31 research outputs found

    Unstable vortices do not confine

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    Recently, a geometric model for the confinement of magnetic charges in the context of type II string compactifications was constructed by Greene, Morrison and Vafa. This model assumes the existence of stable magnetic vortices with quantized flux in the low energy theory. However, quantization of flux alone does not imply that the vortex is stable, since the flux may not be confined to a tube of definite size. We show that in the field theoretical model which underlies the geometric model of confinement, static, cylindrically symmetric magnetic vortices do not exist. While our results do not preclude the existence of confinement in a different low-energy regime of string theory, they show that confinement is not a universal outcome of the string picture, and its origin in the low energy theory remains to be understood.Comment: Latex, 8 page

    Comments on the classification of orientifolds

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    The simple current construction of orientifolds based on rational conformal field theories is reviewed. When applied to SO(16) level 1, one can describe all ten-dimensional orientifolds in a unified framework.Comment: 9 pages, Contribution to proceedings of RTN-workshop in Leuven, Belgium, September 200

    Theory and Phenomenology of Type I strings and M-theory

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    The physical motivations and the basic construction rules for Type I strings and M-theory compactifications are reviewed in light of the recent developments. The first part contains the basic theoretical ingredients needed for building four-dimensional supersymmetric models, models with broken supersymmetry and for computing low-energy actions and quantum corrections to them. The second part contains some phenomenological applications to brane world scenarios with low values of the string scale and large extra dimensions.Comment: 129 pages, 7 eps figures, LaTeX, version to appear in Class. Quantum Gra

    Crosscaps, Boundaries and T-duality

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    Open descendants with boundaries and crosscaps of non-trivial automorphism type are studied. We focus on the case where the bulk symmetry is broken to a Z 2 orbifold subalgebra. By requiring positivity and integrality for the open sector, we derive a unique crosscap of automorphism type g 2 Z 2 and a corresponding g-twisted Klein bottle for a charge conjugation invariant. As a specic example, we use T-duality to construct the descendants of the true diagonal invariant with symmetry preserving crosscaps and boundaries. 1 Introduction The general prescription to construct open unoriented strings from closed oriented ones is known as the method of open descendants [1]. It is not limited to circle compactications and orbifolds of circles, as orientifolds are. In short, one has to nd a set of crosscap and boundary coecients from which one can calculate the Klein bottle, annulus and M\u7fobius strip partition function that together with the torus generate the full spectrum of the ope..

    Open descendants of non-diagonal invariants

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    The open descendants of simple current automorphism invariants are constructed. We consider the case where the order of the current is two or odd. We prove that our solutions satisfy the completeness conditions, positivity and integrality of the open and closed sectors and the Klein bottle constraint (apart from an interesting exception). In order to do this, we derive some new relations between the tensor Y and the fixed point conformal field theory. Some non-standard Klein After a ten year period of neglect, open strings have received more interest recently for a variety of reasons: their rĂ´le in the duality picture, the discovery of D-branes and the appearance of non-commutative geometry, and recent developments in phenomenological string theory, such as brane worl
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