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(ed.). Gravitational waves (IOP, 2001)(422s).

(ed.). Gravitational waves (IOP, 2001)(422s).

(ed.). Gravitational waves (IOP, 2001)(422s).

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Chapter 9The Earth-bas<strong>ed</strong> large interferometer Virgoand the Low Frequency FacilityAngela Di VirgilioINFN Sezione di Pisa, via Vecchia Livornese 1265,56010 S. Piero a Grado (Pisa), ItalyE-mail: angela.divirgilio@pi.infn.itThe principle of the Earth-bas<strong>ed</strong> interferometer and the parameters of Virgo, theCNRS-INFN antenna under construction in Cascina near Pisa, are present<strong>ed</strong>. TheSuper-Attenuator (SA), the suspension ad hoc design<strong>ed</strong> for Virgo, and the LowFrequency Facility, the project devot<strong>ed</strong> to study the SA with a sensitivity close tothe Virgo one, are shortly describ<strong>ed</strong>.9.1 IntroductionThe detection of gravitational <strong>waves</strong> (GW), produc<strong>ed</strong> in astrophysical processes,is one of the most challenging fields of modern physics, aim<strong>ed</strong> at findinggravitational-wave astronomy. Lectures about GW production and expect<strong>ed</strong>sources can be found in this book, but let me very briefly remind you ofthe essentials. General relativity pr<strong>ed</strong>icts that accelerat<strong>ed</strong> matter producesgravitational <strong>waves</strong>, ripples of spacetime travelling with the spe<strong>ed</strong> of light. GWcan be defin<strong>ed</strong> as a perturbation of the metric, h αβ , and the observational effect ofits passage through the Earth is a change among the relative distance of massivebodies. If A and B are the space-state locations of the two testmasses and if weset AB = (x α ), the vector (x α ) obeys the equation of geodesic deviation in weakfield:d 2 x αdt 2 = 1 ∂ 2 h TTαβ2 ∂t 2 x β (9.1)103

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