  We propose a novel interpretation that gamma-rays from nearby radio galaxies
are hadronic emission from magnetically arrested disks (MADs) around central
black holes (BHs). The magnetic energy in MADs is higher than the thermal
energy of the accreting plasma, where the magnetic reconnection or turbulence
may efficiently accelerate non-thermal protons. They emit gamma-rays via
hadronic processes, which can account for the observed gamma-rays for M87 and
NGC 315. Non-thermal electrons are also accelerated with protons and produce
MeV gamma-rays, which is useful to test our model by proposed MeV satellites.
The hadronic emission from the MADs may significantly contribute to the GeV
gamma-ray background and produce the multi-PeV neutrino background detectable
by IceCube-Gen2. In addition, gamma-rays from MADs provide electron-positron
pairs through two-photon pair production at the BH magnetosphere. These pairs
can screen the vacuum gap, which affects high-energy emission and jet-launching
mechanisms in radio galaxies.
