145 research outputs found

### Wrapped fluxbranes

We consider the construction of fluxbranes in certain curved geometries,
generalizing the familiar construction of the Melvin fluxtube as a quotient of
flat space. The resulting configurations correspond to fluxbranes wrapped on
cycles in curved spaces. The non-trivial transverse geometry leads in some
instances to solutions with asymptotically constant dilaton profiles. We
describe explicitly several supersymmetric solutions of this kind. The
solutions inherit some properties from their flat space cousins, like flux
periodicity. Interestingly type IIA/0A fluxbrane duality holds near the core of
these fluxbranes, but does not persist in the asymptotic region, precisely
where it would contradict perturbative inequivalence of IIA/0A theories.Comment: 22 pages, latex, no figures. Added reference

### Comments on Non-Supersymmetric Orientifolds at Strong Coupling

We consider several properties of a set of anti-D$p$-branes in the presence
of orientifold $p$-planes in type II theory. This system breaks all the
supersymmetries of the theory, but is free of tachyons. In particular, we
center on the case of a single anti-D$p$-brane stuck at a negatively charged
orientifold $p$-plane, and study its strong coupling behaviour for $p=2,3,4$.
Interestingly enough, as the coupling increases the system undergoes a phase
transition where an additional antibrane is created. We conclude with some
remarks on the limit of large number of antibranes on top of orientifold
planes.Comment: 14 pages, Latex. Orientifold-antibrane short distance interaction
corrected, references adde

### Brane Configurations for Branes at Conifolds

We study the T duality between a set of type IIB D3 branes atnon-orbifold
threefold singularities, and type IIA configurations of D4 branes stretched
between relatively rotated NS fivebranes. The four-dimensional N=1 field
theories on the D3 brane world-volume can be easily described using the IIA
brane configuration. These models include families of chiral theories
continuously connected to the theories appearing in brane box models (or D3
branes at orbifold singularities). We propose that phase transitions in the
K\"ahler moduli space of the singularity are related to the crossing of rotated
NS fivebranes in the T dual picture, and thus to Seiberg's duality in one of
the gauge factors. We also comment on the inclusion of orientifold planes in
the IIA brane picture.Comment: 34 pages, Latex, 7 eps figures. Several comments added, and important
clarifications concerning Seiberg dualit

### Brane Boxes and Branes on Singularities

Brane Box Models of intersecting NS and D5 branes are mapped to D3 branes at
C^3/Gamma orbifold singularities and vise versa, in a setup which gives rise to
N=1 supersymmetric gauge theories in four dimensions. The Brane Box Models are
constructed on a two-torus. The map is interpreted as T-duality along the two
directions of the torus. Some Brane Box Models contain NS fivebranes winding
around (p,q) cycles in the torus, and our method provides the geometric T-dual
to such objects. An amusing aspect of the mapping is that T-dual configurations
are calculated using D=4 N=1 field theory data. The mapping to the singularity
picture allows the geometrical interpretation of all the marginal couplings in
finite field theories. This identification is further confirmed using the
AdS/CFT correspondence for orbifold theories. The AdS massless fields coupling
to the marginal operators in the boundary appear as stringy twisted sectors of
S^5/Gamma. The mapping for theories which are non-finite requires the
introduction of fractional D3 branes in the singularity picture.Comment: 55 pages, 13 figure

### Chiral Type II Orientifold Constructions as M Theory on G_2 holonomy spaces

We summarize some recent progress in constructing four-dimensional
supersymmetric chiral models from Type II orientifolds. We present the
construction a supersymmetric Standard-like Model and a supersymmetric GUT
model to illustrate the new features of this approach and its connection to M
theory on compact, singular G_2 holonomy spaces. The Standard-like model
presented is the first example of a three-family supersymmetic orientifold
model with the Standard Model as part of the gauge structure. We also discuss
the connection of how chiral fermions arise in this class of models with recent
results of M theory compactified on G_2 holonomy spaces.Comment: 10 pages SUSY '01 Proceedings Contributio

### A Chern-Simons Pandemic

In this paper we study the consistency of generalized global symmetries in
theories of quantum gravity, in particular string theory. Such global
symmetries arise in theories with $(p+1)$-form gauge fields, and for spacetime
dimension $d\leq p+3$ there are obstructions to their breaking even by quantum
effects of charged objects. In 4d theories with a 2-form gauge field (or with
an axion scalar), these fields endow Schwarzschild black holes with quantum
hair, a global charge leading to usual trouble with remnants. We describe
precise mechanisms, and examples from string compactifications and holographic
pairs, in which these problems are evaded by either gauging or breaking the
global symmetry, via (suitable versions of) Stuckelberg or Kaloper-Sorbo
couplings. We argue that even in the absence of such couplings, the generic
solution in string theory is the breaking of the global symmetries by cubic
Chern-Simons terms involving different antisymmetric tensor fields. We
conjecture that any theory with (standard or higher-degree antisymmetric
tensor) gauge fields is in the Swampland unless its effective action includes
such Chern-Simons terms. This conjecture implies that many familiar theories,
like QED (even including the charged particles required by the Weak Gravity
Conjecture) or $\mathcal{N}=8$ supergravity in four dimensions, are
inconsistent in quantum gravity unless they are completed by these Chern-Simons
terms.Comment: 60 pages, 2 figure

### From quiver diagrams to particle physics

Recent scenarios of phenomenologically realistic string compactifications
involve the existence of gauge sectors localized on D-branes at singular points
of Calabi-Yau threefolds. The spectrum and interactions in these gauge sectors
are determined by the local geometry of the singularity, and can be encoded in
quiver diagrams. We discuss the physical models arising for the simplest case
of orbifold singularities, and generalize to non-orbifold singularities and
orientifold singularities. Finally we show that relatively simple singularities
lead to gauge sectors surprisingly close to the standard model of elementary
particles.Comment: 14 pages, Latex, 3 figures. (Slightly modified version of)
contribution to proceedings of the 3rd European Congress of Mathematic

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