On the Spectrum of Modified Theories of Gravity

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Sharif Digital Repository / Sharif University of Technology - On the Spectrum of Modified Theories of Gravity, Seraj, Ali

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بررسی طیف نظریه های گرانش تعمیم یافته

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Type of Document: M.Sc. Thesis
Language: Farsi
Document No: 42114 (04)
University: Sharif University of Technology
Department: Physics
Advisor(s): Golshani, Mehdi; Sheikh Jabbari, Mohammad Mehdi
Abstract:
There are different approaches in modifications of General Relativity as the theory of gravity. The modified theories of gravity are important cases in this context, which mostly start by modifying the Einstein-Hilbert action, while keeping the general covariance. Within the modified theories of gravity, we consider two cases. The first is the f(R) theories of gravity, and the second is curvature squared theories of gravity with an action like S = ∫d4x pg( 116GR + (R)2 + R2 +(R)2). Curvature squared theories of gravity have interesting feautures, most important of which is renormalizability, in contrast with General Relativity. But this advantage, as noted by K.S. Stelle in 1977 comes at the price of introducing ghosts, degrees of freedom with negative norm and energy. In this thesis, we study the degrees of freedom, as well as the maximally symmetric solutions of these modified theories of gravity, and investigate the effect of background space-time on the dynamics of degrees of freedom. Also we will review the proposals for solving the ghost problem and show that no complete one is still presented
Keywords:
Generalized Gravity ; Ghost Inflation ; Freedom Dynamical Degrees ; Maximally Symmetric Solutions