CMB birefringence from ultra-light axion string networks

Andrew J. Long; Mudit Jain; Mustafa A. Amin

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CMB birefringence from ultra-light axion string networks

Mudit Jain, Andrew J. Long, Mustafa A. Amin

Cosmology and Nongalactic Astrophysics · Submitted 19 Mar 2021

abstract compiled · 2026-09-23 · no language-model review

The authors' main claim We find that the angular correlation function has a characteristic angular scale set by $\theta_\mathrm{min}$, which corresponds to the angular extent of the loops at the time of recombination.

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What the abstract itself states, as probabilities: claims first 0.04 · states limitation 0.22 · human participants 0.01 · controlled comparison 0.02 · randomized assignment 0.01 · states quantitative result 0.37 · compares with prior results 0.07 · mentions code or data availability 0.02.

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The polarization of Cosmic Microwave Background (CMB) photons is rotated as they pass through (ultralight-) axion string loops. Studying this birefringence can reveal valuable information about the axion-photon coupling and the structure of the string network. We develop an approximate analytic formalism and identify a kernel function that can be used to calculate the two-point correlation function for CMB birefringence induced by an arbitrary axion string network. Using this formalism, we evaluate the birefringence signal for some simple loop distributions (including scaling and network collapse). We find that the angular correlation function has a characteristic angular scale set by $\theta_\mathrm{min}$, which corresponds to the angular extent of the loops at the time of recombination. This results in a peak in the birefringence power spectrum around $\ell_p \sim 1/\theta_\mathrm{min}$. An additional scale, controlled by the axion's mass, is introduced if the network collapses before today.

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What the classifier reports for each sentence. The number is the probability it gave the label.
#	sentence	role	the authors' own work	states the main conclusion	strength
s0	The polarization of Cosmic Microwave Background (CMB) photons is rotated as they pass through (ultralight-) axion string loops.	background 0.99	0.14	0.09	asserted 1.00
s1	Studying this birefringence can reveal valuable information about the axion-photon coupling and the structure of the string network.	background 0.85	0.07	0.07	hedged possibility 0.77
s2	We develop an approximate analytic formalism and identify a kernel function that can be used to calculate the two-point correlation function for CMB birefringence induced by an arbitrary axion string network.	method 0.53	0.97	0.12	asserted 1.00
s3	Using this formalism, we evaluate the birefringence signal for some simple loop distributions (including scaling and network collapse).	method 0.52	0.96	0.06	asserted 0.99
s4	We find that the angular correlation function has a characteristic angular scale set by $\theta_\mathrm{min}$, which corresponds to the angular extent of the loops at the time of recombination.	result 0.99	0.94	0.37	asserted 1.00
s5	This results in a peak in the birefringence power spectrum around $\ell_p \sim 1/\theta_\mathrm{min}$.	result 0.96	0.86	0.26	asserted 1.00
s6	An additional scale, controlled by the axion's mass, is introduced if the network collapses before today.	result 0.93	0.55	0.08	asserted 0.90

What kind of paper the classifier reports this is: theoretical result 0.72 · evidence from proof or derivation 1.00.

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The paper

Original abstract

The polarization of Cosmic Microwave Background (CMB) photons is rotated as they pass through (ultralight-) axion string loops. Studying this birefringence can reveal valuable information about the axion-photon coupling and the structure of the string network. We develop an approximate analytic formalism and identify a kernel function that can be used to calculate the two-point correlation function for CMB birefringence induced by an arbitrary axion string network. Using this formalism, we evaluate the birefringence signal for some simple loop distributions (including scaling and network collapse). We find that the angular correlation function has a characteristic angular scale set by $\theta_\mathrm{min}$, which corresponds to the angular extent of the loops at the time of recombination. This results in a peak in the birefringence power spectrum around $\ell_p \sim 1/\theta_\mathrm{min}$. An additional scale, controlled by the axion's mass, is introduced if the network collapses before today.

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References

Forward citations

Cited by 5 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

Constraining Ultralight Axions with Galaxy Surveys
astro-ph.CO 2021-04 conditional novelty 6.0 of 10

BOSS galaxy clustering multipoles bound the ultralight axion share of dark matter to Omega_a h^2 < 0.004 at 95% confidence for masses between 10^-31 and 10^-26 eV, improving on CMB-only limits.
Distinguishing the origin of cosmic birefringence: dark energy, dark matter, and neutrino asymmetry
astro-ph.CO 2026-10 conditional novelty 5.0 of 10

The redshift evolution of cosmic birefringence sources imprints a distinctive shape on the CMB EB power spectrum that can distinguish neutrino asymmetry from axion dark energy and dark matter.
Cosmic Birefringence and Electroweak Axion Dark Energy
hep-ph 2021-06 conditional novelty 5.0 of 10

An extended electroweak axion quintessence model, built to produce a large electromagnetic anomaly, converts the reported CMB birefringence angle into a narrow range for the dark energy equation of state, w = -0.994 t...
Quintessential interpretation of the evolving dark energy in light of DESI
astro-ph.CO 2024-04 conditional novelty 4.0 of 10

A canonical quintessence field can reproduce the DESI preference for evolving dark energy over the observed redshift range, with the phantom crossing falling beyond the pivot redshift where the data are most constraining.
Feebly Interacting Particles: FIPs 2022 workshop report
hep-ph 2023-05 accept novelty 3.0 of 10

The FIPs 2022 workshop report surveys the theory, astrophysical bounds, and planned experiments for feebly interacting particles below the GeV scale, and argues for a diversified multi-laboratory program over the next decade.

How the literature uses it

33 arXiv papers cite this in 56 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 36 sentences without a confident label

Contests it 1 paper

Concerning the axionic string and string-wall networks, recent works have discussed the isotropic birefringence and concluded that the isotropic signal cannot be obtained in this case because it would violate current upper bounds on the anisotropic component [ref] .

Axionic defects in the CMB: birefringence and gravitational waves · Introduction · contest 0.76

Builds on it 1 paper

Building on that work, some of us developed semi-analytic models to calculate the expected power spectrum of axion-defect-induced birefringence for different ranges of ALP masses and network dynamics [ref] .

Searching for axion-like particles through CMB birefringence from string-wall networks · Introduction · 0.91

Cites it as support 1 paper

These pseudoscalar fields are naturally very light as a result of an approximate global symmetry [ref] , and are also a good fit to the birefringence measurement [ref] .

Constraints on Global Symmetry Breaking in Quantum Gravity from Cosmic Birefringence Measurements · Introduction · 0.96

Cites it as background 15 papers

As the origin of the isotropic cosmic birefringence (ICB), an axion-like particle (ALP) is widely studied [ref] .

Isotropic cosmic birefringence from an oscillating axion-like field · Introduction · 0.97
Then, after the measurement of the nonzero ICB has been reported, most of the previous studies have focused on the implications for the ALP [ref] .

Can we explain cosmic birefringence without a new light field beyond Standard Model? · Introduction · 0.91
The axion coupling to photons $-1/4g_aγaFF̃$ has been widely studied in terrestrial, astrophysical, and cosmological contexts as a messenger of new physics [ref] .

Cosmic Birefringence from CP-Violating Axion Interactions · Introduction · 0.98

What it cites · 86 sentences without a confident label

Builds on 1 paper

Building upon the work of [ref] , our goal is to develop an analytical formalism to calculate cosmic birefringence due to string loop networks, and also accommodate a broader class of them.

A CMB Millikan Experiment with Cosmic Axiverse Strings · Introduction · 1.00

Uses the method or tool of 1 paper

To do so, we work with a simple model for the propagation of CMB photons through the string network that was proposed in Ref. [ref] .

A CMB Millikan Experiment with Cosmic Axiverse Strings · The loop-crossing model · 0.99

Uses data or values from 2 papers

We take $H_0 = 70 km/Mpc/sec$, $Ω_Λ= 0.7$, $Ω_m = 0.3$ and $Ω_r = 9×10^-5$ (including neutrinos) [ref] .] For instance, during the matter-dominated epoch we have the scaling $a ∼τ^2$ and $H ∼τ^-3$.

Planck 2018 results. VI. Cosmological parameters · The loop-crossing model · 0.93
Most notable are limits from the CAST helioscope which imposes $|g_aγγ| ≲0.66 ×10^-10 GeV^-1$ for axion masses below roughly $10^-2 eV$ [ref] .

New CAST Limit on the Axion-Photon Interaction · An ultralight axion coupled to light · 0.94

Cites as background 25 papers

The effect of axion strings on CMB birefringence was studied recently by Agrawal, Hook, and Huang [ref] .

A CMB Millikan Experiment with Cosmic Axiverse Strings · Introduction · 0.89
The strings' gravitational influence on light and matter can be probed through distortions of the cosmic microwave background (CMB) radiation [ref] and gravitational wave measurements (e.g., pulsar timing array or interferometry) [ref] .

Irreducible background of gravitational waves from a cosmic defect network: update and comparison of numerical techniques · Introduction · 0.85
The strings' gravitational influence on light and matter can be probed through distortions of the cosmic microwave background (CMB) radiation [ref] and gravitational wave measurements (e.g., pulsar timing array or interferometry) [ref] .

The QCD Axion and Gravitational Waves in light of NANOGrav results · Introduction · 0.85

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