Les Rencontres du Vietnam

Hot Topics in General Relativity and Gravitation

July 28 — August 3, 2013 • Quy Nhon, Viet Nam



Our understanding of the Universe at astrophysical scales and its fundamental laws is rapidly growing, thanks to many advances in observational astrophysics and cosmology. These insights enable us to refine predictions of General Relativity (GR) theory, the concordance model of cosmology (Lambda-CDM), and the Standard Model (SM) of particle physics and their extensions.

Concerning the astrophysics and the physics of black hole (BH), probing the Universe with gravitational waves (GW), by using ground-based and space-based GW detectors, will open a new window of observation in astronomy which should be extremely powerful, with possibly new types of sources and richness of discoveries. The detailed study of the coalescence of compact binary systems is likely to be the "bread and butter" of GW detectors. In the case of neutron star coalescences, one expects a wealth of information concerning their masses and probably the equation of state of nuclear matter inside neutron stars. They might be the basic mechanism for production of short gamma ray bursts (GRB); and their observations should open a New Multi-messenger astronomy. The coalescence of supermassive BH binaries, when galaxies collide, is expected to be observed at cosmological distances. Among other issues, measurements of BH spin and accurate tests of the basic no-hair theorem for BH in GR will be performed.

Moreover, improvements also take place in testing GR and the equivalence principle (EP), and the inverse square-law of gravity by using high-precision experiments: e.g., torsion balance experiments and the Lunar laser ranging for testing the EP, observations in the Solar system which are compared and fitted by the best planetary ephemerides for constraining the parametrized-post-Newtonian (PPN) parameters, …. Space missions, such as Microscope and STE-Quest, will test further the EP, as well as atomic clocks in space (ACES experiment), which measure accurately the gravitational redshift.

In cosmology, the concordance model Lambda-CDM, based on Friedmann-Lemaître-Robertson-Walker (FLRW) universe, associates a cosmological constant and Cold Dark Matter (CDM) as the main component of massive gravitational sources, completed with a primordial inflation era, and stands for the state-of-the-art model. Parameters of this model are obtained by fitting jointly several types of data, which has permitted to transform cosmology into a high-precision science. This approach has known a remarkable success in explaining and predicting diverse observations corresponding to the Universe at its largest scales. However, it addresses the question of the nature of the fundamental constituents of the Universe.  Although the cosmological constant, viewed as a fundamental constant of nature, is the simplest interpretation, the attempts at explaining it as being a vacuum energy have failed. High redshift surveys enable us to check possible alternatives, named dark energy (DE) or sometimes "quintessence". Moreover, CDM accounts for non-baryonic weakly interacting massive particles, while there is no SM candidate.  Faced with these issues, one has to improve or study alternatives to the standard model of cosmology, notably with new insights on the nature of the DE, in which gravity is modified by the presence of new fundamental fields, or even more drastically, by interpreting dark matter using the possibility that GR may no longer be correct in a certain regime. This last proposal goes under the name of MOND, and attempts at solving difficulties of the standard cosmological model at explaining the extremely fine-tuned distribution of dark matter at galactic scales. Additional improvements for the understanding of the dynamics at large scale will be provided with inhomogeneous cosmology, which takes into account the irregularities in the distribution of gravitational sources.

Our aims are to discuss and review recent developments on
  • Astrophysics of compact objects
  • Gravitational waves (experimental and theoretical)
  • Experimental gravity and tests of General Relativity
  • Alternative gravity theories and Cosmology related issues

Last updated : July 24th 2013