Starting the Universe: Stable Violation of the Null Energy Condition and Non-standard Cosmologies

  title={Starting the Universe: Stable Violation of the Null Energy Condition and Non-standard Cosmologies},
  author={Paolo Creminelli and Markus A. Luty and Alberto Nicolis and Leonardo Senatore},
  journal={Journal of High Energy Physics},
We present a consistent effective theory that violates the null energy condition (NEC) without developing any instabilities or other pathological features. The model is the ghost condensate with the global shift symmetry softly broken by a potential. We show that this system can drive a cosmological expansion with > 0. Demanding the absence of instabilities in this model requires H2. We then construct a general low-energy effective theory that describes scalar fluctuations about an arbitrary… 

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