U duality and symplectic formulation of dilaton-axion gravityстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:We study a bosonic four-dimensional effective action corresponding to the heterotic string compactified on a six-tonus (dilaton-axion gravity with one vector field) on a curved space-time manifold possessing a timelike Killing vector field. Previously the existence of the SO(2,3)similar to Sp(4,R) global symmetry (U duality) as well as the symmetric space property of the corresponding sigma model have been established following the Neugebauer-Kramer approach. Here we present an explicit form of the Sp(4,R) generators in terms of coset variables and construct a representation of the coset in terms of the physical target space coordinates. A complex symmetric 2X2 matrix Z (''matrix dilaton-axion'') is then introduced for which U duality takes the matrix-valued SL (2,R) form. In terms of this matrix the theory is further presented as a Kahler sigma model. This leads to a more economic 2X2 formulation suggesting some new solution-generating techniques. A new solution (corresponding to constant ImZ) is obtained which describes the system of point massless magnetic monopoles endowed with axion charges. In such a system mutual magnetic repulsion is exactly balanced by axion attraction so that the resulting space-time is focally flat but possesses multiple Taub-NUT singularities.