Gravitation

About: Gravitation is a research topic. Over the lifetime, 29306 publications have been published within this topic receiving 821510 citations.

Quantum effects in the early universe. I. Influence of trace anomalies on homogeneous, isotropic, classical geometries

Abstract: The use of the effective-action method to calculate quantum effects in the early universe is described. An application is made to the calculation of the effect of one-loop contributions of conformally invariant matter fields on the evolution of homogeneous, isotropic, spatially flat classical geometries containing classical radiation.

On the Formation and Evolution of Disk Galaxies: Cosmological Initial Conditions and the Gravitational Collapse

Abstract: We use a semianalytical approach and the standard σ8 = 1 cold dark matter (SCDM) cosmological model to study the gravitational collapse and virialization, the structure, and the global and statistical properties of isolated dark matter galactic halos that emerge from primordial Gaussian fluctuations First, from the statistical properties of the primordial density fluctuation field, the possible mass aggregation histories (MAHs) are generated Second, these histories are used as the initial conditions of the gravitational collapse To calculate the structure of the virialized systems, we have generalized the secondary infall model to allow arbitrary MAHs and internal thermal motions The average halo density profiles we obtained agree with the profile derived as a fitting formula to results of N-body cosmological simulations by Navarro, Frenk, & White The comparison of the density profiles with the observational data is discussed, and some possible solutions to the disagreement found in the inner regions are proposed The results of our approach, after considering the gravitational dragging of the baryon matter that forms a central disk in centrifugal equilibrium, show that the empirical Tully-Fisher (TF) relation and its scatter can be explained through the initial cosmological conditions, at least for the isolated systems The σ8 = 1 SCDM model produces galaxies with high velocities when compared with observations, but when the SCDM power spectrum is normalized to σ8 = 057, an excellent agreement with the observable TF relation is found, suggesting that this relation is the natural extension to galactic scales of the observed galaxy distribution power spectrum The theoretical TF scatter is close to the measured one The slope of the TF relation is practically invariant with respect to the spin parameter λ

The Black holes of topologically massive gravity

Abstract: We show that an analytical continuation of the Vuorio solution to three-dimensional topologically massive gravity leads to a two-parameter family of black-hole solutions, which are geodesically complete and causally regular within a certain parameter range. No observers can remain static in these spacetimes. We discuss their global structure, and evaluate their mass, angular momentum and entropy, which satisfy a slightly modified form of the first law of thermodynamics.

Non-perturbative 2 particle scattering amplitudes in 2+1 dimensional quantum gravity

Abstract: A quantum theory for scalar particles interacting only gravitationally in 2+1 dimensions is considered. Since there are no real gravitons the interaction is entirely topological. Nevertheless, there is non-trivial scattering. We show that the two-particle amplitude can be computed exactly. Although the complete “theory” is not well understood we suggest an approach towards formulating theN particle problem.