Ab initio many-body calculations of the $^4$He photo-absorption cross section

Using the no-core shell model approach with a similarity renormalization group (SRG) evolved two- and three-nucleon (NN+NNN) Hamiltonian, we compute the dipole strength function of $^4$He, using the Lorentz integral transform (LIT) method to obtain the continuum response. We then compute the total photo-absorption cross section of $^4$He. We pay particular attention to the convergence of the total strength and of the LIT of the dipole response as we increase the size of the harmonic oscillator basis.