Abstract
We revisit gauge invariant cosmological perturbations in UV-modified, z = 3 Hořava gravity with one scalar matter field, which has been proposed as a renormalizable gravity theory without the ghost problem in four dimensions. We confirm that there is no extra graviton modes and general relativity is recovered in IR, which achieves the consistency of the model. From the UV-modification terms which break the detailed balance condition in UV, we obtain scale-invariant power spectrums for non-inflationary backgrounds, like the power-law expansions, without knowing the details of early expansion history of Universe. This could provide a new framework for the Big Bang cosmology.
Highlights
We revisit gauge invariant cosmological perturbations in UV-modified, z = 3 Horava gravity with one scalar matter field, which has been proposed as a renormalizable gravity theory without the ghost problem in four dimensions
The small fluctuations in CMB are thought to be due to fluctuations in the early epoch of our (Big Bang) Universe, which should be described by General Relativity (GR)
GR alone can not have scalar mode but only the tensor mode (2 polarizations, called gravitational waves) ! The cosmological/primordial tensor modes have not been discovered yet, though astrophysical tensor modes from black hole mergers have been detected in LIGO
Summary
I will consider another modified gravity theory but without the scalar gravitation mode so that the usual scalar matters are needed in explaining the cosmology data. This theory may provide inflationary effect without “inflationary phase (i.e., early de Sitter or accelerating phase)" so that scale-invariant (scalar/tensor) spectrum can be produced.
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