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The String landscape, black holes and gravity as the weakest force
We conjecture a general upper bound on the strength of gravity relative to gauge forces in quantum gravity. This implies, in particular, that in a four-dimensional theory with gravity and a U(1)
Galileon as a local modification of gravity
In the Dvali-Gabadadze-Porrati (DGP) model, the "self-accelerating" solution is plagued by a ghost instability, which makes the solution untenable. This fact, as well as all interesting departures
Causality, analyticity and an IR obstruction to UV completion
We argue that certain apparently consistent low-energy effective field theories described by local, Lorentzinvariant Lagrangians, secretly exhibit macroscopic non-locality and cannot be embedded in
Starting the Universe: Stable Violation of the Null Energy Condition and Non-standard Cosmologies
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
Classical and Quantum Consistency of the DGP Model
We study the Dvali-Gabadadze-Porrati model by the method of the boundary effective action. The truncation of this action to the bending mode π consistently describes physics in a wide range of
Cosmological non-linearities as an effective fluid
The universe is smooth on large scales but very inhomogeneous on small scales. Why is the spacetime on large scales modeled to a good approximation by the Friedmann equations? Are we sure that
Galilean Genesis: An Alternative to inflation
We propose a novel cosmological scenario, in which standard inflation is replaced by an expanding phase with a drastic violation of the Null Energy Condition (NEC): >> H2. The model is based on the
Holography and the electroweak phase transition
We study through holography the compact Randall-Sundrum (RS) model at flnite temperature. In the presence of radius stabilization, the system is described at low enough temperature by the RS
Solid Inflation
We develop a cosmological model where primordial inflation is driven by a 'solid', defined as a system of three derivatively coupled scalar fields obeying certain symmetries and spontaneously
Limits on non-Gaussianities from WMAP data
We develop a method for constraining the level of non-Gaussianity of density perturbations when the three-point function is of the 'equilateral' type. Departures from Gaussianity of this form are