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Equation of state for dark energy in gravity
Kazuharu Bamba, Chao-Qiang Geng, Chung-Chi Lee +1
We study the cosmological evolutions of the equation of state for dark energy in the exponential and logarithmic as well as their combination theories. We…
Comment on "Einstein's Other Gravity and the Acceleration of the Universe''
Kazuharu Bamba, Chao-Qiang Geng, Chung-Chi Lee
We show that in the exponential model studied by E. Linder [arXiv:1005.3039, Phys.Rev.D 81, 127301 (2010)], it is impossible to have the crossing of the phantom divide line…
Cosmological birefringence due to CPT-even Chern-Simons-like term with Kalb-Ramond and scalar fields
Shih-Hao Ho, W. F. Kao, Kazuharu Bamba +1
We study the CPT-even dimension-six Chern-Simons-like term by including dynamical Kalb-Ramond and scalar fields to examine the cosmological birefringence. We show that the combined…
Generic feature of future crossing of phantom divide in viable gravity models
Kazuharu Bamba, Chao-Qiang Geng, Chung-Chi Lee
We study the equation of state for dark energy and explicitly demonstrate that the future crossings of the phantom divide line are the generic feature in the e…
Thermodynamics in gravity in the Palatini formalism
Kazuharu Bamba, Chao-Qiang Geng
We investigate thermodynamics of the apparent horizon in gravity in the Palatini formalism with non-equilibrium and equilibrium descriptions. We demonstrate that it is more…
Cosmological evolution in exponential gravity
Kazuharu Bamba, Chao-Qiang Geng, Chung-Chi Lee
We explore the cosmological evolution in the exponential gravity (). We summarize various viability conditions and expli…