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f(R) Theories Of Gravity
Modified gravity theories have received increased attention lately due to combined motivation coming from high-energy physics, cosmology, and astrophysics. Among numerous alternatives to Einstein'sExpand
Black holes in Einstein-aether and Hořava-Lifshitz gravity
We study spherical black hole solutions in Einstein-aether theory, a Lorentz-violating gravitational theory consisting of general relativity with a dynamical unit timelike vector (the ``aether'')Expand
Quantum gravity without Lorentz invariance
There has been a significant surge of interest in Hoyrava's model for 3+1 dimensional quantum gravity, this model being based on anisotropic scaling at a z = 3 Lifshitz point. Hoyrava's model, andExpand
f(T) gravity and local Lorentz invariance
We show that in theories of generalized teleparallel gravity, whose Lagrangians are algebraic functions of the usual teleparallel Lagrangian, the action and the field equations are not invariantExpand
String dynamics and ejection along the axis of a spinning black hole
Relativistic current carrying strings moving axisymmetrically on the background of a Kerr black hole are studied. The boundaries and possible types of motion of a string with a given energy andExpand
Strong coupling in extended Hořava–Lifshitz gravity
Abstract An extension of Hořava–Lifshitz gravity was recently proposed in order to address the pathological behavior of the scalar mode all previous versions of the theory exhibit. We show that evenExpand
Black hole hair in generalized scalar-tensor gravity: An explicit example
In a recent paper we showed that in shift-symmetric Horndeski theory the scalar field is forced to obtain a nontrivial configuration in black hole spacetimes, unless a linear coupling with theExpand
Overspinning a black hole with a test body.
It has long been known that a maximally spinning black hole cannot be overspun by tossing in a test body. Here we show that if instead the black hole starts out with below maximal spin, then indeedExpand
Black holes in scalar-tensor gravity.
Hawking has proven that black holes which are stationary as the end point of gravitational collapse in Brans-Dicke theory (without a potential) are no different than in general relativity. We extendExpand
Metric-affine f(R) theories of gravity
Abstract General Relativity assumes that spacetime is fully described by the metric alone. An alternative is the so called Palatini formalism where the metric and the connections are taken asExpand