Status of the VIRGO experiment

Abstract

The Virgo detector will be a 3 km long interferometer antenna with a design sensitivity aiming at the direct observation of gravitational waves.The construction of this detector which will be installed near Pisa is under way. The data taking should start in year 2000 with a design sensitivity close to h¯≃10−23Hz−1/2. The motivations, detector principle, main sources of noise and status of the experiment are presented

Gauge invariant formalism for second order perturbations of Schwarzschild spacetimes

“…In the next few years gravitational wave antennas [1][2][3][4] will go into operation with the possibility of detecting astrophysical sources. A plausible, and certainly fascinating, origin of such waves would be the powerful burst of radiation generated in the merger of two approximately equal mass black holes to form a single final hole [5].…”

“…αβ is the Schwarzschild metric in our case; g (1) αβ is called the first order perturbation to the metric; g (2) αβ is called the second order perturbation to the metric, and so forth. Let us now consider a parameterized family of coordinate transformations, also called transformations of the coordinate gauge, or simply "gauge transformations," x µ new = F µ (x α , ǫ), that can be expanded as…”

“…If ξ (1)µ = 0, we call the transformation a purely second order transformation. Note that g (1) αβ is invariant under this type of transformation, but g (2) αβ , g (3) αβ · · · are not. The Moncrief [23] formalism is based on a certain linear combination of first order perturbations g (1) αβ that can be determined purely from hypersurface information, i.e., from the first and second fundamental form of a hypersurface that, to zero order in ǫ is a constant time surface in the Schwarzschild geometry.…”

“…[We will present this combination explicitly below in (19) after we have introduced multipole decomposition and the appropriate notation.] We will use L (2) to represent the same combination of second order perturbations g (2) αβ . It follows immediately that the second order combination L (2) is invariant under purely second order gauge transformations.…”

Status of String Cosmology: Phenomenological Aspects

“…As a consequence, we know the slope (ω 3 ) of this "dilatonic" branch of the spectrum, but we don't know the position, in the (Ω, ω) plane, of the peak frequency ω s . This uncertainty is, however, interesting, because the effects of the string phase could shift the spectrum (3.1) to a low enough frequency band, so as to overlap with the possible future sensitivity of large interferometric detectors such as LIGO [31] and VIRGO [32]. I will discuss this possibility in terms of a two-parameter model of background evolution, presented in the following Section.…”