Interactions Between Branes and Matrix Theories

We review some tests of the 0-brane and instanton matrix models based on comparing long-distance interaction potentials between branes and their bound states (with 1/2,1/4 or 1/8 of supersymmetry) in supergravity and in super Yang-Mills descriptions. We first consider the supergravity-SYM correspondence at the level of the leading term in the interaction potential, and then describe some recent results concerning the subleading term and their implications for the structure of the 2-loop F^6 term in the SYM effective action.Comment: 12 pages, latex. Contribution to Proceedings of STRINGS'97 (misprints corrected

On field redefinitions and exact solutions in string theory

String backgrounds associated with gauged $G/H$ WZNW models in general depend non-trivially on $\alpha'$. We note, however, that there exists a local covariant \a'-dependent field redefinition that relates the exact metric-dilaton background corresponding to the $SL(2,R)/U(1)$ model to its leading-order form ($D=2$ black hole). As a consequence, there exists a `scheme' in which the string effective equations have the latter as an exact solution. However, the corresponding equation for the tachyon (which, like other Weyl anomaly coefficients, has scheme-dependent form) still contains corrections of all orders in $\alpha'$. As a result, the `probes' (the tachyons) still feel the $\alpha'$-corrected background. The field redefinitions we discuss contain the dilaton terms in the metric transformation law. We comment on exact forms of the duality transformation in different `schemes'.Comment: 11 pages, harvmac, CERN-TH.6970/93 [ A new section on tachyonic equation is added: while there exists a scheme where the exact D=2 `black hole' metric-dilaton background has semiclassical form, the equation for the tachyon still contains \alpha'-corrections, i.e. the tachyon still feels the \alpha'-corrected background

T-Duality and Two-Loop Renormalization Flows

Manifest T-duality covariance of the one-loop renormalization group flows is shown for a generic bosonic sigma model with an abelian isometry, by referring a set of previously derived consistency conditions to the tangent space of the target. For a restricted background, T-duality transformations are then studied at the next order, and the ensuing consistency conditions are found to be satisfied by the two-loop Weyl anomaly coefficients of the model. This represents an extremely non-trivial test of the covariance of renormalization group flows under T-duality, and a stronger condition than T-duality invariance of the string background effective action.Comment: 18 pp., plain TeX + harvmac. Typos in Eqs. (4.3), (4.5) and (4.7) corrected, and references adde

Supergravity Solutions for Branes Localized Within Branes

We construct supergravity solutions describing branes (D2-branes or NS5-branes or waves) localized within D6-branes in the region close to the core of the D6-branes. Other similar string-theory and M-theory `near-core' localized solutions can be found by applying U-duality and/or lifting D=10 solutions to D=11. In particular, the D2-branes localized on D6-branes is T-dual to a special case of the background describing (D)strings localized on (D)5-branes and thus is also related to a localized intersection of M2-branes and M5-branes. D6+wave configuration is U-dual to a D0-brane localized on a Kaluza-Klein 5-brane or to the fundamental string intersecting a D5-brane with the point of intersection localized on the D5-brane.Comment: 11 pages, version to appear in Phys. Lett.

Massive fields dynamics in open bosonic string theory

We consider the theory of open bosonic string in massive background fields. The general structure of renormalization is investigated. A general covariant action for a string in background fields of the first massive level is suggested and its symmetries are described. Equations of motion for the background fields are obtained by demanding that the renormalized operator of the energy-momentum tensor trace vanishes.Comment: 13 page

String vacuum backgrounds with covariantly constant null Killing vector and 2d quantum gravity

We consider a $2d$ sigma model with a $2+N$ - dimensional Minkowski signature target space metric having a covariantly constant null Killing vector. We study solutions of the conformal invariance conditions in $2+N$ dimensions and find that generic solutions can be represented in terms of the RG flow in $N$ - dimensional ``transverse space'' theory. The resulting conformal invariant sigma model is interpreted as a quantum action of the $2d$ scalar (``dilaton") quantum gravity model coupled to a (non-conformal) `transverse' sigma model. The conformal factor of the $2d$ metric is identified with a light cone coordinate of the $2+N$ - dimensional sigma model. We also discuss the case when the transverse theory is conformal (with or without the antisymmetric tensor background) and reproduce in a systematic way the solutions with flat transverse space known before.Comment: 26 p., revised (a discussion of tachyon coupling is added at the end of section 4), DAMTP-92-4

Self-duality of Born-Infeld action and Dirichlet 3-brane of type IIB superstring theory

D-brane actions depend on a world-volume abelian vector field and are described by Born-Infeld-type actions. We consider the vector field duality transformations of these actions. Like the usual 2d scalar duality rotations of isometric string coordinates imply target space T-duality, this vector duality is intimately connected with SL(2,Z)-symmetry of type IIB superstring theory. We find that in parallel with generalised 4-dimensional Born-Infeld action, the action of 3-brane of type IIB theory is SL(2,Z) self-dual. This indicates that 3-brane should play a special role in type IIB theory and also suggests a possibility of its 12-dimensional reformulation.Comment: 22 pages, harvmac (minor changes

A Study of a Non-Abelian Generalization of the Born-Infeld Action

A new type of non-Abelian generalization of the Born-Infeld action is proposed, in which the spacetime indices and group indices are combined. The action is manifestly Lorentz and gauge invariant. In its power expansion, the lowest order term is the Yang-Mills action and the second term corresponds to the bosonic stringy correction to this action. Solutions of the Euler-Lagrange equation for the SU(2) case are considered and we show that there exists an instanton-like solution which has winding number one and finite action.Comment: 11 pages, three figures, LaTe