6,427 research outputs found
The Gelfand map and symmetric products
If A is an algebra of functions on X, there are many cases when X can be
regarded as included in Hom(A,C) as the set of ring homomorphisms. In this
paper the corresponding results for the symmetric products of X are introduced.
It is shown that the symmetric product Sym^n(X) is included in Hom(A,C) as the
set of those functions that satisfy equations generalising f(xy)=f(x)f(y).
These equations are related to formulae introduced by Frobenius and, for the
relevant A, they characterise linear maps on A that are the sum of ring
homomorphisms. The main theorem is proved using an identity satisfied by
partitions of finite sets.Comment: 14 pages, Late
Signals of R-parity violating supersymmetry in neutrino scattering at muon storage rings
Neutrino oscillation signals at muon storage rings can be faked by
supersymmetric (SUSY) interactions in an R-parity violating scenario. We
investigate the -appearance signals for both long-baseline and near-site
experiments, and conclude that the latter is of great use in distinguishing
between oscillation and SUSY effects. On the other hand, SUSY can cause a
manifold increase in the event rate for wrong-sign muons at a long-baseline
setting, thereby providing us with signatures of new physics.Comment: 7 pages LaTeX, 4 ps figures, accepted for publication in Phys. Rev.
On the nature of the near-UV extended light in Seyfert galaxies
We study the nature of the extended near-UV emission in the inner kiloparsec
of a sample of 15 Seyfert galaxies which have both near-UV (F330W) and narrow
band [OIII] high resolution Hubble images. For the majority of the objects we
find a very similar morphology in both bands. From the [OIII] images we
construct synthetic images of the nebular continuum plus the emission line
contribution expected through the F330W filter, which can be subtracted from
the F330W images. We find that the emission of the ionised gas dominates the
near-UV extended emission in half of the objects. A further broad band
photometric study, in the bands F330W (U), F547M (V) and F160W (H), shows that
the remaining emission is dominated by the underlying galactic bulge
contribution. We also find a blue component whose nature is not clear in 4 out
of 15 objects. This component may be attributed to scattered light from the
AGN, to a young stellar population in unresolved star clusters, or to
early-disrupted clusters. Star forming regions and/or bright off-nuclear star
clusters are observed in 4/15 galaxies of the sample.Comment: 23 pages, 6 figures, 3 tables; accepted for publication in MNRA
On the massless "just-so" solution to the solar neutrino problem
We study the effect of the non-resonant, vacuum oscillation-like neutrino
flavor conversion induced by non-standard flavor changing and non-universal
flavor diagonal neutrino interactions with electrons in the sun. We have found
an acceptable fit for the combined analysis for the solar experiments total
rates, the Super-Kamiokande (SK) energy spectrum and zenith angle dependence.
Phenomenological constraints on non-standard flavor changing and non-universal
flavor diagonal neutrino interactions are considered.Comment: 4 pages, Latex, uses eps
Measuring the Density Matrix by Local Addressing
We introduce a procedure to measure the density matrix of a material system.
The density matrix is addressed locally in this scheme by applying a sequence
of delayed light pulses. The procedure is based on the stimulated Raman
adiabatic passage (STIRAP) technique. It is shown that a series of population
measurements on the target state of the population transfer process yields
unambiguous information about the populations and coherences of the addressed
states, which therefore can be determined.Comment: 4 pages, 1 figur
Lepton number violating interactions and their effects on neutrino oscillation experiments
Mixing between bosons that transform differently under the standard model
gauge group, but identically under its unbroken subgroup, can induce
interactions that violate the total lepton number. We discuss four-fermion
operators that mediate lepton number violating neutrino interactions both in a
model-independent framework and within supersymmetry (SUSY) without R-parity.
The effective couplings of such operators are constrained by: i) the upper
bounds on the relevant elementary couplings between the bosons and the
fermions, ii) by the limit on universality violation in pion decays, iii) by
the data on neutrinoless double beta decay and, iv) by loop-induced neutrino
masses. We find that the present bounds imply that lepton number violating
neutrino interactions are not relevant for the solar and atmospheric neutrino
problems. Within SUSY without R-parity also the LSND anomaly cannot be
explained by such interactions, but one cannot rule out an effect
model-independently. Possible consequences for future terrestrial neutrino
oscillation experiments and for neutrinos from a supernova are discussed.Comment: 28 pages, 2 figures, Late
Neutrino Anomalies without Oscillations
I review explanations for the three neutrino anomalies (solar, atmospheric
and LSND) which go beyond the ``conventional'' neutrino oscillations induced by
mass-mixing. Several of these require non-zero neutrino masses as well.Comment: 14pages, LATEX format, 3 figure
An Atlas of the circumnuclear regions of 75 Seyfert galaxies in the near-UV with HST Advanced Camera for Surveys
We present an atlas of the central regions of 75 Seyfert galaxies imaged in
the near-UV with the Advanced Camera for Surveys of the Hubble Space Telescope
at an average resolution of ~10pc. These data complement archival high
resolution data from the Space Telescope at optical and near-IR wavelengths,
creating an extremely valuable dataset for astronomers with a broad range of
scientific interests. Our goal is to investigate the nature of the near-UV
light in these objects, its relation to the circumnuclear starburst phenomenon,
and the connection of this to the evolution and growth of the galaxy bulge and
central black hole. In this paper, we describe the near-UV morphology of the
objects and characterize the near-UV emission. We estimate the size and the
luminosity of the emitting regions and extract the luminosity profile. We also
determine the presence of unresolved compact nuclei. In addition, the
circumnuclear stellar cluster population is identified, and the contribution of
the stellar clusters to the total light, at this wavelength, is estimated. The
size of the sample allows us to draw robust statistical conclusions. We find
that {Seyfert 1} galaxies are completely dominated by its bright and compact
nucleus, that remains point-like at this resolution, while we find almost no
unresolved nucleus in Seyfert 2. The Seyfert types 1 and 2 are quite segregated
in an asymmetry vs compactness plot. Stellar clusters are found somewhat more
frequently in Sy2 (in ~70% of the galaxies) than in Sy1 (~57%), and contribute
more to the total light in Sy2, but this two differences seem to be mostly due
to the large contribution of the compact nucleus in Sy1, as the luminosity
distribution of the clusters is similar in both Sy types.Comment: Accepted for publication in AJ, 58 pages, 20 figures. High-resolution
figures for all the objects are available at
http://www.iaa.es/~manuel/publications/paper01.htm
Embedding variables in finite dimensional models
Global problems associated with the transformation from the Arnowitt, Deser
and Misner (ADM) to the Kucha\v{r} variables are studied. Two models are
considered: The Friedmann cosmology with scalar matter and the torus sector of
the 2+1 gravity. For the Friedmann model, the transformations to the Kucha\v{r}
description corresponding to three different popular time coordinates are shown
to exist on the whole ADM phase space, which becomes a proper subset of the
Kucha\v{r} phase spaces. The 2+1 gravity model is shown to admit a description
by embedding variables everywhere, even at the points with additional symmetry.
The transformation from the Kucha\v{r} to the ADM description is, however,
many-to-one there, and so the two descriptions are inequivalent for this model,
too. The most interesting result is that the new constraint surface is free
from the conical singularity and the new dynamical equations are linearization
stable. However, some residual pathology persists in the Kucha\v{r}
description.Comment: Latex 2e, 29 pages, no figure
Two-photon linewidth of light "stopping" via electromagnetically induced transparency
We analyze the two-photon linewidth of the recently proposed adiabatic
transfer technique for ``stopping'' of light using electromagnetically induced
transparency (EIT). We shown that a successful and reliable transfer of
excitation from light to atoms and back can be achieved if the spectrum of the
input probe pulse lies within the initial transparency window of EIT, and if
the two-photon detuning is less than the collective coupling strength
(collective vacuum Rabi-frequency) divided by ,
with being the radiative decay rate, the effective number of atoms
in the sample, and the pulse duration. Hence in an optically thick medium
light ``storage'' and retrieval is possible with high fidelity even for systems
with rather large two-photon detuning or inhomogeneous broadening.Comment: 2 figure
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