  We calculate the spectral energy distribution (SED) of electromagnetic
radiation and the spectrum of high energy neutrinos from BL Lac objects in the
context of the Synchrotron Proton Blazar Model. In this model, the high energy
hump of the SED is due to accelerated protons, while most of the low energy
hump is due to synchrotron radiation by co-accelerated electrons. To accelerate
protons to sufficiently high energies to produce the high energy hump, rather
high magnetic fields are required. Assuming reasonable emission region volumes
and Doppler factors, we then find that in low-frequency peaked BL Lacs (LBLs),
which have higher luminosities than high-frequency peaked BL Lacs (HBLs), there
is a significant contribution to the high frequency hump of the SED from pion
photoproduction and subsequent cascading, including synchrotron radiation by
muons. In contrast, in HBLs we find that the high frequency hump of the SED is
dominated by proton synchrotron radiation. We are able to model the SED of
typical LBLs and HBLs, and to model the famous 1997 flare of Markarian 501. We
also calculate the expected neutrino output of typical BL Lac objects, and
estimate the diffuse neutrino intensity due to all BL Lacs. Because pion
photoproduction is inefficient in HBLs, as protons lose energy predominantly by
synchrotron radiation, the contribution of LBLs dominates the diffuse neutrino
intensity. We suggest that nearby LBLs may well be observable with future
high-sensitivity TeV gamma-ray telescopes.
