We investigate the shock acceleration of particles in massive galaxy mergers or collisions, and show that cosmic rays (CRs) can be accelerated up to the second knee energy ~0.1-1 EeV and possibly beyond, with a hard spectral index Gamma ~ 2. Such CRs
lose their energy via hadronuclear interactions within a dynamical timescale of the merger shock, producing gamma rays and neutrinos as a by-product. If ~ 10 % of the shock dissipated energy goes into CR acceleration, some local merging galaxies will produce gamma-ray counterparts detectable by CTA. Also, based on the concordance cosmology, where a good fraction of the massive galaxies experience a major merger in a cosmological timescale, the neutrino counterparts can constitute ~ 20-60 % of the isotropic background detected by IceCube.
We calculate the high energy neutrino spectrum from gamma-ray bursts where the emission arises in a dissipative jet photosphere determined by either baryonically or magnetically dominated dynamics, and compare these neutrino spectra to those obtained
in conventional internal shock models. We also calculate the diffuse neutrino spectra based on these models, which appear compatible with the current IceCube 40+59 constraints. While a re-analysis based on the models discussed here and the data from the full array would be needed, it appears that only those models with the most extreme parameters are close to being constrained at present. A multi-year operation of the full IceCube and perhaps a next generation of large volume neutrino detectors may be required in order to distinguish between the various models discussed.
