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Register a new userBlack holes in an Effective Field Theory extension of GR
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Effective field theory methods suggest that some rather-general extensions of General Relativity include, or are mimicked by, certain higher-order curvature corrections, with coupling constants expected to be small but otherwise arbitrary. Thus, the tantalizing prospect to test the fundamental nature of gravity with gravitational-wave observations, in a systematic way, emerges naturally. Here, we build black hole solutions in such a framework and study their main properties. Once rotation is included, we find the first purely gravitational example of geometries without $mathbb{Z}_2$-symmetry. Despite the higher-order operators of the theory, we show that linearized fluctuations of such geometries obey second-order differential equations. We find nonzero tidal Love numbers. We study and compute the quasinormal modes of such geometries. These results are of interest to gravitational-wave science but also potentially relevant for electromagnetic observations of the galactic center or $X$-ray binaries.
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A topological extension of general relativity is presented. The superposition principle of quantum mechanics, as formulated by the Feynman path integral, is taken as a starting point. It is argued that the trajectories that enter this path integral are distinct, despite any quantum uncertainty in geometry, and thus that space-time topology is multiply connected. Specifically, space-time at the Planck scale consists of a lattice of three-tori that facilitates many distinct paths for particles to travel along. To add gravity, mini black holes are attached to this lattice. These mini black holes represent Wheelers quantum foam and result from the fact that GR is not conformally invariant. The stable creation of such mini black holes is found to be caused by the existence of macroscopic (so long-lived) black holes. This connection, by which macroscopic black holes induce mini black holes, is a topological expression of Machs principle. The proposed topological extension of GR can be tested because, if correct, the dark energy density of the universe should be linearly proportional to the total number of macroscopic black holes in the universe at any time. This prediction, although strange, agrees with current astrophysical observations.
Effective theory of fluctuations based on underlying symmetry plays very important role in understanding the low energy phenomena. Using this powerful technique we study the fluctuation dynamics keeping in mind the following central question: does the effective theory of black hole provide any information about the possible existence of hair? Assuming the symmetry of the hair being that of the underlying black hole space-time, we start by writing down the most general action for the background and the fluctuation in the effective field theory framework. Considering the asymptotically flat and de Sitter black hole background with a spherically symmetric hair we derived the most general equation of motion for the fluctuation. For a particular choice of theory parameters, quasinormal modes corresponding to those fluctuations appeared to have distinct features compared to that of the usual black hole quasinormal modes. The background equations from the effective theory Lagrangian, on the other hand, seemed to suggest that the underlying theory of the hair under consideration should be higher derivative in nature. Therefore as a concrete example we construct a class of higher derivative scalar field theory which gives rise to spherically symmetric hair through background cosmological constant. We also calculate the quasinormal modes whose behaviour turned out to be similar to the one discussed from the effective theory.
We present a family of new rotating black hole solutions to Einsteins equations that generalizes the Kerr-Newman spacetime to include an anisotropic matter. The geometry is obtained by employing the Newman-Janis algorithm. In addition to the mass, the charge and the angular momentum, an additional hair exists thanks to the negative radial pressure of the anisotropic matter. The properties of the black hole are analyzed in detail including thermodynamics. This black hole can be used as a better engine than the Kerr-Newman one in extracting energy.
In this paper, we systematically study spherically symmetric static spacetimes in the framework of Einstein-aether theory, and pay particular attention to the existence of black holes (BHs). In the present studies we first clarify several subtle issues. In particular, we find that, out of the five non-trivial field equations, only three are independent, so the problem is well-posed, as now generically there are only three unknown functions, {$F(r), B(r), A(r)$, where $F$ and $B$ are metric coefficients, and $A$ describes the aether field.} In addition, the two second-order differential equations for $A$ and $F$ are independent of $B$, and once they are found, $B$ is given simply by an algebraic expression of $F,; A$ and their derivatives. To simplify the problem further, we explore the symmetry of field redefinitions, and work first with the redefined metric and aether field, and then obtain the physical ones by the inverse transformations. These clarifications significantly simplify the computational labor, which is important, as the problem is highly involved mathematically. In fact, it is exactly because of these, we find various numerical BH solutions with an accuracy that is at least two orders higher than previous ones. More important, these BH solutions are the only ones that satisfy the self-consistent conditions and meantime are consistent with all the observational constraints obtained so far. The locations of universal horizons are also identified, together with several other observationally interesting quantities, such as the innermost stable circular orbits (ISCO), the ISCO frequency, and the maximum redshift $z_{max}$ of a photon emitted by a source orbiting the ISCO. All of these quantities are found to be quite close to their relativistic limits.
We describe the evolution of slowly spinning compact objects in the late inspiral with Newtonian corrections due to spin, tides, dissipation and post-Newtonian corrections to the point mass term in the action within the effective field theory framework. We evolve the system numerically using a simple algorithm for point particle simulations and extract the lowest-order Newtonian gravitational waveform to study its phase evolution due to the different effects. We show that the matching of coefficients of the effective field theory for compact objects from systems that the gravitational wave observatories LIGO-Virgo currently detects might be possible and it can place tight constraints on fundamental physics.
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