  We apply the ab initio no-core shell model/resonating group method approach
to calculate the cross sections of the 3H(d,n)4He and 3He(d,p)4He fusion
reactions. These are important reactions for the Big Bang nucleosynthesis and
the future of energy generation on Earth. Starting from a selected
similarity-transformed chiral nucleon-nucleon interaction that accurately
describes two-nucleon data, we performed many-body calculations that predict
the S-factor of both reactions. Virtual three-body breakup effects are obtained
by including excited pseudostates of the deuteron in the calculation. Our
results are in satisfactory agreement with experimental data and pave the way
for microscopic investigations of polarization and electron screening effects,
of the 3H(d,gamma)5He radiative capture and other reactions relevant to fusion
research.
