Gravitation

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

The published extended rotation curves of spiral galaxies: Confrontation with modified dynamics

Abstract: A sample of 22 spiral galaxy rotation curves, measured in the 21 cm line of neutral hydrogen, is considered in the context of Milgrom's modified dynamics (MOND). Combined with the previous, highly selected sample of Begeman et al., this constitutes the current total sample of galaxies with published (or available) extended rotation curves and photometric observations of the light distribution. This is the observational basis of present quantitative understanding of the discrepancy between the visible mass and classical dynamical mass in galaxies. It is found that the gravitational force calculated from the observed distribution of luminous material and gas by use of the simple MOND formula can account for the overall shape and amplitude of these 22 rotation curves, and in some cases, the predicted curve agrees with the observed rotation curve in detail. The fitted rotation curves have, in 13 cases, only one free parameter, which is the mass-to-light ratio of the luminous disk; in nine cases, there is an additional free parameter, which is M/L of a central bulge or light concentration. The values of the global M/L (bulge plus disk) are reasonable and, when the gas mass is also included, show a scatter consistent with that in the Tully-Fisher relation. The success of the MOND prescription in predicting the rotation curves in this larger, less stringently selected sample lends further support to the idea that dynamics or gravity is non-Newtonian in the limit of low acceleration and that it is unnecessary to invoke the presence of large quantities of unseen matter.

Dark energy problem : from phantom theory to modified Gauss-Bonnet gravity

Abstract: The solution of the dark energy problem in models without scalars is presented. It is shown that a late-time accelerating cosmology may be generated by an ideal fluid with some implicit equation of state. The evolution of the universe within modified Gauss–Bonnet gravity is considered. It is demonstrated that such a gravitational approach may predict the (quintessential, cosmological constant or transient phantom) acceleration of the late-time universe with a natural transition from deceleration to acceleration (or from non-phantom to phantom era in the last case).

Asymptotic fragility, near AdS$_{2}$ holography and $ T\overline{T} $

Abstract: We present the exact solution for the scattering problem in the flat space Jackiw-Teitelboim (JT) gravity coupled to an arbitrary quantum field theory. JT gravity results in a gravitational dressing of field theoretical scattering amplitudes. The exact expression for the dressed S-matrix was previously known as a solvable example of a novel UV asymptotic behavior, dubbed asymptotic fragility. This dressing is equivalent to the $$ T\overline{T} $$ deformation of the initial quantum field theory. JT gravity coupled to a single mass-less boson provides a promising action formulation for an integrable approximation to the worldsheet theory of confining strings in 3D gluodynamics. We also derive the dressed S-matrix as a flat space limit of the near AdS2 holography. We show that in order to preserve the flat space unitarity the conventional Schwarzian dressing of boundary correlators needs to be slightly extended. Finally, we propose a new simple expression for flat space amplitudes of massive particles in terms of correlators of holographic CFT’s.

On hawking radiation as tunneling with back-reaction

Abstract: Recently, Angheben et al1 have presented a refined method for calculating the (tree-level) black hole temperature by way of the tunneling paradigm Here, we demonstrate how their formalism can be suitably adapted to accommodate the (higher-order) effects of the gravitational back-reaction

N-body simulations for f(R) gravity using a self-adaptive particle-mesh code.

Abstract: We perform high resolution N-body simulations for f(R) gravity based on a self-adaptive particlemesh code MLAPM. The Chameleon mechanism that recovers General Relativity on small scales is fully taken into account by self-consistently solving the non-linear equation for the scalar field. We independently confirm the previous simulation results, including the matter power spectrum, halo mass function and density profiles, obtained by Oyaizu et al. (Phys.Rev.D 78, 123524, 2008) and Schmidt et al. (Phys.Rev.D 79, 083518, 2009), and extend the resolution up to k � 20 h/Mpc for the measurement of the matter power spectrum. Based on our simulation results, we discuss how the Chameleon mechanism affects the clustering of dark matter and halos on full non-linear scales.