7,030 research outputs found
Heterotic compactifications with principal bundles for general groups and general levels
We examine to what extent heterotic string worldsheets can describe arbitrary
E8xE8 gauge fields. The traditional construction of heterotic strings builds
each E8 via a Spin(16)/Z2 subgroup, typically realized as a current algebra by
left-moving fermions, and as a result, only E8 gauge fields reducible to
Spin(16)/Z2 gauge fields are directly realizable in standard constructions.
However, there exist perturbatively consistent E8 gauge fields which can not be
reduced to Spin(16)/Z2, and so cannot be described within standard heterotic
worldsheet constructions. A natural question to then ask is whether there
exists any (0,2) SCFT that can describe such E8 gauge fields. To answer this
question, we first show how each ten-dimensional E8 partition function can be
built up using other subgroups than Spin(16)/Z2, then construct ``fibered WZW
models'' which allow us to explicitly couple current algebras for general
groups and general levels to heterotic strings. This technology gives us a very
general approach to handling heterotic compactifications with arbitrary
principal bundles. It also gives us a physical realization of some elliptic
genera constructed recently by Ando and Liu.Comment: 48 pages, LaTeX; v2: references added; v3: typos fixe
Quantization of Fayet-Iliopoulos Parameters in Supergravity
In this short note we discuss quantization of the Fayet-Iliopoulos parameter
in supergravity theories. We argue that in supergravity, the Fayet-Iliopoulos
parameter determines a lift of the group action to a line bundle, and such
lifts are quantized. Just as D-terms in rigid N=1 supersymmetry are interpreted
in terms of moment maps and symplectic reductions, we argue that in
supergravity the quantization of the Fayet-Iliopoulos parameter has a natural
understanding in terms of linearizations in geometric invariant theory (GIT)
quotients, the algebro-geometric version of symplectic quotients.Comment: 21 pages, utarticle class; v2: typos and tex issue fixe
GLSM realizations of maps and intersections of Grassmannians and Pfaffians
In this paper we give gauged linear sigma model (GLSM) realizations of a
number of geometries not previously presented in GLSMs. We begin by describing
GLSM realizations of maps including Veronese and Segre embeddings, which can be
applied to give GLSMs explicitly describing constructions such as the
intersection of one hypersurface with the image under some map of another. We
also discuss GLSMs for intersections of Grassmannians and Pfaffians with one
another, and with their images under various maps, which sometimes form exotic
constructions of Calabi-Yaus, as well as GLSMs for other exotic Calabi-Yau
constructions of Kanazawa. Much of this paper focuses on a specific set of
examples of GLSMs for intersections of Grassmannians G(2,N) with themselves
after a linear rotation, including the Calabi-Yau case N=5. One phase of the
GLSM realizes an intersection of two Grassmannians, the other phase realizes an
intersection of two Pfaffians. The GLSM has two nonabelian factors in its gauge
group, and we consider dualities in those factors. In both the original GLSM
and a double-dual, one geometric phase is realized perturbatively (as the
critical locus of a superpotential), and the other via quantum effects.
Dualizing on a single gauge group factor yields a model in which each geometry
is realized through a simultaneous combination of perturbative and quantum
effects.Comment: LaTeX, 50 pages; v2: typos fixed and a few comments on other
dualities adde
More Toda-like (0,2) mirrors
In this paper, we extend our previous work to construct (0,2) Toda-like
mirrors to A/2-twisted theories on more general spaces, as part of a program of
understanding (0,2) mirror symmetry. Specifically, we propose (0,2) mirrors to
GLSMs on toric del Pezzo surfaces and Hirzebruch surfaces with deformations of
the tangent bundle. We check the results by comparing correlation functions,
global symmetries, as well as geometric blowdowns with the corresponding (0,2)
Toda-like mirrors. We also briefly discuss Grassmannian manifolds.Comment: 49 pages, LaTeX; v2: references adde
Heavy-Meson Observables at One-Loop in Partially Quenched Chiral Perturbation Theory
I present one-loop level calculations of the Isgur-Wise functions for B ->
D^{(*)} + e + nu, of the matrix elements of isovector twist-2 operators in B
and D mesons, and the matrix elements for the radiative decays D^* -> D + gamma
in partially quenched heavy quark chiral perturbation theory. Such expressions
are required in order to extrapolate from the light quark masses used in
lattice simulations of the foreseeable future to those of nature.Comment: 13 pages, 3 fig
Radiative, actively cooled panel tests results
The radiative, actively cooled panel designed to withstand a uniform incident heat flux of 136 kW/sq m to a 444 K surface temperature was evaluated. The test program consisted of preliminary static thermal mechanical loading and aerothermal flow tests. Test results are briefly discussed
Levels of Ca\u3csub\u3ev\u3c/sub\u3e1.2 L-Type Ca\u3csup\u3e2+\u3c/sup\u3e Channels Peak in the First Two Weeks in Rat Hippocampus Whereas Ca\u3csub\u3ev\u3c/sub\u3e1.3 Channels Steadily Increase through Development
Influx of calcium through voltage-dependent channels regulates processes throughout the nervous system. Specifically, influx through L-type channels plays a variety of roles in early neuronal development and is commonly modulated by G-protein-coupled receptors such as GABAB receptors. Of the four isoforms of L-type channels, only Cav1.2 and Cav1.3 are predominately expressed in the nervous system. Both isoforms are inhibited by the same pharmacological agents, so it has been difficult to determine the role of specific isoforms in physiological processes. In the present study, Western blot analysis and confocal microscopy were utilized to study developmental expression levels and patterns of Cav1.2 and Cav1.3 in the CA1 region of rat hippocampus. Steady-state expression of Cav1.2 predominated during the early neonatal period decreasing by day 12. Steady-state expression of Cav1.3 was low at birth and gradually rose to adult levels by postnatal day 15. In immunohistochemical studies, antibodies against Cav1.2 and Cav1.3 demonstrated the highest intensity of labeling in the proximal dendrites at all ages studied (P1–72). Immunohistochemical studies on one-week-old hippocampi demonstrated significantly more colocalization of GABAB receptors with Cav1.2 than with Cav1.3, suggesting that modulation of L-type calcium current in early development is mediated through Cav1.2 channels
Quenched Chiral Perturbation Theory for Vector Mesons
We develop quenched chiral perturbation theory for vector mesons made of
light quarks, in the limit where the vector meson masses are much larger than
the pion mass. We use this theory to extract the leading nonanalytic dependence
of the vector meson masses on the masses of the light quarks. By comparing with
analogous quantities computed in ordinary chiral perturbation theory, we
estimate the size of quenching effects, observing that in general they can be
quite large. This estimate is relevant to lattice simulations, where the
mass is often used to set the lattice spacing.Comment: 18 pages, 8 figures, uses REVTeX and epsf.st
Chiral Perturbation Theory for the Quenched Approximation of QCD
[This version is a minor revision of a previously submitted preprint. Only
references have been changed.] We describe a technique for constructing the
effective chiral theory for quenched QCD. The effective theory which results is
a lagrangian one, with a graded symmetry group which mixes Goldstone bosons and
fermions, and with a definite (though slightly peculiar) set of Feynman rules.
The straightforward application of these rules gives automatic cancellation of
diagrams which would arise from virtual quark loops. The techniques are used to
calculate chiral logarithms in , , , and the ratio of
to . The leading
finite-volume corrections to these quantities are also computed. Problems for
future study are described.Comment: 14 page
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