Some new views on the low-energy side of gravity (2009)
Common wisdom associates all the unraveled and theoretically challenging aspects of gravity with its UV-completion. However, there appear to be few difficulties afflicting the effective framework for...
The universe is accelerating. Do we need a new mass scale? (2009)
Nesseris, Savvas, Piazza, Federico, Tsujikawa, Shinji
We try to address quantitatively the question whether a new mass is needed to fit current supernovae data. For this purpose, we consider an infra-red modification of gravity that does not contain any...
The IR-Completion of Gravity: What happens at Hubble Scales? (2009)
We have recently proposed an "Ultra-Strong" version of the Equivalence Principle (EP) that is not satisfied by standard semiclassical gravity. In the theory that we are conjecturing, the vacuum...
Modifying Gravity in the Infra-Red by imposing an "Ultra-Strong" Equivalence Principle (2009)
The equivalence principle suggests to consider gravity as an infra-red phenomenon, whose effects are visible only outside Einstein's free-falling elevator. By curving spacetime, General Relativity...
Rapidly-Varying Speed of Sound, Scale Invariance and Non-Gaussian Signatures (2008)
Khoury, Justin, Piazza, Federico
We show that curvature perturbations acquire a scale invariant spectrum for any constant equation of state, provided the fluid has a suitably time-dependent sound speed. In order for modes to exit...
Modelling a Particle Detector in Field Theory (2008)
Costa, Fabio, Piazza, Federico
The Hamiltonian of traditionally adopted ("Unruh-DeWitt") detector models features off diagonal elements between the vacuum and the one particle states of the field to be detected. We argue that in...
Renormalized Thermal Entropy in Field Theory (2008)
Cacciatori, Sergio, Costa, Fabio, Piazza, Federico
Standard entropy calculations in quantum field theory, when applied to a subsystem of definite volume, exhibit area-dependent UV divergences that make a thermodynamic interpretation troublesome. In...
Volumes of Space as Subsystems (2007)
Piazza, Federico, Costa, Fabio
As a novel approach with possible relevance to semiclassical gravity, we propose to define regions of space as quantum subsystems. After recalling how to divide a generic quantum system into...
Measuring deviations from a cosmological constant: a field-space parameterization (2007)
Crittenden, Robert, Majerotto, Elisabetta, Piazza, Federico
Most parameterizations of the dark energy equation of state do not reflect realistic underlying physical models. Here, we develop a relatively simple description of dark energy based on the dynamics...
SNLS data are consistent with acceleration at z=3 (2006)
Amendola, Luca, Gasperini, M., Piazza, Federico
We point out that the Type Ia supernovae in the SNLS dataset are consistent with an early beginning of the cosmic acceleration if dark energy interacts strongly with dark matter. We find that the...
Quantum degrees of freedom of a region of spacetime (2005)
The holographic principle and the thermodynamics of de Sitter space suggest that the total number of fundamental degrees of freedom associated with any finite-volume region of space may be finite....
Enhanced gravitational scattering from large extra dimensions (2005)
Koyama, Kazuya, Piazza, Federico, Wands, David
We investigate whether enhanced gravitational scattering on small scales (< 0.1mm), which becomes possible in models with large extra dimensions, can establish statistical equilibrium between...
Glimmers of a pre-geometric perspective (2005)
Space-time measurements and gravitational experiments are made by using objects, matter fields or particles and their mutual relationships. As a consequence, any operationally meaningful assertion...
Fitting Type Ia supernovae with coupled dark energy (2004)
Amendola, Luca, Gasperini, Maurizio, Piazza, Federico
We discuss the possible consistency of the recently discovered Type Ia supernovae at z>1 with models in which dark energy is strongly coupled to a significant fraction of dark matter, and in which an...
Dilatonic ghost condensate as dark energy (2004)
Piazza, Federico, Tsujikawa, Shinji
We explore a dark energy model with a ghost scalar field in the context of the runaway dilaton scenario in low-energy effective string theory. We address the problem of vacuum stability by...
The Gravitational Suppression Hypothesis: Dynamical Analysis in the Small Velocity Regime (2003)
Marinoni, Christian, Piazza, Federico
In a previous paper we have proposed a non--Newtonian, phenomenological description of the effective gravitational force acting between exotic dark matter and baryons, which was shown to fit well the...
The GraS Hypothesis: a Model for Dark Matter-Baryons Gravitational Interaction (2003)
Piazza, Federico, Marinoni, Christian
According to the gravitational suppression (GraS) hypothesis the gravitational interaction between exotic (dark) and standard (visible) matter is suppressed below the kpc scales. We review the...
Model for Gravitational Interaction between Dark Matter and Baryons (2003)
Piazza, Federico, Marinoni, Christian
We propose a phenomenological model where the gravitational interaction between dark matter and baryons is suppressed on small, subgalactic scales. We describe the gravitational force by adding a...
Runaway dilaton and equivalence principle violations (2002)
Damour, Thibault, Piazza, Federico, Veneziano, Gabriele
In a recently proposed scenario, where the dilaton decouples while cosmologically attracted towards infinite bare string coupling, its residual interactions can be related to the amplitude of density...
Quasi-normal modes of charged, dilaton black holes (2000)
Ferrari, Valeria, Pauri, Massimo, Piazza, Federico
In this paper we study the perturbations of the charged, dilaton black hole, described by the solution of the low energy limit of the superstring action found by Garfinkle, Horowitz and Strominger....