We investigate possible interactions between neutrinos and massive scalar bosons via g _ { \phi } \overline { \nu } \nu \phi ( or massive vector bosons via g _ { V } \overline { \nu } \gamma ^ { \mu } \nu V _ { \mu } ) and explore the allowed parameter space of the coupling constant g _ { \phi } ( or g _ { V } ) and the scalar ( or vector ) boson mass m _ { \phi } ( or m _ { V } ) by requiring that these secret neutrino interactions ( SNIs ) should not spoil the success of Big Bang nucleosynthesis ( BBN ) .
Incorporating the SNIs into the evolution of the early Universe in the BBN era , we numerically solve the Boltzmann equations and compare the predictions for the abundances of light elements with observations .
It turns out that the constraint on g _ { \phi } and m _ { \phi } in the scalar-boson case is rather weak , due to a small number of degrees of freedom .
However , in the vector-boson case , the most stringent bound on the coupling g _ { V } \lesssim 6 \times 10 ^ { -10 } at 95 ~ { } \% confidence level is obtained for m _ { V } \simeq 1 ~ { } { MeV } , while the bound becomes much weaker g _ { V } \lesssim 8 \times 10 ^ { -6 } for smaller masses m _ { V } \lesssim 10 ^ { -4 } ~ { } { MeV } .
Moreover , we discuss in some detail how the SNIs affect the cosmological evolution and the abundances of the lightest elements .