We have studied an effect of possible deviation of fundamental physical constants on the yields of light nuclei ²D, ³He, ⁴He, ⁷Li, etc. during the primordial nucleosynthesis. The deviation of fundamental constants from their present values has been considered in the framework of the low-energy approach of string theories. These theories predict the existence of a scalar field which is supposed to be a partner of tensor gravity field and defines the spatial geometry as well. In the frames of such approach we have elaborated two-parameter ({eta},{delta}) model of the primordial nucleosynthesis. Parameter {eta}=n_B/n_{gamma} characterizes the baryon-to-photon ratio by number. Parameter {delta} characterizes the deviation of values of fundamental physical constants at the primordial nucleosynthesis epoch from the present ones. In the framework of the model a functional relation between {eta} and {delta} is obtained under condition that primordial helium abundance is Y_p=f({eta},{delta})=Const, where Const corresponds to the observational data available. Thus it is shown that the relative baryon density {eta} (as well as {Omega}_B) determined from the observational data may satisfy the experimental constraints in essentially wider range of values than it was allowed by the standard nucleosynthesis model.

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