Null energy condition and superluminal propagation

Sergei Dubovsky, Thomas Grégoire, Alberto Nicolis, Riccardo Rattazzi

    Research output: Contribution to journalArticlepeer-review


    We study whether a violation of the null energy condition necessarily implies the presence of instabilities. We prove that this is the case in a large class of situations, including isotropic solids and fluids relevant for cosmology. On the other hand we present several counter-examples of consistent effective field theories possessing a stable background where the null energy condition is violated. Two necessary features of these counter-examples are the lack of isotropy of the background and the presence of superluminal modes. We argue that many of the properties of massive gravity can be understood by associating it to a solid at the edge of violating the null energy condition. We briefly analyze the difficulties of mimicking Ḣ > 0 in scalar tensor theories of gravity.

    Original languageEnglish (US)
    Pages (from-to)615-659
    Number of pages45
    JournalJournal of High Energy Physics
    Issue number3
    StatePublished - Mar 1 2006


    • Classical Theories of Gravity
    • Cosmology of Theories beyond the SM

    ASJC Scopus subject areas

    • Nuclear and High Energy Physics


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