147 research outputs found

### D-branes and Discrete Torsion II

We derive D-brane gauge theories for C^3/Z_n x Z_n orbifolds with discrete
torsion and study the moduli space of a D-brane at a point. We show that, as
suggested in previous work, closed string moduli do not fully resolve the
singularity, but the resulting space -- containing n-1 conifold singularities
-- is somewhat surprising. Fractional branes also have unusual properties.
We also define an index which is the CFT analog of the intersection form in
geometric compactification, and use this to show that the elementary D6-brane
wrapped about T^6/Z_n x Z_n must have U(n) world-volume gauge symmetry.Comment: harvmac, 25 p

### Moduli Spaces for D-branes at the Tip of a Cone

For physicists: We show that the quiver gauge theory derived from a
Calabi-Yau cone via an exceptional collection of line bundles on the base has
the original cone as a component of its classical moduli space. For
mathematicians: We use data from the derived category of sheaves on a Fano
surface to construct a quiver, and show that its moduli space of
representations has a component which is isomorphic to the anticanonical cone
over the surface.Comment: 8 page

### The Breakdown of Topology at Small Scales

We discuss how a topology (the Zariski topology) on a space can appear to
break down at small distances due to D-brane decay. The mechanism proposed
coincides perfectly with the phase picture of Calabi-Yau moduli spaces. The
topology breaks down as one approaches non-geometric phases. This picture is
not without its limitations, which are also discussed.Comment: 12 pages, 2 figure

### Solitons in Seiberg-Witten Theory and D-branes in the Derived Category

We analyze the "geometric engineering" limit of a type II string on a
suitable Calabi-Yau threefold to obtain an N=2 pure SU(2) gauge theory. The
derived category picture together with Pi-stability of B-branes beautifully
reproduces the known spectrum of BPS solitons in this case in a very explicit
way. Much of the analysis is particularly easy since it can be reduced to
questions about the derived category of CP1.Comment: 20 pages, LaTex2

### String-String triality for d=4, Z_2 orbifolds

We investigate the perturbative and non-perturbative correspondence of a
class of four dimensional dual string constructions with N=4 and N=2
supersymmetry, obtained as Z_2 or Z_2 x Z_2 orbifolds of the type II, heterotic
and type I string. In particular, we discuss the heterotic and type I dual of
all the symmetric Z_2 x Z_2 orbifolds of the type II string, classified in
hep-th/9901123. .Comment: latex, 50 pages, figures, final published versio

### C^2/Z_n Fractional branes and Monodromy

We construct geometric representatives for the C^2/Z_n fractional branes in
terms of branes wrapping certain exceptional cycles of the resolution. In the
process we use large radius and conifold-type monodromies, and also check some
of the orbifold quantum symmetries. We find the explicit Seiberg-duality which
connects our fractional branes to the ones given by the McKay correspondence.
We also comment on the Harvey-Moore BPS algebras.Comment: 34 pages, v1 identical to v2, v3: typos fixed, discussion of
Harvey-Moore BPS algebras update

### Quivers from Matrix Factorizations

We discuss how matrix factorizations offer a practical method of computing
the quiver and associated superpotential for a hypersurface singularity. This
method also yields explicit geometrical interpretations of D-branes (i.e.,
quiver representations) on a resolution given in terms of Grassmannians. As an
example we analyze some non-toric singularities which are resolved by a single
CP1 but have "length" greater than one. These examples have a much richer
structure than conifolds. A picture is proposed that relates matrix
factorizations in Landau-Ginzburg theories to the way that matrix
factorizations are used in this paper to perform noncommutative resolutions.Comment: 33 pages, (minor changes

### On explicit results at the intersection of the Z_2 and Z_4 orbifold subvarieties in K3 moduli space

We examine the recently found point of intersection between the Z_2 and Z_4
orbifold subvarieties in the K3 moduli space more closely. First we give an
explicit identification of the coordinates of the respective Z_2 and Z_4
orbifold theories at this point. Secondly we construct the explicit
identification of conformal field theories at this point and show the
orthogonality of the two subvarieties.Comment: Latex, 23 page

### Quantum symmetries and exceptional collections

We study the interplay between discrete quantum symmetries at certain points
in the moduli space of Calabi-Yau compactifications, and the associated
identities that the geometric realization of D-brane monodromies must satisfy.
We show that in a wide class of examples, both local and compact, the monodromy
identities in question always follow from a single mathematical statement. One
of the simplest examples is the Z_5 symmetry at the Gepner point of the
quintic, and the associated D-brane monodromy identity

### Type IIB Flux Vacua from M-theory via F-theory

We study in detail some aspects of duality between type IIB and M-theory. We
focus on the duality between type IIB string theory on K3 x T^2/Z_2 orientifold
and M-theory on K3 x K3, in the F-theory limit. We give the explicit map
between the fields and in particular between the moduli of compactification,
studying their behavior under the F-theory limit. Turning on fluxes generates a
potential for the moduli both in type IIB and in M-theory. We verify that the
type IIB analysis gives the same results of the F-theory analysis. In
particular, we check that the two potentials match.Comment: 24 pages; reference correcte

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