2,113 research outputs found
Magnetofossil Spike During the Paleocene-Eocene Thermal Maximum: Ferromagnetic Resonance, Rock Magnetic, and Electron Microscopy Evidence from Ancora, New Jersey, USA
Previous workers identified a magnetically anomalous clay layer deposited on the northern United States Atlantic Coastal Plain during the Paleocene-Eocene Thermal
Maximum (PETM). The finding inspired the highly controversial hypothesis that a cometary impact triggered the PETM. Here we present ferromagnetic resonance (FMR), isothermal and anhysteretic remanent magnetization, first order reversal curve, and transmission electron microscopy analyses of late Paleocene and early Eocene sediments in drillcore from Ancora, New Jersey. A novel paleogeographic analysis applying a recent paleomagnetic pole from the
Faeroe Islands indicates that New Jersey during the initial Eocene had a ~6-9 degrees lower paleolatitude (~27.3 degrees for Ancora) and a more zonal shoreline trace than in conventional reconstructions. Our investigations of the PETM clay from Ancora reveal abundant magnetite nanoparticles bearing signature traits of crystals produced by magnetotactic bacteria. This result, the first identification of ancient biogenic magnetite using FMR, argues that the anomalous magnetic properties of the PETM sediments are not produced by an impact. They instead reflect environmental changes along the eastern margin of North America during the PETM that led to enhanced production and/or preservation of magnetofossils
Instability of ion kinetic waves in a weakly ionized plasma
The fundamental higher-order Landau plasma modes are known to be generally
heavily damped. We show that these modes for the ion component in a weakly
ionized plasma can be substantially modified by ion-neutral collisions and a dc
electric field driving ion flow so that some of them can become unstable. This
instability is expected to naturally occur in presheaths of gas discharges at
sufficiently small pressures and thus affect sheaths and discharge structures.Comment: Published in Phys. Rev. E, see
http://link.aps.org/doi/10.1103/PhysRevE.85.02641
Some Implications of a Supersymmetric Model with R-Parity Breaking Bilinear Interactions
We investigate a supersymmetric scenario where R-parity is explicitly broken
through a term bilinear in the lepton and Higgs superfields in the
superpotential. We show that keeping such a term alone can lead to trilinear
interactions, similar to those that are parametrized by -and
in the literature, involving the physical fields. The upper limits
of such interactions are predictable from the constraints on the parameter
space imposed by the lepton masses and the neutrino mass limits. It is observed
that thus the resulting trilinear interactions are restricted to values that
are smaller than the existing bounds on most of the -and
-parameters. Some phenomenological consequences of such a scenario
are discussed.Comment: 26 Pages, 6 Postscript figures, Latex. An additional set of
references has been included. Typographic corrections have been made. Figures
remain all unchanged. An additional typographic correction has been mad
See-saw Enhancement of Lepton Mixing
The see-saw mechanism of neutrino mass generation may enhance lepton mixing
up to maximal even if the Dirac mass matrices of leptons have structure similar
to that in the quark sector. Two sets of conditions for such an enhancement are
found. The first one includes the see-saw generation of heavy Majorana masses
for right-handed neutrinos and a universality of
Yukawa couplings which can follow from the unification of neutrinos with new
superheavy neutral leptons. The second set is related to lepton number symmetry
of the Yukawa interactions in the Dirac basis of neutrinos. Models which
realize these conditions have strong hierarchy or strong degeneration of
Majorana masses of the right-handed neutrinos.Comment: 16 pages, plain TeX document, Institute for Advanced Study number AST
93/1
Is Large Lepton Mixing Excluded?
The original \bnum -(or -) energy spectrum from the
gravitational collapse of a star has a larger average energy than the spectrum
for \bnue since the opacity of \bnue exeeds that of \bnum (or ).
Flavor neutrino conversion, \bnue \bnum, induced by lepton
mixing results in partial permutation of the original \bnue and \bnum spectra.
An upper bound on the permutation factor, (99 CL) is derived
using the data from SN1987A and the different models of the neutrino burst. The
relation between the permutation factor and the vacuum mixing angle is
established, which leads to the upper bound on this angle. The excluded region,
, covers the regions of large mixing angle
solutions of the solar neutrino problem: ``just-so" and, partly, MSW, as well
as part of region of oscillation space which could be
responsible for the atmospheric muon neutrino deficit. These limits are
sensitive to the predicted neutrino spectrum and can be strengthened as
supernova models improve.Comment: 20 pages, TeX file. For hardcopy with figures contact
[email protected]. Institute for Advanced Study number AST 93/1
Quasi-1D spin-1/2 Heisenberg magnets in their ordered phase: correlation functions
We study weakly coupled antiferromagnetic spin chains in their ordered phase
by combinining an exact solution of the single-chain problem with an RPA
analysis of the interchain interaction. A single chain is described by a
quantum Sine-Gordon model and dynamical staggered susceptibilities are
determined by employing the formfactor approach to quantum correlation
functions. We consider both antiferromagnetic order encountered in quasi-1D
materials like and spin-Peierls order as found in .Comment: 16 pages of revtex, 12 figure
Probing the neutrino mass hierarchy and the 13-mixing with supernovae
We consider in details the effects of the 13-mixing (sin^2 theta_{13}) and of
the type of mass hierarchy/ordering (sign[ Delta m^2_{13}]) on neutrino signals
from the gravitational collapses of stars. The observables (characteristics of
the energy spectra of nu_e and antinu_e events) sensitive to sin^2 theta_{13}
and sign[Delta m^2_{13}] have been calculated. They include the ratio of
average energies of the spectra, r_E = /, the ratio of widths of
the energy distributions, r_Gamma, the ratios of total numbers of nu_e and
antinu_e events at low energies, S, and in the high energy tails, R_{tail}. We
construct and analyze scatter plots which show the predictions for the
observables for different intervals of sin^2 theta_{13} and signs of Delta
m^2_{13}, taking into account uncertainties in the original neutrino spectra,
the star density profile, etc.. Regions in the space of observables r_E,
r_Gamma, S, R_{tail} exist in which certain mass hierarchy and intervals of
sin^2 theta_{13} can be identified or discriminated. We elaborate on the method
of the high energy tails in the spectra of events. The conditions are
formulated for which sin^2 theta_{13} can be (i) measured, (ii) restricted from
below, (iii) restricted from above. We comment on the possibility to determine
sin^2 theta_{13} using the time dependence of the signals due to the
propagation of the shock wave through the resonance layers of the star. We show
that the appearance of the delayed Earth matter effect in one of the channels
(nu_e or antinu_e) in combination with the undelayed effect in the other
channel will allow to identify the shock wave appeareance and determine the
mass hierarchy.Comment: LaTeX, 56 pages, 12 figures; a few clarifications added; typos
corrected. Version to appear in JCA
Phenomenology of Maximal and Near-Maximal Lepton Mixing
We study the phenomenological consequences of maximal and near-maximal mixing
of the electron neutrino with other (=tau and/or muon) neutrinos. We
describe the deviations from maximal mixing in terms of a parameter
and quantify the present experimental
status for . We find that the global analysis of solar neutrino
data allows maximal mixing with confidence level better than 99% for
eV^2\lsim\Delta m^2\lsim2\times10^{-7} eV. In the mass ranges \Delta
m^2\gsim 1.5\times10^{-5} eV and eV^2\lsim\Delta
m^2\lsim2\times10^{-7} eV the full interval is allowed
within 4(99.995 % CL). We suggest ways to measure in future
experiments. The observable that is most sensitive to is the rate
[NC]/[CC] in combination with the Day-Night asymmetry in the SNO detector. With
theoretical and statistical uncertainties, the expected accuracy after 5 years
is . We also discuss the effects of maximal and
near-maximal -mixing in atmospheric neutrinos, supernova neutrinos, and
neutrinoless double beta decay.Comment: 49 pages Latex file using RevTeX. 16 postscript figures included. (
Fig.2 and Fig.4 bitmapped for compression,better resolution at
http://ific.uv.es/~pppac/). Improved presentation: some statements included
and labels added in figures. Some misprint corrected. Final version to appear
in Phys. Rev D. Report no: IFIC/00-40, IASSNS-HEP-00-5
Correlations of Solar Neutrino Observables for SNO
Neutrino oscillation scenarios predict correlations, and zones of avoidance,
among measurable quantities such as spectral energy distortions, total fluxes,
time dependences, and flavor content. The comparison of observed and predicted
correlations will enhance the diagnostic power of solar neutrino experiments. A
general test of all presently-allowed (two neutrino) oscillation solutions is
that future measurements must yield values outside the predicted zones of
avoidance. To illustrate the discriminatory power of the simultaneous analysis
of multiple observables, we map currently allowed regions of neutrino masses
and mixing angles onto planes of quantities measurable with the Sudbury
Neutrino Observatory (SNO). We calculate the correlations that are predicted by
vacuum and MSW (active and sterile) neutrino oscillation solutions that are
globally consistent with all available neutrino data. We derive approximate
analytic expressions for the dependence of individual observables and specific
correlations upon neutrino oscillations parameters. We also discuss the
prospects for identifying the correct oscillation solution using multiple SNO
observables.Comment: Accepted Phys Rev D. Included new figure. Related material
http://www.sns.ias.edu/~jn
Neutrino - Modulino Mixing
We suggest the existence of a light singlet fermion, , which interacts
with observable matter only via a Planck mass suppressed interaction: , where is the supergravity gravitino mass. If the mass
of the singlet equals , then resonance
conversion solves the solar neutrino problem or leads to observable effects.
The -mixing changes supernova neutrino fluxes and has an impact on the
primordial nucleosynthesis. The singlet can originate as the supersymmetric
partner of the moduli fields in supergravity or low energy effective theory
steaming from superstrings. The -mixing may be accompanied by observable
R-parity breaking effects.Comment: Text compressed to 4 pages and references added. Version to appear in
Phys. Rev. Let
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