Journal
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
Volume -, Issue 11, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1475-7516/2015/11/043
Keywords
power spectrum; gravity; primordial gravitational waves (theory); cosmological perturbation theory
Funding
- John Templeton Foundation
- D-ITP consortium, a program of the Netherlands organization for scientific research (NWO)
- Dutch Ministry of Education, Culture and Science (OCW)
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Fermi Normal Coordinates (FNC) are a useful frame for isolating the locally observable, physical effects of a long-wavelength spacetime perturbation. Their cosmological application, however, is hampered by the fact that they are only valid on scales much smaller than the horizon. We introduce a generalization that we call Conformal Fermi Coordinates (CFC). CFC preserve all the advantages of FNC, but in addition are valid outside the horizon. They allow us to calculate the coupling of long- and short-wavelength modes on all scales larger than the sound horizon of the cosmological fluid, starting from the epoch of inflation until today, by removing the complications of the second order Einstein equations to a large extent, and eliminating all gauge ambiguities. As an application, we present a calculation of the effect of long-wavelength tensor modes on small scale density fluctuations. We recover previous results, but clarify the physical content of the individual contributions in terms of locally measurable effects and projection terms.
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