# DGP model

The **DGP model** is a model of gravity proposed by Gia Dvali, Gregory Gabadadze, and Massimo Porrati in 2000.^{[1]} The model is popular among some model builders, but has resisted being embedded into string theory.

## OverviewEdit

The DGP 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^{[2]} 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 acoustic oscillations by the Sloan Digital Sky Survey, and measurements of the cosmic microwave background and type 1a supernovae) is in direct conflict with the DGP cosmology^{[3]} unless a cosmological constant or some other form of dark energy is added.^{[4]} However, this negates the appeal of the DGP cosmology, which accelerates without needing to add dark energy.

## See alsoEdit

## ReferencesEdit

**^**Gia Dvali; Gregory Gabadadze; Massimo Porrati (2000). "4D gravity on a brane in 5D Minkowski space".*Physics Letters*.**B485**(1–3): 208–214. arXiv:hep-th/0005016. Bibcode:2000PhLB..485..208D. doi:10.1016/S0370-2693(00)00669-9.**^**Gorbunov, Dimitry; Koyama, Kazuya; Sibiryakov, Sergei (2006). "More on ghosts in the Dvali-Gabadaze-Porrati model".*Physical Review*.**D73**(4): 044016. arXiv:hep-th/0512097. Bibcode:2006PhRvD..73d4016G. doi:10.1103/PhysRevD.73.044016.**^**Wenjuan Fang; Sheng Wang; Wayne Hu; Zoltán Haiman; Lam Hui; Morgan May (2008). "Challenges to the DGP model from horizon-scale growth and geometry".*Physical Review*.**D78**(10): 103509. arXiv:0808.2208. Bibcode:2008PhRvD..78j3509F. doi:10.1103/PhysRevD.78.103509.**^**Lucas Lombriser; Wayne Hu; Wenjuan Fang; Uroš Seljak (2009). "Cosmological constraints on DGP braneworld gravity with brane tension".*Physical Review*.**D80**(6): 063536. arXiv:0905.1112. Bibcode:2009PhRvD..80f3536L. doi:10.1103/PhysRevD.80.063536.

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