DHOST Bounce
  We present a new class of nonsingular bounce cosmology free from
instabilities, using a single scalar field coupled to gravity within the
framework of the Degenerate Higher-Order Scalar-Tensor (DHOST) theories. In
this type of scenarios, the gradient instability that widely exists in
nonsingular bounce cosmologies in the framework of scalar-tensor and
Horndeski/Galileon theories is removed by the effects of new operators
introduced by the DHOST, due to the modification that they later bring about to
the dispersion relation of perturbations. Hence, our results demonstrate that
there is indeed a loophole for this type of bounce scenarios to be free from
pathologies when primordial perturbations evolve through the bounce phase, and
thus the theoretical {\it no-go} theorem for nonsingular bounce cosmology of
Horndeski/Galileon theories can be delicately evaded in DHOST extensions.
