2,206 research outputs found
Anomaly Cancelation in Field Theory and F-theory on a Circle
We study the manifestation of local gauge anomalies of four- and
six-dimensional field theories in the lower-dimensional Kaluza-Klein theory
obtained after circle compactification. We identify a convenient set of
transformations acting on the whole tower of massless and massive states and
investigate their action on the low-energy effective theories in the Coulomb
branch. The maps employ higher-dimensional large gauge transformations and
precisely yield the anomaly cancelation conditions when acting on the one-loop
induced Chern-Simons terms in the three- and five-dimensional effective theory.
The arising symmetries are argued to play a key role in the study of the
M-theory to F-theory limit on Calabi-Yau manifolds. For example, using the fact
that all fully resolved F-theory geometries inducing multiple Abelian gauge
groups or non-Abelian groups admit a certain set of symmetries, we are able to
generally show the cancelation of pure Abelian or pure non-Abelian anomalies in
these models.Comment: 48 pages, 2 figures; v2: typos corrected, comments on circle fluxes
adde
Singlet fission and tandem solar cells reduce thermal degradation and enhance lifespan
The economic value of a photovoltaic installation depends upon both its lifespan and power conversion efficiency. Progress toward the latter includes mechanisms to circumvent the Shockley-Queisser limit, such as tandem designs and multiple exciton generation (MEG). Here we explain how both silicon tandem and MEG-enhanced silicon cell architectures result in lower cell operating temperatures, increasing the device lifetime compared to standard c-Si cells. Also demonstrated are further advantages from MEG enhanced silicon cells: (i) the device architecture can completely circumvent the need for current-matching; and (ii) upon degradation, tetracene, a candidate singlet fission (a form of MEG) material, is transparent to the solar spectrum. The combination of (i) and (ii) mean that the primary silicon device will continue to operate with reasonable efficiency even if the singlet fission layer degrades. The lifespan advantages of singlet fission enhanced silicon cells, from a module perspective, are compared favorably alongside the highly regarded perovskite/silicon tandem and conventional c-Si modules
Structure in 6D and 4D N=1 supergravity theories from F-theory
We explore some aspects of 4D supergravity theories and F-theory vacua that
are parallel to structures in the space of 6D theories. The spectrum and
topological terms in 4D supergravity theories correspond to topological data of
F-theory geometry, just as in six dimensions. In particular, topological
axion-curvature squared couplings appear in 4D theories; these couplings are
characterized by vectors in the dual to the lattice of axion shift symmetries
associated with string charges. These terms are analogous to the Green-Schwarz
terms of 6D supergravity theories, though in 4D the terms are not generally
linked with anomalies. We outline the correspondence between F-theory topology
and data of the corresponding 4D supergravity theories. The correspondence of
geometry with structure in the low-energy action illuminates topological
aspects of heterotic-F-theory duality in 4D as well as in 6D. The existence of
an F-theory realization also places geometrical constraints on the 4D
supergravity theory in the large-volume limit.Comment: 63 page
F-Theory and the Mordell-Weil Group of Elliptically-Fibered Calabi-Yau Threefolds
The Mordell-Weil group of an elliptically fibered Calabi-Yau threefold X
contains information about the abelian sector of the six-dimensional theory
obtained by compactifying F-theory on X. After examining features of the
abelian anomaly coefficient matrix and U(1) charge quantization conditions of
general F-theory vacua, we study Calabi-Yau threefolds with Mordell-Weil
rank-one as a first step towards understanding the features of the Mordell-Weil
group of threefolds in more detail. In particular, we generate an interesting
class of F-theory models with U(1) gauge symmetry that have matter with both
charges 1 and 2. The anomaly equations --- which relate the Neron-Tate height
of a section to intersection numbers between the section and fibral rational
curves of the manifold --- serve as an important tool in our analysis.Comment: 29 pages + appendices, 5 figures; v2: minor correction
Six-dimensional (1,0) effective action of F-theory via M-theory on Calabi-Yau threefolds
The six-dimensional effective action of F-theory compactified on a singular
elliptically fibred Calabi-Yau threefold is determined by using an M-theory
lift. The low-energy data are derived by comparing a circle reduction of a
general six-dimensional (1,0) gauged supergravity theory with the effective
action of M-theory on the resolved Calabi-Yau threefold. The derivation
includes six-dimensional tensor multiplets for which the (anti-) self-duality
constraints are imposed on the level of the five-dimensional action. The vector
sector of the reduced theory is encoded by a non-standard potential due to the
Green-Schwarz term in six dimensions. This Green-Schwarz term also contains
higher curvature couplings which are considered to establish the full map
between anomaly coefficients and geometry. F-/M-theory duality is exploited by
moving to the five-dimensional Coulomb branch after circle reduction and
integrating out massive vector multiplets and matter hypermultiplets. The
associated fermions then generate additional Chern-Simons couplings at
one-loop. Further couplings involving the graviphoton are induced by quantum
corrections due to excited Kaluza-Klein modes. On the M-theory side integrating
out massive fields corresponds to resolving the singularities of the Calabi-Yau
threefold, and yields intriguing relations between six-dimensional anomalies
and classical topology.Comment: 55 pages, v2: typos corrected, discussion of loop corrections
improve
T-Branes and Monodromy
We introduce T-branes, or "triangular branes," which are novel non-abelian
bound states of branes characterized by the condition that on some loci, their
matrix of normal deformations, or Higgs field, is upper triangular. These
configurations refine the notion of monodromic branes which have recently
played a key role in F-theory phenomenology. We show how localized matter
living on complex codimension one subspaces emerge, and explain how to compute
their Yukawa couplings, which are localized in complex codimension two. Not
only do T-branes clarify what is meant by brane monodromy, they also open up a
vast array of new possibilities both for phenomenological constructions and for
purely theoretical applications. We show that for a general T-brane, the
eigenvalues of the Higgs field can fail to capture the spectrum of localized
modes. In particular, this provides a method for evading some constraints on
F-theory GUTs which have assumed that the spectral equation for the Higgs field
completely determines a local model.Comment: 110 pages, 5 figure
Anomaly Equations and Intersection Theory
Six-dimensional supergravity theories with N=(1,0) supersymmetry must satisfy
anomaly equations. These equations come from demanding the cancellation of
gravitational, gauge and mixed anomalies. The anomaly equations have
implications for the geometrical data of Calabi-Yau threefolds, since F-theory
compactified on an elliptically fibered Calabi-Yau threefold with a section
generates a consistent six-dimensional N=(1,0) supergravity theory. In this
paper, we show that the anomaly equations can be summarized by three
intersection theory identities. In the process we also identify the geometric
counterpart of the anomaly coefficients---in particular, those of the abelian
gauge groups---that govern the low-energy dynamics of the theory. We discuss
the results in the context of investigating string universality in six
dimensions.Comment: 29 pages + appendices, 8 figures; v2: minor corrections, references
added; v3: minor corrections, reference adde
Stringy instanton corrections to N=2 gauge couplings
We discuss a string model where a conformal four-dimensional N=2 gauge theory
receives corrections to its gauge kinetic functions from "stringy" instantons.
These contributions are explicitly evaluated by exploiting the localization
properties of the integral over the stringy instanton moduli space. The model
we consider corresponds to a setup with D7/D3-branes in type I' theory
compactified on T4/Z2 x T2, and possesses a perturbatively computable heterotic
dual. In the heteoric side the corrections to the quadratic gauge couplings are
provided by a 1-loop threshold computation and, under the duality map, match
precisely the first few stringy instanton effects in the type I' setup. This
agreement represents a very non-trivial test of our approach to the exotic
instanton calculus.Comment: 63 pages, 5 figures. V2: final version with minor corrections
published on JHEP05(2010)10
On Global Flipped SU(5) GUTs in F-theory
We construct an SU(4) spectral divisor and its factorization of types (3,1)
and (2,2) based on the construction proposed in [1]. We calculate the chiral
spectra of flipped SU(5) GUTs by using the spectral divisor construction. The
results agree with those from the analysis of semi-local spectral covers. Our
computations provide an example for the validity of the spectral divisor
construction and suggest that the standard heterotic formulae are applicable to
the case of F-theory on an elliptically fibered Calabi-Yau fourfold with no
heterotic dual.Comment: 45 pages, 12 tables, 1 figure; typos corrected, footnotes added, and
a reference adde
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