Differentiating between modified gravity and dark energy
Abstract
The nature of the fuel that drives today’s cosmic acceleration is an open and tantalizing mystery. We entertain the suggestion that the acceleration is not the manifestation of yet another new ingredient in the cosmic gas tank, but rather a signal of our first real lack of understanding of gravitational physics. By requiring that the underlying gravity theory respect Birkhoff’s law, we derive the modified gravitational force law necessary to generate any given cosmology, without reference to the fundamental theory, revealing modifications of gravity at scales typically much smaller than today’s horizon. We discuss how, through these modifications, the growth of density perturbations, the latetime integrated SachsWolfe effect, and even solarsystem measurements may be sensitive to whether today’s cosmic acceleration is generated by dark energy or modified gravitational dynamics, and are subject to imminent observational discrimination. We argue how these conclusions can be more generic, and probably not dependent on the validity of Birkhoff’s law.
 Publication:

Physical Review D
 Pub Date:
 February 2004
 DOI:
 10.1103/PhysRevD.69.044005
 arXiv:
 arXiv:astroph/0307034
 Bibcode:
 2004PhRvD..69d4005L
 Keywords:

 04.50.+h;
 98.80.Jk;
 Gravity in more than four dimensions KaluzaKlein theory unified field theories;
 alternative theories of gravity;
 Mathematical and relativistic aspects of cosmology;
 Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Phenomenology;
 High Energy Physics  Theory
 EPrint:
 19 pages revtex. 2 figure. MAJOR ADDITION: New section on latetime ISW effect, including discriminating modified gravity from dark energy using SDSSWMAP cross correlation