Study the nature of dynamical dark energy by measuring the CMB polarization rotation angle

TL;DR

The paper investigates dynamical dark energy by coupling a dark-energy scalar to photons via a Chern-Simons term, which induces cosmic birefringence and rotates CMB polarization by a uniform angle $β$, generating TB and EB power spectra. It develops a Fisher-matrix framework using foreground-based calibration (the Minami-Komatsu method) to jointly constrain the instrumental angle $α$ and the isotropic rotation $β$, while also enabling reconstruction of an anisotropic rotation field through a quadratic estimator for the rotation harmonics $β_{LM}$ and its scale-invariant amplitude $A_{CB}$. For AliCPT, the authors forecast a $5σ$ detection of $β$ with about $11$ module-years when combined with Planck HFI data, and predict a roughly sixfold improvement in anisotropic rotation sensitivity with a large-aperture telescope achieving $σ_{A_{CB}}\sim 9\times 10^{-3}$ after $50$ module-years. These results provide a microphysical probe of dynamical dark energy through photon interactions, complementing DESI’s dynamical constraints and enabling tests of spatial fluctuations in the dark-energy field via CMB polarization.

Abstract

Recent results from the Dark Energy Spectroscopic Instrument (DESI) support the dynamical dark energy. Intriguingly, the data favor a transition of the dark energy equation of state across $w=-1$, a hallmark of the Quintom scenario. In this paper, we consider a different approach to the dynamical nature of dark energy by investigating its interaction with ordinary matters, specifically the Chern-Simons (CS) interaction with photons. In cosmology, this interaction rotates the polarized plane of the cosmic microwave background (CMB) photons, which induces non-zero polarized TB and EB power spectra. We forecast this measurement with the Ali CMB Polarization Telescope (AliCPT) experiment. We take the best-fit value of the isotropic rotation angle from Planck data as our fiducial input. We project that 11 module-year (modyr) of observations will yield an improved detection sensitivity with a significance $\sim 5σ$, given a calibration precision of $0.1^\circ$ in the polarization angle. We also forecast AliCPT's sensitivity to the amplitude of a scale invariant spectrum of the anisotropic polarization rotation field. With $50$~modyr of observations, the large-aperture configuration is expected to reach $σ_{A_{\mathrm{CB}}}\sim10^{-2}$, offering a sixfold improvement over the small-aperture design and enabling competitive tests of spatial fluctuations in the dark energy field.

Figures (9)

• Figure 1: The left panel shows the sky coverage of the AliCPT-1 wide scan, with the background representing the dust polarization intensity from Planck $353$GHz map. The right panel displays noise standard deviation corresponding to $1$ module year observation in the selected 44% sky area.
• Figure 2: Constraints on $\beta$ with varied $\ell_{\max}$ ($\ell_{\min}=30$ fixed; left panel) and varied $\ell_{\min}$ ($\ell_{\max}=1500$ fixed; right panel), for AliCPT-1 (95/150 GHz, 20 module-years), PLK HFI (100, 143, 217, 353 GHz), and PLK LFI (44, 70 GHz) simulations.
• Figure 3: Evolution of $\sigma_\beta$ with $\sigma^{cali}_\alpha$ for different data combinations. "caliAliCPT-1": prior applied to both AliCPT-1 bands; "caliPLK": same prior assumed for Planck bands.
• Figure 4: Evolution of $\sigma_\beta$ with AliCPT-1 data accumulation, under $\sigma^{cali}_\alpha = 0.2^\circ, 0.1^\circ, 0.05^\circ$ for AliCPT-1 bands.
• Figure 5: Forecasted sensitivity of the anisotropic polarization rotation amplitude $A_{\mathrm{CB}}$ as a function of AliCPT data accumulation (module-years).