Faraday Rotation of the Cosmic Microwave Background Polarization and Primordial Magnetic Field Properties

Campanelli, Leonardo; Dolgov, A. D.; Giannotti, Maurizio; Villante, F. L.

doi:10.1086/424840

Cited by 92 publications

(89 citation statements)

References 17 publications

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“…For example, Faraday rotation only provides an estimate of the line of sight component of the magnetic field. Even by observing the Faraday rotation from different sources, the information is insufficient to estimate the helicity [16,17,18]. An estimate of the helicity necessarily requires sensitivity to all components of the magnetic field and hence it is a challenging theoretical problem to devise means by which it may be measured.…”

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confidence: 99%

Detection of magnetic helicity

Kahniashvili

Vachaspati

2006

Phys. Rev. D

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Magnetic fields in various astrophysical settings may be helical and, in the cosmological context, may provide a measure of primordial CP violation during baryogenesis. Yet it is difficult, even in principle, to devise a scheme by which magnetic helicity may be detected, except in some very special systems. We propose that charged cosmic rays originating from known sources may be useful for this purpose. We show that the correlator of the arrival momenta of the cosmic rays is sensitive to the helicity of an intervening magnetic field. If the sources themselves are not known, the method may still be useful provided we have some knowledge of their spatial distribution.PACS numbers: 98.80. Cq, 98.62.En Magnetic fields pervade all astrophysical objects [1,2] and there are good theoretical reasons to believe that a weak magnetic field is present throughout the universe. In astrophysical systems the magnetic field is often helical which means that the field lines are twisted (like corkscrews), or that closed magnetic lines are linked. Mathematically, the average helicity density in a volume V is defined as:In cosmology, a number of scenarios predict the creation of a primordial field with non-zero helicity. In the scenario discussed in Refs. [3,4,5,6], a magnetic field is produced at the electroweak phase transition. The helicity of the magnetic field is related to the cosmological baryon asymmetry arising from CP violation in the fundamental particle physics theory, and the sign of the helicity is predicted to be left-handed [6]. There are also several other scenarios for the generation of primordial helical magnetic fields that do not depend on the dynamics through a phase transition [7,8,9,10,11,12,13]. The helicity of magnetic fields in astrophysical jets can be deduced from the polarization of synchrotron radiation [14,15]. In such situations, the velocity of electrons in the jets is known and this additional information is crucial to the determination of helicity. In other situations, it is much harder to find the helicity. For example, Faraday rotation only provides an estimate of the line of sight component of the magnetic field. Even by observing the Faraday rotation from different sources, the information is insufficient to estimate the helicity [16,17,18]. An estimate of the helicity necessarily requires sensitivity to all components of the magnetic field and hence it is a challenging theoretical problem to devise means by which it may be measured. In Ref. [19,20,21] the imprint of cosmological magnetic helicity in parity-odd cross correlations of the cosmic microwave background (CMB) fluctuations was investigated, while in Ref. [22] it was shown that helicity would introduce circular polarization of induced relic gravitational waves. Both these potential signatures of helicity are limited to cosmological magnetic fields since they rely on properties of the cosmic microwave background or on the cosmic gravitational wave background. Further, the signals are small for several reasons: the cosmic magnetic f...

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confidence: 99%

Detection of magnetic helicity

Kahniashvili

Vachaspati

2006

Phys. Rev. D

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“…[33]. Limits on a cosmological magnetic field that can be obtained through the formalism we have developed here will compliment those obtained through the CMB polarization Faraday rotation effect [30,34,35,36] and the non-zero cross-correlations between CMB temperature and B-polarization anisotropies [20,37].…”

Section: Discussionmentioning

confidence: 54%

CMB temperature anisotropy from broken spatial isotropy due to a homogeneous cosmological magnetic field

Kahniashvili

Lavrelashvili²,

Ratra

2008

Phys. Rev. D

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“…Such off-diagonal parity-odd cross correlations also occur in the case of an homogeneous magnetic field from the Faraday rotation effect [21], but not in the case of a stochastic magnetic field, even one with non-zero helicity [20]. Faraday rotation measurements cannot be used to detect magnetic helicity [18,19,20]. A possible way of detecting magnetic helicity directly from CMB fluctuation data is to detect the above parity-odd CMB correlations or to detect the effects magnetic helicity has on parity-even CMB fluctuations.…”

Section: Parity-odd Cmb Fluctuations From Magnetic Helicitymentioning

confidence: 99%

“…We propose a scheme to constrain cosmological magnetic helicity from CMB temperature and polarization anisotropy observations. The symmetric part of the magnetic field spectrum can be reconstructed from measurements of the rotation of the CMB polarization plane as a consequence of the Faraday effect [17]; this is because magnetic helicity does not contribute to the Faraday rotation effect [18,19,20]. On the other hand, the helical part of the magnetic field spectrum induces parity-odd cross correlations between temperature and B-polarization anisotropies, and between E-and B-polarization anisotropies [10,14]; such cross correlations are not induced by the Faraday effect [20].…”

Section: Introductionmentioning

confidence: 99%

“…16 However, it has to be emphasized that a B-polarization anisotropy signal can also arise in other ways, such as from primordial tensor perturbations [25], gravitational lensing [29], or Faraday rotation of the CMB anisotropy polarization plane [17,19,20]. The B-polarization anisotropy power spectrum l 2 C BB l peak position may help identify the B-polarization source.…”

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confidence: 99%

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Effects of cosmological magnetic helicity on the cosmic microwave background

2005

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Cosmological magnetic fields induce temperature and polarization fluctuations in the cosmic microwave background (CMB) radiation. A cosmological magnetic field with current amplitude of order 10 −9 G is detectable via observations of CMB anisotropies. This magnetic field (with or without helicity) generates vector perturbations through vortical motions of the primordial plasma. This paper shows that magnetic field helicity induces parity-odd cross correlations between CMB temperature and B-polarization fluctuations and between E-and B-polarization fluctuations, correlations which are zero for fields with no helicity (or for any parity-invariant source). Helical fields also contribute to parity-even temperature and polarization anisotropies, cancelling part of the contribution from the symmetric component of the magnetic field. We give analytic approximations for all CMB temperature and polarization anisotropy vector power spectra due to helical magnetic fields. These power spectra offer a method for detecting cosmological helical magnetic fields, particularly when combined with Faraday rotation measurements which are insensitive to helicity.PACS numbers: 98.70. Vc,

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Faraday Rotation of the Cosmic Microwave Background Polarization and Primordial Magnetic Field Properties

Cited by 92 publications

References 17 publications

Detection of magnetic helicity

Detection of magnetic helicity

CMB temperature anisotropy from broken spatial isotropy due to a homogeneous cosmological magnetic field

Effects of cosmological magnetic helicity on the cosmic microwave background

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