  Dark matter is a key piece of the current cosmological scenario, with weakly
interacting massive particles (WIMPs) a leading dark matter candidate. WIMPs
have not been detected in their conventional parameter space (100 GeV $\lesssim
M_{\chi} \lesssim$ 100 TeV), a mass range accessible with current Imaging
Atmospheric Cherenkov Telescopes. As ultraheavy dark matter (UHDM; $M_{\chi}
\gtrsim$ 100 TeV) has been suggested as an under-explored alternative to the
WIMP paradigm, we search for an indirect dark matter annihilation signal in a
higher mass range (up to 30 PeV) with the VERITAS gamma-ray observatory. With
216 hours of observations of four dwarf spheroidal galaxies, we perform an
unbinned likelihood analysis. We find no evidence of a $\gamma$-ray signal from
UHDM annihilation above the background fluctuation for any individual dwarf
galaxy nor for a joint-fit analysis, and consequently constrain the
velocity-weighted annihilation cross section of UHDM for dark matter particle
masses between 1 TeV and 30 PeV. We additionally set constraints on the allowed
radius of a composite UHDM particle.
