Stochastization of BKL dynamics and Anisotropic Sky Patterns

TL;DR

This paper analyzes the stochastic behavior of BKL cosmological billiards in 4D spacetime, establishing new invariant measures, probabilities, and classifications of trajectories to understand anisotropic sky patterns.

Contribution

It introduces new invariant measures, probabilistic classifications, and proofs of statistical equivalence between big and small billiards in BKL dynamics.

Findings

New densities of invariant measures for billiard systems.

Proof of statistical equivalence between big and small billiards.

Classified trajectories using new probabilistic measures.

Abstract

The dynamics of cosmological billiards in $4=3+1$ spacetime dimensions is analyzed; the different statistical maps are characterized within the stochastic limit, reached after a large number of iterations of the billiard maps. New densities of invariant measures have been established, also for billiard systems which contain symmetry walls, according to the content of Weyl reflections in the maps, which account for the change of sign of the non-oscillating scale factors in the solution to the Einstein field equations. The statistical equivalence between the big billiard and the small billiard, posed in [Phys. Rev. D83, 044038 (2011)], is here proven by means of these new definitions of probabilities for the small billiard. Further new classes of BKL probabilities have also been defined especially for the one-variable map and for the two-variable map, for the early-time BKL dynamics, for a stochastizing BKL dynamics and for a completely stochastized dynamics, both for the big billiard and for the small billiard. The trajectories have been classified according to these new probabilties, and different specifications of probabilties comparing classes of initial conditions have been assigned for the stochastization of the dynamics. As a result, is is possible to establish a definition of BKL probabilities for the unquotiented dynamics of the big billiard, where the different patterns of Weyl reflections are encoded. The statistical description of BKL probabilities for the occurrence of a given number of epochs in each era are therefore further characterized by the most probable number of Weyl reflections contained in such eras, which is inferred from the implications of the billiard maps on the UPHP. These new constructions have been considered for the determination of the connection between the observed values of anisotropy by a stochastic limit of the BKL dynamics.