(Loop) quantum gravity and the inflationary scenario

TL;DR

This paper explores how loop quantum gravity might influence the early universe's inflationary phase, highlighting potential observable effects and fundamental challenges in unifying quantum gravity with cosmological models.

Contribution

It systematically investigates the potential observable signatures of loop quantum gravity in the inflationary universe, revealing generic high-curvature phenomena and discussing theoretical obstacles.

Findings

Potential observable effects in cosmic structures.

Emergence of high-curvature phenomena at large densities.

Challenges in formulating a complete loop quantum gravity model.

Abstract

Quantum gravity, as a fundamental theory of space-time, is expected to reveal how the universe may have started, perhaps during or before an inflationary epoch. It may then leave a potentially observable (but probably minuscule) trace in cosmic large-scale structures that seem to match well with predictions of inflation models. A systematic quest to derive such tiny effects using one approach, loop quantum gravity, has, however, led to unexpected obstacles. Such models remain incomplete, and it is not clear whether loop quantum gravity can be consistent as a full theory. But some surprising effects appear to be generic and would drastically alter our understanding of space-time at large density. These new high-curvature phenomena are a consequence of a widening gap between quantum gravity and ordinary quantum-field theory on a background.