The energy generated in the sun comes from an exothermic set of reactions,
where the first one, pp fusion, is governed by the weak interaction. This makes it
the slowest reaction by far, and therefore it determines the lifetime of the Sun.
However, its slow rate entails that a measurement of its cross-section is
impossible. Instead, the cross-section must be calculated from theory. In our
theoretical work we have calculated the pp fusion by using a method named
pionless Effective Field Theory (  EFT ) and fixing the corresponding coupling
constants from a different weak decay, namely triton β decay. We were able to
calculate the pp fusion rate due to the universality and the consistency of (  EFT )
in the transition between one, two and three nucleon electroweak reactions . In
addition, this universality enabled us to show that a prediction of pp fusion rate
highly dpends on recent new measurements of the neutron half-life.