Is cosmic birefringence due to dark energy or dark matter? A tomographic approach

Understand

A pseudoscalar "axionlike" field, $\phi$, may explain the $3\sigma$ hint of cosmic birefringence observed in the $EB$ power spectrum of the cosmic microwave background (CMB) polarization data.

• Is $\phi$ dark energy or dark matter? A tomographic approach can answer this question.
• The effective mass of dark energy field responsible for the accelerated expansion of the Universe today must be smaller than $m_\phi\simeq 10^{-33}$ eV.
• If $m_\phi \gtrsim 10^{-32}$ eV, $\phi$ starts evolving before the epoch of reionization and we should observe different amounts of birefringence from the $EB$ power spectrum at low ($l\lesssim 10$) and high multipoles.