Matter Loops Corrected Modified Gravity in Palatini Formulation |
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Authors: | MENG Xin-He WANG Peng |
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Institution: | 1. Department of Physics, Nankai University, Tianjin 300071, China
;2. Department of Physics and SLAC, Stanford University, California, USA
;3. BK21 Division of Advanced Research and Education in
Physics, Department of Physics, Hanyang University, Seoul 133 791, Korea |
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Abstract: | Recently, corrections to the standard Einstein-Hilbert action were
proposed to explain the current cosmic acceleration in stead of introducing dark energy. In the Palatini formulation of those modified gravity models, there is an important observation due to Arkani-Hamed: matter loops will give rise to a correction to the modified gravity action proportional to the Ricci scalar of the
metric. In the presence of such a term, we show that the current forms of modified gravity models in Palatini formulation, specifically, the 1/R gravity and ln R gravity, will have
phantoms. Then we study the possible instabilities due to the presence of phantom fields. We show that the strong instability in the metric formulation of 1/R gravity indicated by Dolgov and
Kawasaki will not appear and the decay timescales for the phantom fields may be long enough for the theories to make sense as effective field theory . On the other hand, if we change the sign
of the modification terms to eliminate the phantoms, some other
inconsistencies will arise for the various versions of the modified gravity models. Finally, we comment on the universal property of the Palatini formulation of the matter loops corrected modified gravity models and its implications. |
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Keywords: | modified gravity accelerated cosmic expansion loop correction and dark energy |
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