36 research outputs found
Behavior of tachyon in string cosmology based on gauged WZW model
We investigate a string theoretic cosmological model in the context of the
gauged Wess-Zumino-Witten model. Our model is based on a product of non-compact
coset space and a spectator flat space; . We
extend the formerly studied semiclassical consideration with infinite Kac-Moody
level to a finite one. In this case, the tachyon field appears in the
effective action, and we solve the Einstein equation to determine the behavior
of tachyon as a function of time. We find that tachyon field dominates over
dilaton field in early times. In particular, we consider the energy conditions
of the matter fields consisting of the dilaton and the tachyon which affect the
initial singularity. We find that not only the strong energy but also the null
energy condition is violated.Comment: 10 figure
Knizhnik-Zamolodchikov-type equations for gauged WZNW models
We study correlation functions of coset constructions by utilizing the method
of gauge dressing. As an example we apply this method to the minimal models and
to the Witten 2D black hole. We exhibit a striking similarity between the
latter and the gravitational dressing. In particular, we look for logarithmic
operators in the 2D black hole.Comment: 24 pages, latex, no figures. More discussion of logarithmic operators
was adde
Electromagnetic duality and light-front coordinates
We review the light-front Hamiltonian approach for the Abelian gauge theory
in 3+1 dimensions, and then study electromagnetic duality in this framework.Comment: 18 pages, LaTeX, 2 references and a typo in an eqn. (19) corrected,
minor revisions in response to referee's repor
Expansion for Excited Baryons
We derive consistency conditions which constrain the possible form of the
strong couplings of the excited baryons to the pions. The consistency
conditions follow from requiring the pion-excited baryon scattering amplitudes
to satisfy the large-N_c Witten counting rules and are analogous to consistency
conditions used by Dashen, Jenkins and Manohar and others for s-wave baryons.
The consistency conditions are explicitly solved, giving the most general
allowed form of the strong vertices for excited baryons in the large-N_c limit.
We show that the solutions to the large-N_c consistency conditions coincide
with the predictions of the nonrelativistic quark model for these states,
extending the results previously obtained for the s-wave baryons. The 1/N_c
corrections to these predictions are studied in the quark model with arbitrary
number of colors N_c.Comment: 56 pages, REVTeX; one new Appendix added containing a discussion of
the results in the language of quark operator
Spacetimes for λ-deformations
We examine a recently proposed class of integrable deformations to two-dimensional conformal field theories. These {\lambda}-deformations interpolate between a WZW model and the non-Abelian T-dual of a Principal Chiral Model on a group G or, between a G/H gauged WZW model and the non-Abelian T-dual of the geometric coset G/H. {\lambda}-deformations have been conjectured to represent quantum group q-deformations for the case where the deformation parameter is a root of unity. In this work we show how such deformations can be given an embedding as full string backgrounds whose target spaces satisfy the equations of type-II supergravity. One illustrative example is a deformation of the Sl(2,R)/U(1) black-hole CFT. A further example interpolates between the SU(2)×SU(2)SU(2)×SL(2,R)×SL(2,R)SL(2,R)×U(1)4 gauged WZW model and the non-Abelian T-dual of AdS3×S3×T4 supported with Ramond flux
On Global Aspects Of Gauged Wess-Zumino-Witten Model
This is a thesis for Rigaku-Hakushi( Ph. D.). It clarifies the
geometric meaning and field theoretical consequences of the spectral flows
acting on the space of states of the ` coset model'. As suggested by Moore
and Seiberg, the spectral flow is realized as the response of states to certain
change of background gauge field together with the gauge transformation on a
circle. Applied to the boundary circle of a disc with field insertion, such a
realization leads to a certain relation among correlators of the gauged WZW
model for various principal -bundles. In the course of derivation, we find
an expression of a (dressed) gauge invariant field as an integral over the flag
manifold of and an expression of a correlator as an integral over a certain
moduli space of holomorphic -bundles with quasi-flag structure at the insertion point. We also find
that the gauge transformation on the circle corresponding to the spectral flow
determines a bijection of the set of isomorphism classes of holomorphic -bundles with quasi-flag structure of one topological type to that of
another. As an application, it is pointed out that problems arising from the
field identification fixed points may be resolved by taking into account of all
principal -bundles.Comment: (Thesis) 125 pages, UT-Komaba/94-3 (Latex errors are corrected