arXiv subjects

Subhendra Mohanty

Publications and source records attributed to Subhendra Mohanty.

At least 127 records · Page 7Linked to original sources

arXiv1998

Texture of a Four-Neutrino Mass Matrix

We propose a simple texture of the neutrino mass matrix with one sterile neutrino along with the three standard ones. It gives maximal mixing angles for $ν_e \to ν_S$ and $ν_μ\to ν_τ$ oscillations or vice versa. Thus with only four parameters, this mass matrix can explain the solar neutrino anomaly, atmospheric neutrino anomaly, LSND result and the hot dark matter of the universe, while satisfying all other Laboratory constraints. Depending on the choice of parameters, one can get the vacuum oscillation or the large angle MSW solution of the solar neutrino anomaly.

hep-ph↗

arXiv1998

Constraints on background torsion field from K physics

We point out that a background torsion field will produce an effective potential to the $K$ and $\bar{K}$ with opposite signs. This allows us to constrain the background torsion field from the $K_L$ and $K_S$ mass difference, CPT violating $K^\circ$ and $\bar{K^\circ}$ mass difference and the CP violating quantities $ε$ and $η_{+-}$. The most stringent bound on the cosmological background torsion $< T^0 > < 10^{-25}$ GeV comes from the direct measurement of the CPT violation.

hep-ph↗

arXiv1998

Photon propagation in Einstein and Higher Derivative Gravity

In the wave equation obeyed by electromagnetic fields in curved spacetime there are Riemann and Ricci curvature coupling terms to the photon polarisation, which result in a polarisation dependent deviation of the photon trajectories from null geodesics. Photons are found to have an effective mass in an external gravitational field and their velocity in an inertial frame is in general less than $c$. A consequence of this is that the curvature corrections to the propagation of electromagnetic radiation keep the velocities subluminal provided the strong energy condition is satisfied. We further show that the claims of superluminal velocities in higher derivative gravity theories are erroneous and arise due to the neglect of Riemann and Ricci coupling terms in the wave equation, which exists in Einstein's gravity itself.

gr-qc↗

arXiv1997

Emission of electron density waves by neutrinos in a dense medium

We study the production of electron density waves by neutrinos propagating through a plasma. We treat this process in field theoretically as a Cerenkov emission of phonons (quanta of electron density waves) by neutrinos. We compute the energy transfered to the plasma by the neutrinos and apply it to the shock wave revival problem of supernovae.

hep-ph↗

arXiv1997

Optical Activity of a Neutrino Gas

For photons that propagate through a gas of neutrinos with a non-zero chemical potential, the left-handed and right-handed polarization modes acquire different dispersion relations. This is due to the CP and CPT-odd terms induced by such a background on the photon self-energy. We present a detailed calculation of this effect, which does not depend on any physical assumptions beyond those of the standard electroweak model. Some possible cosmological and astrophysical implications of our results are considered in several contexts, including the recent discussions regarding the rotation of the plane of polarization of electromagnetic waves over cosmological distances.

hep-ph↗

arXiv1997

Neutrino helicity flip by Cerenkov emission and absorption of plasmons in supernova

We show that in a supernova core the longitudinal photon (plasmon) has a space-like dispersion and Cerenkov absorption and emission of such photons is kinematically allowed. If the neutrino has a non-zero magnetic moment, then helicity flipping Cerenkov absorption of a plasmon $ν_L+γ\toν_R$ is the most efficient cooling mechanism of the supernova core, and this allows us to put a restrictive bound on the neutrino magnetic moment $μ_ν~<~0.7\times 10^{-13}μ_B$.

hep-ph↗

arXiv1997

Covariant treatment of neutrino oscillations

We perform a covariant wavepacket analysis of neutrino oscillations taking into account the lifetime of the neutrino production process . We find that flavour oscillations in space are washed out when the neutrinos are produced from long lived resonances - and what may be observed in appearance/disappearance experiments is a uniform conversion probability independent of distance. The lifetime of the resonance which produces the neutrinos acts as the the effective baseline of the experiment. For this reason the LSND experiment where neutrinos are produced from muon decay has two orders of magnitude more sensitivity to neutrino mass square difference than other experiments where the neutrinos are produced from pion or kaon decays.We also show that there are no EPR type oscillations of the secondary decay particles.

hep-ph↗

arXiv1997

Production process dependence of neutrino flavor conversion

We perform a covariant wave-packet analysis of neutrino oscillations taking into account the lifetime of the neutrino production process . We find that flavor oscillations in space are washed out when the neutrinos are produced from long lived resonances - and what may be observed in appearance/disappearance experiments is a uniform conversion probability independent of distance. The lifetime of the resonance which produces the neutrinos acts as the the effective baseline of the experiment. For this reason the LSND experiment where neutrinos are produced from muon decay has two orders of magnitude more sensitivity to neutrino mass square difference than other experiments where the neutrinos are produced from pion or kaon decays.

hep-ph↗

arXiv1997

Source lifetime dependence of neutrino oscillations - a simple wave-function derivation

When neutrinos are produced from long lived particles the life-time of the source particle affects the flavour conversion probability formula. Due to this source dependence experiments (like LSND) which use muon decay neutrinos are two orders of magnitude more sensitive to lower values of mass square difference compared to other experiments where the sources are pions or kaons.

hep-ph↗

arXiv1997

Comment on ''Cerenkov radiation by neutrinos in a supernova core"

The helicity changing Cerenkov radiation in a supernova core was used earlier to put a restrictive bound on the neutrino magnetic moment. Subsequently it was pointed out, that this result was based on a numerical error in the calculationn of the refractive index of the SN core and using the correct numbers it was shown that the photons in a SN core do not have a space-like dispersion relation, so the Cerenkov process would not occur. Here we show that the earlier estimate of refractive index was based on the thermodynamic formula for susceptibility which is inapplicable for real photons or plasmons. However in an ultrarelativistic plasma the plasmon has a space-like branch in the dispersion relation hence the Cerenkov radiation of a plasmon is kinematically allowed. We show that the observations of neutrino flux from SN1987A put a constraint on the neutrino magnetic moment $μ_ν < 0.6\times 10^{-11}μ_B$.

hep-ph↗

arXiv1997

Geodesic Deviation of Photons in Einstein and Higher Derivative Gravity

We derive the wave equation obeyed by electromagnetic fields in curved spacetime. We find that there are Riemann and Ricci curvature coupling terms to the photon polarisation which result in a polarisation dependent deviation of the photon trajectories from null geodesics. Photons are found to have an effective mass in an external gravitational field and their velocity in a local inertial frame is in general less than $c$. The effective photon mass in the Schwarzschild metric is $m_γ= ( 2GM/r^3 )^{1/2}$ and near the horizon it is larger than the Hawking temperature of the blackhole. Our result implies that Hawking radiation of photons would not take place. We also conclude that there is no superluminal photon velocity in higher derivative gravity theories (arising from QED radiative corrections), as has been claimed in literature. We show that these erroneous claims are due to the neglect of the Riemann and Ricci coupling terms which exist in Einstein's gravity.

gr-qc↗

arXiv1996

Cerenkov radiation by neutrinos in a supernova core

Neutrinos with a magnetic dipole moment propagating in a medium with a velocity larger than the phase velocity of light emit photons by the Cerenkov process. The Cerenkov radiation is a helicity flip process via which a left-handed neutrino in a supernova core may change into a sterile right-handed one and free-stream out of the core. Assuming that the luminosity of such sterile right-handed neutrinos is less than $10^{53}$ ergs/sec gives an upper bound on the neutrino magnetic dipole moment $μ_ν< 0.2 \times 10^{-13} μ_B$. This is two orders of magnitude more stringent than the previously established bounds on $μ_ν$ from considerations of supernova cooling rate by right-handed neutrinos.

hep-ph↗

arXiv1995

Astrophysical signals of P and T violation by gravity

We study the observational consequences of the leading order P and T violating gauge invariant graviton-photon interactions. Such interactions give rise to gravitational birefringence - the velocity of light signals depends upon their polarisation, which is absent in Einstein's gravity. Using experimentally established limits on the differential time delay in the radio signals from pulsars we put constraints on the magnitude of P and T violating graviton-photon couplings.

astro-ph↗

arXiv1995

Cerenkov radiation by charged particles in an external gravitational field

Charged particles in the geodesic trajectory of an external gravitational field do not emit electromagnetic radiation. This is expected from the application of the equivalence principle. We show here that charged particles propagating in an external gravitational field with non-zero components of the Ricci tensor can emit radiation by the Čerenkov process. The external gravitational field acts like an effective refractive index for light. Since the Ricci tensor cannot be eliminated by a change of coordinates, there is no violation of the equivalence principle in this process.

astro-ph↗

arXiv1994

Particle Physics Bounds from the Hulse-Taylor Binary

The orbital period of the binary pulsar PSR 1913+16 has been observed to decrease at the rate of $2.40\times 10^{-12}$ s/s which agrees with the prediction of the quadropole formula for gravitational radiation to within one percent. The decrease in orbital period may also occur by radiation of other massless particles like scalars and pseudoscalar Nambu-Goldstone bosons. Assuming that this energy loss is less than one percent of the gravitational radiation, we can establish bounds on couplings of these particles to nucleons. For a scalar nucleon coupling of the form $g_s~ϕ~\barψ~ψ$ we find that $g_s< 3\times 10^{-19}$. From the radiation loss of massless Goldstone bosons we establish the upper bound $θ/f< 7.5\times 10^{-16}$ GeV$^{-1}$ on the QCD vacuum angle $θ$ and the scale $f$ at which the baryon number symmetry can be broken spontaneously.

hep-ph↗

arXiv1994

Solution of the Strong CP problem in the low energy effective Standard Model

We consider the low energy effective chiral theory of QCD mesons and the electroweak Goldstone bosons. In this effective theory the pion sector contributes to the gauge boson masses and the Yukawa couplings of the fermions. Consequently the Yukawa sector of quarks and leptons can have a $SU(2)_L\times U(1)_Y\times U(1)_A$ global symmetry even with nonvanishing fermion masses. The extra chiral $U(1)_A$ symmetry can be used to rotate the CP violating $\bar θG\tilde G $ term away which therefore makes no contribution to low energy CP violating effects like the neutron electric dipole momment. The Goldstone mode associated with this $U(1)_A$ symmetry may be identified with the $SU(2)$ singlet meson $η_0$.

hep-ph↗

arXiv1993

Determination of pseudo-Goldstone boson-photon coupling by the differential time delay of pulsar signals

Pseudo-Goldstone bosons couple with photons through a P and T violating interaction of the form ${\cal {L_I}}=g_{aγγ}~ a F\tilde F$. Strong magnetic fields in rotating compact stars induce a non-zero ${\vec E}\cdot{\vec B}$ outside the stellar surface which acts as a source for the pseudo-scalar field. Pulsar signals propagating through this pseudo-scalar `hair' suffer a differential time lag between the left and the right circularly polarised modes because of the P and T violating pseudoscalar boson-photon interaction. Determination of this time lag upto a microsecond accuracy can lead to a measurment of (or rule out) pseudo-Goldstone boson-photon coupling upto $g_{a γγ}\leq 4.6 \times 10^{-9}~GeV^{-1}$.

hep-ph↗

arXiv1993

Determination of pseudo-Goldstone boson-photon coupling by the differential time delay of pulsar signals

astro-ph↗