= Solution
If the weak-rate coefficient is reduced, equality with the expansion rate occurs at a higher temperature, since $\Gamma_W/H$ scales as that coefficient times $T^3$. The <freeze-out temperature and interaction strength> relation is $T_f\propto C_W^{-1/3}$. The frozen neutron-to-proton ratio is then closer to one, so \b[the primordial <helium mass fraction> increases], potentially approaching unity if nearly equal numbers survive to nucleosynthesis. If the same weaker interaction also slows free-neutron decay, it reinforces this trend; changing conversion rates alone would instead require a separate treatment of the decay interval.
Less primordial <hydrogen> means less <hydrogen> fuel and, for otherwise comparable stellar physics, helium enrichment raises the mean molecular weight, tending to make a fixed-mass star hotter and more luminous and to shorten its hydrogen-burning lifetime. A genuinely weaker <weak interaction> also changes proton-proton fusion itself, so a quantitative lifetime cannot be inferred from composition alone. Much less <hydrogen> and fewer long-lived suitable stars would alter planet formation, water availability and the timescales needed for life on Earth. These are physical implications of the changed initial composition, not a numerical prediction of habitability from the helium fraction alone.
Back to article page
