Ghost Condensation and a Consistent Infrared Modification of Gravity

TL;DR

This paper introduces a consistent infrared modification of gravity via ghost condensation, which can drive cosmic acceleration and modify gravitational interactions, offering new approaches to cosmological issues like dark energy.

Contribution

It proposes a novel gravity modification mechanism using ghost condensate, with a systematic effective field theory and distinctive low-energy excitations, expanding theoretical options for cosmology.

Findings

Ghost condensate can drive de Sitter expansion.

Modified Newtonian potential with oscillatory behavior.

Presence of a scalar excitation with k^4/M^2 dispersion relation.

Abstract

We propose a theoretically consistent modification of gravity in the infrared, which is compatible with all current experimental observations. This is an analog of Higgs mechanism in general relativity, and can be thought of as arising from ghost condensation--a background where a scalar field \phi has a constant velocity, <\dot\phi> = M^2. The ghost condensate is a new kind of fluid that can fill the universe, which has the same equation of state, \rho = -p, as a cosmological constant, and can hence drive de Sitter expansion of the universe. However, unlike a cosmological constant, it is a physical fluid with a physical scalar excitation, which can be described by a systematic effective field theory at low energies. The excitation has an unusual low-energy dispersion relation \omega^2 \sim k^4 / M^2. If coupled to matter directly, it gives rise to small Lorentz-violating effects and a new long-range 1/r^2 spin dependent force. In the ghost condensate, the energy that gravitates is not the same as the particle physics energy, leading to the possibility of both sources that can gravitate and antigravitate. The Newtonian potential is modified with an oscillatory behavior starting at the distance scale M_{Pl}/M^2 and the time scale M_{Pl}^2/M^3. This theory opens up a number of new avenues for attacking cosmological problems, including inflation, dark matter and dark energy.