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Chapter 11Detection of scalar gravitational wavesFrancesco FucitoINFN, sez. di Roma 2, Via della Ricerca Scientifica, 00133 Rome,ItalyE-mail: Fucito@roma2.infn.itIn this talk I review recent progress in the detection of scalar gravitational waves.Furthermore, in the framework of the Jordan–Brans–Dicke theory, I compute thesignal-to-noise ratio for a resonant mass detector of spherical shape and for binarysources and collapsing stars. Finally, I compare these results with those obtainedfrom laser interferometers and from Einsteinian gravity.11.1 IntroductionThe efforts aimed at the detection of gravitational waves (GW) started more thana quarter of a century ago and have been, so far, unsuccessful [1,2]. Resonant barshave proved their reliability, being capable of continous data gathering for longperiods of time [3, 4]. Their energy sensitivity has improved by more than fourorders of magnitude since Weber’s pioneering experiment. However, a furtherimprovement is still necessary to achieve successful detection. While furtherdevelopments of bar detectors are underway, two new generations of Earth-basedexperiments have been proposed: detectors based on large laser interferometersare already under construction [5] and resonant detectors of spherical shape areunder study [2].In this lecture I report on a series of papers [6] in which the opportunity ofintroducing resonant mass detectors of spherical shape was studied. As a generalmotivation for their study, spherical detectors have the advantage over bar-shapeddetectors of a larger degree of symmetry. This translates into the possibility ofbuilding detectors of greater mass and consequently of higher cross section.Besides this obvious observation, the higher degree of symmetry enjoyed bythe spherical shape puts such a detector in the unique position of being able to152