950 research outputs found
Higgs inflation: consistency and generalisations
We analyse the self-consistency of inflation in the Standard Model, where the
Higgs field has a large non-minimal coupling to gravity. We determine the
domain of energies in which this model represents a valid effective field
theory as a function of the background Higgs field. This domain is bounded
above by the cutoff scale which is found to be higher than the relevant
dynamical scales throughout the whole history of the Universe, including the
inflationary epoch and reheating. We present a systematic scheme to take into
account quantum loop corrections to the inflationary calculations within the
framework of effective field theory. We discuss the additional assumptions that
must be satisfied by the ultra-violet completion of the theory to allow
connection between the parameters of the inflationary effective theory and
those describing the low-energy physics relevant for the collider experiments.
A class of generalisations of inflationary theories with similar properties is
constructed.Comment: 25 pages, 1 figur
Hyperon production asymmetries in 500 GeV/c pion nucleus interactions
We present a preliminary study from Fermilab experiment E791 of Lambda^0 /
Lambda^0 bar, Xi^- / Xi^+ and Omega^- /Omega^+ production asymmetries from pi^-
nucleus interactions at 500 Gev/c. The production asymmetries for these
particles are studied as a function of x_F and pt^2. We observed an asymmetry
in the target fragmentation region for Lambda^0's larger than that for Xi's,
suggesting diquark effects. The asymmetry for Omega's is significatively
smaller than for the other two hyperons consistent with the fact that Omega's
do not share valence quarks with either the pion or the target particle. In the
beam fragmentation region, the asymmetry tends to 0.1 for both Lambda^0's and
Xi's. The asymmetries vs pt^2 are approximately constant for the three strange
baryons under study.Comment: Typos correcte
The Charm of the Proton and the Production
We propose a two component model for charmed baryon production in
collisions consisting of the conventional parton fusion mechanism and
fragmentation plus quarks recombination in which a valence diquark from
the proton recombines with a -sea quark to produce a . Our
two-component model is compared with the intrinsic charm two-component model
and experimental data.Comment: 6 pages, LaTex, 2 figures included, aipproc.sty included. Talk
presented at Simposio Latino Americano de Fisica de Altas Energias, Merida,
Mexico, November 199
The Polarization and the Recombination Mechanism
We use the recombination and the Thomas Precession Model to obtain a
prediction for the polarization in the
reaction. We study the effect of the recombination function on the
polarization.Comment: 4 pages, LaTex, 1 figures included, aipproc.sty included. Talk
presented at Simposio Latino Americano de Fisica de Altas Energias, Merida,
Mexico, November 199
Asymmetry studies in Lambda 0/Lambda 0-bar, Xi-/Xi+ and Omega-/Omega+ production
We present a study on hyperon/anti-hyperon production asymmetries in the
framework of the recombination model. The production asymmetries for Lambda
0/Lambda 0-bar, Xi-/Xi+ and Omega-/Omega+ are studied as a function of x_F.
Predictions of the model are compared to preliminary data on
hyperon/anti-hyperon production asymmetries in 500 GeV/c pi- p interactions
from the Fermilab E791 experiment. The model predicts a growing asymmetry with
the number of valence quarks shared by the target and the produced hyperons in
the x_F < 0 region. In the positive x_F region, the model predicts constant
asymmetries for Lambda 0/Lambda 0-bar and Omega-/Omega+ production and a
growing asymmetry with x_F for Xi-/Xi+. We found a qualitatively good agreement
between the model predictions and data, showing that recombination is a
competitive mechanism in the hadronization process.Comment: One reference correcte
Heisenberg-limited eavesdropping on the continuous-variable quantum cryptographic protocol with no basis switching is impossible
The Gaussian quantum key distribution protocol based on coherent states and
heterodyne detection [Phys. Rev. Lett. 93, 170504 (2004)] has the advantage
that no active random basis switching is needed on the receiver's side. Its
security is, however, not very satisfyingly understood today because the bounds
on the secret key rate that have been derived from Heisenberg relations are not
attained by any known scheme. Here, we address the problem of the optimal
Gaussian individual attack against this protocol, and derive tight upper bounds
on the information accessible to an eavesdropper. The optical scheme achieving
this bound is also exhibited, which concludes the security analysis of this
protocol.Comment: 10 pages, 6 figure
Introduction to 2D and 3D tomographic methods based on straight line propagation: X-ray, emission and ultrasonic tomography
This paper presents the basic principles of computerized tomography (CT), and its evolution towards three dimensional (3D )
imaging . Since the modelisation of CT reconstruction relies on the Radon transform, its definition and major properties are firs t
recalled. After a brief summary on conventional 2D methods, we present the imaging principles for two modalities appropriate d
to this modelisation : X-Ray and emission tomography. We describe the evolution of the instrumentation for these two techniques ,
and emphasize the approximations introduced by a modelisation using the Radon transform taking into account the physics o f
the problem . We also describe the principles of ultrasonic tomography systems, and their major differences with the two previou s
technics . At last, we formulate the general problematic of 3D image reconstruction from 2D projections . We consider four classe s
of reconstruction methods corresponding to the classification chosen for the synthetic presentation of methods, accompanying thi s
paper.Cet article présente les principes de base de la tomographie assistée par ordinateur, ainsi que son évolution vers le tridimen -
sionnel (3D) . La modélisation mathématique du problème de reconstruction tomographique s'appuie sur la transformatio n
de Radon dont la définition et quelques propriétés sont rappelées . Après un bref résumé sur les méthodes conventionnelle s
2D, nous présentons les principes physiques pour deux modalités bien appropriées à cette modélisation : la tomographie de
transmission par rayons X et la tomographie d'émission par rayons ,y . Nous nous attachons à décrire l'évolution de l'instru -
mentation dans ces deux techniques, ainsi que les approximations introduites par une modélisation de type Transformée de
Radon par rapport à la physique du problème . Nous décrivons également les principes des systèmes de tomographie ultrasonore,
et leurs différences majeures par rapport aux deux techniques précédentes . Enfin, nous reprenons la problématiqu e
générale des méthodes de reconstruction 3D à partir de projections 2D . Nous faisons apparaître quatre classes correspondan t
au découpage choisi pour la présentation des fiches techniques accompagnant cet article
- …