Di. Santiago et al., NUCLEOSYNTHESIS CONSTRAINTS ON SCALAR-TENSOR THEORIES OF GRAVITY, Physical review. D. Particles and fields, 56(12), 1997, pp. 7627-7637
We study the cosmological evolution of massless single-field scalar-te
nsor theories of gravitation from the time before the onset of e(+)e(-
) annihilation and nucleosynthesis up to the present. The cosmological
evolution together with the observational bounds on the abundances of
the lightest elements (those mostly produced in the early universe) p
lace constraints on the coefficients of the Taylor series expansion of
alpha(phi), which specifies the coupling of the scalar field to matte
r and is the only free function in the theory. In the case when alpha(
phi) has a minimum (i.e., when the theory evolves towards general rela
tivity) these constraints translate into a stronger limit on the post-
Newtonian parameters gamma and beta than any other observational test.
Moreover, our bounds imply that, even at the epoch of annihilation an
d nucleosynthesis, the evolution of the universe must be very close to
that predicted by general relativity if we do not want to over-or und
erproduce He-4. Thus the amount of scalar field contribution to gravit
y is very small even at such an early epoch. [S0556-2821(97)04724-3].