Dirac Fields in Loop Quantum Gravity and Big Bang Nucleosynthesis

TL;DR

This paper investigates quantum gravity corrections to the equations of state for photons and Dirac fermions within loop quantum gravity, assessing their impact on Big Bang nucleosynthesis and deriving bounds on these quantum effects.

Contribution

It derives quantum gravity corrections for Maxwell and Dirac fields from a canonical loop quantum gravity perspective and compares their effects on early universe physics.

Findings

Quantum corrections appear as an expansion-dependent multiplicative factor in density.

Classical actions for Maxwell and Dirac fields yield similar quantum corrections.

Bounds on quantum gravity effects are established using Big Bang nucleosynthesis data.

Abstract

Big Bang nucleosynthesis requires a fine balance between equations of state for photons and relativistic fermions. Several corrections to equation of state parameters arise from classical and quantum physics, which are derived here from a canonical perspective. In particular, loop quantum gravity allows one to compute quantum gravity corrections for Maxwell and Dirac fields. Although the classical actions are very different, quantum corrections to the equation of state are remarkably similar. To lowest order, these corrections take the form of an overall expansion-dependent multiplicative factor in the total density. We use these results, along with the predictions of Big Bang nucleosynthesis, to place bounds on these corrections.