672 research outputs found
D6-branes and torsion
The D6-brane spectrum of type IIA vacua based on twisted tori and RR
background fluxes is analyzed. In particular, we compute the torsion factors of
the (co)homology groups H_n and describe the effect that they have on D6-brane
physics. For instance, the fact that H_3 contains Z_N subgroups explains why RR
tadpole conditions are affected by geometric fluxes. In addition, the presence
of torsional (co)homology shows why some D6-brane moduli are lifted, and it
suggests how the D-brane discretum appears in type IIA flux compactifications.
Finally, we give a clear, geometrical understanding of the Freed-Witten anomaly
in the present type IIA setup, and discuss its consequences for the
construction of semi-realistic flux vacua.Comment: 35 pages, 1 figure. One reference adde
Effects of training on sand or hard surfaces on sprint and jump performance of team-sport players: a systematic review with meta-analysis
We examined the effectiveness of training on sand and compared the effects of sand and hard surface training programs on the sprint and jump performance of team-sport players. PubMed MEDLINE, SPORTDiscus, and Web of Science databases were used in the literature search. A total of 377 records were initially identified and six studies comprising 136 athletes were included in the meta-analysis. Pre- and post-comparisons showed that sand training interventions were effective at improving both jump and sprint capacities. When comparing sand and hard surfaces, no significant differences in favor of any of the interventions were observed. In summary, this review revealed that sand training is an efficient strategy to improve jump and sprint performances in team-sport players. Moreover, sand surfaces produced similar gains to those observed after hard surface training schemes. Strength and conditioning coaches and sport scientists who work with team-sports can use both sand and hard surface training programs as part of their regular training practices, during distinct phases of the season
Heterotic compactifications and nearly-Kahler manifolds
We propose that under certain conditions heterotic string compactifications
on half-flat and nearly-Kahler manifolds are equivalent. Based on this
correspondence we argue that the moduli space of the nearly-Kahler manifolds
under discussion consists only of the Kahler deformations moduli space and
there is no correspondent for the complex structure deformations.Comment: 5 pages, references added, typos correcte
On the Taxonomy of Flux Vacua
We investigate several predictions about the properties of IIB flux vacua on
Calabi-Yau orientifolds, by constructing and characterizing a very large set of
vacua in a specific example, an orientifold of the Calabi-Yau hypersurface in
. We find support for the prediction of Ashok and Douglas
that the density of vacua on moduli space is governed by where and are curvature and K\"ahler forms on the moduli
space. The conifold point on moduli space therefore serves as an
attractor, with a significant fraction of the flux vacua contained in a small
neighborhood surrounding . We also study the functional dependence of
the number of flux vacua on the D3 charge in the fluxes, finding simple power
law growth.Comment: 22 pages, harvmac; v2 typos corrected, refs added; v3 minor error
correcte
Branes on Generalized Calibrated Submanifolds
We extend previous results on generalized calibrations to describe
supersymmetric branes in supergravity backgrounds with diverse fields turned
on, and provide several new classes of examples. As an important application,
we show that supersymmetric D-branes in compactifications with field strength
fluxes, and on SU(3)-structure spaces, wrap generalized calibrated
submanifolds, defined by simple conditions in terms of the underlying globally
defined, but non-closed, 2- and 3-forms. We provide examples where the
geometric moduli of D-branes (for instance D7-branes in 3-form flux
configurations) are lifted by the generalized calibration condition. In
addition, we describe supersymmetric D6-branes on generalized calibrated
3-submanifolds of half-flat manifolds, which provide the mirror of B-type
D-branes in IIB CY compactifications with 3-form fluxes. Supersymmetric sets of
such D-branes carrying no homology charges are mirror to supersymmetric sets of
D-branes which are homologically non-trivial, but trivial in K-theory. As an
additional application, we describe models with chiral gauge sectors, realized
in terms of generalized calibrated brane box configurations of NS- and
D5-branes, which are supersymmetric but carry no charges, so that no
orientifold planes are required in the compactification.Comment: 40 pages, 3 figures, references adde
Fluxes, moduli fixing and MSSM-like vacua in a simple IIA orientifold
We study the effects of adding RR, NS and metric fluxes on a T^6/(\Omega
(-1)^{F_L} I_3) Type IIA orientifold. By using the effective flux-induced
superpotential we obtain Minkowski or AdS vacua with broken or unbroken
supersymmetry. In the Minkowski case some combinations of real moduli remain
undetermined, whereas all can be stabilized in the AdS solutions. Many flux
parameters are available which are unconstrained by RR tadpole cancellation
conditions allowing to locate the minima at large volume and small dilaton. We
also find that in AdS supersymmetric vacua with metric fluxes, the overall flux
contribution to RR tadpoles can vanish or have opposite sign to that of
D6-branes, allowing for new model-building possibilities. In particular, we
construct the first N=1 supersymmetric intersecting D6-brane models with
MSSM-like spectrum and with all closed string moduli stabilized. Some
axion-like fields remain undetermined but they are precisely required to give
St\"uckelberg masses to (potentially anomalous) U(1) brane fields. We show that
the cancellation of the Freed-Witten anomaly guarantees that the axions with
flux-induced masses are orthogonal to those giving masses to the U(1)'s.
Cancellation of such anomalies also guarantees that the D6-branes in our N=1
supersymmetric AdS vacua are calibrated so that they are forced to preserve one
unbroken supersymmetry.Comment: 61 pages, Latex, v2: added references, v3: minor correction
Building MSSM Flux Vacua
We construct N=1 and N=0 chiral four-dimensional vacua of flux
compactification in Type IIB string theory. These vacua have the common
features that they are free of tadpole instabilities (both NSNS and RR) even
for models with N=0 supersymmetry. In addition, the dilaton/complex structure
moduli are stabilised and the supergravity background metric is warped. We
present an example in which the low energy spectrum contains the MSSM spectrum
with three generations of chiral matter. In the N=0 models, the background
fluxes which stabilise the moduli also induce soft supersymmetry breaking terms
in the gauge and chiral sectors of the theory, while satisfying the equation of
motion. We also discuss some phenomenological features of these three
generation MSSM flux vacua. Our techniques apply to other closed string
backgrounds as well and, in fact, also allow to find new N=1 D-brane models
which were believed not to exist. Finally, we discuss in detail the consistency
conditions of these flux compactifications. Cancellation of K-theory charges
puts additional constraints on the consistency of the models, which render some
chiral D-brane models in the literature inconsistent.Comment: 33 pages, 1 figure. Minor correction
Holographic dual of the Standard Model on the throat
We apply recent techniques to construct geometries, based on local Calabi-Yau
manifolds, leading to warped throats with 3-form fluxes in string theory, with
interesting structure at their bottom. We provide their holographic dual
description in terms of RG flows for gauge theories with almost conformal
duality cascades and infrared confinement. We describe a model of a throat with
D-branes at its bottom, realizing a 3-family Standard Model like chiral sector.
We provide the explicit holographic dual gauge theory RG flow, and describe the
appearance of the SM degrees of freedom after confinement. As a second
application, we describe throats within throats, namely warped throats with
discontinuous warp factor in different regions of the radial coordinate, and
discuss possible model building applications.Comment: 46 pages, 21 figures, reference adde
D3 Brane Action and Fermion Zero Modes in Presence of Background Flux
We derive the fermion bilinear terms in the world volume action for a D3
brane in the presence of background flux. In six-dimensional compactifications
non-perturbative corrections to the superpotential can arise from an Euclidean
D3-brane instanton wrapping a divisor in the internal space. The bilinear terms
give rise to fermion masses and are important in determining these corrections.
We find that the three-form flux generically breaks a U(1) subgroup of the
structure group of the normal bundle of the divisor. In an example of
compactification on T^6/Z_2, six of the sixteen zero modes originally present
are lifted by the flux.Comment: Important factor of ``i'' was overlooked in Euclidean continuation of
WZ term. This changes the count of zero-modes in the T^6/Z_2 example. Main
result stays unchanged. We thank Bergshoeff, Kallosh, Kashani-Poor, Sorokin
and Tomasiello for pointing this ou
The heat kernel of the compactified D=11 supermembrane with non-trivial winding
We study the quantization of the regularized hamiltonian, , of the
compactified D=11 supermembrane with non-trivial winding. By showing that
is a relatively small perturbation of the bosonic hamiltonian, we construct a
Dyson series for the heat kernel of and prove its convergence in the
topology of the von Neumann-Schatten classes so that is ensured to be
of finite trace. The results provided have a natural interpretation in terms of
the quantum mechanical model associated to regularizations of compactified
supermembranes. In this direction, we discuss the validity of the Feynman path
integral description of the heat kernel for D=11 supermembranes and obtain a
matrix Feynman-Kac formula.Comment: 19 pages. AMS LaTeX. A whole new section was added and some other
minor changes in style where mad
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