MG12 - Talk detail
 

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Abstract

Violation of causality in f(R) gravity

We examine the question as whether the f(R) gravity theories that satisfy the local gravity constraints as well as the conditions for cosmological viability permit space-times in which the causality principle is violated. We show that the field equations of these f(R) gravity theories do not exclude solutions with violation of causality for a physically well-motivated perfect-fluid matter content, despite its Lorentzian character which leads to the local validity of the causality principle.

Testing non-Gaussianity in foreground-reduced CMB maps

A detection or nondetection of primordial non-Gaussianity in the CMB data is vital to ddiscriminate among inflationary models and also to distinguish them from alternative primordial scenarios. However, on the one hand, there are various non-cosmological effects that can also produce non-Gaussianity. On the other hand, different statistical tools can in principle provide information about distinct forms of non-Gaussianity. Thus, any single statistical estimator cannot be sensitive to all possible forms of non-Gaussianity. It is therefore important to test CMB data for non-Gaussianity by using different statistical indicators. We propose two new non-Gaussianity indicators, based on skewness and kurtosis of large-angle patches of CMB temperature maps, which provide a measure of non-Gaussianity on large angular scales. Our indicators provide sky maps of non-Gaussianity of CMB data, thus allowing a possible window into their origins. We use our indicators to build maps of non-Gaussianity from the WMAP three and five-year CMB adata, and thus estimate the statistical significance. We find a significant deviation from Gaussianity in the available three and five-year foreground-reduced WMAP maps. These results suggest that the detected non-Gaussianity in these cleaned maps is independent of the foreground cleaning processes employed.

Constraints on dark energy from cosmic topology

Despite our present-day inability to predict the topology of the universe we should be able to detect it in the near future. A nontrivial topology of the space section of the universe is an observable, which can be probed for all homogeneous and isotropic universes, without any assumption on the cosmological parameters. We shall discuss how one can use this observable to set constraints on the dark energy equation of state parameters.

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