53,606 research outputs found
Ultraviolet modified photons and anisotropies in the cosmic microwave background radiation
We discuss a minimal canonical modification of electrodynamics in order to
account for ultraviolet Lorentz violating effects. This modification creates a
birefringence that rotates the polarization planes from different directions.
Such effects might be detectable in the anisotropic polarization of the Cosmic
Microwave Background radiation.Comment: RevTeX, 4p
The seesaw portal in testable models of neutrino masses
A Standard Model extension with two Majorana neutrinos can explain the
measured neutrino masses and mixings, and also account for the
matter-antimatter asymmetry in a region of parameter space that could be
testable in future experiments. The testability of the model relies to some
extent on its minimality. In this paper we address the possibility that the
model might be extended by extra generic new physics which we parametrize in
terms of a low-energy effective theory. We consider the effects of the
operators of the lowest dimensionality, , and evaluate the upper bounds on
the coefficients so that the predictions of the minimal model are robust. One
of the operators gives a new production mechanism for the heavy neutrinos at
LHC via higgs decays. The higgs can decay to a pair of such neutrinos that,
being long-lived, leave a powerful signal of two displaced vertices. We
estimate the LHC reach to this process.Comment: 19 pages, 11 figure
A high-speed bi-polar outflow from the archetypical pulsating star Mira A
Optical images and high-dispersion spectra have been obtained of the ejected
material surrounding the pulsating AGB star Mira A. The two streams of knots on
either side of the star, found in far ultra-viollet (FUV) GALEX images, have
now been imaged clearly in the light of Halpha. Spatially resolved profiles of
the same line reveal that the bulk of these knots form a bi-polar outflow with
radial velocity extremes of +- 150 km/s with respect to the central star. The
South stream is approaching and the North stream receding from the observer. A
displacement away from Mira A between the position of one of the South stream
knots in the new Halpha image and its position in the previous Palomar
Observatory Sky Survey (POSS I) red plate has been noted. If interpreted as a
consequence of expansion proper motions the bipolar outflow is tilted at 69deg
+- 2deg to the plane of the sky, has an outflow velocity of 160 +- 10 km/s and
is ~1000 y old.Comment: 8 pages, 5 figures. Accepted for pubication by A&
Investment in Information and Communication Technologies: an Empirical Analysis
Recent economic literature has identified sizeable differences across industrialised countries in the diffusion of Information and Communication Technologies (ICTs) throughout the production structure. This paper addresses the question of whether differences in the price elasticity of demand for ICTs could explain why Europe lags behind the United States in terms of ICT diffusion. We use annual macroeconomic data covering the period 1975-2001 and consider five countries: France, Germany, the Netherlands, the United Kingdom and the United States. Europe's lag in ICT diffusion does not appear to be linked to cross-country differences in the price elasticity of demand for ICT products. Our results suggest that at least part of the gap in ICT diffusion should be ascribed to more structural cross-country differences. The estimated value of the price-elasticity of computer hardware and software is generally lower than -1 which, given the decline in the relative price of these products, explains the increase in their share of investment expenditure and GDP. This situation is characteristic of a diffusion stage and is necessarily temporary.ICT ; Investment ; Factor demand
A Layman's guide to SUSY GUTs
The determination of the most straightforward evidence for the existence of
the Superworld requires a guide for non-experts (especially experimental
physicists) for them to make their own judgement on the value of such
predictions. For this purpose we review the most basic results of Super-Grand
unification in a simple and clear way. We focus the attention on two specific
models and their predictions. These two models represent an example of a direct
comparison between a traditional unified-theory and a string-inspired approach
to the solution of the many open problems of the Standard Model. We emphasize
that viable models must satisfy {\em all} available experimental constraints
and be as simple as theoretically possible. The two well defined supergravity
models, and , can be described in terms of only a few
parameters (five and three respectively) instead of the more than twenty needed
in the MSSM model, \ie, the Minimal Supersymmetric extension of the Standard
Model. A case of special interest is the strict no-scale
supergravity where all predictions depend on only one parameter (plus the
top-quark mass). A general consequence of these analyses is that supersymmetric
particles can be at the verge of discovery, lurking around the corner at
present and near future facilities. This review should help anyone distinguish
between well motivated predictions and predictions based on arbitrary choices
of parameters in undefined models.Comment: 25 pages, Latex, 11 figures (not included), CERN-TH.7077/93,
CTP-TAMU-65/93. A complete ps file (1.31MB) with embedded figures is
available by request from [email protected]
Are constant loop widths an artifact of the background and the spatial resolution?
We study the effect of the coronal background in the determination of the
diameter of EUV loops, and we analyze the suitability of the procedure followed
in a previous paper (L\'opez Fuentes, Klimchuk & D\'emoulin 2006) for
characterizing their expansion properties. For the analysis we create different
synthetic loops and we place them on real backgrounds from data obtained with
the Transition Region and Coronal Explorer (\textit{TRACE}). We apply to these
loops the same procedure followed in our previous works, and we compare the
results with real loop observations. We demonstrate that the procedure allows
us to distinguish constant width loops from loops that expand appreciably with
height, as predicted by simple force-free field models. This holds even for
loops near the resolution limit. The procedure can easily determine when loops
are below resolution limit and therefore not reliably measured. We find that
small-scale variations in the measured loop width are likely due to
imperfections in the background subtraction. The greatest errors occur in
especially narrow loops and in places where the background is especially bright
relative to the loop. We stress, however, that these effects do not impact the
ability to measure large-scale variations. The result that observed loops do
not expand systematically with height is robust.Comment: Accepted for publication in Ap
An assembly to provide a time reference for the JPL Network Operations Control Center, Real-Time
A device is described which provides the value of date coordinated universal time (date UTC) to the JPL Network Operations Control Center, Real Time (NOCC-RT) facility. The NOCC-RT is the real time portion of the NOCC upgrade task. The time scale is generated in the NOCC-RT clock processor; however, there is a continuous reference to UTC, as realized by the National Institute of Standards and Technology and transmitted by Earth orbiting satellites. An important functional design requirement is the 99.9 pct. availability
The seesaw path to leptonic CP violation
Future experiments such as SHiP and high-intensity colliders will
have a superb sensitivity to heavy Majorana neutrinos with masses below .
We show that the measurement of the mixing to electrons and muons of one such
state could imply the discovery of leptonic CP violation in the context of
seesaw models. We quantify in the minimal model the CP discovery potential of
these future experiments, and demonstrate that a 5 CL discovery of
leptonic CP violation would be possible in a very significant fraction of
parameter space.Comment: An error has been fixed, main conclusions unchange
Dynamics of Holes and Universality Class of the Antiferromagnetic Transition in the Two Dimensional Hubbard Model
The dynamics of a single hole (or electron) in the two dimensional Hubbard
model is investigated. The antiferromagnetic background is described by a
N\`eel state, and the hopping of the carrier is analyzed within a configuration
interaction approach. Results are in agreement with other methods and with
experimental data when available. All data are compatible with the opening of a
mean field gap in a Fermi liquid of spin polarons, the so called Slater type of
transition. In particular, this hypothesis explains the unusual dispersion
relation of the quasiparticle bands near the transition. Recent photoemission
data for CaCuOCl are analyzed within this context.Comment: New results and comparison with recent data adde
SUSY signals at HERA in the no-scale flipped SU(5) supergravity model
Sparticle production and detection at HERA are studied within the recently
proposed no-scale flipped supergravity model. Among the various
reaction channels that could lead to sparticle production at HERA, only the
following are within its limit of sensitivity in this model: , where are the
two lightest neutralinos and is the lightest chargino. We study the
elastic and deep-inelastic contributions to the cross sections using the
Weizs\"acker-Williams approximation. We find that the most promising
supersymmetric production channel is right-handed selectron ()
plus first neutralino (), with one hard electron and missing energy
signature. The channel leads to comparable rates but also
allows jet final states. A right-handedly polarized electron beam at HERA would
shut off the latter channel and allow preferentially the former one. With an
integrated luminosity of {\cal L}=100\ipb, HERA can extend the present LEPI
lower bounds on by
\approx25\GeV, while {\cal L}=1000\ipb will make HERA competitive with
LEPII. We also show that the Leading Proton Spectrometer (LPS) at HERA is an
excellent supersymmetry detector which can provide indirect information about
the sparticle masses by measuring the leading proton longitudinal momentum
distribution.Comment: 11 pages, 8 figures (available upon request as uuencoded file or
separate ps files), tex (harvmac) CTP-TAMU-15/93, CERN/LAA/93-1
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