Radial excitations of hadronic bags

We investigate the spectrum of radial excitations of the bag model. Breathing excitations of the surface of the bag couple to the radially excited states of quarks in the bag, resulting in a spectrum of states which interpolates between the energy levels of the fixed-cavity approximation. We discuss this effect in detail for a bag containing bosons. We apply our results to fermionic systems and find that the radial excitations of baryons contain an $\mathrm{NP}11\left(1410\right)\mathrm{}$ Roper-resonance candidate as a natural consequence of the effects of breathing modes.