Measuring the speed of cosmological gravitational waves

Abstract

In general relativity gravitational waves propagate at the speed of light, however in alternative theories of gravity that might not be the case. We study the effects of a modified speed of gravity, $c_T^2$, on the B-modes of the Cosmic Microwave Background (CMB) anisotropy in polarisation. We find that a departure from the light speed value would leave a characteristic imprint on the BB spectrum part induced by tensors, manifesting as a shift in the angular scale of its peaks. We derive constraints by using the available {\it Planck} and BICEP2 datasets showing how $c_T^2$ can be measured, albeit obtaining weak constraints due to the overall poor accuracy of the current BB power spectrum measurements. The present constraint corresponds to $c_T^2=1.30\pm 0.79$ and $c_T^2<2.85$ at $95$ C.L. by assuming a power law primordial tensor power spectrum and $c_T^2<2.33$ at $95$ C.L. if the running of the spectral index is allowed. We derive forecasts for the next generation CMB satellites, which we find capable of tightly constraining $c_T^2$ at percent level, comparable with bounds from binary pulsar measurements, largely due to the absence of degeneracy with other cosmological parameters.

arXiv comment5 pages, 3 figure. Minor edits to match the version submitted to the journal

References in corpus (36)

• Planck 2013 results. XVI. Cosmological parameters
• Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Parameter Results
• Modified Gravity and Cosmology
• The Confrontation between General Relativity and Experiment
• Cosmological parameters from CMB and other data: a Monte-Carlo approach
• Quantum Gravity at a Lifshitz Point
• The Confrontation between General Relativity and Experiment
• BICEP2 I: Detection Of B-mode Polarization at Degree Angular Scales
• Generalized G-inflation: Inflation with the most general second-order field equations
• An All-Sky Analysis of Polarization in the Microwave Background
• The Effective Field Theory of Inflation
• From k-essence to generalised Galileons
• Planck 2013 results. XV. CMB power spectra and likelihood
• Tests of Lorentz invariance: a 2013 update
• COBE, Gravitational Waves, Inflation and Extended Inflation
• A Measurement of the Cosmic Microwave Background B-Mode Polarization Power Spectrum at Sub-Degree Scales with POLARBEAR
• Phases of massive gravity
• Cosmology with Nonminimal Derivative Couplings
• Anisotropic stress as signature of non-standard propagation of gravitational waves
• PRISM (Polarized Radiation Imaging and Spectroscopy Mission): An Extended White Paper
• Lower Bound on the Propagation Speed of Gravity from Gravitational Cherenkov Radiation
• Inflationary non-Gaussianities in the most general second-order scalar-tensor theories
• Resilience of the standard predictions for primordial tensor modes
• Perturbative instabilities in Horava gravity
• Inflation and primordial non-Gaussianities of "generalized Galileons"
• Effects of modified gravity on B-mode polarization
• Galileon Radiation from Binary Systems
• Measuring Speed of Gravitational Waves by Observations of Photons and Neutrinos from Compact Binary Mergers and Supernovae
• Signatures of a Graviton Mass in the Cosmic Microwave Background
• Gravitational wave signal from massive gravity
• Gravity Gets There First with Dark Matter Emulators
• Testing quantum gravity effects with latest CMB observations
• Pulsar Constraints on Screened Modified Gravity
• Scalar radiation from Chameleon-shielded regions
• A useful guide for gravitational wave observers to test modified gravity models
• Measuring primordial gravitational waves from CMB B-modes in cosmologies with generalized expansion histories

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• Horava Gravity in the Effective Field Theory formalism: from cosmology to observational constraints
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