Planckian Scattering Beyond the Eikonal Approximation in the   Quasi-potential Approach
  Asymptotic behavior of the scattering amplitude for two scalar particles by scalar, vector and tensor exchanges at high energy and fixed momentum transfers is reconsidered in quantum field theory. In the framework of the quasi-potential approach and the modified perturbation theory a systematic scheme of finding the leading eikonal scattering amplitudes and its corrections are developed and constructed. The connection between the solutions obtained by quasi-potential and functional approaches is also discussed. The first correction to leading eikonal amplitude is found. 
Nguyen Suan Han and Nguyen Nhu Xuan