Pre-inflation from the multiverse: can it solve the quadrupole problem in the cosmic microwave background?

Abstract

We analyze a quantized toy model of a universe undergoing eternal inflation using a quantum-field-theoretical formulation of the Wheeler–DeWitt equation. This so-called third quantization method leads to the picture that the eternally inflating universe is converted to a multiverse in which sub-universes are created and exhibit a distinctive phase in their evolution before reaching an asymptotic de Sitter phase. From the perspective of one of these sub-universes, we can thus analyze the pre-inflationary phase that arises naturally. Assuming that our observable universe is represented by one of those sub-universes, we calculate how this pre-inflationary phase influences the power spectrum of the cosmic microwave background (CMB) anisotropies and analyze whether it can explain the observed discrepancy of the power spectrum on large scales, i.e. the quadrupole issue in the CMB. While the answer to this question is negative in the specific model analyzed here, we point out a possible resolution of this issue.

Emergence of multiverse in third quantized varying constants cosmologies

“…The scenarios in which the components of the multiverse experience their mutual presence via quantum entanglement was considered in [25,26]. Concepts of that kind can constitute a basis for introducing models in which the quantum entanglement between different universes influences the cosmological observables making the idea of multiverse observationally testable [27,28].…”

Quantum-gravity effects for excited states of inflationary perturbations

“…Looking for potentially observable effects of a candidate theory of quantum gravity is one of the crucial tasks necessary to eventually decide how to properly quantize gravity. Given that the standard paradigm of the beginning of the evolution of our universe with an inflationary phase is one of the physical scenarios with the highest energies available to be tested by measuring the anisotropies of the cosmic microwave background (CMB), many studies have focused on finding quantum-gravity corrections for inflationary perturbations that might lead to a measurable deviation of the CMB anisotropy spectrum; see, for example, [1][2][3][4][5][6][7][8].…”

Quantum Cosmology with Third Quantisation

“…In the former case, the last term in (288) represents a matter-like content in the universe (∼a −3 ), and in the latter it mimics a radiation energy content (∼a −4 ). In both cases, it can be shown [99][100][101] that a matter-or radiation-predominated pre-inflationary period might, under some conditions, leave some observable imprints in the power spectrum of the CMB. However, it is sometimes considered [3,4,102] that n max ≈ Ha, which means accounting only for the backreaction of the superhorizon modes.…”

“…Even with the value E > 0 in (116), there is still room for the universes to be created from nothing, i.e., from the Euclidean region without the need of a pre-existing spacetime. However, as we have seen, the process cannot be the one studied in Section 2.5.1 for the creation of a single universe from the single Euclidean instanton (101). Instead, one has to consider more elaborated instantons.…”