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Null energy condition and superluminal propagation
S. Dubovsky, T. Gregoire, A. Nicolis +1
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, includin…
Limits on non-Gaussianities from WMAP data
Paolo Creminelli, Alberto Nicolis, Leonardo Senatore +2
We develop a method to constrain the level of non-Gaussianity of density perturbations when the 3-point function is of the "equilateral" type. Departures from Gaussianity of this f…
Ghosts in Massive Gravity
Paolo Creminelli, Alberto Nicolis, Michele Papucci +1
In the context of Lorentz-invariant massive gravity we show that classical solutions around heavy sources are plagued by ghost instabilities. The ghost shows up in the effective fi…