12,217 research outputs found
High spatial resolution and high contrast optical speckle imaging with FASTCAM at the ORM
In this paper, we present an original observational approach, which combines,
for the first time, traditional speckle imaging with image post-processing to
obtain in the optical domain diffraction-limited images with high contrast
(1e-5) within 0.5 to 2 arcseconds around a bright star. The post-processing
step is based on wavelet filtering an has analogy with edge enhancement and
high-pass filtering. Our I-band on-sky results with the 2.5-m Nordic Telescope
(NOT) and the lucky imaging instrument FASTCAM show that we are able to detect
L-type brown dwarf companions around a solar-type star with a contrast DI~12 at
2" and with no use of any coronographic capability, which greatly simplifies
the instrumental and hardware approach. This object has been detected from the
ground in J and H bands so far only with AO-assisted 8-10 m class telescopes
(Gemini, Keck), although more recently detected with small-class telescopes in
the K band. Discussing the advantage and disadvantage of the optical regime for
the detection of faint intrinsic fluxes close to bright stars, we develop some
perspectives for other fields, including the study of dense cores in globular
clusters. To the best of our knowledge this is the first time that high
contrast considerations are included in optical speckle imaging approach.Comment: Proceedings of SPIE conference - Ground-based and Airborne
Instrumentation for Astronomy III (Conference 7735), San Diego 201
Experimental aspects of SU(5)xU(1) supergravity
We study various aspects of supergravity as they relate to
the experimental verification or falsification of this model. We consider two
string-inspired, universal, one-parameter, no-scale soft-supersymmetry-breaking
scenarios, driven by the -terms of the moduli and dilaton fields. The model
is described in terms of the supersymmetry mass scale (\ie, the chargino mass
), , and the top-quark mass. We first determine the
combined effect on the parameter space of all presently available direct and
indirect experimental constraints, including the LEP lower bounds on sparticle
and Higgs-boson masses, the rate, the anomalous magnetic moment
of the muon, the high-precision electroweak parameters
(which imply m_t\lsim180\GeV), and the muon fluxes in underground detectors
(neutrino telescopes). For the still-allowed points in
parameter space, we re-evaluate the experimental
situation at the Tevatron, LEPII, and HERA. In the 1994 run, the Tevatron could
probe chargino masses as high as 100 GeV. At LEPII the parameter space could be
explored with probes of different resolutions: Higgs boson searches, selectron
searches, and chargino searches. Moreover, for m_t\lsim150\GeV, these
Higgs-boson searches could explore all of the allowed parameter space with
\sqrt{s}\lsim210\GeV.Comment: latex, 36 pages, 25 figures (not included). Figures are available via
anonymous ftp from hplaa02.cern.ch (/pub/lopez) as either 33 ps files
(Easpects*.ps, 8.1MB) or one uuencoded file (AllFigures.uu, 3.7MB
Supersymmetric QCD flavor changing top quark decay
We present a detailed and complete calculation of the gluino and scalar
quarks contribution to the flavour-changing top quark decay into a charm quark
and a photon, gluon, or a Z boson within the minimal supersymmetric standard
model including flavour changing gluino-quarks-scalar quarks couplings in the
right-handed sector. We compare the results with the ones presented in an
earlier paper where we considered flavour changing couplings only in the
left-handed sector. We show that these new couplings have important
consequences leading to a large enhancement when the mixing of the scalar
partners of the left- and right-handed top quark is included. Furthermore CP
violation in the flavour changing top quark decay will occur when a SUSY phase
is taken into account.Comment: 14 pages, latex, 3 figure
Probing Supergravity Models with Indirect Experimental Signatures
We explore the one-loop electroweak radiative corrections in the context of
the traditional minimal and the string-inspired
supergravity models by calculating explicitly vacuum-polarization and
vertex-correction contributions to the and
parameters. We also include in this analysis the constraint from whose inclusive branching ratio has been
actually measured very recently by CLEO. We find that by combining these three
most important indirect experimental signatures and using the most recent
experimental values for them, is excluded for
in both the minimal supergravity and the no-scale supergravity. We also find that is
excluded for any sign of in the minimal () supergravity
model.Comment: RevTeX 3.0, 16 Pages+4 figures(not included but available as a
uuencoded file from [email protected]), SNUTP-94-9
QCD Improved Constraints on the Minimal Supergravity Model
Recent advances in the QCD corrections to decay in the MSSM
include i.) evaluation of the relevant operators, Wilson coefficients and
anomalous dimension matrix elements for the various MSSM effective theories
valid at scales beyond , ii.) calculations of most of the needed
anomalous dimension matrix elements to next-to-leading order for scales
m_b\alt Q , and iii.) calculations of virtual and
bremsstrahlung corrections to the decay operators at scale
. We assemble all these known results to gain an estimate of for the parameter space of the minimal supergravity model (mSUGRA).
We find a much reduced scale dependence of our result compared to usual
leading-log evaluations. Comparison with the latest CLEO results yields
stringent constraints on parameter space. Much of mSUGRA parameter space is
ruled out for , especially for large . We compare these
results with other constraints from cosmology and non-standard vacua. Also, we
compare with expectations for discovering mSUGRA at LEP2, the Tevatron and the
CERN LHC.Comment: 14 pages REVTEX plus 7 PS figures; this version contains revised
figures and text due to discovery of a bug in the program used to generate
results for the previous version of this manuscrip
New Supersymmetric Contributions to
We calculate the electroweak-like one-loop supersymmetric contributions to
the rare and flavor-violating decay of the top quark into a charm quark and a
gauge boson: , with . We consider loops of both charginos
and down-like squarks (where we identify and correct an error in the
literature) and neutralinos and up-like squarks (which have not been calculated
before). We also account for left-right and generational squark mixing. Our
numerical results indicate that supersymmetric contributions to can be
upto 5 orders of magnitude larger than their Standard Model counterparts.
However, they still fall short of the sensitivity expected at the
next-generation top-quark factories.Comment: 13 pages, LaTex, 1 figure included. Final version to appear in
Physical Review D. Chargino contribution dealt with in greater detail. Minor
revisions in tex
Effects of supersymmetric grand unification scale physics on
Although calculations of the rate in supersymmetric
grand unified models have always either ignored the gluino mediated
contribution or found it to be negligible, we show that taking universal
supersymmetry breaking masses at the Planck scale, rather than at the gauge
unification scale as is customary, leads to the gluino contribution being more
significant and in fact sometimes even larger than the chargino mediated
contributions when and is of order 1. The impact is
greatest felt when the gluinos are relatively light. Taking the universal
boundary condition at the Planck scale also has an effect on the chargino
contribution by increasing the effect of the wino and higgsino-wino mediated
decays. The neutralino mediated contribution is found to be enhanced, but
nevertheless it remains relatively insignificant.Comment: Title changed, final version as accepted for PRD, 12 pages, 6 Figures
(Figs.2-6 included, uuencoded, epsf.tex
The Supersymmetric Particle Spectrum
We examine the spectrum of supersymmetric particles predicted by grand
unified theoretical (GUT) models where the electroweak symmetry breaking is
accomplished radiatively. We evolve the soft supersymmetry breaking parameters
according to the renormalization group equations (RGE). The minimization of the
Higgs potential is conveniently described by means of tadpole diagrams. We
present complete one-loop expressions for these minimization conditions,
including contributions from the matter and the gauge sectors. We concentrate
on the low fixed point region (that provides a natural explanation
of a large top quark mass) for which we find solutions to the RGE satisfying
both experimental bounds and fine-tuning criteria. We also find that the
constraint from the consideration of the lightest supersymmetric particle as
the dark matter of the universe is accommodated in much of parameter space
where the lightest neutralino is predominantly gaugino. The supersymmetric mass
spectrum displays correlations that are model-independent over much of the GUT
parameter space.Comment: 62 pages + 10 PS figures included (uuencoded), MAD/PH/80
Magnetic domain wall curvature induced by wire edge pinning
open14In this study, we report on the analysis of the magnetic domain wall (DW) curvature due to magnetic field induced motion in Ta/CoFeB/MgO and Pt/Co/Pt wires with perpendicular magnetic anisotropy. In wires of 20 mu m and 25 mu m, a large edge pinning potential produces the anchoring of the DW ends to the wire edges, which is evidenced as a significant curvature of the DW front as it propagates. As the driving magnetic field is increased, the curvature reduces as a result of the system moving away from the creep regime of DW motion, which implies a weaker dependence of the DW dynamics on the interaction between the DW and the wire edge defects. A simple model is derived to describe the dependence of the DW curvature on the driving magnetic field and allows us to extract the parameter sigma (E), which accounts for the strength of the edge pinning potential. The model describes well the systems with both weak and strong bulk pinning potentials like Ta/CoFeB/MgO and Pt/Co/Pt, respectively. This provides a means to quantify the effect of edge pinning induced DW curvature on magnetic DW dynamics.embargoed_20210815Herrera Diez, L.; Ummelen, F.; Jeudy, V.; Durin, G.; Lopez-Diaz, L.; Diaz-Pardo, R.; Casiraghi, A.; Agnus, G.; Bouville, D.; Langer, J.; Ocker, B.; Lavrijsen, R.; Swagten, H. J. M.; Ravelosona, D.Herrera Diez, L.; Ummelen, F.; Jeudy, V.; Durin, G.; Lopez-Diaz, L.; Diaz-Pardo, R.; Casiraghi, A.; Agnus, G.; Bouville, D.; Langer, J.; Ocker, B.; Lavrijsen, R.; Swagten, H. J. M.; Ravelosona, D
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