Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Particle production in a bouncing universe

Mustafa Saeed, Irfan Javed, Aiman Nauman

TL;DR

This work studies how a bouncing universe imprints on quantum matter by tracking particle production of a massless scalar field across contraction, bounce, and expansion. Using two complementary approaches—quantum field theory on curved backgrounds (QFTCB) and semiclassical gravity (SG) with backreaction—the authors show that the bounce yields a distinct multi-mode particle spectrum that at late times resembles a Planckian distribution, with a temperature around 3.4×10^-2 in the QFTCB analysis and 1.3×10^-2 when backreaction is included. The effective dynamics reveal that the bounce can occur later under SG, and backreaction enhances overall particle production; the spectra are highly sensitive to the curvature history and the polymer scale. These results strengthen the connection between gravity and thermodynamics, provide bounce-specific signatures for observational probes, and highlight methodological caveats such as the Gaussian matter-state ansatz and the need for future extensions (cosmological constant, anisotropies, mass, and spin).

Abstract

In massless scalar field cosmology, imposing the universe's physical volume as fundamentally discrete resolves the big bang singularity via a big bounce. We use quantum field theory on curved background to numerically track the number of particles created in the vacuum of a quantum field that propagates through the cosmological bounce. We find that due to geometry's evolution, particle production in all modes initially rises, sharply peaks at the bounce, and varies slowly afterwards. Further, by comparing with the case of a quantum field propagating on an expanding universe, we discover that the bouncing universe's imprints on quantum matter are distinct: notably, the late time particle production across modes resembles a thermal spectrum. We then use semiclassical gravity and find similar qualitative results. Here, we also determine how particle production affects geometry's evolution. Our study adds to existing literature on gravity-matter interactions in the context of a bouncing universe, contributes to searches of a bouncing universe's signatures, and strengthens the link between gravity and thermodynamics.

Particle production in a bouncing universe

TL;DR

This work studies how a bouncing universe imprints on quantum matter by tracking particle production of a massless scalar field across contraction, bounce, and expansion. Using two complementary approaches—quantum field theory on curved backgrounds (QFTCB) and semiclassical gravity (SG) with backreaction—the authors show that the bounce yields a distinct multi-mode particle spectrum that at late times resembles a Planckian distribution, with a temperature around 3.4×10^-2 in the QFTCB analysis and 1.3×10^-2 when backreaction is included. The effective dynamics reveal that the bounce can occur later under SG, and backreaction enhances overall particle production; the spectra are highly sensitive to the curvature history and the polymer scale. These results strengthen the connection between gravity and thermodynamics, provide bounce-specific signatures for observational probes, and highlight methodological caveats such as the Gaussian matter-state ansatz and the need for future extensions (cosmological constant, anisotropies, mass, and spin).

Abstract

In massless scalar field cosmology, imposing the universe's physical volume as fundamentally discrete resolves the big bang singularity via a big bounce. We use quantum field theory on curved background to numerically track the number of particles created in the vacuum of a quantum field that propagates through the cosmological bounce. We find that due to geometry's evolution, particle production in all modes initially rises, sharply peaks at the bounce, and varies slowly afterwards. Further, by comparing with the case of a quantum field propagating on an expanding universe, we discover that the bouncing universe's imprints on quantum matter are distinct: notably, the late time particle production across modes resembles a thermal spectrum. We then use semiclassical gravity and find similar qualitative results. Here, we also determine how particle production affects geometry's evolution. Our study adds to existing literature on gravity-matter interactions in the context of a bouncing universe, contributes to searches of a bouncing universe's signatures, and strengthens the link between gravity and thermodynamics.
Paper Structure (11 sections, 38 equations, 8 figures)

This paper contains 11 sections, 38 equations, 8 figures.

Table of Contents

  1. Introduction
  2. A bouncing universe
  3. Particle production in cosmology
  4. Quantum field on a cosmological background
  5. Formalism
  6. Results
  7. Other bouncing universes
  8. Semiclassical cosmology
  9. Formalism
  10. Results
  11. Reflections

Figures (8)

  • Figure 1: Particle production in the contracting, expanding and bouncing universes
  • Figure 2: Late time particle production spectrum
  • Figure 3: Late time particle production spectrum
  • Figure 4: Late time particle production spectrum for different polymer scales $\lambda$
  • Figure 5: Late time particle production spectrum for different bouncing universes
  • ...and 3 more figures