NEC Violation and String Inspired Alternatives to Inflation

          @misc{ scivideos_PIRSA:09050060,
            doi = {10.48660/09050060},
            url = {https://pirsa.org/09050060},
            author = {Watson, Scott},
            keywords = {Cosmology},
            language = {en},
            title = {NEC Violation and String Inspired Alternatives to Inflation},
            publisher = {Perimeter Institute for Theoretical Physics},
            year = {2009},
            month = {may},
            note = {PIRSA:09050060 see, \url{https://scivideos.org/index.php/pirsa/09050060}}
          }
          

Abstract

Inflationary cosmology provides a causal mechanism for the generation of super-Hubble cosmological fluctuations. There have been many alternative proposals suggested to accomplish this feat, however these all seem to share the need to violate at least the Null Energy Condition. I will attempt to make this statement more precise, and focusing on the case of string motivated models that contain a gravi-scalar in their spectrum (such as the string theoretic dilaton) we will find a "no-go" theorem. This provides an important challenge for models such as String Gas Cosmology and the Pre-Big Bang, if such models are to become more predictive.