Implications of DESI for Dark Matter & Cosmic Birefringence

Abstract

We explore an interacting dark matter (DM)-dark energy (DE) framework that naturally yields an effective dynamical DE equation of state crossing the phantom barrier at early times, as indicated by recent DESI data, while also accounting for the observed isotropic rotation of the cosmic microwave background (CMB) linear polarization. Within this unified framework, we also explain the DM relic abundance without introducing additional fields or couplings. Depending on the DE potential, we identify two viable scenarios: a superheavy freeze-in DM requiring a high reheating temperature, or a strongly interacting dark sector with a GeV-TeV scale thermal DM candidate.

Figures (3)

• Figure 1: Top left: Evolution of the field as a function of scale factor $a$ for the polynomial potential. Top right: Nature of the $w_{\rm eff}$ as a function of redshift extrapolated to high redshift. It diverges momentarily, becomes positive, and approaches zero as one extrapolates to higher redshift. Bottom: Fit of the effective equation of state ($w_{\rm eff}$) as a function of redshift to the DESI data (blue dots) with binned error bars. All relevant parameters are tabulated in Tab. \ref{['tab:BP']}.
• Figure 2: Similar to Fig. \ref{['fig:fitPoly']} for the axion potential in Eq. \ref{['Eq:VeffAxion']} following Ref. Khoury:2025txd. All relevant parameters are mentioned in the inset and tabulated in Tab. \ref{['tab:BPAxion']}.
• Figure 3: Top left: Comparison of 2-to-2 reaction density, obtained analytically (blue dashed) with the one obtained numerically (black solid), for BP1, considering a DM of mass $10^{10}$ GeV. Top right: Contours of right relic abundance in $T_\text{rh}-m_\psi$ plane, corresponding to the benchmarks in Tab. \ref{['tab:BP']}. The arrowheads indicate the viable region of the parameter space that satisfies the EFT bound $f>T_\text{rh}$ for each of the benchmarks. Bottom: Contours of right DM abundance for a fixed $T_\text{rh}=10^{15}$ GeV, where different contours correspond to different DM masses. The benchmarks BP1, BP2, and BP3 in Tab. \ref{['tab:BP']} are denoted by the star, box, and crossed-circle, respectively. The shaded regions are disallowed from the instantaneous reheating condition $(m_\psi<T_\text{rh})$ and super-Planckian value of the effective scale $(f<M_P)$.