Professor Pedro Ferreira

Abstract:

We reexamine Wald's no-hair theorem for global anisotropy in the brane world scenarios. We derive a set of sufficient conditions which must be satisfied by the brane matter and bulk metric so that a homogeneous and anisotropic brane asymptotically evolves to a de Sitter spacetime in the presence of a positive cosmological constant on the brane. We discuss the violations of these sufficient conditions and we show that a negative nonlocal energy density or the presence of strong anisotropic stress (i.e., a magnetic field) may lead the brane to collapse. We discuss the generality of these conditions.

Abstract:

We describe here an iterative method for jointly estimating the noise power spectrum from a CMB experiment's time-ordered data, together with the maximum-likelihood map. We test the robustness of this method on simulated Boomerang datasets with realistic noise.

Abstract:

We propose a new formalism to handle asymmetric beams in the data analysis of cosmic microwave background anisotropy experiments. For any beam shape, the formalism finds the optimal circularly symmetric equivalent and is thus easily adaptable to existing data analysis methods. We demonstrate certain key points by using a simulated highly elliptic beam and the beams and data of the MAXIMA-1 experiment, where the asymmetry is mild. We show that in both cases the formalism does not bias the angular power spectrum estimates. We analyze the limitations of the formalism and find that it is well suited for most practical situations.

Abstract:

The anisotropy of the cosmic microwave background radiation contains information about the contents and history of the universe. We report new limits on cosmological parameters derived from .the angular power spectrum measured in the first Antarctic flight of the Boomerang experiment. Within the framework of models, : with adiabatic perturbations, and using only'weakly restrictive prior probabilities on the age of the universe and the Hubble expansion parameter h, we find.that the curvature is consistent with flat and that the primordial fluctuation spectrum is consistent with scale invariant, in agreement with the basic inflation paradigm. We find that the data prefer a baryon density Ωbh2 above, though similar to, the estimates from light element abundances and big bang nucleosynthesis. When combined with large scale structure observations, the Boomerang data provide clear detections of both dark matter and dark energy contributions to the total energy density fltot, independent of data from high-redshift supernovae. ©2001 The American Physical Society.