Özen, Gökçen Deniz
General Relativity is succesful in understanding the phenomena such as light bending by the Sun and the perihelion precession of Mercury that could not be understood in Newton’s gravity. Within solar system scales, General Relativity is a very powerful theory but for very small or very large distances, the theory has non-renormalization issues and lack of explanation of the accelerated expansion of the universe and the galaxy rotation curves which give a hint at the need for modifications. In this thesis, Born-Infeld type modifications of General Relativity are considered. In 1998 Deser and Gibbons proposed Born-Infeld gravity theory that has some common features with the Eddington’s gravitational action and the Born-Infeld electrodynamics. The Born-Infeld gravity theory, like the other two, has a determinantal action but the free variable of the theory is the metric not the connection as in the Eddington’s gravity theory. In this thesis we have calculated the Wald entropy of the Born-Infeld gravity theories and showed that this dynamical entropy reduces to the geometric Bekenstein- Hawking entropy with the appropriate choice of effective gravitational constant. We also discuss black hole entropy in generic dimensions for the Born-Infeld theories.


Conserved charges in various theories of gravity
Özşahin, Hikmet; Tekin, Bayram; Department of Physics (2022-9)
The first law of black hole thermodynamics in the presence of a cosmological constant $\Lambda$ can be generalized by introducing a term containing the variation $\delta\Lambda$. Similar to other terms in the first law, which are variations of some conserved charges like mass, entropy, angular momentum, electric charge etc and it has been shown in \cite{1} that the new term has the same structure: $\Lambda$ is a conserved charge associated with a gauge symmetry. In this work, first we propose and prove the...
Energy in Reboucas-Tiomno-Korotkii-Obukhov and Godel-type space-times in Bergmann-Thomson's formulations
Aydogdu, O; Salti, M; Korunur, M (2005-12-01)
We calculate the total energy (the matter plus fields) of the universe considering Bergmann-Thomson's energy-momentum formulation in both Einstein's theory of general relativity and tele-parallel gravity on two different space-times; namely Reboucas-Tiomno-Korotkii-Obukhov and the Godel-type metrics. We also compute some kinematical quantities for these space-times and find that these space-times have shear-free expansion and non-vanishing four-acceleration and vorticity. Different approximations of the Ber...
Massive higher derivative gravity theories
Güllü, İbrahim; Tekin, Bayram; Department of Physics (2011)
In this thesis massive higher derivative gravity theories are analyzed in some detail. One-particle scattering amplitude between two covariantly conserved sources mediated by a graviton exchange is found at tree-level in D dimensional (Anti)-de Sitter and flat spacetimes for the most general quadratic curvature theory augmented with the Pauli-Fierz mass term. From the amplitude expression, the Newtonian potential energies are calculated for various cases. Also, from this amplitude and the propagator structu...
Spin-spin interactions in massive gravity and higher derivative gravity theories
Gullu, Ibrahim; Tekin, Bayram (Elsevier BV, 2014-01-20)
We show that, in the weak field limit, at large separations, in sharp contrast to General Relativity (GR), all massive gravity theories predict distance-dependent spin alignments for spinning objects. For all separations GR requires anti-parallel spin orientations with spins pointing along the line joining the sources. Hence total spin is minimized in GR. On the other hand; while massive gravity at small separations (m(g)r <= 1.62) gives the same result as GR, for large separations (m(g)r > 1.62) the spins ...
Neutrino oscillations induced by spacetime torsion
Adak, M; Dereli, T; Ryder, LH (IOP Publishing, 2001-04-21)
The gravitational neutrino oscillation problem is studied by considering the Dirac Hamiltonian in a Riemann-Cartan spacetime and calculating the dynamical phase. Torsion contributions which depend on the spin direction of the mass eigenstates are found. These effects are of the order of Planck scales.
Citation Formats
G. D. Özen, “GRAVITY THEORIES AT LARGE NUMBER OF DIMENSIONS,” Ph.D. - Doctoral Program, Middle East Technical University, 2021.