Gravitational wave detectors are driven away from thermodynamic equilibrium. Why we should care

Ground based gravitational wave detectors show extremely high displacement sensitivity which approaches the level set by the quantum limit. However it is likely that a detection will be achieved at a low signal-to-noise ratio and thus it is mandatory to know the noise budget and statistics. The RareNoise project has outlined a few mechanisims that cause the instruments to operate at non-equilibrium states. We argue that this aspect has not been given appropriate consideration in the past and that it could alter the overall predicted performance of the detector. It is also known that, most often, the rare fluctuations away from the mean of a nonequilibrium object have a statistical footprint different from those commonly studied at thermodynamic equilibrium. We present the RareNoise project whose experimental and theoretical activity are devised to further investigate this question; we also show first results which confirm the non-equilibrium hypothesis for the case of a resonant detector.