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Recent Developments in Superstring Theory
, 2000
"... The talk contains a brief introduction string theory, followed by a discussion of some of the recent developments. This talk will begin with a brief review of pre1994 string theory. Then I shall describe the develoments during 19941996 which include duality symmetries, Dbranes and black holes. Fi ..."
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The talk contains a brief introduction string theory, followed by a discussion of some of the recent developments. This talk will begin with a brief review of pre1994 string theory. Then I shall describe the develoments during 19941996 which include duality symmetries, Dbranes and black holes. Finally I shall turn to the discussion of some of the developments during 19972000. The topics covered will include (M)atrix theory, Maldacena conjecture, noncommutative geometry, tachyon condensation, special limits of string theory in which gravity decouples (little string theories, OM theory etc.) and large radius compactification. This however is not an exhaustive review of string theory. Indeed, many of the important developments in this subject, like mirror symmetry, new ideas about cosmological constant, etc. will be left out of this review. I shall work in the convention ¯h = 1, c = 1.
Recent Developments in String Theory: A Brief Review for Particle Physicists,” hepph/9710470
"... At the present time, string theory (and its generalizations) remain relatively abstruse subjects to the particle phenomenologist and experimentalist. Yet, striking developments of the last two years offer hope that a fundamental nonperturbative formulation of this theory will be found, and that thi ..."
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At the present time, string theory (and its generalizations) remain relatively abstruse subjects to the particle phenomenologist and experimentalist. Yet, striking developments of the last two years offer hope that a fundamental nonperturbative formulation of this theory will be found, and that this formulation will permit us to make contact with supersymmetric standardmodel physics. This article is based on a talk which attempted to convey the essence of these recent developments in string theory, in a nontechnical manner, to an audience of particle theorists, phenomenologists and experimentalists.
Yukawa Hierarchies From Extra Dimensions With Small FCNC
, 2003
"... Abstract: We investigate a class of extra dimensional models where all of the Standard Model fermions are localized to a single fixed point in an S1/Z2 orbifold, and each species is localized with an exponential wavefunction with a different width. We show that this naturally generates Yukawa hierar ..."
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Abstract: We investigate a class of extra dimensional models where all of the Standard Model fermions are localized to a single fixed point in an S1/Z2 orbifold, and each species is localized with an exponential wavefunction with a different width. We show that this naturally generates Yukawa hierarchies of the size present in the Standard Model, and we find a set of model parameters that reproduces the observed masses and mixings to experimental accuracy. In addition, the dominant constraints, arising from flavor changing neutral currents, are shown to restrict the compactification scale to be 1/R ≥ 2 − 5 TeV, which is a much less stringent constraint than in similar extra
Gauge Unification in Highly Anisotropic String Compactifications
, 2004
"... It is wellknown that heterotic string compactifications have, in spite of their conceptual simplicity and aesthetic appeal, a serious problem with precision gauge coupling unification in the perturbative regime of string theory. Using both a dualitybased and a fieldtheoretic definition of the bou ..."
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It is wellknown that heterotic string compactifications have, in spite of their conceptual simplicity and aesthetic appeal, a serious problem with precision gauge coupling unification in the perturbative regime of string theory. Using both a dualitybased and a fieldtheoretic definition of the boundary of the perturbative regime, we reevaluate the situation in a quantitative manner. We conclude that the simplest and most promising situations are those where some of the compactification radii are exceptionally large, corresponding to highly anisotropic orbifold models. Thus, one is led to consider constructions which are known to the effective fieldtheorist as higherdimensional or orbifold grand unified theories (orbifold GUTs). In particular, if the discrete symmetry used to break the GUT group acts freely, a nonlocal breaking in the larger compact dimensions can be realized, leading to a precise gauge coupling unification as expected on the basis of the MSSM particle spectrum. Furthermore, a somewhat more model dependent but nevertheless very promising scenario arises if the GUT breaking is restricted to certain