7,781 research outputs found
GLSM's for gerbes (and other toric stacks)
In this paper we will discuss gauged linear sigma model descriptions of toric
stacks. Toric stacks have a simple description in terms of (symplectic, GIT)
quotients of homogeneous coordinates, in exactly the same
form as toric varieties. We describe the physics of the gauged linear sigma
models that formally coincide with the mathematical description of toric
stacks, and check that physical predictions of those gauged linear sigma models
exactly match the corresponding stacks. We also check in examples that when a
given toric stack has multiple presentations in a form accessible as a gauged
linear sigma model, that the IR physics of those different presentations
matches, so that the IR physics is presentation-independent, making it
reasonable to associate CFT's to stacks, not just presentations of stacks. We
discuss mirror symmetry for stacks, using Morrison-Plesser-Hori-Vafa techniques
to compute mirrors explicitly, and also find a natural generalization of
Batyrev's mirror conjecture. In the process of studying mirror symmetry, we
find some new abstract CFT's, involving fields valued in roots of unity.Comment: 43 pages, LaTeX, 3 figures; v2: typos fixe
Mass dependence of the hairpin vertex in quenched QCD
The pseudoscalar ``hairpin'' vertex (i.e. quark-disconnected vertex) plays a
key role in quenched chiral perturbation theory. Direct calculations using
lattice simulations find that it has a significant dependence on quark mass. I
show that this mass dependence can be used to determine the quenched
Gasser-Leutwyler constant L5. This complements the calculation of L5 using the
mass dependence of the axial decay constant of the pion. In an appendix, I
discuss power counting for quenched chiral perturbation theory and describe the
particular scheme used in this paper.Comment: 12 pages, 4 figures. Version to appear in Phys. Rev. D. Central
result unchanged, but explanation of calculation improved and minor errors
corrected. New appendix discusses power counting schemes in quenched chiral
perturbation theor
Non-perturbative Renormalization of Improved Staggered Bilinears
We compute Z-factors for general staggered bilinears on fine (a \approx 0.09
fm) MILC ensembles using both asqtad and HYP-smeared valence actions, comparing
the results to the predictions of one-loop perturbation theory. This is an
extension of previous work on the coarse (a \approx 0.12 fm) MILC ensembles. It
provides a laboratory for studying NPR methodology in the staggered context,
and is an important stepping stone for fully non-perturbative matching factors
in ongoing computations of B_K and other weak matrix elements. We also
implement non-exceptional RI/SMOM renormalization conditions using the asqtad
action and present first results.Comment: 7 pages, 4 figures. Contribution to the 30th International Symposium
on Lattice Field Theory, June 24-29, 2012, Cairns, Australi
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