  Complete flavour decompositions of the scalar, axial and tensor charges of
the proton, deuteron, diproton and $^3$He at SU(3)-symmetric values of the
quark masses corresponding to a pion mass $m_\pi\sim806$ MeV are determined
using lattice QCD. At the physical quark masses, the scalar charges constrain
mean-field models of nuclei and the low-energy interactions of nuclei with
potential dark matter candidates. The axial and tensor charges of nuclei
constrain their spin content, integrated transversity and the quark
contributions to their electric dipole moments. External fields are used to
directly access the quark-line connected matrix elements of quark bilinear
operators, and a combination of stochastic estimation techniques is used to
determine the disconnected sea-quark contributions. Significant nuclear
modifications are found, with particularly large, O(10%), effects in the scalar
charges. Typically, these nuclear effects reduce the effective charge of the
nucleon (quenching), although in some cases an enhancement is not excluded.
Given the size of the nuclear modifications of the scalar charges resolved
here, contributions from correlated multi-nucleon effects should be quantified
in the analysis of dark matter direct-detection experiments using nuclear
targets.
