph↗
arXiv2010

Inverse see-saw, leptogenesis, observable proton decay and $Δ^{\pm\pm}_{\rm R}$ in SUSY SO(10) with heavy W_R

We explore low-scale leptogenesis in a class of supersymmetric SO(10) models using extra singlet neutrinos and the Higgs representations {126}_H\oplus {\ovl{126}}_H as well as {16}_H \oplus {\bar {16}}_H. A singlet neutrino, which can be as light as 10^5-10^6 GeV, decays through its small mixings with right-handed neutrinos creating a lepton asymmetry which is shown to be flavor dependent. While the doublet vacuum expectation value in {\ovl{16}}_H triggers the generation of desired mixings, it also induces a large RH triplet vev that breaks the LR intermediate gauge symmetry and gives large RH neutrino masses. Manifest unification of gauge couplings and generation of heavy RH neutrino masses are achieved by renormalizable interactions. The canonical (Type-I) see-saw contributions to the light neutrino mass matrix cancel out while the Type-II see-saw contribution is negligible. Determining the parameters of the dominant inverse see-saw formula using the underlying quark-lepton symmetry and neutrino oscillation data, we show how leptogenesis under the gravitino constraint is successfully implemented. New formulas for the decay rate and the asymmetry parameter are derived leading to baryon asymmetry within the observed range. The model is found to work for hierarchical as well as inverted hierarchical light neutrino masses. Testable predictions of the model are RH doubly charged Higgs bosons which may be leptophilic and accessible to the Tevatron, LHC or a linear collider. In a model-independent manner, the Drell-Yan pair production cross section is shown to be bounded between 59%-79% of their left-handed counterparts with same mass. In contrast to single-step breaking SUSY GUTs, which predict a long proton lifetime for p\to e^+π^0, here this lifetime is substantially reduced, bringing it within one order of the current experimental limit.

hep-ph↗
arXiv2010

An SO(10) model with adjoint fermions for double seesaw neutrino masses

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 $\bar{16}_H$. The $\bar{16}_H$ 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 $\bar{16}_H$ 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.

hep-ph↗
arXiv2010

Dimension-5 operators and the unification condition in SO(10) and E(6)

Effective dimension-5 operators which modify the gauge kinetic term in Grand Unified Theories may arise as a consequence of quantum gravity or string compactification. We exhaustively calculate the modification of the gauge unification condition due to such operators for all viable rank-preserving symmetry breakings of SO(10) and E(6) grand unified models.

hep-ph↗
arXiv2010

GUTs with dim-5 interactions: Gauge Unification and Intermediate Scales

Dimension-5 corrections to the gauge kinetic term of Grand Unified Theories (GUTs) may capture effects of quantum gravity or string compactification. Such operators modify the usual gauge coupling unification prediction in a calculable manner. Here we examine SU(5), SO(10), and E(6) GUTs in the light of all such permitted operators and calculate the impact on the intermediate scales and the unification programme. We show that in many cases at least one intermediate scale can be lowered to even 1-10 TeV, where a neutral Z' and possibly other states are expected.

hep-ph↗
arXiv2009

Exploring the Universal Extra Dimension at the LHC

Besides supersymmetry, the other prime candidate of physics beyond the standard model (SM), crying out for verification at the CERN Large Hadron Collider (LHC), is extra-dimension. To hunt for effects of Kaluza-Klein (KK) excitations of known fermions and bosons is very much in the agenda of the LHC. These KK states arise when the SM particles penetrate in the extra space-like dimension(s). In this paper, we consider a 5d scenario, called `Universal Extra Dimension', where the extra space coordinate, compactified on an orbifold $S^1/Z_2$, is accessed by {\em all} the particles. The KK number ($n$) is conserved at all tree level vertices. This entails the production of KK states in pairs and renders the lightest KK particle stable, which leaves the detector carrying away missing energy. The splitting between different KK flavors is controlled by the zero mode masses and the bulk- and brane-induced one-loop radiative corrections. We concentrate on the production of an $n=1$ KK electroweak gauge boson in association with an $n=1$ KK quark. This leads to a signal consisting of {\em only one} jet, one or more leptons and missing $p_T$. For definiteness we usually choose the inverse radius of compactification to be $R^{-1} = 500$ GeV, which sets the scale of the lowest lying KK states. We show on a case-by-case basis (depending on the number of leptons in the final state) that with 10 ${\rm fb}^{-1}$ integrated luminosity at the LHC with $\sqrt{s}$ = 14 TeV this signal can be detected over the SM background by imposing appropriate kinematic cuts. We record some of the expectations for a possible intermediate LHC run at $\sqrt{s}$ = 10 TeV and also exhibit the integrated luminosity required to obtain a 5$σ$ signal as a function of $R^{-1}$.

hep-ph↗
arXiv2009

A note on dimension-5 operators in GUTs and their impact

Quantum gravity or string compactification can lead to effective dimension-5 operators in Grand Unified Theories which modify the gauge kinetic terms. We exhaustively discuss the group-theoretic nature of such operators for the popular SU(5), SO(10), and E(6) models. In particular, for SU(5) only a Higgs in the 200 representation can help bring the couplings to unification below the Planck scale and in consistency with proton decay limits while for a supersymmetric version 24, 75, or 200 representations are all acceptable. The results also have a direct application in non-universality of gaugino masses in a class of supersymmetric models where identical group-theoretic features obtain.

hep-ph↗
arXiv2008

CERN-INO magical Beta-beam experiment: A high precision probe for neutrino parameters

This talk is an attempt to underscore in detail the physics reach of an experimental set-up where neutrinos produced in a beta-beam facility at CERN would be observed in the proposed large magnetized iron calorimeter detector (ICAL) at the India-based Neutrino Observatory (INO). The "magical" CERN-INO beta-beam set-up offers an excellent avenue to use the "Golden" channel ($ν_e \to ν_μ$) oscillation probability for a simultaneous determination of the neutrino mass ordering and $θ_{13}$ avoiding the impact of the CP phase $δ_{CP}$ on these measurements. With Lorentz boost $γ=650$ and irrespective of the true value of $δ_{CP}$, the neutrino mass hierarchy could be determined at $3σ$ C.L. if $\sin^22θ_{13}{\rm {(true)}} > 5.6 \times 10^{-4}$ and we can expect an unambiguous signal for $θ_{13}$ at $3σ$ C.L. if $\sin^22θ_{13}{\rm {(true)}} > 5.1 \times 10^{-4}$ independent of the true neutrino mass hierarchy.

hep-ph↗
arXiv2008

Probing neutrino parameters with a Two-Baseline Beta-beam set-up

We discuss the prospects of exploring the neutrino mass parameters with a CERN based Beta-beam experiment using two different detectors at two different baselines. The proposed set-up consists of a 50 kton iron calorimeter (ICAL) at a baseline of around 7150 km which is roughly the magic baseline, e.g., ICAL@INO, and a 50 kton Totally Active Scintillator Detector at a distance of 730 km, e.g., at Gran Sasso. We take 8B and 8Li source ions with a boost factor $γ$ of 650 for the magic baseline while for the closer detector we consider 18Ne and 6He ions with a range of Lorentz boosts. We find that the locations of the two detectors complement each other leading to an exceptional high sensitivity. With $γ=650$ for 8B/8Li and $γ=575$ for 18Ne/6He and total luminosity corresponding to $5\times (1.1\times 10^{19})$ and $5\times (2.9\times 10^{19})$ useful ion decays in neutrino and antineutrino modes respectively, we find that the two-detector set-up can probe maximal CP violation and establish the neutrino mass ordering if $\sin^22θ_{13}$ is $1.8 \times 10^{-5}$ and $4.6 \times 10^{-5}$, respectively, or more. The sensitivity reach for $\sin^22θ_{13}$ itself is $5.3 \times 10^{-5}$. CP violation can be discovered for 64% of the possible $δ_{CP}$ values for $\sin^22θ_{13} \geq 8\times 10^{-5}$.

hep-ph↗
arXiv2008

Neutrino mass and low-scale leptogenesis in a testable SUSY SO(10) model

It is shown that a supersymmetric SO(10) model extended with fermion singlets can accommodate the observed neutrino masses and mixings as well as generate the desired lepton asymmetry in concordance with the gravitino constraint. A necessary prediction of the model is near-TeV scale doubly-charged Higgs scalars which should be detectable at the LHC.

hep-ph↗
arXiv2008

Exceptional Sensitivity to Neutrino Parameters with a Two Baseline Beta-Beam Set-up

We examine the reach of a Beta-beam experiment with two detectors at carefully chosen baselines for exploring neutrino mass parameters. Locating the source at CERN, the two detectors and baselines are: (a) a 50 kton iron calorimeter (ICAL) at a baseline of around 7150 km which is roughly the magic baseline, e.g., ICAL@INO, and (b) a 50 kton Totally Active Scintillator Detector at a distance of 730 km, e.g., at Gran Sasso. We choose 8B/8Li source ions with a boost factor γof 650 for the magic baseline while for the closer detector we consider 18Ne/6He ions with a range of Lorentz boosts. We find that the locations of the two detectors complement each other leading to an exceptional high sensitivity. With γ=650 for 8B/8Li and γ=575 for 18Ne/6He and total luminosity corresponding to 5\times (1.1 \times 10^{18}) and 5\times (2.9\times 10^{18}) useful ion decays in neutrino and antineutrino modes respectively, we find that our two detector set-up can probe maximal CP violation and establish the neutrino mass ordering if \sin^22θ_{13} is 1.4\times 10^{-4} and 2.7\times 10^{-4}, respectively, or more. The sensitivity reach for \sin^22θ_{13} itself is 5.5 \times 10^{-4}. With a factor of 10 higher luminosity, the corresponding \sin^22θ_{13} reach of this set-up would be 1.8\times 10^{-5}, 4.6\times 10^{-5} and 5.3\times 10^{-5} respectively for the above three performance indicators. CP violation can be discovered for 64% of the possible δ_{CP} values for \sin^22θ_{13} \geq 10^{-3} (\geq 8\times 10^{-5}), for the standard luminosity (10 times enhanced luminosity). Comparable physics performance can be achieved in a set-up where data from CERN to INO@ICAL is combined with that from CERN to the Boulby mine in United Kingdom, a baseline of 1050 km.

hep-ph↗
arXiv2008

Optimizing the greenfield Beta-beam

We perform a comprehensive and detailed comparison of the physics reach of Beta-beam neutrino experiments between two pairs of plausible source ions, (8B, 8Li) and (18Ne, 6He). We study the optimal choices for the baseline, boost factor, and luminosity. We take a 50 kton iron calorimeter, a la ICAL@INO, as the far detector. We follow two complementary approaches for our study: (i) Fixing the number of useful ion decays and boost factor of the beam, and optimizing for the sensitivity reach between the two pairs of ions as a function of the baseline. (ii) Matching the shape of the spectrum between the two pairs of ions, and studying the requirements for baseline, boost factor, and luminosity. We find that for each pair of ions there are two baselines with very good sensitivity reaches: a short baseline with $L [km]/ γ\simeq 2.6$ (8B+8Li) and $L [km]/γ\simeq 0.8$ (18Ne+6He), and a long ``magic'' baseline. For $γ\sim 500$, one would optimally use 18Ne and 6He at the short baseline for CP violation, 8B and 8Li at the magic baseline for the mass hierarchy, and either 18Ne and 6He at the short baseline or 8B and 8Li at the magic baseline for the $\sin^22θ_{13}$ discovery.

hep-ex↗
arXiv2008

Unraveling neutrino parameters with a magical beta-beam experiment at INO

We expound in detail the physics reach of an experimental set-up in which the proposed large magnetized iron detector at the India-based Neutrino Observatory (INO) would serve as the far detector for a so-called beta-beam. If this pure $\nue$ and/or $\anue$ beam is shot from some source location like CERN such that the source-detector distance $L \simeq 7500$ km, the impact of the CP phase $δ_{CP}$ on the oscillation probability and associated parameter correlation and degeneracies are almost negligible. This ``magical'' beta-beam experiment would have unprecedented sensitivity to the neutrino mass hierarchy and $θ_{13}$, two of the missing ingredients needed for our understanding of the neutrino sector. With Lorentz boost $γ=650$ and irrespective of the true value of $δ_{CP}$, the neutrino mass hierarchy could be determined at $3σ$ C.L. if $\sin^22θ_{13}{\rm {(true)}} > 5.6 \times 10^{-4}$ and we can expect an unambiguous signal for $θ_{13}$ at $3σ$ C.L. if $\sin^22θ_{13}{\rm {(true)}} > 5.1 \times 10^{-4}$ independent of the true neutrino mass hierarchy.

hep-ph↗
arXiv2008

A GEANT-based study of atmospheric neutrino oscillation parameters at INO

We have studied the dependence of the allowed space of the atmospheric neutrino oscillation parameters on the time of exposure for a magnetized Iron CALorimeter (ICAL) detector at the India-based Neutrino Observatory (INO). We have performed a Monte Carlo simulation for a 50 kTon ICAL detector generating events by the neutrino generator NUANCE and simulating the detector response by GEANT. A chi-square analysis for the ratio of the up-going and down-going neutrinos as a function of $L/E$ is performed and the allowed regions at 90% and 99% CL are displayed. These results are found to be better than the current experimental results of MINOS and Super-K. The possibilities of further improvement have also been discussed.

hep-ph↗
arXiv2007

Physics with Beta-Beam

A Beta-beam would be a high intensity source of pure $ν_e$ and/or $\barν_e$ flux with known spectrum, ideal for precision measurements. Myriad of possible set-ups with suitable choices of baselines, detectors and the beta-beam neutrino source with desired energies have been put forth in the literature. In this talk we present a comparitive discussion of the physics reach of a few such experimental set-ups.

hep-ph↗
arXiv2007

SU(6), Triquark states, and the pentaquark

The purported observation of a state $Θ^+$ with strangeness S = +1 led to its quark model interpretation in terms of a pentaquark combination involving a triquark-diquark structure -- the Karliner-Lipkin model. In this work, the proper colour-spin symmetry properties for the $q q \bar{q}$ triquark are elucidated by calculating the SU(6) unitary scalar factors and Racah coefficients. Using these results, the colour-spin hyperfine interactions, including flavour symmetry breaking therein, become straight-forward to incorporate and the pentaquark masses are readily obtained. We examine the effect on the pentaquark mass of (a) deviations from the flavour symmetric limit and (b) different strengths of the doublet and triplet hyperfine interactions. Reference values of these parameters yield a $Θ^+$ mass prediction of 1601 MeV but it can comfortably accommodate 1540 MeV for alternate choices. In the same framework, other pentaquark states $Ξ$ (S=--2) and $Θ^c $ (with charm C=--1) are expected at 1783 MeV and 2757 MeV, respectively.

hep-ph↗
arXiv2007

Extra-dimensional relaxation of the upper limit of the lightest supersymmetric neutral Higgs mass

The upper limit on the mass of the lightest CP-even neutral Higgs in the minimal supersymmetric standard model is around 135 GeV for soft supersymmetry breaking masses in the 1 TeV range. We demonstrate that this upper limit may be sizably relaxed if supersymmetry is embedded in extra dimensions. We calculate, using the effective potential technique, the radiative corrections to the lightest Higgs mass induced by the Kaluza-Klein towers of quarks and squarks with one and two compactified directions. We observe that the lightest Higgs may comfortably weigh around 200 GeV (300 GeV) with one (two) extra dimension(s).

hep-ph↗