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Showing 1 to 14 of 14 for “"f(R)-gravity"”.
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Covariant perturbations in f (R) - gravity of multi-component fluid cosmologies
… formalism for generic f(R) theories of gravity. Working in the energy frame of the total matter, we give a complete set equations describing the evolution of matter and curvature fluctuations for a multi-fluid cosmological medium. We then specialize to a radiation-dust fluid described by …
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Investigating the parameter space of viable models for f(R) gravity
… the growth of the research field of modified gravity theories. Of these, f(R) theories of gravity is the first and simplest modification to General Relativity, and have been studied extensively for their astrophysical and cosmological predictions. Power law f(R) modifications have been shown …
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1+1+2 covariant approach to gravitational lensing in f(R) gravity
… spacetimes in for fourth order theories of gravity. Using this formalism, we derive equations for a static and spherically symmetric spacetime for general f(R) gravity. We apply these master eqautions to derive some exact solutions, which are used to gain insight on Birkhoff's theorem in …
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Cosmological dynamics of exponential gravity
… issues in modern cosmology, with a focus on f(R) gravity. In chapter 1 we present a review of modern theoretical cosmology. We begin by introducing some fundamental cosmological concepts, followed by a discussion of the field equations of general relativity, which underlie both the behavior of …
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A study of solutions and perturbations of spherically symmetric spacetimes in fourth order gravity.
… of rotationally symmetric spacetimes in f(R) gravity, one of the most widely studied classes of fourth order gravity. We begin by introducing f(R) theories of gravity and present the general equations for these theories. We investigate the problem of matching different regions of spacetime, …
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Gravitational lensing
… the gravitational lensing analysis in f(R) gravity theories.
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Classical, quantum and numerical aspects of modified theories of gravity
… some specific aspects of two classes of modified gravity theories: ghostfree infinite-derivative gravity and so-called f(R) gravity. Regarding the former, we consider the four-dimensional theory at the level of the quadratic action and study the single graviton exchange of two massive spin-0 …
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Galaxy-Scale Signatures of Screened Modified Gravities
In recent years, theories of gravity incorporating a scalar field coupled to gravity---'scalar-tensor' theories---have been subject to increased attention. In these theories, the scalar field mediates gravitational-strength 'fifth forces'. For such scalar fields to retain cosmological relevance …
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Perturbations and symmetry in gravitational theories : wormholes, wave dynamics, and quantum effects in rotating spacetimes.
… perturbation theory, applying it to linearized gravity and horizonless rotating space-times. The central thesis is that gauge invariance and geometric symmetry provide a unifying language for identifying physical degrees of freedom, distinguishing observables from coordinate artifacts, and …
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Exploring gravity
… that could be observed assuming metric f(R)-gravity as an effective alternative theory. Gravitational radiation is modified, as are planetary precession rates. Both give a means of testing GR. However, existing laboratory measurements already place tighter constraints on f(R)-gravity, unless …
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Stability and gravitational collapse in extended theories of gravity: from singularities to bouncing scenarios
… proposed in [85] for the quadratic model in f(R) gravity, for spherically symmetric and static neutron stars, using two different viable equations of state. We also check the accuracy of our code through a forward-backward integration technique, to show that in both directions, we obtain the same …
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Topics in Theoretical Gravity
… Chapter 5 explores a modified theory of gravity called F(R) gravity which was proposed to solve the dark energy problem. We consider forms of F(R) that are intended to mimic standard General Relativity at high densities, but have low-density behavior that can explain the observed …
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Neutron Star Models in Alternative Theories of Gravity
… in a broad class of alternative theories of gravity. In particular, we focus on Scalar-Tensor theories and <italic>f(R)<italic> theories of gravity. We construct static and slowly rotating numerical star models for a set of equations of state, including a polytropic model and more realistic …