6,378 research outputs found
Spectra of D-branes with Higgs vevs
In this paper we continue previous work on counting open string states
between D-branes by considering open strings between D-branes with nonzero
Higgs vevs, and in particular, nilpotent Higgs vevs, as arise, for example,
when studying D-branes in orbifolds. Ordinarily Higgs vevs can be interpreted
as moving the D-brane, but nilpotent Higgs vevs have zero eigenvalues, and so
their interpretation is more interesting -- for example, they often correspond
to nonreduced schemes, which furnishes an important link in understanding old
results relating classical D-brane moduli spaces in orbifolds to Hilbert
schemes, resolutions of quotient spaces, and the McKay correspondence. We give
a sheaf-theoretic description of D-branes with Higgs vevs, including nilpotent
Higgs vevs, and check that description by noting that Ext groups between the
sheaves modelling the D-branes, do in fact correctly count open string states.
In particular, our analysis expands the types of sheaves which admit on-shell
physical interpretations, which is an important step for making derived
categories useful for physics.Comment: 46 pages, LaTeX; v2: typos fixed; v3: more typos fixe
Notes on nonabelian (0,2) theories and dualities
In this paper we explore basic aspects of nonabelian (0,2) GLSM's in two
dimensions for unitary gauge groups, an arena that until recently has largely
been unexplored. We begin by discussing general aspects of (0,2) theories,
including checks of dynamical supersymmetry breaking, spectators and weak
coupling limits, and also build some toy models of (0,2) theories for bundles
on Grassmannians, which gives us an opportunity to relate physical anomalies
and trace conditions to mathematical properties. We apply these ideas to study
(0,2) theories on Pfaffians, applying recent perturbative constructions of
Pfaffians of Jockers et al. We discuss how existing dualities in (2,2)
nonabelian gauge theories have a simple mathematical understanding, and make
predictions for additional dualities in (2,2) and (0,2) gauge theories.
Finally, we outline how duality works in open strings in unitary gauge
theories, and also describe why, in general terms, we expect analogous
dualities in (0,2) theories to be comparatively rare.Comment: 93 pages, LaTeX; v2: typos fixe
Performance of a hypersonic hot fuselage structure with a carbon dioxide frost projected, nonintegral cryogenic tank
A model which consisted of a hot structure and a nonintegral tank protected by a carbon dioxide frost thermal protection system was tested under the following conditions: (1) room temperature loading and (2) heating and loading corresponding to the Mach 8 flight of an air-breathing launch vehicle. In the simulated flight tests, liquid nitrogen inside the tank was withdrawn at the rate fuel would be consumed. Prior to each simulated flight test, carbon dioxide was cryodeposited in the insulation surrounding the tank; during the tests, subliming CO2 frost absorbed heat and provided a purge gas for the space between the tank and the structure. A method of flame spraying the joints between panels with a nickel-aluminum material was developed to prevent excessive leakage of the purge gas through the outer structure. The tests indicated that the hot structure (with a joint repaired by riveting), the nonintegral tank and suspension system, and the carbon dioxide frost thermal protection system provide a workable concept with predictable performance
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
Chiral corrections to the axial charges of the octet baryons from quenched QCD
We calculate one-loop correction to the axial charges of the octet baryons
using quenched chiral perturbation theory, in order to understand chiral
behavior of the axial charges in quenched approximation to quantum
chromodynamics (QCD). In contrast to regular behavior of the full QCD chiral
perturbation theory result, , we find
that the quenched chiral perturbation theory result,
, is
singular in the chiral limit.Comment: standard LaTeX, 16 pages, 4 epsf figure
Non-birational twisted derived equivalences in abelian GLSMs
In this paper we discuss some examples of abelian gauged linear sigma models
realizing twisted derived equivalences between non-birational spaces, and
realizing geometries in novel fashions. Examples of gauged linear sigma models
with non-birational Kahler phases are a relatively new phenomenon. Most of our
examples involve gauged linear sigma models for complete intersections of
quadric hypersurfaces, though we also discuss some more general cases and their
interpretation. We also propose a more general understanding of the
relationship between Kahler phases of gauged linear sigma models, namely that
they are related by (and realize) Kuznetsov's `homological projective duality.'
Along the way, we shall see how `noncommutative spaces' (in Kontsevich's sense)
are realized physically in gauged linear sigma models, providing examples of
new types of conformal field theories. Throughout, the physical realization of
stacks plays a key role in interpreting physical structures appearing in GLSMs,
and we find that stacks are implicitly much more common in GLSMs than
previously realized.Comment: 54 pages, LaTeX; v2: typo fixe
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