Joint constraints on cosmic birefringence and early dark energy from ACT, Planck, DESI, and PantheonPlus

TL;DR

The paper investigates whether a Chern-Simons coupling between an axion-like field in early dark energy (EDE) and CMB photons can produce cosmic birefringence while addressing the Hubble tension. It models the birefringent propagation within an EDE framework using a CLASS_EDE-based Boltzmann solver and performs nine-parameter MCMC fits to Planck-$EB$ and ACT-$EB$ data, each combined with DESI and Pantheon+ data. The results favor a sizable EDE component ($f_{\rm EDE} \approx 0.21$–$0.23$) and a nonzero birefringence coupling ($g M_{Pl} \approx 0.13$–$0.16$), yielding $H_0$ values around $76$–$77$ km s$^{-1}$ Mpc$^{-1}$ and $S_8 \approx 0.964$–$0.967$, with degeneracies linking early-time physics to late-time expansion. This birefringent-EDE scenario can reconcile CMB polarization observations with late-time distance indicators, offering a compelling path toward alleviating the Hubble tension, with ACT-$EB$ providing particularly stringent, complementary constraints and motivating future polarization missions.

Abstract

With the increasing number of high-precision astronomical observations, physical quantities that were previously inaccessible to accurate calculations, such as cosmic birefringence, have once again become a focal point of interest. Such phenomena induce a nonvanishing cross-correlation between the $E$- and $B$-mode polarizations of the cosmic microwave background (CMB), thereby providing a direct observational signature of parity violation. The Chern-Simons coupling between the scalar field in early dark energy (EDE) models and CMB photons is regarded as a plausible mechanism for generating cosmic birefringence. Recent data from the Atacama Cosmology Telescope (ACT) deliver $EB$ measurements at higher multipole moments than those previously achieved by {Planck}, while DESI and PantheonPlus datasets provide new and stringent constraints on the late-time expansion history. Using a joint analysis of {Planck}, DESI DR1, Pantheon+, and ACT data, we perform a full-parameter constraint on the cosmic birefringence effects induced by the EDE-CMB photon coupling. Our results favor a higher Hubble constant, $H_0 = 76.9^{+2.9}_{-2.5}\,\rm km\,s^{-1}\,Mpc^{-1}$, and a relatively large EDE fraction, $f_{\mathrm{EDE}} = 0.232^{+0.074}_{-0.047}$. By comparing the cosmological evolution of this model across different data combinations, we find that the ACT-$EB$ data combined with {Planck} + DESI + PantheonPlus provide good constraints to both early- and late-Universe observations.

Figures (6)

• Figure 1: One and two-dimensional distributions of $H_0$, $\Omega_\mathrm{b} h^2$, $\Omega_\mathrm{c} h^2$, $f_\mathrm{EDE}$, $gM_\mathrm{Pl}$, and $\log_{10}z_c$, where the contour lines represent 68$\%$ and 95$\%$ C.L., respectively. The blue color contour corresponds to the fitting results from the Planck-EB with Planck+DESI+Pantheon+ dataset. The purple color corresponds to the fitting results from the ACT-EB with Planck+DESI+Pantheon+ dataset.
• Figure 2: The ratio of the EDE density $\Omega_{\mathrm{EDE}}$ as a function of redshift $z$.
• Figure 3: The ratio of the EDE scalar field $\phi$ to its initial value $\phi_0$ as a function of redshift $z$.
• Figure 4: The CMB $D_\ell^{EB}$ power spectra with the best-fit result from four groups' data. The Planck-$EB$ data and ACT-$EB$ data points with errorbars are shown in tomato and light-blue colors, while the plot excludes the overlapping multipole range of the Planck-$EB$ data.
• Figure 5: The evolution of the Hubble parameter as a function of conformal time $\eta$ for the four data combinations. The left side figure (a) shows the range of $\eta$ from 0 to 12000, while the right side figure (b) provides a zoomed-in view of $\eta$ from 8000 to 12000.