The ⁴He total photo-absorption cross section with two- plus three-nucleon interactions from chiral effective field theory

The total photo-absorption cross section of $^4$He is evaluated microscopically using two- (NN) and three-nucleon (NNN) interactions based upon chiral effective field theory ($\chi$EFT). The calculation is performed using the Lorentz integral transform method along with the {\em ab initio} no-core shell model approach. An important feature of the present study is the consistency of the NN and NNN interactions and also, through the Siegert theorem, of the two- and three-body current operators. This is due to the application of the $\chi$EFT framework. The inclusion of the NNN interaction produces a suppression of the low-energy peak and enhancement of the high-energy tail of the cross section. We compare to calculations obtained using other interactions and to representative experiments. The rather confused experimental situation in the giant resonance region prevents discrimination among different interaction models.