Ioav Waga

The end of unified dark matter

Despite the interest in dark matter and dark energy, it has never been shown that they are in fact two separate substances. We provide the first strong evidence that they are separate by ruling out a broad class of so-called unified dark matter models that have attracted much recent interest. We find that they produce oscillations or exponential blowup of the dark matter power spectrum inconsistent with observation. For the particular case of generalized Chaplygin gas models, 99.999% of the previously allowed parameter space is excluded, leaving essentially only the standard

Constraints on the generalized Chaplygin gas from supernovae observations

\ensuremath{\Lambda}\mathrm{CDM}

On the thermodynamics of matter creation in cosmology

limit allowed.

Challenges for scaling cosmologies

Abstract We explore the implications of type Ia supernovae (SNIa) observations on flat cosmological models whose matter content is an exotic fluid with equation of state, p =− M 4( α +1) / ρ α . In this scenario, a single fluid component may drive the Universe from a nonrelativistic matter dominated phase to an accelerated expansion phase behaving, first, like dark matter and in a more recent epoch as dark energy. We show that these models are consistent with current SNIa data for a rather broad range of parameters. However, future SNIa experiments will place stringent constraints on these models, and could safely rule out the special case of a Chaplygin gas ( α =1) if the Universe is dominated by a true cosmological constant.

Dark interactions and cosmological fine-tuning

Abstract The recent phenomenological approach to the process of matter creation in the cosmological context, as proposed by Prigogine and collaborators, is reexamined within a manifestly covariant formulation. It is shown that if the specific entropy is not constant some of their results are no longer valid. The expressions for the entropy production rate and the temperature evolution equation are deduced and some of their consequences are also discussed.

From cosmic deceleration to acceleration: new constraints from SN Ia and BAO/CMB

A cosmological model that aims at solving the coincidence problem should show that dark energy and dark matter follow the same scaling solution from some time onward. At the same time, the model should contain a sufficiently long matter-dominated epoch that takes place before acceleration in order to guarantee a decelerated epoch and structure formation. So a successful cosmological model requires the occurrence of a sequence of epochs, namely a radiation era, a matter-dominated era and a final accelerated scaling attractor with

Constraints from high redshift supernovae upon scalar field cosmologies

\Omega_{\phi} \simeq 0.7

Viable singularity-free f(R) gravity without a cosmological constant.

. In this paper we derive the generic form of a scalar-field Lagrangian that possesses scaling solutions in the case where the coupling

Observational constraints on Chaplygin quartessence: Background results

Q

Cosmological constraints from lensing statistics and supernovae on the cosmic equation of state

between dark energy and dark matter is a free function of the field