arXiv subjects

Mohan Narayan

Publications and source records attributed to Mohan Narayan.

18 recordsLinked to original sources

arXiv2009

Relation between CPT Violation in Neutrino masses and mixings

The neutrino parameters determined from the solar neutrino data and the anti-neutrino parameters determined from KamLAND reactor experiment are in good agreement with each other. However, the best fit points of the two sets differ from each other by about $10^{-5}$ eV$^2$ in mass-square differenc and by about $2^\circ$ in the mixing angle. Future solar neutrino and reactor anti-neutrino experiments are likely to reduce the uncertainties in these measurements. This, in turn, can lead to a signal for CPT violation in terms a non-zero difference between neutrino and anti-neutrino parameters. In this paper, we propose a CPT violating mass matrix which can give rise to the above differences in both mass-squared difference and mixing angle and study the constraints imposed by the data on the parameters of the mass matrix.

hep-ph↗

arXiv2007

Phenomenological constraints on low-scale gravity

We study the constraints on gravity scale $M_P$ in extra-dimension gravitational theory, obtained from gravity-induced processes. The obtained constraints are subdivided into strong (though not robust) and reliable (though less strong). The strong constraints can be in principle relaxed due to some broken gauge symmetries, e.g. family symmetry. The strongest constraint is given by neutrino oscillations. For different assumptions the lower bound on $M_P$ is $10^{15} - 10^{18}$ GeV. However, it can be, in principle, reduced by broken family symmetry. More reliable bounds are due to flavor-conserved operators or those which change the flavors within one family. These bounds, obtained using the electron mass and width of $π\to eν$ decay, are $1\times 10^5$ GeV and $5\times 10^5$ GeV, for these two cases, respectively.

hep-ph↗

arXiv2006

Deviation from Bimaximality due to Planck scale effects

We consider the effect of Planck scale operators on neutrino mixing. We assume that GUT scale operators give rise to degenerate neutrino masses with bimaximal mixing. Quantum gravity (Planck scale) effects lead to an effective SU(2)L*U(1) invariant dimension-5 Lagrangian involving neutrino and Higgs fields. This gives rise to additional terms in the neutrino mass matrix on electroweak symmetry breaking. These additional terms can be considered as a perturbation to the GUT scale bi-maximal neutrino mass matrix. We assume that the gravitational interaction is flavour blind and compute the deviations of the three neutrino mixing angles due to the Planck scale effects. We find that the changes in theta13, and theta23 are very small but the change in solar mixing angle theta12 can be as large as 3.5 degrees.

hep-ph↗

arXiv2006

Possible CPT Violation from Planck Scale Effects

At present there is good agreement between the neutrino mass-squared difference determined from the solar neutrino data and the anti-neutrino mass-squared difference determined from the KamLAND reactor anti-neutrino experiment. However, the central values of the two cases differ from each other by about $10^{-5}$ eV$^2$. An improvement in the accuracy of both the solar neutrino experiments and reactor anti-neutrino experiments can establish the existence of a non-zero difference between neutrino and anti-neutrino mass-squared differences and provide a signal for CPT violation. In this paper, we show how such a difference can arise through the CPT violating neutrino mass terms from Planck scale physics.

hep-ph↗

arXiv2005

Low scale gravity as the source of neutrino masses?

We address the question whether low-scale gravity alone can generate the neutrino mass matrix needed to accommodate the observed phenomenology. In low-scale gravity the neutrino mass matrix in the flavor basis is characterized by one parameter (the gravity scale M_X) and by an exact or approximate flavor blindness (namely, all elements of the mass matrix are of comparable size). Neutrino masses and mixings are consistent with the observational data for certain values of the matrix elements, but only when the spectrum of mass is inverted or degenerate. For the latter type of spectra the parameter M_{ee} probed in double beta experiments and the mass parameter probed by cosmology are close to existing upper limits.

hep-ph↗

arXiv2005

Do two flavour oscillations explain both KamLAND data and the Solar Neutrino Spectrum?

The recent measurement of Delta_{sol} by the KamLAND experiment with very small errors, makes definitive predictions for the energy dependence of the solar neutrino survival probability P_{ee}. We fix Delta_{sol} to be the KamLAND best fit value of 8*10^{-5} eV^2 and study the energy dependence of P_{ee} for solar neutrinos in the framework of two flavour oscillations and also of three flavour oscillations. For the case of two flavour oscillations, P_{ee} has a measurable slope in the 5-8 MeV range but the solar spectrum measurements in this range find P_{ee} to be flat. The predicted values of P_{ee}, even for the best fit value of theta_{sol}, differ by 2 to 3 sigma from the Super-K measured values in each of the three energy bins of the 5-8 MeV range. If future measurements of solar neutrinos by Super-K and SNO find a flat spectrum with reduced error bars (by a factor of 2), it will imply that two flavour oscillations can no longer explain both KamLAND data and the solar spectrum. However a flat solar neutrino spectrum and the Delta_{sol} measured by KamLAND can be reconciled in a three flavour oscillation framework with a moderate value of theta_{13} approx 13 degrees.

hep-ph↗

arXiv2003

U(e3) from physics above the GUT scale

We consider non-renormalizable 1/M_X interaction terms as a perturbation of the conventional neutrino mass matrix. Particular attention is given to the gravitational interaction with M_X=M_Pl. We find that for the degenerate neutrino mass spectrum, the considered perturbation generates a non-zero U(e3) which is within reach of the high performance neutrino factories and just on the borderline to be of interest for supernova physics. For the hierarchical mass spectrum this effect is small. For 1/M_X interaction terms with M_X about the GUT scale, a detectable U(e3) term is induced for the hierarchical mass spectra also. Numerical estimates are given for all the above mentioned cases and renormalization effects are considered.

hep-ph↗

arXiv2003

Mirror model for sterile neutrinos

Sterile neutrinos are studied as subdominant contribution to solar neutrino physics. The mirror-matter neutrinos are considered as sterile neutrinos. We use the symmetric mirror model with gravitational communication between mirror and visible sectors. This communication term provides mixing between visible and mirror neutrinos with the basic scale mu=v^2/M_Pl=5*10^-6 eV, where v=174 GeV is the vacuum expectation value of the standard electroweak group and M_Pl is the Planckian mass. It is demonstrated that each mass eigenstate of active neutrinos splits into two states separated by small Delta m^2. Unsuppressed oscillations between active and sterile neutrinos nu_a --> nu_s occur only in transitions between each of these close pairs (``windows''). These oscillations are characterized by very small Delta m^2 and can suppress the flux and distort spectrum of pp-neutrinos in detectable way. The other observable effect is anomalous seasonal variation of neutrino flux, which appears in LMA solution. The considered subdominant neutrino oscillations nu_a <--> nu_s can reveal itself as big effects in observations of supernova neutrinos and high energy (HE) neutrinos. In the case of HE neutrinos they can provide a very large diffuse flux of active neutrinos unconstrained by the e-m cascade upper limit.

hep-ph↗

arXiv2001

Analytical calculation of matter effects in two mass-scale neutrino oscillations

We consider three active flavor neutrino oscillations where both the mass-square differences play a role in atmospheric neutrino problem. We calculate the matter effects arising due to propagation through earth. We demonstrate that these effects improve the fit to the electron data vis-a-vis vacuum oscillations but make the fit to the muon data far worse, thus worsening the overall fit. The results of our analytical calculation verify the numerical investigations of this scheme presented earlier by Fogli et al.

hep-ph↗

arXiv2001

Determining the sign of $Δ_{31}$ at long baseline neutrino experiments

Recently it is advocated that high intensity and low energy $(E_ν\sim 2 GeV)$ neutrino beams should be built to probe the $(13)$ mixing angle $ϕ$ to a level of a few parts in $10^4$. Experiments using such beams will have better signal to background ratio in searches for $ν_μ\to ν_e$ oscillations. We propose that such experiments can also determine the sign of $Δ_{31}$ even if the beam consists of {\it neutrinos} only. By measuring the $ν_μ\to ν_e$ transitions in two different energy ranges, the effects due to propagation of neutrinos through earth's crust can be isolated and the sign of $Δ_{31}$ can be determined. If the sensitivity of an experiment to $ϕ$ is $ε$, then the same experiment is automatically sensitive to matter effects and the sign of $Δ_{31}$ for values of $ϕ\geq 2 ε$.

hep-ph↗

arXiv2000

Matter effects for `just so' oscillations

We study the effect of the matter term on the evolution of the solar neutrinos when the neutrino parameters are those of the `just-so' case. The extreme non-adiabatic effects at the edge of the sun reduce the expression for the survival probability in the just-so case to that of the vacuum case. This conclusion is independent of the width of the extreme non-adiabatic region, which is a function of the density profile of the sun beyond $r > 0.9 R_s$. However, in its propagation, neutrino encounters regions of moderate (non-extreme) non-adiabticity. Neutrino traversal through these regions give corrections to the survival probability which are profile dependent.

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

Probing the matter term at long baseline experiments

We consider (ν_μ--> ν_e) oscillations in long baseline experiments within a three flavor framework. A non-zero measurement of this oscillation probability implies that the (13) mixing angle `phi' is non-zero. We consider the effect of neutrino propagation through the matter of earth's crust and show that, given the constraints from solar neutrino and CHOOZ data, matter effects enhance the mixing for neutrinos rather than for anti-neutrinos. We need data from two different experiments with different baseline lengths (such as K2K and MINOS) to distinguish matter effects unambiguously.

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↗

arXiv1997

Solar neutrinos - Eclipse effect

It is pointed out that the enhancement of the solar neutrino rate in a real time detector like Super-Kamioka, SNO or Borexino due to neutrino oscillations in the moon during a partial or total solar eclipse may be observable. 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.

astro-ph↗

arXiv1997

Atmospheric neutrinos with three flavor mixing

We analyze the atmospheric neutrino data in the context of three flavor neutrino oscillations taking account of the matter effects in the earth. With the hierarchy among the vacuum mass eigenvalues $μ_3^2 \gg μ_2^2 \geq μ_1^2$, the solution of the atmospheric neutrino problem depends on $δ_{31}=μ_3^2 - μ_1^2$ and the $13$ and $23$ mixing angles $ϕ$ and $ψ$. Whereas the sub-GeV atmospheric neutrino data imposes only a lower limit on $δ_{31} > 10^{-3} eV^2$, the zenith angle dependent suppression observed in the multi-GeV data limits $δ_{31}$ from above also. The allowed regions of the parameter space are strongly constrained by the multi-GeV data. Combined with our earlier solution to the solar neutrino problem which depends on $δ_{21}= μ_2^2-μ_1^2$ and the $12$ and $13$ mixing angles $ω$ and $ϕ$, we have obtained the ranges of values of the five neutrino parameters which solve both the solar and the atmospheric neutrino problems simultaneously.

hep-ph↗

arXiv1995

Solar and atmospheric neutrino oscillations with three flavours

We analyze the solar and the atmospheric neutrino problems in the context of three flavour neutrino oscillations. We assume a mass hierarchy in the vacuum mass eigenvalues $μ_3^2 \gg μ_2^2 \geq μ_1^2$, but make no approximation regarding the magnitudes of the mixing angles. We find that there are small but continuous bands in the parameter space where the constraints imposed by the current measurements of $ \ {}^{71} Ga$, ${}^{37} Cl$ and Kamiokande experiments are satisfied at $1 σ$ level. The allowed parameter space increases dramatically if the error bars are enlarged to $1.6 σ$. The electron neutrino survival probability has different energy dependence in different regions of the parameter space. Measurement of the recoil electron energy spectrum in detectors that use $ν- e$ scattering may distinguish between some of the allowed regions of parameter space. Finally we use the results for the parameter space admitted by the solar neutrinos as an input for the atmospheric neutrino problem and show that there exists a substantial region of parameter space in which both problems can be solved.

hep-ph↗