Relativistic effects on parity-violating phenomena in the low-energy np to dγ process

Abstract

The photon circular polarisation Pgamma and the asymmetry Agamma in the process n+p to d+ gamma are investigated in a Lorentz and gauge-invariant formalism in which the deuteron and initial np-distorted wavefunctions involve negative-energy components. In the low-energy limit, the formalism gives the conventional non-relativistic amplitude plus the relativistic correction terms associated with the negative-energy components of the deuteron and initial np-distorted wavefunctions. A large relativistic contribution to Pgamma , but a smaller one to Agamma , are suggested by estimates from certain models of the weak and strong interactions. The large relativistic contribution to Pgamma is not suppressed by terms required by gauge invariance.