Investigating clustering dark energy with 3d weak cosmic shear
  As observational evidence increasingly consolidates the case for a cosmological constant being the source of the Universe's accelerated expansion, the question whether, and if so, how well, future experiments could detect deviations from this standard scenario is raised with urgency. Assuming a dark energy component different from a cosmological constant, the observable effects in general include gravitational clustering described by the fluid's (rest-frame) speed of sound. We employ 3d weak cosmic shear, a proposed method to take advantage of the full three-dimensional information inherent to the cosmic shear field, to explore the capability of future surveys to detect dark energy clustering and the signature of an enhanced amplitude of the matter power spectrum on large scales. For this purpose, we present adequate numerical methods facilitating 3d weak cosmic shear calculations. We find that the possible constraints heavily depend on the dark energy equation of state w. If w is not very close to -1, constraining the squared sound speed within an order of magnitude seems possible with a combination of Euclid and Planck data. 
Youness Ayaita, Bjoern Malte Schaefer, Maik Weber
astro-ph.CO