The Impact of Primordial Magnetic Fields on Future CMB Bounds on Inflationary Gravitational Waves

Abstract

We discuss whether an unaccounted contribution to the Cosmic Microwave Background polarization $B$-mode by primordial magnetic fields (PMFs) can bias future constraints on inflationary gravitational waves. As a case-study, we consider a scale-invariant PMF spectrum with amplitude of $\approx 1\mathrm{nG}$ on $1\mathrm{Mpc}$ scales, compatible with current cosmological bounds. We find a degeneracy in the $B$-mode spectra between PMFs and inflationary gravitational waves. If PMFs of this amplitude are not accounted for, future CMB experiments could claim a false detection of a tensor-to-scalar ratio $r\approx 0.007$, close to the predictions of Starobinsky and $\alpha$-attractor models. The degeneracy can be broken if $B$-modes are measured also at multipoles $\ell \gtrsim 900$: more precisely experiments like CMB-S4 or CORE-M5 would be able to discriminate PMFs from primordial GWs at high statistical significance. Experiments like LiteBIRD or PIXIE will not be able to break the degeneracy and will need complementary bounds coming, for example, from measurements of anisotropies in the Faraday rotation angle of CMB polarization. This reinforces the importance of future experimental constraints on PMFs.

arXiv comment16 pages, 8 figures, matches JCAP version

References in corpus (64)

• Planck 2015 results. XIII. Cosmological parameters
• Efficient Computation of CMB anisotropies in closed FRW models
• Cosmological parameters from CMB and other data: a Monte-Carlo approach
• Magnetic Fields in the Early Universe
• Cosmological Magnetic Fields: Their Generation, Evolution and Observation
• Superconformal Inflationary $\alpha$-Attractors
• Cosmological Signature of New Parity-Violating Interactions
• The Primordial Inflation Explorer (PIXIE): A Nulling Polarimeter for Cosmic Microwave Background Observations
• BICEP2 / Keck Array VI: Improved Constraints On Cosmology and Foregrounds When Adding 95 GHz Data From Keck Array
• The origin, evolution and signatures of primordial magnetic fields
• Planck intermediate results. XLVI. Reduction of large-scale systematic effects in HFI polarization maps and estimation of the reionization optical depth
• Advanced ACTPol Cryogenic Detector Arrays and Readout
• SPT-3G: A Next-Generation Cosmic Microwave Background Polarization Experiment on the South Pole Telescope
• Probing cosmological parameters with the CMB: Forecasts from full Monte Carlo simulations
• Towards a cosmological neutrino mass detection
• A review of Axion Inflation in the era of Planck
• Microwave Background Signatures of a Primordial Stochastic Magnetic Field
• Microwave Background Signals from Tangled Magnetic Fields
• Measurement of Cosmic Microwave Background Polarization Power Spectra from Two Years of BICEP Data
• CMB anisotropies from primordial inhomogeneous magnetic fields
• Gravitational wave production: A strong constraint on primordial magnetic fields
• Delensing CMB Polarization with External Datasets
• Scale-dependent gravitational waves from a rolling axion
• CLASS: The Cosmology Large Angular Scale Surveyor
• Faraday Rotation of the Cosmic Microwave Background Polarization by a Stochastic Magnetic Field
• CMB mapping experiments: a designer's guide
• Massive Neutrinos and Magnetic Fields in the Early Universe
• Testing Parity-Violating Mechanisms with Cosmic Microwave Background Experiments
• Robust forecasts on fundamental physics from the foreground-obscured, gravitationally-lensed CMB polarization
• Probing polarization states of primordial gravitational waves with CMB anisotropies
• Finding the chiral gravitational wave background of an axion-SU(2) inflationary model using CMB observations and laser interferometers
• Schwinger Effect in 4D de Sitter Space and Constraints on Magnetogenesis in the Early Universe
• Delensing the CMB with the Cosmic Infrared Background
• Large Tensor Non-Gaussianity from Axion-Gauge Fields Dynamics
• POLARBEAR Constraints on Cosmic Birefringence and Primordial Magnetic Fields
• The full contribution of a stochastic background of magnetic fields to CMB anisotropies
• De-Rotation of the Cosmic Microwave Background Polarization: Full-Sky Formalism
• CMB Constraints on a Stochastic Background of Primordial Magnetic Fields
• The Impact of Stochastic Primordial Magnetic Fields on the Scalar Contribution to Cosmic Microwave Background Anisotropies
• Primordial Magnetic Fields from the Post-Inflationary Universe
• Tensor Non-Gaussianity from Axion-Gauge-Fields Dynamics : Parameter Search
• Constraining a spatially dependent rotation of the Cosmic Microwave Background Polarization
• Updated Constraints and Forecasts on Primordial Tensor Modes
• Constraints on Primordial Magnetic Fields from Planck combined with the South Pole Telescope CMB B-mode polarization measurements
• Cross-Correlation of Cosmological Birefringence with CMB Temperature
• BICEP2 / Keck Array IX: New Bounds on Anisotropies of CMB Polarization Rotation and Implications for Axion-Like Particles and Primordial Magnetic Fields
• Did BICEP2 see vector modes? First B-mode constraints on cosmic defects
• Can topological defects mimic the BICEP2 B-mode signal?
• Can primordial magnetic fields be the origin of the BICEP2 data?
• BICEP3 performance overview and planned Keck Array upgrade
• Primordial Magnetic Field Limits from CMB Trispectrum - Scalar Modes and Planck Constraints
• Magnetized initial conditions for CMB anisotropies
• Primordial Magnetism in the CMB: Exact Treatment of Faraday Rotation and WMAP7 Bounds
• Constraints on a Stochastic Background of Primordial Magnetic Fields with WMAP and South Pole Telescope data
• Testing chirality of primordial gravitational waves with Planck and future CMB data: no hope from angular power spectra
• Magnetic fields from inflation: The CMB temperature anisotropies
• CMB Faraday rotation as seen through the Milky Way
• Constraints on Primordial Magnetic Fields from Inflation
• Current and Future Constraints on Primordial Magnetic Fields
• Searching for Primordial Magnetic Fields with CMB B-modes
• Probing large-scale magnetism with the Cosmic Microwave Background
• Generation of Curvature Perturbations with Extra Anisotropic Stress
• Magnification bias as a novel probe for primordial magnetic fields
• Reduced bispectrum seeded by helical primordial magnetic fields

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• Recent Advances on Inflation
• Searching for Anisotropic Cosmic Birefringence with Polarization Data from SPTpol
• A fake Interacting Dark Energy detection?
• Constraints on primordial magnetic fields from magnetically-induced perturbations: current status and future perspectives with LiteBIRD and future ground based experiments
• Improved CMB anisotropy constraints on primordial magnetic fields from the post-recombination ionization history
• Current and Future constraints on single-field $\alpha$-Attractor model
• Optimistic estimation on probing primordial gravitational waves with CMB B-mode polarization
• Distinguishing Primordial Magnetic Fields from Inflationary Tensor Perturbations in the Cosmic Microwave Background