  There is currently a discrepancy in the measured value of the amplitude of
matter clustering, parameterised using $\sigma_8$, inferred from galaxy weak
lensing, and cosmic microwave background data, which could be an indication of
new physics, such as massive neutrinos or a modification to the gravity law, or
baryon feedback. In this paper we make the assumption that the cosmological
parameters are well determined by Planck, and use weak lensing data to
investigate the implications for baryon feedback and massive neutrinos, as well
as possible contributions from intrinsic alignments and biases in photometric
redshifts. We apply a non-parametric approach to model the baryonic feedback on
the dark matter clustering, which is flexible enough to reproduce the OWLS and
Illustris simulation results. The statistic we use, 3D cosmic shear, is a
method that extracts cosmological information from weak lensing data using a
spherical-Bessel function power spectrum approach. We analyse the CFHTLenS weak
lensing data and, assuming best fit cosmological parameters from the Planck CMB
experiment, find that there is no evidence for baryonic feedback on the dark
matter power spectrum, but there is evidence for a bias in the photometric
redshifts in the CFHTLenS data, consistent with a completely independent
analysis by Choi et al. (2015), based on spectroscopic redshifts; and that
these conclusions are robust to assumptions about the intrinsic alignment
systematic. We also find an upper limit on the sum of neutrino masses
conditional on other $\Lambda$CDM parameters being fixed, of $< 0.28$ eV
($1\sigma$).
