Archive ouverte UNIGE | last documents for author 'Anna Rissone'https://archive-ouverte.unige.ch/Latest objects deposited in the Archive ouverte UNIGE for author 'Anna Rissone'engElectronic contribution to the oscillations of a gravitational antennahttps://archive-ouverte.unige.ch/unige:156689https://archive-ouverte.unige.ch/unige:156689We carefully analyse the contribution to the oscillations of a metallic gravitational antenna due to the interaction between the electrons of the bar and the incoming gravitational wave. To this end, we first derive the total microscopic Hamiltonian of the wave-antenna system and then compute the contribution to the attenuation factor due to the electron-graviton interaction. As compared to the ordinary damping factor, which is due to the electron viscosity, this term turns out to be totally negligible. This result confirms that the only relevant mechanism for the interaction of a gravitational wave with a metallic antenna is its direct coupling with the bar normal modes.Wed, 24 Nov 2021 15:16:06 +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 +0100Perturbative and non-perturbative aspects of the two-dimensional string/Yang–Mills correspondencehttps://archive-ouverte.unige.ch/unige:35707https://archive-ouverte.unige.ch/unige:35707It is known that YM2 with gauge group SU(N) is equivalent to a string theory with coupling gs=1/N, order by order in the 1/N expansion. We show how this result can be obtained from the bosonization of the fermionic formulation of YM2, improving on results in the literature, and we examine a number of non-perturbative aspects of this string/YM correspondence. We find contributions to the YM2 partition function of order exp{−kA/(πα′gs)} with k an integer and A the area of the target space, which would correspond, in the string interpretation, to D1-branes. Effects which could be interpreted as D0-branes are instead strictly absent, suggesting a non-perturbative structure typical of type 0B string theories. We discuss effects from the YM side that are interpreted in terms of the stringy exclusion principle of Maldacena and Strominger. We also find numerically an interesting phase structure, with a region where YM2 is described by a perturbative string theory separated from a region where it is described by a topological string theoryTue, 15 Apr 2014 10:42:43 +0200