Cosmic birefringence from monodromic axion dark energy

Abstract

The recently reported non-zero isotropic birefringence angle in Planck 2018 polarization data provides a tantalizing hint for new physics of axions. In this paper, we explain this by a string theory motivated axion with a monodromy potential that plays the role of dark energy. Upon using the birefringence measurement and the constraint on the equation of state for dark energy in this scenario, we find an upper bound on the axion decay constant as fa ≲ 1016 GeV. This naturally gives an energy scale of order GUT and can resolve the theoretical issue of super-Planckian field range of the conventional axion dark energy model. We further study the implications of cosmic birefringence for the underlying theory and its consequences for the string swampland conjectures. We finally discuss oscillatory features in the dark energy sector and the expected cosmic birefringence tomography.

Improved constraints on cosmic birefringence from the WMAP and Planck cosmic microwave background polarization data

“…β Dust EB model Planck PR3 HFI [33] 0.34°AE 0.14°N o Planck PR4 HFI [35] 0.30°AE 0.11°N o Planck PR4 HFI [35] 0.36°AE 0.11°Y e s Planck PR4 HFI þ LFI [37] 0.33°AE 0.10°N o Planck PR4 þ WMAP 0.342°þ 0.094°− 0.091°Y es experiments are expected to lead to a convincing discovery (or otherwise) of cosmic birefringence. If proven to be a cosmological signal, isotropic cosmic birefringence would have a profound impact on cosmology, particle physics, and quantum gravity [71][72][73][74][75][76][77][78][79][80][81].…”

Power spectrum of domain-wall network, and its implications for isotropic and anisotropic cosmic birefringence

“…See refs [32,[36][37][38][39][40]. for analysis using spatially uniform ALP and refs [41][42][43][44].…”

Cosmic birefringence from the Axiverse

“…We focus on axion fields produced via the misalignment mechanism with decay constant f a greater than the energy scale of inflation H I , such that each field is mostly uniform in our observable patch of the Universe [14][15][16][17]. This is the most common scenario discussed in the literature [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] to explain the static and isotropic nature of the signal, which is generated through the evolution of the axion background. In this case, the unavoidable fluctuations that would be generated during inflation are suppressed by a factor of ∼ H I /f a with respect to the isotropic component, in line with the current absence of evidence of an anisotropic counterpart [34][35][36].…”

“…In the case of dark energy the maximum displacement was set from the upper bound on the equation of state, whereas the abundance was used to fix the initial field value[32].…”