Exploring circular polarization in the CMB due to conventional sources of cosmic birefringence

Montero-Camacho, Paulo; Hirata, Christopher M.

doi:10.1088/1475-7516/2018/08/040

Cited by 28 publications

(59 citation statements)

References 62 publications

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“…That work builds upon a re-calculation [21], obtained with the TAM formalism [22,23], of circular polarization induced by photon-photon scattering, in Ref. [7], which itself extends several earlier analyses [2][3][4]6] of this effect. Note that the circular polarization induced through the photon-photon scattering is much larger than that induced through the photon-graviton scattering [20].…”

supporting

confidence: 54%

“…This Thomson scattering does not, however, induce circular polarization. Recent work has shown that circular polarization can be generated, from primordial perturbations through post-recombination photon-photon scattering [2][3][4][5][6][7], at second order in the density-perturbation amplitude. Still, the mean value of the circular polarization, when averaged over the sky, is predicted to be zero.…”

mentioning

confidence: 99%

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Chiral Photons from Chiral Gravitational Waves

Inomata

Kamionkowski

2019

Phys. Rev. Lett.

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We show that a parity-breaking uniform (averaged over all directions on the sky) circular polarization of amplitude V00 ≃ 2.6×10 −17 ∆χ(r/0.06) can be induced by chiral gravitational-wave (GW) background with tensor-to-scalar ratio r and chirality parameter ∆χ (which is ±1 for a maximally chiral background). We also show, however, that a uniform circular polarization can arise from a realization of a non-chiral GW background that spontaneously breaks parity. The magnitude of this polarization is drawn from a distribution of root-variance V 2 00 ≃ 1.5 × 10 −18 (r/0.06) 1/2 implying that the chirality parameter must be ∆χ 0.12(r/0.06) −1/2 to establish that the GW background is chiral. Although these values are too small to be detected by any experiment in the foreseeable future, the calculation is a proof of principle that cosmological parity breaking in the form of a chiral gravitational-wave background can be imprinted in the chirality of the photons in the cosmic microwave background. It also illustrates how a seemingly parity-breaking cosmological signal can arise from parity-conserving physics.

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supporting

confidence: 54%

mentioning

confidence: 99%

Chiral Photons from Chiral Gravitational Waves

Inomata

Kamionkowski

2019

Phys. Rev. Lett.

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“…In the framework of cosmological perturbation theory, this arises as a second order effect, similar to the production of V due to photon-photon scattering [5,[7][8][9][10]14]. The relevant scattering process in this case is gravitonphoton scattering [32] .…”

Section: Primordial V-modes In the Cmbmentioning

confidence: 99%

“…[3][4][5][6][7][8][9][10][11][12]) has been on 'conventional' sources of circular polarization, e.g. Faraday conversion [3], which in many cases leads to a negligible large-scale CMB signal [5] ( 10 −14 K). However, no attempt has been made to quantify this expectation, and with this in mind, in this work we consider in detail the production and evolution of primordial circular polarization.…”

Section: Introductionmentioning

confidence: 99%

Primordial circular polarization in the cosmic microwave background

Alexander

McDonough

2019

Physics Letters B

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Circular ("V-mode") polarization is expected to be vanishing in the CMB, since it is not produced in Thomson scattering. However, considering that the conventional CMB anisotropies are generated via an early universe mechanism such as inflation or a bouncing scenario, it is possible that circular polarization could be primordially produced and survive to the surface of last scattering. We study this in detail, and find a large class of inflationary models that produce a nearly scale invariant spectrum of scalar V-mode anisotropies. We study the inflationary production and subsequent evolution via the Boltzmann hierarchy, and show that V-mode polarization present in the CMB is suppressed by a factor of at least 10 10 20 relative to the primordial V , consistent with expectation of negligible V-mode polarization from inflation. We consider alternative possibilities for sourcing V primordially, such as the V-mode polarization induced by circularly polarized primordial gravitational waves, or producing V after inflation, via new interactions at recombination.

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“…An additional possibility is that circular polarization can be generated at second order in cosmological perturbation theory, via photon-photon scattering. This was studied by [8], and expanded on in [9], which found a Faraday conversion (4.20)…”

Section: One-loop Qed (Second Order Cosmological Perturbation Theory)mentioning

confidence: 98%

Physics beyond the Standard Model with circular polarization in the CMB and CMB-21cm cross-correlation

Alexander

McDonough

Pullen

et al. 2020

J. Cosmol. Astropart. Phys.

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Circular polarization is a relatively unexplored realm of CMB physics. Given the substantial community effort towards building next generation CMB polarization experiments, including those which will be sensitive to circular polarization, it behooves theorists to understand the possible sources and relevant physics of circular polarization, as encoded in the Stokes V parameter. In this work we develop and derive the requisite formalism, namely the Boltzmann hierarchy for V-mode scalar, vector, and tensor, anisotropies. We derive the V-mode anisotropies induced by a general source term, and demonstrate how existing proposals for the generation of V can be incorporated as source terms in the Boltzmann hierarchy. A subset of these effects may be correlated with 21cm intensity; we provide a worked example and derive an estimator to extract this information from observations. We conclude by computing the CMB T V cross-correlation generated by axions, and find a relation between T V and V V spectra in axion models.

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Exploring circular polarization in the CMB due to conventional sources of cosmic birefringence

Cited by 28 publications

References 62 publications

Chiral Photons from Chiral Gravitational Waves

Chiral Photons from Chiral Gravitational Waves

Primordial circular polarization in the cosmic microwave background

Physics beyond the Standard Model with circular polarization in the CMB and CMB-21cm cross-correlation

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