Savvas Nesseris

Observational constraints on Galileon cosmology

We study the cosmology of a covariant Galileon field φ with five covariant Lagrangians and confront this theory with the most recent cosmological probes: the type Ia supernovae data (Constitution and Union2 sets), cosmic microwave background (WMAP7), and the baryon acoustic oscillations (SDSS7). In the Galileon cosmology with a late-time de Sitter attractor, there is a tracker that attracts solutions with different initial conditions to a common trajectory. Including the cosmic curvature K, we place observational constraints on two distinct cases: (i) the tracker, and (ii) the generic solutions to the equations of motion. We find that the tracker solution can be consistent with the individual observational data, but it is disfavored by the combined data analysis. The generic solutions fare quite well when a nonzero curvature parameter Ω (0) K is taken into account, but the Akaike and Bayesian information criteria show that they are not particularly favored over the ACDM model.

Viable

We investigate the cosmological predictions of several

f(T)

f(T)

models are practically indistinguishable from

models, with up to two parameters, at both the background and the perturbation levels. Using current cosmological observations (geometric supernovae type Ia, cosmic microwave background and baryonic acoustic oscillation and dynamical growth data) we impose constraints on the distortion parameter, which quantifies the deviation of these models from the concordance

\Lambda

\Lambda

CDM

cosmology at the background level. In addition we constrain the growth index

Massive, massless and ghost modes of gravitational waves from higher-order gravity

\gamma

Observational constraints on viable f(R) parametrizations with geometrical and dynamical probes

predicted in the context of these models using the latest perturbation growth data in the context of three parametrizations for

Newton's constant in f(R,R_munuR^munu,Box R) theories of gravity and constraints from BBN

\gamma

Cosmological perturbations and observational constraints on nonlocal massive gravity

. The evolution of the best fit effective Newton constant, which incorporates the