3,798 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
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Fluxes and Warping for Gauge Couplings in F-theory
We compute flux-dependent corrections in the four-dimensional F-theory
effective action using the M-theory dual description. In M-theory the 7-brane
fluxes are encoded by four-form flux and modify the background geometry and
Kaluza-Klein reduction ansatz. In particular, the flux sources a warp factor
which also depends on the torus directions of the compactification fourfold.
This dependence is crucial in the derivation of the four-dimensional action,
although the torus fiber is auxiliary in F-theory. In M-theory the 7-branes are
described by an infinite array of Taub-NUT spaces. We use the explicit metric
on this geometry to derive the locally corrected warp factor and M-theory
three-from as closed expressions. We focus on contributions to the 7-brane
gauge coupling function from this M-theory back-reaction and show that terms
quadratic in the internal seven-brane flux are induced. The real part of the
gauge coupling function is modified by the M-theory warp factor while the
imaginary part is corrected due to a modified M-theory three-form potential.
The obtained contributions match the known weak string coupling result, but
also yield additional terms suppressed at weak coupling. This shows that the
completion of the M-theory reduction opens the way to compute various
corrections in a genuine F-theory setting away from the weak string coupling
limit.Comment: 46 page
Five-Brane Superpotentials, Blow-Up Geometries and SU(3) Structure Manifolds
We investigate the dynamics of space-time filling five-branes wrapped on
curves in heterotic and orientifold Calabi-Yau compactifications. We first
study the leading N=1 scalar potential on the infinite deformation space of the
brane-curve around a supersymmetric configuration. The higher order potential
is also determined by a brane superpotential which we compute for a subset of
light deformations. We argue that these deformations map to new complex
structure deformations of a non-Calabi-Yau manifold which is obtained by
blowing up the brane-curve into a four-cycle and by replacing the brane by
background fluxes. This translates the original brane-bulk system into a
unifying geometrical formulation. Using this blow-up geometry we compute the
complete set of open-closed Picard-Fuchs differential equations and identify
the brane superpotential at special points in the field space for five-branes
in toric Calabi-Yau hypersurfaces. This has an interpretation in open mirror
symmetry and enables us to list compact disk instanton invariants. As a first
step towards promoting the blow-up geometry to a supersymmetric heterotic
background we propose a non-Kaehler SU(3) structure and an identification of
the three-form flux.Comment: 95 pages, 4 figures; v2: Minor corrections, references update
Massive Abelian Gauge Symmetries and Fluxes in F-theory
F-theory compactified on a Calabi-Yau fourfold naturally describes
non-Abelian gauge symmetries through the singularity structure of the elliptic
fibration. In contrast Abelian symmetries are more difficult to study because
of their inherently global nature. We argue that in general F-theory
compactifications there are massive Abelian symmetries, such as the uplift of
the Abelian part of the U(N) gauge group on D7-branes, that arise from
non-Kahler resolutions of the dual M-theory setup. The four-dimensional
F-theory vacuum with vanishing expectation values for the gauge fields
corresponds to the Calabi-Yau limit. We propose that fluxes that are turned on
along these U(1)s are uplifted to non-harmonic four-form fluxes. We derive the
effective four-dimensional gauged supergravity resulting from F-theory
compactifications in the presence of the Abelian gauge factors including the
effects of possible fluxes on the gauging, tadpoles and matter spectrum.Comment: 49 page
Molecular characterization of the Hansenula polymorpha FLD1 gene encoding formaldehyde dehydrogenase
Glutathione-dependent formaldehyde dehydrogenase (FLD) is a key enzyme required for the catabolism of methanol as a carbon source and certain primary amines. such as methylamine as nitrogen sources in methylotrophic yeasts. Here we describe the molecular characterization of the FLD1 gene from the yeast Hansenula polymorpha. Unlike the recently described Pichia pastoris homologue, the H. polymorpha gene does not contain an intron. The predicted FLD1 product (Fld1p) is a protein of 380 amino acids (ca. 41 kDa) with 82% identity to P. pastoris Fld1p, 76% identity to the FLD protein sequence from n-alkane-assimilating yeast Candida maltosa and 63-64% identity to dehydrogenase class III enzymes from humans and other higher eukaryotes. The expression of FLD1 is strictly regulated and can be controlled at two expression levels by manipulation of the growth conditions. The gene is strongly induced under methylotrophic growth conditions; moderate expression is obtained under conditions in which a primary amine, e.g. methylamine, is used as nitrogen source. These properties render the FLD1 promoter of high interest for heterologous gene expression. The availability of the H. polymorpha FLD1 promoter provides an attractive alternative for expression of foreign genes besides the commonly used alcohol oxidase promoter. The sequence has been deposited in the GenBank/NCBI data library under Accession No. AF364077. Copyright (C) 2002 John Wiley Sons, Ltd.</p
Ecological Modeling of Aedes aegypti (L.) Pupal Production in Rural Kamphaeng Phet, Thailand
Background - Aedes aegypti (L.) is the primary vector of dengue, the most important arboviral infection globally. Until an effective vaccine is licensed and rigorously administered, Ae. aegypti control remains the principal tool in preventing and curtailing dengue transmission. Accurate predictions of vector populations are required to assess control methods and develop effective population reduction strategies. Ae. aegypti develops primarily in artificial water holding containers. Release recapture studies indicate that most adult Ae. aegypti do not disperse over long distances. We expect, therefore, that containers in an area of high development site density are more likely to be oviposition sites and to be more frequently used as oviposition sites than containers that are relatively isolated from other development sites. After accounting for individual container characteristics, containers more frequently used as oviposition sites are likely to produce adult mosquitoes consistently and at a higher rate. To this point, most studies of Ae. aegypti populations ignore the spatial density of larval development sites. Methodology - Pupal surveys were carried out from 2004 to 2007 in rural Kamphaeng Phet, Thailand. In total, 84,840 samples of water holding containers were used to estimate model parameters. Regression modeling was used to assess the effect of larval development site density, access to piped water, and seasonal variation on container productivity. A varying-coefficients model was employed to account for the large differences in productivity between container types. A two-part modeling structure, called a hurdle model, accounts for the large number of zeroes and overdispersion present in pupal population counts. Findings - The number of suitable larval development sites and their density in the environment were the primary determinants of the distribution and abundance of Ae. aegypti pupae. The productivity of most container types increased significantly as habitat density increased. An ecological approach, accounting for development site density, is appropriate for predicting Ae. aegypti population levels and developing efficient vector control program
Evolutionary variation in the expression of phenotypically plastic color vision in Caribbean mantis shrimps, genus Neogonodactylus
Author Posting. © The Author(s), 2006. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Marine Biology 150 (2006): 213-220, doi:10.1007/s00227-006-0313-5.Many animals have color vision systems that are well suited to their local environments.
Changes in color vision can occur over long periods (evolutionary time), or over relatively short
periods such as during development. A select few animals, including stomatopod crustaceans,
are able to adjust their systems of color vision directly in response to varying environmental
stimuli. Recently, it has been shown that juveniles of some stomatopod species that inhabit a
range of depths can spectrally tune their color vision to local light conditions through spectral
changes in filters contained in specialized photoreceptors. The present study quantifies the
potential for spectral tuning in adults of three species of Caribbean Neogonodactylus
stomatopods that differ in their depth ranges to assess how ecology and evolutionary history
influence the expression of phenotypically plastic color vision in adult stomatopods. After 12
weeks in either a full-spectrum “white” or a narrow-spectrum “blue” light treatment, each of the
three species evidenced distinctive tuning abilities with respect to the light environment that
could be related to its natural depth range. A molecular phylogeny generated using
mitochondrial cytochrome oxidase C subunit 1 (CO-1) was used to determine whether tuning
abilities were phylogenetically or ecologically constrained. Although the sister taxa N. wennerae
and N. bredini both exhibited spectral tuning, their ecology (i.e. preferred depth range) strongly
influenced the expression of the phenotypically plastic color vision trait. Our results indicate
that adult stomatopods have evolved the ability to undergo habitat-specific spectral tuning,
allowing rapid facultative physiological modification to suit ecological constraints.This research was funded partially by NSF
grant (IBN-0235820) to TWC and Sigma Xi Grants-in-Aid to AGC and by the National Coral
Reef Institute through a subaward to PHB and RL Caldwell through the NOAA Coastal Ocean
Program under award #NA16OA2413, to Nova Southeastern University
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
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
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