999 research outputs found

### Unstable vortices do not confine

Recently, a geometric model for the confinement of magnetic charges in the
context of type II string compactifications was constructed by Greene, Morrison
and Vafa. This model assumes the existence of stable magnetic vortices with
quantized flux in the low energy theory. However, quantization of flux alone
does not imply that the vortex is stable, since the flux may not be confined to
a tube of definite size. We show that in the field theoretical model which
underlies the geometric model of confinement, static, cylindrically symmetric
magnetic vortices do not exist. While our results do not preclude the existence
of confinement in a different low-energy regime of string theory, they show
that confinement is not a universal outcome of the string picture, and its
origin in the low energy theory remains to be understood.Comment: Latex, 8 page

### Selfduality of non-linear electrodynamics with derivative corrections

In this paper we investigate how electromagnetic duality survives derivative
corrections to classical non-linear electrodynamics. In particular, we
establish that electromagnetic selfduality is satisfied to all orders in
$\alpha'$ for the four-point function sector of the four dimensional open
string effective action.Comment: 8 page

### Duality symmetry in four-dimensional string actions

We reduce the dual version of $D=10$, $N=1$ supergravity coupled to $n$
vector fields to four dimensions, and derive the $SL(2,R)\times O(6,6+n)$
transformations which leave the equations of motion invariant. For $n=0$
$SL(2,R)$ is also a symmetry of the action, but for $n>0$ only those $SL(2,R)$
transformations which act linearly on all fields leave the action invariant.
The resulting four-dimensional theory is related to the bosonic part of the
usual formulation of $N=4$ supergravity coupled to matter by a duality
transformation.Comment: 9 pages, Latex fil

### Realisations of $W_3$ Symmetry

We perform a systematic investigation of free-scalar realisations of the
Za\-mo\-lod\-chi\-kov $W_3$ algebra in which the operator product of two
spin-three generators contains a non-zero operator of spin four which has
vanishing norm. This generalises earlier work where such an operator was
required to be absent. By allowing this spin-four null operator we obtain
several realisations of the $W_3$ algebra both in terms of two scalars as well
as in terms of an arbitrary number $n$ of free scalars. Our analysis is
complete for the case of two-scalar realisations.Comment: 14 pages, LATEX, UG-6/9

### The effective action for the 4-point functions in abelian open superstring theory

We construct the derivative corrections to the four-point vertices in the
abelian open string effective action to all orders in alpha'. The result is
based on the structure of the string four-point function. Supersymmnetry of
these vertices is guaranteed by the supersymmetry of the F^4 term in the
effective action. By this construction we establish the existence of an
infinite number of supersymmetry invariants, the number of invariants at order
alpha'^n grows linearly with n.Comment: 11 pages, 1 figure, v2: additional remarks in Section 5, added
references, v3: additional remarks in Section 4 and minor correction

### Gauged supergravity from dimensional reduction

We perform a generalised Scherk-Schwarz reduction of the effective action of the heterotic string on T6 to obtain a massive N = 4 supergravity theory in four dimensions. The local symmetry-group of the resulting d = 4 theory includes a Heisenberg group, which is a subgroup of the global 0(6,6 + n) obtained in the standard reduction. We show explicitly that the same theory can be obtained by gauging this Heisenberg group in d = 4, N = 4 supergravity.

### Supersymmetric non-abelian Born-Infeld revisited

We determine the non-abelian Born-Infeld action, including fermions, as it
results from the four-point tree-level open superstring scattering amplitudes
at order alpha'^2. We find that, after an appropriate field redefinition all
terms at this order can be written as a symmetrised trace. We confront this
action with the results that follow from kappa-symmetry and conclude that the
recently proposed non-abelian kappa-symmetry cannot be extended to cubic orders
in the Born-Infeld curvature.Comment: 26 pages, Late

### De Sitter solutions in N=4 matter coupled supergravity

We investigate the scalar potential of gauged N=4 supergravity with matter.
The extremum in the SU(1,1)/U(1) scalars is obtained for an arbitrary number of
matter multiplets. The constraints on the matter scalars are solved in terms of
an explicit parametrisation of an
SO(6,6+n) element. For the case of six matter multiplets we discuss both
compact and noncompact gauge groups.
In an example involving noncompact groups and four scalars we find a
potential with an absolute minimum and a positive cosmological constant.Comment: 14 page

### Intersecting Branes in Matrix Theory

We construct BPS states in the matrix description of M-theory. Starting from
a set of basic M-theory branes, we study pair intersections which preserve
supersymmetry. The fractions of the maximal supersymmetry obtained in this way
are 1/2, 1/4, 1/8, 3/16 and 1/16. In explicit examples we establish that the
matrix BPS states correspond to (intersecting) brane configurations that are
obtained from the d=11 supersymmetry algebra. This correspondence for the 1/2
supersymmetric branes includes the precise relations between the charges.Comment: 11 pages, LaTeX, no figures, minor changes, shortened version to be
published in Physics Letters

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