Jordan and Einstein frames
The Lagrangian in scalar-tensor theory can be expressed in the Jordan frame in which the scalar field or some function of it multiplies the Ricci scalar, or in the Einstein frame in which Ricci scalar is not multiplied by the scalar field. There exist various transformations between these frames. Despite the fact that these frames have been around for some time there is currently heated debate about whether either, both, or neither frame is a 'physical' frame which can be compared to observations and experiment.
Models
Jordan frame gravity can be used to calculate type IV singular bouncing cosmological evolution, to derive the type IV singularity.[1]
Equations
If we perform the Weyl rescaling 
, then the Riemann and Ricci tensors are modified.
![\tilde{R}=\Phi^{2/(d-2)}\left[ R + \frac{2d}{d-2}\frac{\Box \Phi}{\Phi} -\frac{3(d-1)}{(d-2)}\left(\frac{\nabla\Phi}{\Phi}\right)^2 \right]](../I/m/4d6f91dc54b18db35747acd20ebf0f1f.png)
![S = \int d^dx \sqrt{-\tilde{g}} \Phi \tilde{R} =\int d^dx \sqrt{-g} \left[ R - \frac{3(d-1)}{(d-2)}\left( \nabla\left(\ln \Phi \right) \right)^2\right]](../I/m/a4a8797b8fd8d6f998e803744be8cc45.png)
See also
References
- ↑ S.D. Odintsov, V.K. Oikonomou (27 June 2015). "Bouncing cosmology with future singularity from modified gravity". Arxiv. doi:10.1103/PhysRevD.92.024016.
- Valerio Faraoni, Edgard Gunzig, Pasquale Nardone, Conformal transformations in classical gravitational theories and in cosmology, Fundam. Cosm. Phys. 20(1999):121, arXiv:gr-qc/9811047.
- Eanna E. Flanagan, The conformal frame freedom in theories of gravitation, Class. Q. Grav. 21(2004):3817, arXiv:gr-qc/0403063.
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