Cosmic birefringence from the Axiverse

Abstract

We revisit the evidence for CMB birefringence in the context of a rich Axiverse. Using probability density functions (PDFs) for various axion parameters, such as the mass and axion decay constant, we construct the PDF for the cosmic birefringence angle and investigate its properties. By relating the observed value of the birefringence angle to the mean or standard deviation of the constructed PDF, we constrain the shape of the input PDFs, providing insights into the statistical distribution of the Axiverse. We focus on three different types of axion potentials: cosine, quadratic, and asymptotically linear axion monodromy. Our analysis showcases the potential of cosmic birefringence in constraining the distribution of axion parameters and uncovering possible correlations among them. We additionally offer predictions for “birefringence tomography”, anticipating future measurements of birefringence from lower multipoles, and show how it can be used to rule out simpler versions of the Axiverse. Our findings contribute to the ongoing exploration of the Axiverse and its implications for cosmic birefringence.

Isotropic cosmic birefringence from early dark energy

“…Rather, the resultant EE and EB spectra are largely determined by ⟨ϕ⟩ * ,eff and φ * given in Eqs. (25) and (26). Thus, ϕ will be able to explain the ICB with β ∼ 0.3 deg even for m ϕ ≫ 10 −26 eV.…”

“…As the origin of the isotropic cosmic birefringence (ICB), an axion-like particle (ALP) is widely studied [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. When the ALP induces cosmic birefringence, the birefringence angle, β, is determined only by the ALPphoton coupling and the difference of the ALP field value between the emission and observation.…”

Can we explain cosmic birefringence without a new light field beyond Standard Model?

“…A prevailing candidate of the pseudoscalar field ϕ has been provided by an axion-like particle (ALP), and a possibility that photon's birefringence is caused by a cosmic background of the ALP constituting dark energy or dark matter has been developed [27][28][29][30][31][32][33][34]. Then, after the measurement of the nonzero ICB has been reported, most of the previous studies have focused on the implications for the ALP [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]. However, to explain the reported ICB, the ALP mass should be extremely light [35].…”

Axionic defects in the CMB: birefringence and gravitational waves

“…Among the different ideas of explaining the birefringence measurement, two implementations have been singled out. One includes an ultra-light axion, that can be (early) dark energy or a subdominant component of dark matter, and that couples to photons as above [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42]. The second possibility is that the isotropic birefringence is caused by a network of cosmic domain walls (DWs) [43][44][45][46] whose microphysical constituent couples to photons.…”