Searching for axionlike time-dependent cosmic birefringence with data from SPT-3G

K. R. Ferguson et al. (SPT-3G Collaboration)

Phys. Rev. D 106, 042011 – Published 29 August 2022

Abstract

Ultralight axionlike particles (ALPs) are compelling dark matter candidates because of their potential to resolve small-scale discrepancies between $Λ CDM$ predictions and cosmological observations. Axion-photon coupling induces a polarization rotation in linearly polarized photons traveling through an ALP field; thus, as the local ALP dark matter field oscillates in time, distant static polarized sources will appear to oscillate with a frequency proportional to the ALP mass. We use observations of the cosmic microwave background from SPT-3G, the current receiver on the South Pole Telescope, to set upper limits on the value of the axion-photon coupling constant $g_{ϕ γ}$ over the approximate mass range $10^{- 22} - 10^{- 19} eV$ , corresponding to oscillation periods from 12 hours to 100 days. For periods between 1 and 100 days ( $4.7 \times 10^{- 22} eV \leq m_{ϕ} \leq 4.7 \times 10^{- 20} eV$ ), where the limit is approximately constant, we set a median 95% C.L. upper limit on the amplitude of on-sky polarization rotation of 0.071 deg. Assuming that dark matter comprises a single ALP species with a local dark matter density of $0.3 GeV / {cm}^{3}$ , this corresponds to $g_{ϕ γ} < 1.18 \times 10^{- 12} {GeV}^{- 1} \times (\frac{m_{ϕ}}{1.0 \times 10^{- 21} eV})$ . These new limits represent an improvement over the previous strongest limits set using the same effect by a factor of $\sim 3.8$ .

Received 30 March 2022
Accepted 15 July 2022

DOI:https://doi.org/10.1103/PhysRevD.106.042011

Physics Subject Headings (PhySH)

Axions Cosmic microwave background Cosmology Dark matter Particle astrophysics

Polarization

Gravitation, Cosmology & AstrophysicsParticles & Fields

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Vol. 106, Iss. 4 — 15 August 2022

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Images

Figure 1
$ℓ$ -space Wiener filter that is applied to the template coadds to downweight noisy modes. Because the noise properties of the maps differ between Stokes $Q$ (left column) and $U$ (right column), as well as between 95 GHz (top row) and 150 GHz (bottom row) observing bands, each must be filtered independently.
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Figure 2
(left) Time series of polarization rotation angles measured for both the 95 GHz and 150 GHz bands. The gaps where there are no angles for a short period correspond with telescope downtime due to unscheduled drive maintenance. (right) Histograms of $x = \hat{ρ} / σ_{\hat{ρ}}$ for both observing bands. In both cases, this quantity is consistent with a unit Gaussian, plotted as a solid black line.
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Figure 3
95% C.L. upper limits on $Q / U$ rotation angle as a function of oscillation frequency (solid black line), along with simulated background-only median behavior (red) and $1 σ$ (green) and $2 σ$ (yellow) regions. As described in Sec. 3c, averaging over the course of an observation leads to less stringent limits as the oscillation frequency increases. However, this is a small effect; it is on the order of only $\sim 5 %$ at 2.00 inverse-days. Due to the large number of frequency bins, we expect some limits in excess of the $2 σ$ background contour; this does not necessarily constitute evidence for a sinusoidal polarization rotation.
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Figure 4
Window function (in amplitude) of the observation times used in this analysis, which characterizes the extent to which signals at a single frequency produce detectable power at other frequencies in our likelihood analysis. The largest sidelobes are at an amplitude of 14% of the main lobe, and these result from the quasiperiodic pattern of sorption refrigerator cycles and observations that occur between them in time. In an analysis such as ours without a large expected signal, the presence of sidelobes at this level does not impact the interpretation of our results.
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Figure 5
The parameter space for axion-photon coupling $g_{ϕ γ}$ as a function of axion mass $m_{ϕ}$ . The SPT-3G 95% C.L. upper limit is given by the solid red line, and the smoothed fit to this [Eq. (22)] by the dashed black line. The dashed orange lines represent the most recent limits set by the BICEP/Keck collaboration [30] using the AC oscillation effect; the solid green line represents the limit set with Planck data using the washout effect, with the dashed green line providing the strongest possible limit that could be set with the washout effect due to cosmic variance [20]. Projected limits using the AC oscillation effect for the full SPT-3G survey as well as the future CMB-S4 survey are given by the dot-dashed blue and purple lines, respectively (although these projections do not account for the wider mass range that full survey analyses could constrain). The CAST limit on $g_{ϕ γ}$ [17] is given by the horizontal gray line (stronger limits set using data from the supernova SN1987A [38], and Chandra X-ray spectroscopy [39] are excluded from the plot as a result of difficult-to-quantify modeling uncertainties). Lower mass limits from observations of Lyman- $α$ emission [40] and Dark Energy Survey observations of Milky Way satellite galaxies [41] are given by the labeled vertical dashed gray lines (while stronger limits from Lyman- $α$ observations exist [42], we have chosen to plot a more conservative limit). Both the BICEP/Keck and the SPT-3G results assume that axions comprise the entirety of the local dark matter, and that the density of the local dark matter field is $0.3 GeV / {cm}^{3}$ .
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