qu an tph ] 2 0 Ju l 2 01 6 LISA pathfinder appreciably constrains collapse models

LISA Pathfinder’s measurement of a relative acceleration noise between two free-falling test masses with a square root of the power spectral density of 5.2± 0.1 fm s/ √ Hz [1] appreciably constrains collapse models. In particular, we bound the localization rate parameter, λCSL, in the continuous spontaneous localization model (CSL) to be at most (2.96 ± 0.12)× 10 s. Moreover, we bound the regularization scale, σDP, used in the Diosi-Penrose (DP) model to be at least 40.1 ± 0.5 fm. These bounds significantly constrain the validity of these models. In particular: (i) a lower bound of 2.2 × 10s for λCSL has been proposed in [2] (although a lower bound of about 10s is sometimes used), in order for the collapse noise to be substantial enough to explain the phenomenology of quantum measurement, and (ii) 40 fm is larger than the size of any nucleus, while the regularization scale has been proposed to be the size of the nucleus [3, 4].