Equivalence Principle Implications of Modified Gravity Models (2009)
Hui, Lam, Nicolis, Alberto, Stubbs, Christopher
Theories that attempt to explain the observed cosmic acceleration by modifying general relativity all introduce a new scalar degree of freedom that is active on large scales, but is screened on small...
Hinterbichler, Kurt, Nicolis, Alberto, Porrati, Massimo
We reconsider the issue of superluminal propagation in the DGP model of infrared modified gravity. Superluminality was argued to exist in certain otherwise physical backgrounds by using a particular,...
Eternal Inflation, Bubble Collisions, and the Disintegration of the Persistence of Memory (2009)
Freivogel, Ben, Kleban, Matthew, Nicolis, Alberto, Sigurdson, Kris
We compute the probability distribution for bubble collisions in an inflating false vacuum which decays by bubble nucleation. Our analysis generalizes previous work of Guth, Garriga, and Vilenkin to...
CMBPol Mission Concept Study: Probing Inflation with CMB Polarization (2008)
Baumann, Daniel, Jackson, Mark G, Adshead, Peter, Amblard, Alexandre, Ashoorioon, Amjad, Bartolo, Nicola, ...
We summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes of the physics of inflation. We focus on the prospects for using CMB measurements to...
CMBPol Mission Concept Study: Probing Inflation with CMB Polarization (2008)
Baumann, Daniel, Jackson, Mark G., Adshead, Peter, Amblard, Alexandre, Ashoorioon, Amjad, Bartolo, Nicola, ...
We summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes of the physics of inflation. We focus on the prospects for using CMB measurements to...
The galileon as a local modification of gravity (2008)
Nicolis, Alberto, Rattazzi, Riccardo, Trincherini, Enrico
In the 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 from GR are fully captured...
On Super-Planckian Fields at Sub-Planckian Energies (2008)
For a light scalar coupled to gravity, I study the gravitational backreaction associated with large field variations. I show a generic obstruction in sourcing a super-Planckian scalar profile without...
The Phase Transition to Eternal Inflation (2008)
Creminelli, Paolo, Dubovsky, Sergei, Nicolis, Alberto, Senatore, Leonardo, Zaldarriaga, Matias
For slow-roll inflation we study the phase transition to the eternal regime. Starting from a finite inflationary volume, we consider the volume of the universe at reheating as order parameter. We...
Microcausality in Curved Space-Time (2007)
Dubovsky, Sergei, Nicolis, Alberto, Trincherini, Enrico, Villadoro, Giovanni
It is well known that in Lorentz invariant quantum field theories in flat space the commutator of space-like separated local operators vanishes (microcausality). We provide two different arguments...
A Measure of de Sitter Entropy and Eternal Inflation (2007)
Arkani-Hamed, Nima, Dubovsky, Sergei, Nicolis, Alberto, Trincherini, Enrico, Villadoro, Giovanni
We show that in any model of non-eternal inflation satisfying the null energy condition, the area of the de Sitter horizon increases by at least one Planck unit in each inflationary e-folding. This...
Quantum Horizons of the Standard Model Landscape (2007)
Arkani-Hamed, Nima, Dubovsky, Sergei, Nicolis, Alberto, Villadoro, Giovanni
The long-distance effective field theory of our Universe--the Standard Model coupled to gravity--has a unique 4D vacuum, but we show that it also has a landscape of lower-dimensional vacua, with the...
Creminelli, Paolo, Luty, Markus A., Nicolis, Alberto, Senatore, Leonardo
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...
Causality, Analyticity and an IR Obstruction to UV Completion (2006)
Adams, Allan, Arkani-Hamed, Nima, Dubovsky, Sergei, Nicolis, Alberto, Rattazzi, Riccardo
We argue that certain apparently consistent low-energy effective field theories described by local, Lorentz-invariant Lagrangians, secretly exhibit macroscopic non-locality and cannot be embedded in...
The String Landscape, Black Holes and Gravity as the Weakest Force (2006)
Arkani-Hamed, Nima, Motl, Lubos, Nicolis, Alberto, Vafa, Cumrun
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)...
Limits on non-Gaussianities from WMAP data (2005)
Creminelli, Paolo, Nicolis, Alberto, Senatore, Leonardo, Tegmark, Max, Zaldarriaga, Matias
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 form are produced by...
Ghosts in Massive Gravity (2005)
Creminelli, Paolo, Nicolis, Alberto, Papucci, Michele, Trincherini, Enrico
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 field theory at huge...
Perturbations in bouncing cosmologies: dynamical attractor vs scale invariance (2004)
Creminelli, Paolo, Nicolis, Alberto, Zaldarriaga, Matias
For bouncing cosmologies such as the ekpyrotic/cyclic scenarios we show that it is possible to make predictions for density perturbations which are independent of the details of the bouncing phase....
Classical and Quantum Consistency of the DGP Model (2004)
Nicolis, Alberto, Rattazzi, Riccardo
We study the Dvali-Gabadadze-Porrati model by the method of the boundary effective action. The truncation of this action to the bending mode \pi consistently describes physics in a wide range of...
Relic gravitational waves from colliding bubbles and cosmic turbulence (2003)
A stochastic background of gravitational waves can be generated during a cosmological first order phase transition, at least by two distinct mechanisms: collisions of true vacuum bubbles and...
Relic Backgrounds of Gravitational Waves from Cosmic Turbulence (2002)
Dolgov, Alexander D., Grasso, Dario, Nicolis, Alberto
Turbulence may have been produced in the early universe during several kind of non-equilibrium processes. Periods of cosmic turbulence may have left a detectable relic in the form of stochastic...
Holography and the Electroweak Phase Transition (2001)
Creminelli, Paolo, Nicolis, Alberto, Rattazzi, Riccardo
We study through holography the compact Randall-Sundrum (RS) model at finite temperature. In the presence of radius stabilization, the system is described at low enough temperature by the RS...
Gravitational Waves from Electroweak Phase Transitions (2001)
Apreda, Riccardo, Maggiore, Michele, Nicolis, Alberto, Riotto, Antonio
Gravitational waves are generated during first-order phase transitions, either by turbolence or by bubble collisions. If the transition takes place at temperatures of the order of the electroweak...
Detection strategies for scalar gravitational waves with interferometers and resonant spheres (1999)
Maggiore, Michele, Nicolis, Alberto
We compute the response and the angular pattern function of an interferometer for a scalar component of gravitational radiation in Brans-Dicke theory. We examine the problem of detecting a stochastic...