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Assessing Cosmological Evidence for Nonminimal Coupling.

William J Wolf1, Carlos García-García1, Theodore Anton1,2

  • 1University of Oxford, Astrophysics, DWB, Keble Road, Oxford OX1 3RH, United Kingdom.

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|September 10, 2025
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Summary
This summary is machine-generated.

Evidence suggests evolving dark energy may drive cosmic acceleration. Data favor a concave potential energy for the scalar field (quintessence) and a nonminimal coupling to gravity, but this contradicts observations of fifth forces.

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Area of Science:

  • Cosmology
  • Theoretical Physics

Background:

  • Observational data show deviations from the standard Lambda cold dark matter model.
  • These deviations suggest the presence of evolving dark energy, potentially driven by a cosmological scalar field known as quintessence.

Purpose of the Study:

  • To assess the observational evidence for the existence of a scalar field driving cosmic acceleration.
  • To investigate the properties of this scalar field's potential energy and its coupling to gravity.

Main Methods:

  • Analysis of observational data to test cosmological models.
  • Statistical analysis using Bayes factors to determine the preference for different theoretical scenarios.

Main Results:

  • Data favor a concave potential energy for quintessence (d^2V/dφ^2 < 0).
  • Strong evidence (log(B)=7.34±0.6) supports a scalar field nonminimally coupled to gravity.
  • This nonminimal coupling predicts time-varying gravitational constants and fifth forces.

Conclusions:

  • If quintessence drives cosmic acceleration, its potential energy must be concave.
  • The strong preference for nonminimal coupling implies observable fifth forces, which are not detected.
  • This suggests either new physics is required on smaller scales or quintessence is an unlikely explanation for cosmic acceleration.