The DGP model
is a model of gravity
proposed by Gia Dvali
, Gregory Gabadadze
, and Massimo Porrati
in 2000. The model is popular among some model builders
, but has resisted embedding into string theory
The model assumes the existence of a 4+1 dimensional Minkowski space
, within which ordinary 3+1 dimensional Minkowski space is embedded. The model assumes an action
consisting of two terms: One term is the usual Einstein-Hilbert action
, which involves only the 4-D spacetime
dimensions. The other term is the equivalent of the Einstein-Hilbert action, as extended to all 5 dimensions. The 4-D term dominates at short distances, and the 5-D term dominates at long distances.
The model was proposed in part in order to reproduce the cosmic acceleration
of dark energy
without any need for a small but non-zero vacuum energy
density. But critics argue that this branch of the theory is unstable. However, the theory remains interesting because of Dvali's claim that the unusual structure of the graviton propagator
makes non-perturbative effects important in a seemingly linear regime, such as the solar system. Because there is no four-dimensional, linearized effective theory
that reproduces the DGP model for weak-field gravity the theory avoids the vDVZ discontinuity
that otherwise plagues attempts to write down a theory of massive gravity.
In 2008, Fang et al.
argued that recent cosmological observations (including measurements of baryon......