420 research outputs found
Coisotropic D8-branes and Model-building
Up to now chiral type IIA vacua have been mostly based on intersecting
D6-branes wrapping special Lagrangian 3-cycles on a CY three-fold. We argue
that there are additional BPS D-branes which have so far been neglected, and
which seem to have interesting model-building features. They are coisotropic
D8-branes, in the sense of Kapustin and Orlov. The D8-branes wrap 5-dimensional
submanifolds of the CY which are trivial in homology, but contain a worldvolume
flux that induces D6-brane charge on them. This induced D6-brane charge not
only renders the D8-brane BPS, but also creates D=4 chirality when two
D8-branes intersect. We discuss in detail the case of a type IIA Z2 x Z2
orientifold, where we provide explicit examples of coisotropic D8-branes. We
study the chiral spectrum, SUSY conditions, and effective field theory of
different systems of D8-branes in this orientifold, and show how the magnetic
fluxes generate a superpotential for untwisted Kahler moduli. Finally, using
both D6-branes and coisotropic D8-branes we construct new examples of MSSM-like
type IIA vacua.Comment: 63 pages, 11 figures. Typos corrected and comments adde
Zeeman Spectroscopy of the Star Algebra
We solve the problem of finding all eigenvalues and eigenvectors of the
Neumann matrix of the matter sector of open bosonic string field theory,
including the zero modes, and switching on a background B-field. We give the
discrete eigenvalues as roots of transcendental equations, and we give
analytical expressions for all the eigenvectors.Comment: (1, 25) pages, 2 Figure
Kappa symmetry, generalized calibrations and spinorial geometry
We extend the spinorial geometry techniques developed for the solution of
supergravity Killing spinor equations to the kappa symmetry condition for
supersymmetric brane probe configurations in any supergravity background. In
particular, we construct the linear systems associated with the kappa symmetry
projector of M- and type II branes acting on any Killing spinor. As an example,
we show that static supersymmetric M2-brane configurations which admit a
Killing spinor representing the SU(5) orbit of are generalized
almost hermitian calibrations and the embedding map is pseudo-holomorphic. We
also present a bound for the Euclidean action of M- and type II branes embedded
in a supersymmetric background with non-vanishing fluxes. This leads to an
extension of the definition of generalized calibrations which allows for the
presence of non-trivial Born-Infeld type of fields in the brane actions.Comment: 9 pages, latex, references added and minor change
Instantons on Quivers and Orientifolds
We compute the prepotential for gauge theories descending from
SYM via quiver projections and mass deformations.
This accounts for gauge theories with product gauge groups and bifundamental
matter. The case of massive orientifold gauge theories with gauge group SO/Sp
is also described. In the case with no gravitational corrections the results
are shown to be in agreement with Seiberg-Witten analysis and previous results
in the literature.Comment: 28 pages, revised version, references added, some typos correcte
Computing Yukawa Couplings from Magnetized Extra Dimensions
We compute Yukawa couplings involving chiral matter fields in toroidal
compactifications of higher dimensional super-Yang-Mills theory with magnetic
fluxes. Specifically we focus on toroidal compactifications of D=10
super-Yang-Mills theory, which may be obtained as the low-energy limit of Type
I, Type II or Heterotic strings. Chirality is obtained by turning on constant
magnetic fluxes in each of the 2-tori. Our results are general and may as well
be applied to lower D=6,8 dimensional field theories. We solve Dirac and
Laplace equations to find out the explicit form of wavefunctions in extra
dimensions. The Yukawa couplings are computed as overlap integrals of two Weyl
fermions and one complex scalar over the compact dimensions. In the case of
Type IIB (or Type I) string theories, the models are T-dual to (orientifolded)
Type IIA with D6-branes intersecting at angles. These theories may have
phenomenological relevance since particular models with SM group and three
quark-lepton generations have been recently constructed. We find that the
Yukawa couplings so obtained are described by Riemann theta-functions, which
depend on the complex structure and Wilson line backgrounds. Different patterns
of Yukawa textures are possible depending on the values of these backgrounds.
We discuss the matching of these results with the analogous computation in
models with intersecting D6-branes. Whereas in the latter case a string
computation is required, in our case only field theory is needed.Comment: 73 pages, 9 figures. Using JHEP3.cls. Typos and other minor
corrections fixed. References adde
Coupled-mode theory for Bose-Einstein condensates
We apply the concepts of nonlinear guided-wave optics to a Bose-Einstein
condensate (BEC) trapped in an external potential. As an example, we consider a
parabolic double-well potential and derive coupled-mode equations for the
complex amplitudes of the BEC macroscopic collective modes. Our equations
describe different regimes of the condensate dynamics, including the nonlinear
Josephson effect for any separation between the wells. We demonstrate
macroscopic self-trapping for both repulsive and attractive interactions, and
confirm our results by numerical simulations.Comment: 4 pages, 5 figures; typos removed, figures amended; submitted to PR
Supersymmetric (non-)Abelian Bundles in the Type I and SO(32) Heterotic String
We discuss perturbative four-dimensional compactifications of both the SO(32)
heterotic and the Type I string on smooth Calabi-Yau manifolds endowed with
general non-abelian and abelian bundles. We analyse the generalized
Green-Schwarz mechanism for multiple anomalous U(1) factors and derive the
generically non-universal one-loop threshold corrections to the gauge kinetic
function as well as the one-loop corrected Fayet-Iliopoulos terms. The latter
can be interpreted as a stringy one-loop correction to the
Donaldson-Uhlenbeck-Yau condition. Applying S-duality, for the Type I string we
obtain the perturbative Pi-stability condition for non-abelian bundles on
curved spaces. Some simple examples are given, and we qualitatively discuss
some generic phenomenological aspects of this kind of string vacua. In
particular, we point out that in principle an intermediate string scale
scenario with TeV scale large extra dimensions might be possible for the
heterotic string.Comment: LaTeX, 32 pages, v2: refs adde
Level-rank duality of the U(N) WZW model, Chern-Simons theory, and 2d qYM theory
We study the WZW, Chern-Simons, and 2d qYM theories with gauge group U(N).
The U(N) WZW model is only well-defined for odd level K, and this model is
shown to exhibit level-rank duality in a much simpler form than that for SU(N).
The U(N) Chern-Simons theory on Seifert manifolds exhibits a similar duality,
distinct from the level-rank duality of SU(N) Chern-Simons theory on S^3. When
q = e^{2 pi i/(N+K)}, the observables of the 2d U(N) qYM theory can be
expressed as a sum over a finite subset of U(N) representations. When N and K
are odd, the qYM theory exhibits N K duality, provided q = e^{2 pi
i/(N+K)} and theta = 0 mod 2 pi /(N+K).Comment: 19 pages; v2: minor typo corrected, 1 paragraph added, published
versio
Loop-Corrected Compactifications of the Heterotic String with Line Bundles
We consider the E8 x E8 heterotic string theory compactified on Calabi-Yau
manifolds with bundles containing abelian factors in their structure group.
Generic low energy consequences such as the generalised Green-Schwarz mechanism
for the multiple anomalous abelian gauge groups are studied. We also compute
the holomorphic gauge couplings and induced Fayet-Iliopoulos terms up to
one-loop order, where the latter are interpreted as stringy one-loop
corrections to the Donaldson-Uhlenbeck-Yau condition. Such models generically
have frozen combinations of Kaehler and dilaton moduli. We study concrete
bundles with structure group SU(N) x U(1)^M yielding quasi-realistic gauge
groups with chiral matter given by certain bundle cohomology classes. We also
provide a number of explicit tadpole free examples of bundles defined by exact
sequences of sums of line bundles over complete intersection Calabi-Yau spaces.
This includes one example with precisely the Standard Model gauge symmetry.Comment: 47 pages, 6 figures, LaTeX, v2: stability discussion in sect. 2.1
slightly extended, refs. added, v3: normalization of Green-Schwarz term
correcte
Open Superstring Star as a Continuous Moyal Product
By diagonalizing the three-string vertex and using a special coordinate
representation the matter part of the open superstring star is identified with
the continuous Moyal product of functions of anti-commuting variables. We show
that in this representation the identity and sliver have simple expressions.
The relation with the half-string fermionic variables in continuous basis is
given.Comment: Latex, 19 pages; more comments added and notations are simplifie
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