227 research outputs found
What next? Exploring the future of high-energy physics. Proceedings, 16th Annual Montreal-Rochester-Syracuse- Toronto Meeting, MRST'94, Montreal, Canada, May 11-13, 1994
No full textNew measures of the quality and of the reliability of fits applied to forward hadronic data at t = 0
No full text7 pages, presented by J.R. Cudell on behalf of the COMPETE collaboration at the 6th workshop on non-perturbative QCD, American University of Paris, 5-9 June 2001International audienceWe develop five new statistical measures of the quality of fits, which we combine with the usual confidence level to determine the models which fit best all available data for total cross sections and for the real part of the forward hadronic amplitude
Application des réseaux neuronaux à la recherche d’ondes gravitationnelles émises par des systèmes légers
No full textWith GW170817, gravitational waves have shown themselves to be very useful for multi-messenger astronomy. Combining the information from multiple channels such as gravitational waves, gamma-rays, neutrinos, etc. can lead to great physics. Contrarily to the electromagnetic telescopes, a gravitational wave interferometer surveys the entire sky. They do not have to focus on a small portion of the celestial sphere as do standard telescopes. It is also known that for binary neutron stars, the electromagnetic counterpart is produced during the last phase of the merger, whereas the gravitational wave signal can be detected several minutes before these last stages. If one is able to detect this signal before the merger and infer the sky location, gravitational wave astronomy can then send an alert and produce a sky map indicating where the astronomer can point their telescopes to see an electromagnetic counterpart.
The standard technique to detect these compact binary coalescences is matched filtering. The principle is to compute a template bank of pre-computed waveforms and match them with the data strain coming from the LIGO and Virgo interferometers. This thesis starts by illustrating a matched filter search with a project to detect long signals coming from sub-solar coalescence.
Recently, some matched filtering pipelines have started to adapt their method to search for gravitational waves with only the early stage of the signal. Other methods are beginning to be developed for this type of research. This thesis presents new methods, based on machine learning, to detect the early phase of a binary neutron star merger. We have developed multiple convolutional neural networks looking directly at the strain data of the detector to detect binary neutron stars before the merger.
The last step to produce an early warning for the astronomer is to create a sky map indicating the location of the event. We therefore shortly discuss how to accomplish this through a machine learning method for the whole signal, and also mention how it can be adapted to the early part of the signal
Higgs mechanism in the general Two-Higgs-Doublet Model
No full textWe first review the standard Higgs mechanism of the standard model. Then, in the second chapter, we motivate the introduction of a second doublet in the theory. In the third chapter, we talk about the reasons to study the most general two Higgs doublet model and introduce the Minkowski formalism introduced by I.P. Ivanov to simplify this problem. Finally, we study the masses of the Higgs bosons in the most general two-Higgs-doublet model (2HDM) in a basis-independent approach.
We adapt the recently developed Minkowski-space formalism to this problem and
calculate traces of any power of the mass matrix in a compact and reparametrization-invariant form.
Our results can be used to gain insight into the dynamics of the scalar sector of the general 2HDM
Matière noire composite et expériences de recherche directe
No full textpeer reviewedThe results of the direct searches for dark matter are reinterpreted in the
framework of composite dark matter, i.e. dark matter particles that form
neutral bound states, generically called “dark atoms”.
Two different scenarios are presented: milli-interacting dark matter and
dark anti-atoms. In both of them, dark matter interacts sufficiently strongly
with terrestrial matter to be stopped in it before reaching underground detec-
tors, which are typically located at a depth of 1 km. As they drift towards the
center of the earth because of gravity, these thermal dark atoms are radiatively
captured by the atoms of the active medium of underground detectors, which
causes the emission of photons that produce the signals through their interac-
tions with the electrons of the medium. This provides a way of reinterpreting
the results in terms of electron recoils instead of nuclear recoils.
The two models involve milli-charges and are able to reconcile the most
contradictory experiments. We determine, for each model, the regions in the
parameter space that reproduce the experiments with positive results in con-
sistency with the constraints of the experiments with negative results
Axions and polarisation of quasars
No full textSuite à l’observation de la polarisation de la lumière provenant de quasars, une tendance à l’alignement des vecteurs de polarisation de ces lointains objets fut détectée dans certaines régions du ciel, celle-ci restant inexplicable par des effets locaux et semblant mettre en évidence l’existence de corrélations à très grande échelle, sur des distances cosmologiques.
L’objet de ce travail, qui s’inscrit à l’interface entre la physique des particules et l’astrophysique, sera de se pencher sur ce problème et de déterminer dans quelle mesure l’existence d’un certain type de particules encore hypothétiques, nommées axions, pourrait permettre de rendre compte de ce phénomène ; les propriétés prédites pour celles-ci incluant un couplage (faible, mais les distances entrant en jeu étant très grandes, les effets de ce couplage pourraient malgré tout être observables) avec la lumière
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