arXiv subjects

G. Rajasekaran

Publications and source records attributed to G. Rajasekaran.

At least 55 records · Page 3Linked to original sources

arXiv2001

Light Unstable Sterile Neutrino

The three massless active (doublet) neutrinos may mix with two heavy and one \underline {light} sterile (singlet) neutrinos so that the induced masses and mixings among the former are able to explain the present data on atmospheric and solar neutrino oscillations. If the LSND result is also to be explained, one active neutrino mass eigenstate must mix with the light sterile neutrino. A specific model is proposed with the spontaneous and soft explicit breaking of a new global $U(1)_S$ symmetry so that a sterile neutrino will decay into an active antineutrino and a nearly massless pseudo-Majoron.

hep-ph↗

arXiv2001

Neutrinos from Stellar Collapse: Comparison of signatures in water and heavy water detectors

Signatures of neutrino and antineutrino signals from stellar collapse in heavy water detectors are contrasted with those in water detectors. The effects of mixing, especially due to the highly dense matter in the supernova core, are studied. The mixing parameters used are those sets allowed by current understanding of available neutrino data: from solar, atmospheric and laboratory neutrino experiments. Signals at a heavy water detector, especially the dominant charged current reactions on deuteron, are very sensitive to some of these sets of allowed mixing parameters. Theoretical uncertainties on supernova neutrino spectra notwithstanding, a combination of supernova measurements with water and heavy water detectors may be able to distinguish many of these mixing possibilities and thus help in ruling out many of them.

hep-ph↗

arXiv2001

Softly Broken A_4 Symmetry for Nearly Degenerate Neutrino Masses

The leptonic Higgs doublet model of neutrino masses is implemented with an A_4 discrete symmetry (the even permutation of 4 objects or equivalently the symmetry of the tetrahedron) which has 4 irreducible representations: 1, 1', 1'', and 3. The resulting spontaneous and soft breaking of A_4 provides a realistic model of charged-lepton masses as well as a nearly degenerate neutrino mass matrix. Phenomenological consequences at and below the TeV scale are discussed.

hep-ph↗

arXiv2001

Quantum Field Theory for Orthofermions and Orthobosons

Orthofermi statistics is characterized by an exclusion principle which is more ``exclusive'' than Pauli's exclusion principle: an orbital state shall not contain more than one particle, no matter what the spin direction is. The wavefunction is antisymmetric in spatial indices alone with arbitrary symmetry in the spin indices. Orthobose statistics is corresponding Bose analog: the wavefunction is symmetric in spatial indices, with arbitrary symmetry in spin indices. We construct the quantum field theory of particles obeying these new kinds of quantum statistics. Non-relativistic as well as relativistic quantum field theories with interactions are considered.

hep-th↗

arXiv2001

Generalized Fock Spaces and New Forms of Quantum Statistics

The recent discoveries of new forms of quantum statistics require a close look at the under-lying Fock space structure. This exercise becomes all the more important in order to provide a general classification scheme for various forms of statistics, and establish interconnections among them whenever it is possible. We formulate a theory of generalized Fock spaces, which has a three tired structure consisting of Fock space, statistics and algebra. This general formalism unifies various forms of statistics and algebras, which were earlier considered to describe different systems. Besides, the formalism allows us to construct many new kinds of quantum statistics and the associated algebras of creation and destruction operators. Some of these are: orthostatistics, null statistics or statistics of frozen order, quantum group based statistics and its many avatars, and `doubly-infinite' statistics. The emergence of new forms of quantum statistics for particles interacting with singular potential is also highlighted.

hep-th↗

arXiv2000

Light Sterile Neutrinos from Large Extra Dimensions

An experimentally verifiable Higgs-triplet model of neutrino masses from large extra dimensions was recently proposed. We extend it to accomodate a light sterile neutrino which also mixes with the three active neutrinos. A previously proposed phenomenological model of four neutrinos (\underline {the only viable such model now left}, in view of the latest atmospheric and solar neutrino-oscillation data) is specifically realized.

hep-ph↗

arXiv2000

Neutrinos from Stellar Collapse: Comparison of the effects of three and four flavour mixings

We study the effect of non-vanishing masses and mixings among neutrino flavours on the detection of neutrinos from stellar collapse by a water Cerenkov detector. We consider a frame-work in which there are four neutrino flavours, including a sterile neutrino, whose mass squared differences and mixings are constrained by the present understanding of solar, atmospheric and laboratory neutrino detection. We also include the effects of high density matter within the supernova core. Unlike in the three flavour scenario, we find that the number of events due to the dominant process involving electron-antineutrinos changes dramatically for some allowed mixing parameters. Furthermore, contributions from charged-current scattering off oxygen nuclei in the detector can be considerably enhanced due to flavour mixing. We also present a comparison between the two possible scenarios, namely, when only three active neutrino flavours are present and when they are accompanied by a fourth sterile neutrino.

hep-ph↗

arXiv2000

Three Inequivalent Mass-Degenerate Majorana Neutrinos and a Model of Their Splitting for Neutrino Oscillations

The mass matrix of three Majorana neutrinos of equal mass is not necessarily proportional to the identity matrix, but expressible in terms of two angles and one phase. We discuss how such a mass matrix may be stable or unstable against radiative corrections. We then propose a model with additional explicit breaking of the threefold degeneracy to account for the atmospheric neutrino data, while the radiative breaking explains the solar neutrino data, using the large-angle Mikheyev-Smirnov-Wolfenstein solution. Our model requires a nonzero effective $ν_e$ mass for neutrinoless double beta decay close to the present experimental upper limit of 0.2 eV.

hep-ph↗

arXiv2000

Phenomenology of Neutrino Oscillations

The phenomenology of solar, atmospheric, supernova and laboratory neutrino oscillations is described. Analytical formulae for matter effects are reviewed. The results from oscillations are confronted with neutrinoless double beta decay.

hep-ph↗

arXiv1999

Constraints on mixing angles of Majorana neutrinos

By combining the inputs from the neutrinoless double beta decay and the fits of cosmological models of dark matter with solar and atmospheric neutrino data, we obtain constraints on two of the mixing angles of Majorana neutrinos, which become stronger when coupled with the reactor neutrino data. These constraints are strong enough to rule out Majorana neutrinos if the small angle solution of solar neutrino puzzle is borne out.

hep-ph↗

arXiv1999

Solar Neutrinos and the Eclipse Effect

The solar neutrino counting rate in a real time detector like Super--Kamiokanda, SNO, or Borexino is enhanced due to neutrino oscillations in the Moon during a partial or total solar eclipse. The enhancement is calculated as a function of the neutrino parameters in the case of three flavor mixing. This enhancement, if seen, can further help to determine the neutrino parameters.

hep-ph↗

arXiv1999

Hierarchical Four-Neutrino Oscillations With a Decay Option

We present a new and novel synthesis of all existing neutrino data regarding the disappearance and appearance of $ν_e$ and $ν_μ$. We assume four neutrinos: $ν_e, ν_μ, ν_τ$, as well as a heavier singlet neutrino $ν_s$ of a few eV. The latter may decay into a massless Goldstone boson (the singlet Majoron) and a linear combination of the doublet antineutrinos. We comment on how this scenario may be verified or falsified in future experiments.

hep-ph↗

arXiv1999

A new differential calculus on noncommutative spaces

We develop a $GL_{qp}(2)$ invariant differential calculus on a two-dimensional noncommutative quantum space. Here the co-ordinate space for the exterior quantum plane is spanned by the differentials that are commutative (bosonic) in nature.

math-ph↗

arXiv1999

Neutrinos from Stellar Collapse: Effects of flavour mixing

We study the effect of non-vanishing masses and mixings among neutrino flavours on the detection of neutrinos from stellar collapse by a water Cerenkov detector. We consider a realistic framework in which there are three neutrino flavours whose mass squared differences and mixings are constrained by the present understanding of solar and atmospheric neutrinos. We also include the effects of high dense matter within the supernova core. We find that the number of events due to the dominant process involving electron-antineutrinos may change dramatically for some allowed mixing parameters. Furthermore, contributions from charged-current scattering off oxygen atoms in the detector can be considerably enhanced due to flavour mixing; such events have a distinct experimental signature since they are backward-peaked. Hence, mixing has a non-trivial effect on the signature of neutrinos (and antineutrinos) from stellar collapse.

hep-ph↗

arXiv1999

A new mechanism for neutrino mass

A mechanism for generating massive but naturally light Dirac neutrinos is proposed. It involves composite Higgs within the standard model as well as some new interaction beyond the standard model. According to this scenario, a neutrino mass of 0.1 eV or higher, signals new physics at energies of 10--100 TeV or lower.

hep-ph↗

arXiv1998

One pion events by atmospheric neutrinos: A three flavor analysis

We study the one-pion events produced via neutral current (NC) and charged current (CC) interactions by the atmospheric neutrinos. We analyze the ratios of these events in the framework of oscillations between three neutrino flavors. The ratios of the CC events induced by $ν_e$ to that of the NC events and a similar ratio defined with $ν_μ$ help us in distinguishing the different regions of the neutrino parameter space.

hep-ph↗

arXiv1997

Three flavor implications of CHOOZ result

We analyze the recent result of the CHOOZ collaboration in the context of mixing and oscillations between all the three neutrino flavors. If one assumes a hierarchy among the vacuum mass eigenvalues (δ_{21} \ll δ_{31}), then the CHOOZ result limits the (13) mixing angle ϕto quite small values. This in turn limits the contribution of the ν_e <--> ν_μoscillation channel to the atmospheric neutrino anomaly to less than 10 percent. It also implies that the solution to the solar neutrino problem is effectively ν_e <--> ν_μoscillation and that of the atmospheric neutrino problem is effectively ν_μ<--> ν_τ.

hep-ph↗

arXiv1997

Time-of-night variation of solar neutrinos

We investigate the time-of-night variation of solar neutrino rate which will be of relevance to Super-Kamioka and Sudbury neutrino detectors in the framework of oscillations among the three flavors. An analytical method of computing the regeneration in the earth is presented. If day-night effect is seen, we show how the study of the time-of-night variation will allow the determination of the neutrino parameters.

hep-ph↗