  The cores of Arp 220, the closest ultra-luminous infrared starburst galaxy,
provide an opportunity to study interactions of cosmic rays under extreme
conditions. In this paper, we model the populations of cosmic rays produced by
supernovae in the central molecular zones of both starburst nuclei. We find
that ~65 - 100% of cosmic rays are absorbed in these regions due to their huge
molecular gas contents, and thus, the nuclei of Arp 220 nearly complete proton
calorimeters. As the cosmic ray protons collide with the interstellar medium,
they produce secondary electrons that are also contained within the system and
radiate synchrotron emission. Using results from chi-squared tests between the
model and the observed radio spectral energy distribution, we predict the
emergent gamma-ray and high-energy neutrino spectra and find the magnetic field
to be at milligauss levels. Because of the extremely intense far-infrared
radiation fields, the gamma-ray spectrum steepens significantly at TeV energies
due to gamma-gamma absorption.
