Cosmological Perturbations in Antigravity
  We compute the evolution of cosmological perturbations in a recently proposed
Weyl-symmetric theory of two scalar fields with oppositely-signed conformal
couplings to Einstein gravity. It is motivated from the minimal conformal
extension of the Standard Model, such that one of these scalar fields is the
Higgs while the other is a new particle, the dilaton, introduced to make the
Higgs mass conformally symmetric. At the background level, the theory admits
novel geodesically-complete cyclic cosmological solutions characterized by a
brief period of repulsive gravity, or "antigravity", during each successive
transition from a Big Crunch to a Big Bang. We show that despite the
necessarily wrong-signed kinetic term of the dilaton in the full action, its
cosmological solutions are stable at the perturbative level.
