On September 14th 2015 the first gravitational wave signal has been detected by the Advanced LIGO interferometers, opening the era of the gravitational astronomy and giving new opportunities to ...investigate the universe. The Advanced LIGO and Advanced Virgo interferometers are now back in a commissioning phase in order to improve their sensitivity for the next observing run, which will start in the first months of 2019. In the high-frequencies region of their sensitivity band, the detectors are shot-noise limited: the sensitivity in this frequency window could be improved increasing the laser input power, but this increases also the optical aberrations due to the thermal effects. The optical power absorptions in the substrate and coatings of the optics induce both an increase of the optical path length in the substrates of the mirrors (thermal lensing) and a thermal expansion of the optic itself along the optical axis (thermo-elastic deformation). Both these aberrations reduce the sensitivity of the detector, limiting its performances. In order to face and minimize them, an adaptive Thermal Compensation System is required in order to guarantee the proper operation of the interferometer. An overview of the present Thermal Compensation System system installed on Advanced Virgo, with also a focus on the possible improvements of the actual actuators for the next generation of detectors, is presented here.
Thermal effects in the test masses of the gravitational waves interferometric detectors may result in a strong limitation to their operation and sensitivity. Already in initial LIGO and Virgo, these ...effects have been observed and required the installation of dedicated compensation systems. Based on CO2 laser projectors, the thermal compensators heat the peripheral of the input test masses to reduce the lensing effect. In advanced detectors, the power circulating in the interferometer will increase, thus making thermal effects more relevant. In this paper, the concept of the compensation system for Advanced Virgo is described.
Many experiments have searched for supersymmetric WIMP dark matter, with null results. This may suggest to look for more exotic possibilities, for example compact ultra-dense quark nuggets, widely ...discussed in literature with several different names. Nuclearites are an example of candidate compact objects with atomic size cross section. After a short discussion on nuclearites, the result of a nuclearite search with the gravitational wave bar detectors Nautilus and Explorer is reported. The geometrical acceptance of the bar detectors is 19.5 m2 sr, that is smaller than that of other detectors used for similar searches. However, the detection mechanism is completely different and is more straightforward than in other detectors. The experimental limits we obtain are of interest because, for nuclearites of mass less than 10−5 g, we find a flux smaller than that one predicted considering nuclearites as dark matter candidates. Particles with gravitational only interactions (newtorites) are another example. In this case the sensitivity is quite poor and a short discussion is reported on possible improvements.
PDF
