Resolving the Planck-DESI tension by non-minimally coupled quintessence

The Planck measurement of cosmic microwave background (CMB) has established the $Λ$-cold-dark-matter ($Λ$CDM) model as the concordant model along with other observations. However, recent measurements of baryon acoustic oscillations (BAO) from Dark Energy Spectroscopic Instrument (DESI) have renewed the matter fraction $Ω_\mathrm{m}$ tension between Planck-$Λ$CDM and DESI-$Λ$CDM. Directly reconciling this CMB-BAO tension with a dynamical DE in Chevallier-Polarski-Linder (CPL) parametrization seems to imply a crossing of the equation-of-state (EoS) through $w=-1$ at low redshifts. In this letter, we resolve this $Ω_\mathrm{m}$ tension by allowing for the DM non-minimally coupled to gravity via a quintessence field. This non-minimal coupling is preferred over $3σ$ confidence level. Consequently, even though the usual effective EoS of the coupled quintessence apart from the standard CDM part never crosses but always above $w=-1$, a misidentification with the $w_0w_a$CDM model would exactly fake such a crossing behavior, and the tensions on neutrino mass and growth rate in the $Λ$CDM model are also relieved in our model as a result of the resolved $Ω_\mathrm{m}$ tension.

💡 Research Summary

The paper addresses a growing tension between the matter density parameter Ωₘ inferred from the Planck 2018 cosmic‑microwave‑background (CMB) data and that derived from the recent Dark Energy Spectroscopic Instrument (DESI) Year‑3 baryon‑acoustic‑oscillation (BAO) measurements. While the Planck analysis within the ΛCDM framework yields Ωₘ≈0.317±0.0065, DESI BAO prefers a lower value Ωₘ≈0.298±0.009, corresponding to a 1.8–2.3 σ discrepancy. When the data are interpreted using the Chevallier‑Polarski‑Linder (CPL) parametrization (w₀,wₐ) for dynamical dark energy, the tension is amplified and a crossing of the equation‑of‑state (EoS) through w = −1 at low redshift (z≈0.45) appears to be required. However, a single minimally coupled scalar field cannot produce a smooth w = −1 crossing without violating fundamental stability conditions.

To resolve this, the authors propose a non‑minimally coupled quintessence (NMCQ) model in which dark matter (DM) interacts with a quintessence field φ through a conformal factor A(φ)=exp(−βφ/Mₚₗ). The scalar potential is taken to be of the Peebles‑Ratra form V(φ)=αΛ⁴(φ/Mₚₗ)^{−n}. When β=n=0 the model reduces to standard ΛCDM. The action consists of the Einstein‑Hilbert term, a minimally coupled Standard Model sector, a DM sector coupled to the Jordan‑frame metric ˜g_{μν}=A²(φ)g_{μν}, and the canonical scalar‑field term. Varying the action yields modified continuity equations: \