Consistency of Planck, ACT and SPT constraints on magnetically assisted recombination and forecasts for future experiments

Abstract

Primordial magnetic fields can change the recombination history of the universe by inducing clumping in the baryon density at small scales. They were recently proposed as a candidate model to relieve the Hubble tension. We investigate the consistency of the constraints on a clumping factor parameter b in a simplistic model, using the latest CMB data from Planck, ACT DR4 and SPT-3G 2018. For the combined CMB data alone, we find no evidence for clumping being different from zero, though when adding a prior on H 0 based on the latest distanceladder analysis of the SH0ES team, we report a weak detection of b. Our analysis of simulated datasets shows that ACT DR4 has more constraining power with respect to SPT-3G 2018 due to the degeneracy breaking power of the TT band powers (not included in SPT). Simulations also suggest that the TE,EE power spectra of the two datasets should have the same constraining power. However, the ACT DR4 TE,EE constraint is tighter than expectations, while the SPT-3G 2018 one is looser. While this is compatible with statistical fluctuations, we explore systematic effects which may account for such deviations. Overall, the ACT results are only marginally consistent with Planck or SPT-3G, at the 2 − 3σ level within ΛCDM+b and ΛCDM, while Planck and SPT-3G are in good agreement. Combining the CMB data together with BAO and SNIa provides an upper limit of b < 0.4 at 95% c.l. (b < 0.5 without ACT). Adding a SH0ES-based prior on the Hubble constant gives b = 0.31 +0.11 −0.15 and H 0 = 69.28 ± 0.56 km/s/Mpc (b = 0.41 +0.14 −018 and H 0 = 69.70 ± 0.63 km/s/Mpc without ACT). Finally, we forecast constraints on b for the full SPT-3G survey, Simons Observatory, and CMB-S4, finding improvements by factors of 1.5 (2.7 with Planck), 5.9 and 7.8, respectively, over Planck alone.

Hints of Early Dark Energy in Planck, SPT, and ACT data: new physics or systematics?

“…This will not only provide a valuable crosscheck on the Planck measurements, but also an opportunity to obtain tight and robust constraints through joint analyses, which can be of primary importance to test physics scenarios beyond ΛCDM with CMB data (as in the case of e.g. primordial magnetic fields [22,81], sterile neutrino self-interactions [82] and New EDE [75,83] [13]. The inclusion of Planck polarization significantly narrows the posterior for θi and log 10 (zc).…”

Gravitational wave signal from primordial magnetic fields in the Pulsar Timing Array frequency band

“…In these works, it was pointed out that a sub-nanoGauss pre-recombination magnetic field would induce additional baryon inhomogeneities, which would enhance the recombination rate, thereby changing the CMB spectrum in a way that would alleviate the Hubble tension. Refer-ence [78] derived updated constraints on the baryon clumping from data of CMB experiments, of about b < ∼ 0.5 at 95% confidence level, which can be translated into an upper limit on the pre-recombination magnetic field amplitude B rec < ∼ 0.1 nG. In addition, they derive a range b ∈ (0.16, 0.55) that is compatible with a value H 0 ≈ 70 km s −1 Mpc −1 , relieving the Hubble tension.…”

“…The green line indicates the upper limit B < ∼ 0.1 nG, and the range Brec ∈ (0.013, 0.1) nG, proposed to alleviate the Hubble tension, both derived in ref. [78] from CMB constraints on the baryon clumping. The black solid diagonal lines show the Fermi Large Area Telescope (LAT) lower bound on the intergalactic magnetic field from timing of the blazar signal (darker gray area), and from the search of extended emission (lighter gray area) [2].…”

“…The solid red and brown lines indicate the evolutionary paths of an initial field with k * = 2πH * and Ω * M = 0.1 at T * = 100 MeV and g * = 10 (right red dot), and at T * = 150 MeV and g * = 15 (left red dot). The green line indicates the upper limit B < ∼ 0.1 nG, and the range Brec ∈ (0.013, 0.1) nG, proposed to alleviate the Hubble tension, both derived in ref [78]. from CMB constraints on the baryon clumping.…”

Magnetogenesis and the Cosmic Web: A Joint Challenge for Radio Observations and Numerical Simulations

“…Such very low bounds seem to be incompatible with the absence of detected Inverse Compton Cascade emission from blazars e.g., [50][51][52][53][54], which yields limits of ∼10 −16 G 2 . Other stringent limits have been suggested by modelling magnetic effects on post-recombination heating e.g., [57][58][59] or by the small-scale baryonic density fluctuation induced by primordial magnetic fields, which would alter CMB anisotropies by promoting to inhomogeneous recombination and heating e.g., [60][61][62]. Recent limits for the average present-day magnetisation of the Universe have also been derived by the level of excess in diffuse radio emission detected by ARCADE2 and EDGES 21cm line experiments, yielding ≤10 −3 -0.3 nG depending on the unknown spectral index of primordial seed fields [63].…”