2,805 research outputs found
Space-Time Symmetries of Quantized Tensionless Strings
The tensionless limit of the free bosonic string is space-time conformally
symmetric classically. Requiring invariance of the quantum theory in the light
cone gauge tests the reparametrization symmetry needed to fix this gauge. The
full conformal symmetry gives stronger constraints than the Poincar\'e
subalgebra. We find that the symmetry may be preserved in any space-time
dimension, but only if the spectrum is drastically reduced (part of this
reduction is natural in a zero tension limit of the ordinary string spectrum).
The quantum states are required to be symmetric ({\it i.e.} singlets) under
space-time diffeomorphisms, except for the centre of mass wave function.Comment: 15pp, plain latex, USITP-92-
Palatini Variational Principle for -Dimensional Dilaton Gravity
We consider a Palatini variation on a general -Dimensional second order,
torsion-free dilaton gravity action and determine the resulting equations of
motion. Consistency is checked by considering the restraint imposed due to
invariance of the matter action under simple coordinate transformations, and
the special case of N=2 is examined. We also examine a sub-class of theories
whereby a Palatini variation dynamically coincides with that of the "ordinary"
Hilbert variational principle; in particular we examine a generalized
Brans-Dicke theory and the associated role of conformal transformations.Comment: 16 pages, LaTe
ADE-Quiver Theories and Mirror Symmetry
We show that the Higgs branch of a four-dimensional Yang-Mills theory, with
gauge and matter content summarised by an ADE quiver diagram, is identical to
the generalised Coulomb branch of a four-dimensional superconformal strongly
coupled gauge theory with ADE global symmetry. This equivalence suggests the
existence of a mirror symmetry between the quiver theories and the strongly
coupled theories.Comment: 8 pages, 4 figures. Talk delivered by UL at D.V. Volkov Memorial
Conference, July 25-29, 2000, Kharkov, to be published in the proceeding
Sigma models with off-shell N=(4,4) supersymmetry and noncommuting complex structures
We describe the conditions for extra supersymmetry in N=(2,2) supersymmetric
nonlinear sigma models written in terms of semichiral superfields. We find that
some of these models have additional off-shell supersymmetry. The (4,4)
supersymmetry introduces geometrical structures on the target-space which are
conveniently described in terms of Yano f-structures and Magri-Morosi
concomitants. On-shell, we relate the new structures to the known
bi-hypercomplex structures.Comment: 20 pages; v2: significant corrections, clarifications, and
reorganization; v3: discussion of supersymmetry vs twisted supersymmetry
added, relevant signs corrected
Properties of hyperkahler manifolds and their twistor spaces
We describe the relation between supersymmetric sigma-models on hyperkahler
manifolds, projective superspace, and twistor space. We review the essential
aspects and present a coherent picture with a number of new results.Comment: 26 pages. v2: Sign mistakes corrected; Kahler potential explicitly
calculated in example; references added. v3: Published version--several small
clarifications per referee's reques
Generalized Kahler Geometry from supersymmetric sigma models
We give a physical derivation of generalized Kahler geometry. Starting from a
supersymmetric nonlinear sigma model, we rederive and explain the results of
Gualtieri regarding the equivalence between generalized Kahler geometry and the
bi-hermitean geometry of Gates-Hull-Rocek.
When cast in the language of supersymmetric sigma models, this relation maps
precisely to that between the Lagrangian and the Hamiltonian formalisms.
We also discuss topological twist in this context.Comment: 18 page
The Semi-Chiral Quotient, Hyperkahler Manifolds and T-duality
We study the construction of generalized Kahler manifolds, described purely
in terms of N=(2,2) semichiral superfields, by a quotient using the semichiral
vector multiplet. Despite the presence of a b-field in these models, we show
that the quotient of a hyperkahler manifold is hyperkahler, as in the usual
hyperkahler quotient. Thus, quotient manifolds with torsion cannot be
constructed by this method. Nonetheless, this method does give a new
description of hyperkahler manifolds in terms of two-dimensional N=(2,2) gauged
non-linear sigma models involving semichiral superfields and the semichiral
vector multiplet. We give two examples: Eguchi-Hanson and Taub-NUT. By
T-duality, this gives new gauged linear sigma models describing the T-dual of
Eguchi-Hanson and NS5-branes. We also clarify some aspects of T-duality
relating these models to N=(4,4) models for chiral/twisted-chiral fields and
comment briefly on more general quotients that can give rise to torsion and
give an example.Comment: 31 page
Hamiltonian BRST Quantization of the Conformal String
We present a new formulation of the tensionless string () where the
space-time conformal symmetry is manifest. Using a Hamiltonian BRST scheme we
quantize this {\em Conformal String} and find that it has critical dimension
. This is in keeping with our classical result that the model describes
massless particles in this dimension. It is also consistent with our previous
results which indicate that quantized conformally symmetric tensionless strings
describe a topological phase away {}from . We reach our result by
demanding nilpotency of the BRST charge and consistency with the Jacobi
identities. The derivation is presented in two different ways: in operator
language and using mode expansions. Careful attention is payed to
regularization, a crucial ingredient in our calculations.Comment: 33pp (LaTeX), USITP-94-0
Classical and Quantized Tensionless Strings
{}From the ordinary tensile string we derive a geometric action for the
tensionless () string and discuss its symmetries and field equations. The
Weyl symmetry of the usual string is shown to be replaced by a global
space-time conformal symmetry in the limit. We present the explicit
expressions for the generators of this group in the light-cone gauge. Using
these, we quantize the theory in an operator form and require the conformal
symmetry to remain a symmetry of the quantum theory. Modulo details concerning
zero-modes that are discussed in the paper, this leads to the stringent
restriction that the physical states should be singlets under space-time
diffeomorphisms, hinting at a topological theory. We present the details of the
calculation that leads to this conclusion.Comment: 34 pages, Latex, USITP 93-1
Generalized Kahler geometry and gerbes
We introduce and study the notion of a biholomorphic gerbe with connection.
The biholomorphic gerbe provides a natural geometrical framework for
generalized Kahler geometry in a manner analogous to the way a holomorphic line
bundle is related to Kahler geometry. The relation between the gerbe and the
generalized Kahler potential is discussed.Comment: 28 page
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