Narrow Results

The quantum bounce a priori connects several (semi)classical epochs of universe evolution, however determining if and how well the semiclassicality is preserved in this transition is highly nontrivial. We review the present state of knowledge in that regards in the isotropic sector of loop quantum cosmology (LQC). This knowledge is next extended by studies of an isotropic universe admitting positive cosmological constant (featuring an infinite chain of large universe epochs). It is also shown, that such universe always admits a semiclassical epoch thanks to spontaneous coherence, provided it is semiclassical in certain constant of motion playing the role of energy.

We study the radiation profile of the unitarily evolving wave packet constructed for the quantum model of spherically symmetric dust shell collapsing in marginally bound Lemaître-Tolman-Bondi (LTB) model. In this analysis, we consider the quantum model of dust shell collapse in LTB spacetime, where the dust shell collapse to black hole singularity is replaced by a bounce. We identify the observable natural to collapse/expansion character of dust shell, and study the mode decomposition in the quantum model. The incoming/outgoing modes are associated with the eigenfunctions of the Hermitian extension of the operator corresponding to this observable. For the wave packet representing the collapsing and expanding phase of the dust shell, we estimate the contributions of the incoming/outgoing modes. We find that the collapsing and expanding branches do not comprise entirely of incoming and outgoing radiation. The dust shell dynamics is insensitive to the large wavenumber modes as their contribution is negligible. Near the bounce point, the contribution of outgoing (incoming) modes in the collapsing (expanding) branch is substantial and it decreases as the dust shell moves away from the singularity. In the early (later) stage of the collapsing (expanding) phase, the incoming (outgoing) modes dominate. As the dynamics of the dust shell is sensitive to the near-infrared modes of the radiation, the information of the bounce is carried over to infrared modes much before it reaches the observer. In the infrared regime, a flip is observed from largely incoming to largely outgoing radiation as the evolution progresses from collapsing to expanding phase. The information of the short-scale physics is carried over to the longest wavelength in this quantum gravity model.