1,671 research outputs found
Interaction of D-string with F-string: A Path-Integral Formalism
A path integral formalism is developed to study the interaction of an
arbitrary curved Dirichlet (D-) string with elementary excitations of the
fundumental (F-) string in bosonic string theory. Up to the next to leading
order in the derivative expansion, we construct the properly renormalized
vertex operator, which generalizes the one previously obtained for a D-particle
moving along a curved trajectory. Using this vertex, an attempt is further made
to quantize the D-string coordinates and to compute the quantum amplitude for
scattering between elementary excitations of the D- and F-strings. By studying
the dependence on the Liouville mode for the D-string, it is found that the
vertex in our approximation consists of an infinite tower of local vertex
operators which are conformally invariant on their respective mass-shell. This
analysis indicates that, unlike the D-particle case, an off-shell extension of
the interaction vertex would be necessary to compute the full amplitude and
that the realization of symmetry can be quite non-trivial when the dual
extended objects are simultaneously present. Possible future directions are
suggested.Comment: 23 pages, latex, no figure
Generalized symmetries and invariant matter couplings in two-dimensional dilaton gravity
New features of the generalized symmetries of generic two-dimensional dilaton
models of gravity are presented and invariant gravity-matter couplings are
introduced. We show that there is a continuum set of Noether symmetries, which
contains half a de Witt algebra. Two of these symmetries are area-preserving
transformations. We show that gravity-matter couplings which are invariant
under area preserving transformations only contribute to the dynamics of the
dilaton-gravity sector with a reshaping of the dilaton potential. The
interaction with matter by means of invariant metrics is also considered. We
show in a constructive way that there are metrics which are invariant under two
of the symmetries. The most general metrics and minimal couplings that fulfil
this condition are found.Comment: LateX file, no macros, 14pp: minor changes have been made and some
misprints have been correcte
A Unified Approach to Solvable Models of Dilaton Gravity in Two-Dimensions Based on Symmetry
A large class of solvable models of dilaton gravity in two space-time
dimensions, capable of describing black hole geometry, are analyzed in a
unified way as non-linear sigma models possessing a special symmetry. This
symmetry, which can be neatly formulated in the target-space-covariant manner,
allows one to decompose the non-linearly interacting dilaton-gravity system
into a free field and a field satisfying the Liouville equation with in general
non-vanishing cosmological term. In this formulation, all the existent models
are shown to fall into the category with vanishing cosmological constant.
General analysis of the space-time structureinduced by a matter shock wave is
performed and new models, with and without the cosmological term, are
discussed.Comment: 29 pages, LaTe
Conformal and Nonconformal Symmetries in 2d Dilaton gravity
We study finite-dimensional extra symmetries of generic 2D dilaton gravity
models. Using a non-linear sigma model formulation we show that the unique
theories admitting an extra (conformal) symmetry are the models with an
exponential potential (), which include the CGHS
model as a particular though limiting () case. These models give rise
to black hole solutions with a mass-dependent temperature. The underlying extra
symmetry can be maintained in a natural way in the one-loop effective action,
thus implying the exact solubility of the semiclassical theory including
back-reaction. Moreover, we also introduce three different classes of
(non-conformal) transformations which are extra symmetries for generic 2D
dilaton gravity models. Special linear combinations of these transformations
turn out to be the (conformal) symmetries of the CGHS and models. We show that one of the non-conformal extra symmetries
can be converted into a conformal one by means of adequate field redefinitions
involving the metric and the derivatives of the dilaton. Finally, by expressing
the Polyakov-Liouville effective action in terms of an invariant metric, we are
able to provide semiclassical models which are also invariant. This generalizes
the solvable semiclassical model of Bose, Parker and Peleg (BPP) for a generic
2D dilaton gravity model.Comment: Latex, no figures. Revised version published i
Symmetries and solvable models for evaporating 2D black holes
We study the evaporation process of a 2D black hole in thermal equilibrium
when the ingoing radiation is switched off suddenly. We also introduce global
symmetries of generic 2D dilaton gravity models which generalize the extra
symmetry of the CGHS model.Comment: 4 pages, Latex. Talk given at the Second Conference on Quantum
Gravity and Constrained Dynamics. To appear in Proc. Supp. Nucl. Phys.
Heterotic strings on homogeneous spaces
We construct heterotic string backgrounds corresponding to families of
homogeneous spaces as exact conformal field theories. They contain left cosets
of compact groups by their maximal tori supported by NS-NS 2-forms and gauge
field fluxes. We give the general formalism and modular-invariant partition
functions, then we consider some examples such as SU(2)/U(1) ~ S^2 (already
described in a previous paper) and the SU(3)/U(1)^2 flag space. As an
application we construct new supersymmetric string vacua with magnetic fluxes
and a linear dilaton.Comment: JHEP style; 47 pages, one figur
G/G Models and W_N strings
We derive the BRST cohomology of the G/G topological model for the case of
A^{(1)}_{N-1} . It is shown that at level k={p/q}-N the latter describes the
(p,q) W_N minimal model coupled to gravity (plus some extra ``topological
sectors").Comment: 17 page
DeWitt-Virasoro construction
We study a particular approach for analyzing worldsheet conformal invariance
for bosonic string propagating in a curved background using hamiltonian
formalism. We work in the Schrodinger picture of a single particle description
of the problem where the particle moves in an infinite-dimensional space.
Background independence is maintained in this approach by adopting DeWitt's
(Phys.Rev.85:653-661,1952) coordinate independent formulation of quantum
mechanics. This enables us to construct certain background independent notion
of Virasoro generators, called DeWitt-Virasoro (DWV) generators, and invariant
matrix elements of an arbitrary operator constructed out of them in spin-zero
representation. We show that the DWV algebra is given by the Witt algebra with
additional anomalous terms that vanish for Ricci-flat backgrounds. The actual
quantum Virasoro generators should be obtained by first introducing the vacuum
state and then normal ordering the DWV generators with respect to that. We
demonstrate the procedure in the simple cases of flat and pp-wave backgrounds.
This is a shorter version of arXiv:0912.3987 [hep-th] with many technical
derivations omitted.Comment: 18 pages, shorter version of arXiv:0912.3987 [hep-th] accepted for
publication in Pramana - Journal of Physic
c=1 String Theory as a Topological G/G Model
The physical states on the free field Fock space of the {SL(2,R)\over
SL(2,R) model at any level are computed. Using a similarity transformation on
, the cohomology of the latter is mapped into a direct sum of simpler
cohomologies. We show a one to one correspondence between the states of the
model and those of the string model. A full equivalence between
the {SL(2,R)\over SL(2,R) and {SL(2,R)\over U(1) models at the level of
their Fock space cohomologies is found.Comment: 19
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