Ab-initio strength functions in light nuclei

Strength functions are an excellent tool to determine the collective excitation mechanism of a nucleus in the presence of electromagnetic fields. Since the discovery of the giant-dipole resonance in heavy nuclei much theoretical and experimental work has been devoted to studying strength functions. We present strength function calculations for the light nuclei A$=$6, A$=$10 and C-12 within an ab initio framework. We show results for the isoscalar and isovector monopole modes as well as the electric- and magnetic dipole response. The calculations are performed with the No-Core Shell Model. As input we use an isoscalar Hamiltonian derived from a similarity renormalized two-body chiral N3LO interaction and perform the calculation for basis-space sizes up to Nmax$=$14 for A$=$6 and Nmax$=$8 for A$=$10. Further, we present evidence supporting the Brink hypothesis that if a giant dipole resonance is found for the ground-state then the excited states will also exhibit such a resonance.