Archive ouverte UNIGE | last documents for author 'Florian Dubath'https://archive-ouverte.unige.ch/Latest objects deposited in the Archive ouverte UNIGE for author 'Florian Dubath'engMatched filter for multi-transducers resonant GW antennashttps://archive-ouverte.unige.ch/unige:156469https://archive-ouverte.unige.ch/unige:156469We analyze two kinds of matched filters for data output of a spherical resonant GW detector. In order to filter the data of a real sphere, a strategy is proposed, firstly using an omnidirectional in-line filter, which is supposed to select periodograms with excitations, secondly by performing a directional filter on such selected periodograms, finding the wave arrival time, direction and polarization. We point out that, as the analytical simplifications occurring in the ideal 6 transducers TIGA sphere do not hold for a real sphere, using a 5 transducers configuration could be a more convenient choice.Wed, 17 Nov 2021 14:51:20 +0100String hamiltonian from generalized YM gauge theory in two dimensionshttps://archive-ouverte.unige.ch/unige:85284https://archive-ouverte.unige.ch/unige:85284Two dimensional SU(N) Yang-Mills theory is known to be equivalent to a string theory, as found by Gross in the large N limit, using the 1/N expansion. Later it was found that even a generalized YM theory leads to a string theory of the Gross type. In the standard YM theory case, Douglas and others found the string hamiltonian describing the propagation and the interactions of states made of strings winding on a cylindrical space-time. We address the problem of finding a similar hamiltonian for the generalized YM theory. As in the standard case we start by writing the theory as a theory of free fermions. Performing a bosonization, we express the hamiltonian in terms of the modes of a bosonic field, that are interpreted as in the standard case as creation and destruction operators for states of strings winding around the cylindrical space-time. The result is similar to the standard hamiltonian, but with new kinds of interaction vertices.Thu, 14 Jul 2016 14:07:19 +0200A bound on galactic mass loss rates obtained from globular cluster dynamicshttps://archive-ouverte.unige.ch/unige:82080https://archive-ouverte.unige.ch/unige:82080Using tidal disruption of globular clusters by the galactic centre, we put limits on the total mass enclosed into orbits of observed globular clusters. Under the assumption that the rate of mass loss from the galaxy is steady, we then deduce a bound on this rate. In particular, this bound can be used to constrain the galactic gravitational wave luminosity.Wed, 23 Mar 2016 08:50:06 +0100Possible sources of gravitational wave bursts detectable todayhttps://archive-ouverte.unige.ch/unige:35708https://archive-ouverte.unige.ch/unige:35708We discuss the possibility that galactic gravitational wave sources might give burst signals at a rate of several events per year, detectable by state-of-the-art detectors. We are stimulated by the results of the data collected by the EXPLORER and NAUTILUS bar detectors in the 2001 run, which suggest an excess of coincidences between the two detectors, when the resonant bars are orthogonal to the galactic plane. Signals due to the coalescence of galactic compact binaries fulfill the energy requirements but are problematic for lack of known candidates with the necessary merging rate. We examine the limits imposed by galactic dynamics on the mass loss of the Galaxy due to gravitational wave (GW) emission, and we use them to put constraints also on the GW radiation from exotic objects, like binaries made of primordial black holes. We discuss the possibility that the events are due to GW bursts coming repeatedly from a single or a few compact sources. We examine different possible realizations of this idea, such as accreting neutron stars, strange quark stars, and the highly magnetized neutron stars (“magnetars”) introduced to explain soft gamma repeaters. Various possibilities are excluded or appear very unlikely, while others at present cannot be excludedTue, 15 Apr 2014 10:43:20 +0200Upper limits on the gravitational mass loss of the Galaxy and the LIGO burst searcheshttps://archive-ouverte.unige.ch/unige:35681https://archive-ouverte.unige.ch/unige:35681We discuss the relevance, for the search of gravitational-wave bursts, of upper limits on the total mass loss of the Galaxy which come from various astronomical observations. For sub-millisecond bursts we obtain limits on the event rate, as a function of the GW amplitude, which are stronger than the corresponding upper limits set by LIGO in the S2 run. A detection of a burst rate saturating these limits, with the sensitivities of present and near-future runs, would imply that, with some improvement on the accuracy of astronomical observations of the Galaxy, as foreseen with the GAIA mission, it might be possible to detect gravitational waves indirectly from their effect on galactic dynamics.Mon, 14 Apr 2014 16:29:35 +0200On the Sensitivity of a Hollow Sphere as a Multi-modal Resonant Gravitational Wave Detectorhttps://archive-ouverte.unige.ch/unige:13107https://archive-ouverte.unige.ch/unige:13107We present a numerical analysis to simulate the response of a spherical resonant gravitational wave detector and to compute its sensitivity. Under the assump- tion of optimal filtering, we work out the sensitivity curve for a sphere first taking into account only a single transducer, and then using a coherent analysis of the whole set of transducers.Tue, 04 Jan 2011 14:24:33 +0100Experimental signatures of gravitational wave burstershttps://archive-ouverte.unige.ch/unige:2201https://archive-ouverte.unige.ch/unige:2201Gravitational wave bursters are sources which emit repeatedly bursts of gravitational waves, and have been recently suggested as potentially interesting candidates for gravitational wave (GW) detectors. Mechanisms that could give rise to a GW burster can be found for instance in highly magnetized neutron stars (the “magnetars” which explain the phenomenon of soft gamma repeaters), in accreting neutron stars and in hybrid stars with a quark core. We point out that these sources have very distinctive experimental signatures. In particular, as already observed in the -ray bursts from soft gamma repeaters, the energy spectrum of the events is a power-law, dN ∼ E− dE with ≃ 1.6, and they have a distribution of waiting times (the times between one outburst and the next) significantly different from the distribution of uncorrelated events. We discuss possible detection strategies that could be used to search for these events in existing gravitational wave detectors.Tue, 07 Jul 2009 13:38:40 +0200Microlensing modulation by quadrupole variationhttps://archive-ouverte.unige.ch/unige:945https://archive-ouverte.unige.ch/unige:945We investigate microlensing in the case where the lens is considered as an extended object. We use a multipolar expansion of the lens potential and show that the time-varying nature of the quadrupole contribution allows to separate it from the mass and spin contributions and leads to specific modulations of the amplification signal. As example we study the case of binary system lenses in our galaxy. The modulation is observable if the rotation period of the system is smaller than the time over which the amplification is significant and if the impact parameter of the passing light ray is sufficiently close to the Einstein radius so that the amplification is large. Observations of this modulation can reveal important information on the quadrupole and thus on the gravitational radiation emitted by the binary lens. Even if not observed directly, because of their importance the quadrupole modulation has to be included in the error budget for high magnification (µ<=7) microlensing events.Thu, 26 Feb 2009 17:47:39 +0100Theoretical and experimental aspects of gravitational-wave physicshttps://archive-ouverte.unige.ch/unige:407https://archive-ouverte.unige.ch/unige:407La première partie de cette thèse est consacrée à l'étude du fonctionnement des détecteurs d'ondes gravitationnelles résonnants et contient des modèles numériques de détecteurs cylindriques (EXPLORER et NAUTILUS) et sphériques (MiniGRAIL). Suit une description du processus d'analyse des données des détecteurs cylindriques avec, comme résultat, l'obtention d'une borne sur le taux de sursauts d'ondes gravitationnelles. La seconde partie s'inscrit dans la mise en place des outils de l'astonomie des ondes gravitationnelles. Une première étude fait le lien entre l'astrophysique galactique et l'émission d'ondes gravitationnelles. Il en découle une borne sur le taux de sursauts d'ondes gravitationnelles. Vient ensuite la proposition d'une nouvelle classe de sources d'ondes gravitationnelles : les sources d'ondes gravitationnnelles à activité en sursauts répétés. Finalement, il est considéré la possiblité de former des boucles de corde cosmique lors de la collision d'une corde et d'un trou noir en rotation.Wed, 29 Oct 2008 12:47:15 +0100