Star tracks in the ghost condensate

Abstract

We consider the infrared modification of gravity by the ghost condensate. Naively, in thisscenario one expects sizable modification of gravity at distances of order 1000 km, providedthat the characteristic timescale of the theory is of the order of the Hubble time. However,we argue that this is not the case. The main physical reason for the masking is the simplefact that the Earth (and any other object in the Universe) has a velocity at least of order10−3c with respect to the rest frame of the ghost condensate. Taken together with strongretardation effects present in the ghost sector, this implies that no observable modificationof the gravitational field of nearby objects occurs. Instead, the physical manifestation ofthe ghost condensate is the presence of ‘star tracks’—narrow regions of spacewith growing gravitational and ghost fields inside—along the trajectory of anymassive object. We briefly discuss the possibilities for observing these tracks.