We present parameter estimation forecasts for future 3D cosmic shear surveys for a class of Unified Dark Matter ( UDM ) models , where a single scalar field mimics both Dark Matter ( DM ) and Dark Energy ( DE ) .
These models have the advantage that they can describe the dynamics of the Universe with a single matter component providing an explanation for structure formation and cosmic acceleration .
A crucial feature of the class of UDM models we use in this work is characterised by a parameter , { c _ { \infty } } ( in units of the speed of light c = 1 ) , that is the value of the sound speed at late times , and on which structure formation depends .
We demonstrate that the properties of the DM-like behaviour of the scalar field can be estimated with very high precision with large-scale , fully 3D weak lensing surveys .
We found that 3D weak lensing significantly constrains { c _ { \infty } } , and we find minimal errors \Delta { c _ { \infty } } = 3.0 \cdot 10 ^ { -5 } , for the fiducial value { c _ { \infty } } = 1.0 \cdot 10 ^ { -3 } , and \Delta { c _ { \infty } } = 2.6 \cdot 10 ^ { -5 } , for { c _ { \infty } } = 1.2 \cdot 10 ^ { -2 } .
Moreover , we compute the Bayesian evidence for UDM models over the \Lambda CDM model as a function of { c _ { \infty } } .
For this purpose , we can consider the \Lambda CDM model as a UDM model with { c _ { \infty } } = 0 .
We find that the expected evidence clearly shows that the survey data would unquestionably favour UDM models over the \Lambda CDM model , for the values { c _ { \infty } } \gtrsim 10 ^ { -3 } .