We discuss various astrophysical limits on the spatial and time variation of the Fermi coupling constant GF. We consider two cases: (a) GF and the fermion masses vary through a change in the vacuum expectation value of the Higgs field; (b) GF varies while the fermion masses are held constant. In the former case, redshift measurements probe both the spatial and time variation of GF through changes in the electron mass: the agreement between measurements of hyperfine and optical lines in distant galaxies and quasars indicates that GF varies by less than 0.04% on cosmological length scales. Such measurements also show that GF varies by less than 0.2% back to a redshift of z=3.4. If GF varies without any change in the fermion masses, the best constraints on spatial variations in GF come from supernova light curves, whose slopes depend upon the lifetime of Co56. The similarities between light curves argue that the Fermi coupling constant GF varies by less than 5% on cosmological scales. Big bang nucleosynthesis indicates that the Fermi coupling constant at t∼1 sec differed by less than ∼ 10-20% from the contemporary terrestrial value, with the exact limits depending on which model we choose for the variation in GF. Variation in GF would allow big bang nucleosynthesis to produce a lower He4 abundance without changing significantly any of the other element abundances.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Physics and Astronomy (miscellaneous)