Thiago S. Pereira

Beyond ΛCDM: Problems, solutions, and the road ahead

Despite its continued observational successes, there is a persistent (and growing) interest in extending cosmology beyond the standard model, ΛCDM. This is motivated by a range of apparently serious theoretical issues, involving such questions as the cosmological constant problem, the particle nature of dark matter, the validity of general relativity on large scales, the existence of anomalies in the CMB and on small scales, and the predictivity and testability of the inflationary paradigm. In this paper, we summarize the current status of ΛCDM as a physical theory, and review investigations into possible alternatives along a number of different lines, with a particular focus on highlighting the most promising directions. While the fundamental problems are proving reluctant to yield, the study of alternative cosmologies has led to considerable progress, with much more to come if hopes about forthcoming high-precision observations and new theoretical ideas are fulfilled.

Weak lensing B-modes on all scales as a probe of local isotropy

This article introduces a new multipolar hierarchy for the propagation of the weak-lensing shear, convergence, and twist valid in a general spacetime. Our approach is fully covariant and relies on no perturbative expansion. We show that the origin of B-modes, in particular on large angular scales, is related to deviations of isotropy of the spacetime. Known results assuming a Friedmann-Lema^ tre background spacetime are naturally recovered. The example of a Bianchi I spacetime illustrates our formalism and its implications for future observations are stressed.

North-South non-Gaussian asymmetry in PLANCK CMB maps

Planck maps evidence a net dipolar distribution pointing in the direction (l,b) ≃ (245 ◦ ,−35 ◦ ), consistent with the direction of the North-South asymmetry phenomenon. Although the magnitude of this variance dipole is not statistically significant, ∼ 85% CL, as compared with maps produced with similar directional analysis on Gaussian and isotropic realisations of the concordance model, it evidences interesting attributes. First of all, Planck’s variance dipole –magnitude and direction– appears robust against the four different component separation algorithms (employed to clean contaminants in Planck data), various Planck masks, map’s pixelization parameters, and the addition of inhomogeneous real noise. Moreover, Planck’s variance dipole magnitude has a curious behavior: it gets lower values for larger sky-cut masks, independent of the map analyzed, strongly suggesting two causes: either foreground remnants that diminishe their influence when severe masks are used or CMB power from the quadrupole-octopole alignment whose larger influence is localized, and cut off, in the region where the masks act. Extra analyses were performed here to elucidate this point. From one side, we show that Planck’s variance dipole is robust in magnitude and direction against frequency dependence, disfavoring the foreground residuals as a possible explanation. From the other side, we shuffle Planck’s quadrupole and octopole components, leaving their magnitudes intact: the result was a variance dipole with half of its original magnitude pointing in a different direction, showing that these CMB multipoles have a definitive effect on the Planck’s variance dipolar distribution. Albeit the foreground residuals can not be excluded altogether, our analyses suggest that the main reason for this variance dipole is the CMB quadrupole-octopole alignment phenomenon.

Weak-lensing by the large scale structure in a spatially anisotropic universe: theory and predictions

This article details the computation of the two-point correlators of the convergence, E- and Bmodes of the cosmic shear induced by the weak-lensing by large scale structure assuming that the background spacetime is spatially homogeneous and anisotropic. After detailing the perturbation equations and the general theory of weak-lensing in an anisotropic universe, it develops a weak shear approximation scheme in which one can compute analytically the evolution of the Jacobi matrix. It allows one to compute the angular power spectrum of the E- and B-modes. In the linear regime, the existence of B-modes is a direct tracer of a late time anisotropy and their angular power spectrum scales as the square of the shear. It is then demonstrated that there must also exist o-diagonal correlations between the E-modes, B-modes and convergence that are linear in the geometrical shear and allow one to reconstruct the eigendirections of expansion. These spectra can be measured in future large scale surveys, such as Euclid and SKA, and oer a new tool to test the isotropy of the expansion of the universe at low redshift.

Weak-lensing B-modes as a probe of the isotropy of the universe

We compute the angular power spectrum of the

Cosmological Signatures of Anisotropic Spatial Curvature

B

Isotropization of the universe during inflation

-modes of the weak-lensing shear in a spatially anisotropic spacetime. We find that there must also exist off-diagonal correlations between the

Thermodynamics of quantum photon spheres

E

New geometric representations of the CMB two-point correlation function

-modes,

Two-point Correlation Functions in Inhomogeneous and Anisotropic Cosmologies

B