Dark energy from a renormalization group flow
  We present evidence that a special class of gravitationally-coupled hidden
sectors, in which conformal invariance is dynamically broken in a controlled
way, exhibit the properties of dark energy. Such quantum field theories may
appear while embedding the Standard Model in a more fundamental high energy
theory. At late times, an effective dark energy field behaves similarly to an
exponentially small cosmological constant while at early times its energy
density partly tracks that of matter.
