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Graviton - Gravitons and models of quantum gravity

Graviton - Gravitons and models of quantum gravity: Encyclopedia II - Graviton - Gravitons and models of quantum gravity

Graviton: Encyclopedia II - Graviton - Gravitons and models of quantum gravity

Graviton - Gravitons and models of quantum gravity

While the classical theory (i.e. the tree diagrams) and semiclassical corrections (one-loop diagrams) behaved as expected, the Feynman diagrams with two (or more) loops led to ultraviolet divergences - i.e. infinite results that could not be removed because the quantized general relativity was not renormalizable, unlike Quantum electrodynamics. In popular terms, the discreteness of quantum theory is not compatible with the smoothness of Einstein's general relativity. These problems, together with some conceptual puzzles, led many physicists to believe that a theory more complete than just general relativity must regulate the behavior near the Planck length. Superstring theory finally emerged as the most promising solution; it is the only known theory in which the quantum corrections of any order to graviton scattering are finite.

String theory predicts the existence of gravitons and their well-defined interactions which represents one of its most important triumphs. A graviton in perturbative string theory is a closed string in a very particular low-energy vibrational state. The scattering of gravitons in string theory can also be computed from the correlation functions in conformal field theory, as dictated by the AdS/CFT correspondence, or from Matrix theory.

An interesting feature of gravitons in string theory is that, as closed strings without endpoints, they would not be bound to branes and could move freely between them; this "leakage" of gravitons from our brane into higher-dimensional space could explain why gravity is such a weak force, and gravitons from other branes adjacent to our own could provide a potential explanation for dark matter. See brane cosmology for more details.

It should be noted that there exist proposed quantum theories of gravity that do not predict a graviton; for instance, loop quantum gravity has no analogous particle.

Other related archives

AdS/CFT, Bosons, Einstein, Feynman diagrams, LIGO, Matrix theory, Particles, Planck length, Quantum electrodynamics, Quantum gravity, Ricci curvature, String theory, Superstring theory, VIRGO, W and Z bosons, Weyl curvature, boson, brane cosmology, branes, charged particles, classical theory, closed string, coherent states, conformal field theory, correlation functions, dark matter, discreteness, electricity, elementary particle, elementary particles, general relativity, gluons, gravitational waves, gravity, interactions, loop quantum gravity, magnet, magnetism, mass, one-loop diagrams, perturbative, photon, photons, physics, quantum electrodynamics, quantum gravity, quantum theory, renormalizable, rest mass, scattering, semiclassical, smoothness, spin, strong nuclear force, tree diagrams, ultraviolet divergences, universe, weak nuclear force

Adapted from the Wikipedia article "Gravitons and models of quantum gravity", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki

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