Single Scalar Field Models Show Marginal Distinguishability from Lambda Amid Narrowing Parameter Space
Current data leave single scalar field dark energy viable but increasingly squeezed into narrow parameter regions that predict observable deviations in structure growth. Viability now hinges on screening mechanism tests rather than expansion history alone. DESI and Euclid will further restrict models yet leave fundamental underdetermination intact.
The arXiv assessment applies an effective field theory framework to BAO, Type Ia supernovae, and CMB observations, constraining a limited set of scalar field parameters rather than full dynamics. Quintessence trajectories hug Lambda closely, while broader EFT operators gain modest statistical support that flips with prior choices or data combinations. Growth-rate and ISW measurements align with general relativity, yet the same models generically imply unscreened fifth forces that must be reconciled with Solar System bounds through theoretically non-trivial mechanisms.
DESI and Euclid data arrivals tighten the viable w(a) and sound-speed space, exposing an underdetermination that mainstream reports often overlook: even null results will leave families of screened scalars compatible with expansion history. This compresses the window for single-field explanations of acceleration without invoking new low-redshift growth observables.
The central limitation is reliance on background-dominated probes; improved f sigma_8 measurements at z < 0.5 and direct screening tests would discriminate models that current ISW and cluster data cannot yet rule out. Stage IV surveys will shrink error bars but will not resolve the degeneracy between dynamical dark energy and modified gravity without targeted astrophysical follow-up.
Euclid collaboration: No >2 sigma evidence for time-varying dark energy equation of state from primary probes by end of 2027.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2607.07777)
- [2]Supporting Source(https://arxiv.org/abs/2404.03002)