Varying the light quark mass: impact on the nuclear force and Big Bang
  nucleosynthesis
  The quark mass dependences of light element binding energies and nuclear
scattering lengths are derived using chiral perturbation theory in combination
with non-perturbative methods. In particular, we present new, improved values
for the quark mass dependence of meson resonances that enter the nuclear force.
A detailed analysis of the theoretical uncertainties arising in this
determination is presented. As an application we derive from a comparison of
observed and calculated primordial deuterium and helium abundances a stringent
limit on the variation of the light quark mass, $\delta m_q/m_q = 0.02 \pm
0.04$. Inclusion of the neutron lifetime modification under the assumption of a
variation of the Higgs vacuum expectation value that translates into changing
quark, electron, and weak gauge boson masses, leads to a stronger limit,
$|\delta m_q/m_q| < 0.009$.
