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Nonlocal gravity. Conceptual aspects and cosmological predictions
Enis Belgacem, Yves Dirian, Stefano Foffa +1
Even if the fundamental action of gravity is local, the corresponding quantum effective action, that includes the effect of quantum fluctuations, is a nonlocal object. These nonloc…
Stability issues of nonlocal gravity during primordial inflation
Enis Belgacem, Giulia Cusin, Stefano Foffa +2
We study the cosmological evolution of some nonlocal gravity models, when the initial conditions are set during a phase of primordial inflation. We examine in particular three mode…
Conformal symmetry and nonlinear extensions of nonlocal gravity
Giulia Cusin, Stefano Foffa, Michele Maggiore +1
We study two nonlinear extensions of the nonlocal gravity theory. We extend this theory in two different ways suggested by conformal symmetry, either replacing $\Bo…
Non-local gravity with a Weyl-square term
Giulia Cusin, Stefano Foffa, Michele Maggiore +1
Recent work has shown that modifications of General Relativity based on the addition to the action of a non-local term , or on the addition to the equations of motio…
Cosmological dynamics and dark energy from non-local infrared modifications of gravity
Stefano Foffa, Michele Maggiore, Ermis Mitsou
We perform a detailed study of the cosmological dynamics of a recently proposed infrared modification of the Einstein equations, based on the introduction of a non-local term const…
Apparent ghosts and spurious degrees of freedom in non-local theories
Stefano Foffa, Michele Maggiore, Ermis Mitsou
Recent work has shown that non-local modifications of the Einstein equations can have interesting cosmological consequences and can provide a dynamical origin for dark energy, cons…
A braneworld puzzle about entropy bounds and a maximal temperature
Ram Brustein, David Eichler, Stefano Foffa
Entropy bounds applied to a system of N species of light quantum fields in thermal equilibrium at temperature T are saturated in four dimensions at a maximal temperature T_max=M_Pl…
Bouncing pre-big bang on the brane
Stefano Foffa
A regular bouncing universe is obtained in the context of a dilaton-gravity brane world scenario. The scale factor starts in a contracting inflationary phase both in the Einstein a…
Pre-big bang on the brane
Stefano Foffa
The equations of motion and junction conditions for a gravi-dilaton brane world scenario are studied in the string frame. It is shown that they allow Kasner-like solutions on the b…
Causal Entropy Bound for Non-Singular Cosmologies
Ram Brustein, Stefano Foffa, Avraham E. Mayo
The conditions for validity of the Causal Entropy Bound (CEB) are verified in the context of non-singular cosmologies with classical sources. It is shown that they are the same con…
CFT, Holography, and Causal Entropy Bound
R. Brustein, S. Foffa, G. Veneziano
The causal entropy bound (CEB) is confronted with recent explicit entropy calculations in weakly and strongly coupled conformal field theories (CFTs) in arbitrary dimension . Fo…
The Shortest Scale of Quantum Field Theory
Ram Brustein, David Eichler, Stefano Foffa +1
It is suggested that the Minkowski vacuum of quantum field theories of a large number of fields N would be gravitationally unstable due to strong vacuum energy fluctuations unless…
Generalized Second Law in String Cosmology
Ram Brustein, Stefano Foffa, Riccardo Sturani
A generalized second law in string cosmology accounts for geometric and quantum entropy in addition to ordinary sources of entropy. The proposed generalized second law forbids sing…
Loop corrections and graceful exit in string cosmology
Stefano Foffa, Michele Maggiore, Riccardo Sturani
We examine the effect of perturbative string loops on the cosmological pre-big-bang evolution. We study loop corrections derived from heterotic string theory compactified on a $Z_N…