Fossilized Gravitational Wave Relic and Primordial Clocks

Abstract

If long wavelength primordial tensor modes are coupled to short wavelength scalar modes, the scalar curvature two-point function will have an off-diagonal component. This `fossil' remnant is a signature of a mode coupling that cannot be achieved in single clock inflation. Any constraint on its presence allows a cross check of the relationship between the dynamical generation of the fluctuations and the evolution of the inflationary background. We use the example of non-Bunch Davies initial states for the tensor and scalar modes to demonstrate that physically reasonable fossils, consistent with current data, can be observable in the near future. We illustrate how the fossil off-diagonal power spectrum is a complementary probe to the squeezed limit bispectra of the scalar and tensor sectors individually. We also quantify the relation between the observable signal and the squeezed limit bispectrum for a general scalar-scalar-fossil coupling, and note the effect of superhorizon tensor modes on the anisotropy in scalar modes.

11 pages, 2 figures, v2: minor corrections, matches version published in PRD

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• Non-Gaussianity from Axion-Gauge Fields Interactions during Inflation
• Non-Gaussianity Consistency Relations, Initial States and Back-reaction
• Multimessenger Cosmology: correlating CMB and SGWB measurements
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• Testing the Early Universe with Anisotropies of the Gravitational Wave Background
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• Photon-graviton scattering: A new way to detect anisotropic gravitational waves?
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• Primordial tensor non-Gaussianities from general single-field inflation with non-Bunch-Davies initial states
• Small-scale Tests of Inflation
• Possible Signatures of Inflationary Particle Content: Spin-2 Fields
• Role of trans-Planckian modes in cosmology
• Primordial Stochastic Gravitational Wave Background Anisotropies: in-in Formalization and Applications
• Why does the effective field theory of inflation work?
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