As observational evidence increasingly consolidates the case for a cosmological constant \Lambda 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 c _ { s } .
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 c _ { s } ^ { 2 } within an order of magnitude seems possible with a combination of Euclid and Planck data .