  We consider the electromagnetic form factors ratio in the Rosenbluth and
polarization methods. We explore the impact of adding new particles as the
mediators in the electron-proton scattering on these ratios. Consequently, we
find some bound on the scalar coupling as $\alpha_{sc}\sim 10^{-5}$ for
$m_{sc}\sim 5 MeV-2 GeV$ and $\alpha_{sc}\sim 10^{-4}-10^{-3}$ for $m_{sc}\sim
2-10 GeV$. Meanwhile, the vector coupling is bounded as $\alpha_v\sim 10^{-5}$
for $m_v\sim 5 MeV-1.1 GeV$ and $\alpha_v\sim 10^{-4}-10^{-3}$ for $m_v\sim
1.2-10 GeV$. These constraints are in complete agreement with those which is
found from other independent experiments.
