Exact black hole solutions in shift-symmetric quadratic degenerate
  higher-order scalar-tensor theories
  We find various exact black hole solutions in the shift-symmetric subclass of
the quadratic degenerate higher-order scalar-tensor (DHOST) theories with
linearly time dependent scalar field whose kinetic term is constant. The exact
solutions are the Schwarzschild and Schwarzschild-(anti-)de Sitter solutions,
and the Schwarzschild-type solution with a deficit solid angle, which are
accompanied by nontrivial scalar field regular at the black hole event horizon.
We derive the conditions for the coupling functions in the DHOST Lagrangian
that allow the exact solutions, clarify their compatibility with the degeneracy
conditions, and provide general form of coupling functions as well as simple
models that satisfy the conditions.
