13,912 research outputs found
Coherent States for Black Holes
We determine coherent states peaked at classical space-time of the
Schwarzschild black hole in the frame-work of canonical quantisation of general
relativity. The information about the horizon is naturally encoded in the phase
space variables, and the perturbative quantum fluctuations around the classical
geometry depend on the distance from the horizon. For small black holes, space
near the vicinity of the singularity appears discrete with the singular point
excluded from the spectrum.Comment: 48 pages, 18+1 figures, some modifications, references adde
An ansatz for a non-perturbative four-graviton amplitude in type IIB superstring theory
A natural SL(2,Z) invariant generalization of the Veneziano amplitude in type
IIB superstring theory is investigated. It includes certain perturbative and
non-perturbative (D-instanton) contributions, and it reduces to the correct
expressions in different limits. The singularities are poles in the --
channels, corresponding to the exchange of particles with a mass spectrum
coinciding with that of string states. We describe the general
structure of the associated perturbative corrections to the effective action.Comment: Version appeared in Phys.Lett. B. Discussion expanded. 7 pages,
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Constraints and Period Relations in Bosonic Strings at Genus-g
We examine some of the implications of implementing the usual boundary
conditions on the closed bosonic string in the hamiltonian framework. Using the
KN formalism, it is shown that at the quantum level, the resulting constraints
lead to relations among the periods of the basis 1-forms. These are compared
with those of Riemanns' which arise from a different consideration.Comment: 16 pages, (Plain Tex), NUS/HEP/9320
Hyperbolic Spaces in String and M-Theory
We describe string-theory and supergravity solutions involving
symmetric spaces of constant negative curvature. Many examples of
non-supersymmetric string compactifications on hyperbolic spaces of
finite volume are given in terms of suitable cosets of the form ,
where is a discrete group. We describe in some detail the cases of
the non-compact hyperbolic spaces and , representing the fundamental
regions of and under and the Picard group, respectively.
By writing as a U(1) fibration, we obtain new solutions where
gets untwisted by T-duality to . Solutions with time-dependent dilaton field are also constructed by
starting with a solution with NS5-brane flux over . A new class of
non-supersymmetric conformal field theories can be defined via holography.Comment: 17 pages, Latex. Small additions and correction
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