3,037 research outputs found
Pseudoscalar pole light-by-light contributions to the muon in Resonance Chiral Theory
We have studied the transition form-factors
() within a chiral invariant framework that allows us to
relate the three form-factors and evaluate the corresponding contributions to
the muon anomalous magnetic moment , through pseudoscalar pole
contributions. We use a chiral invariant Lagrangian to describe the
interactions between the pseudo-Goldstones from the spontaneous chiral symmetry
breaking and the massive meson resonances. We will consider just the lightest
vector and pseudoscalar resonance multiplets. Photon interactions and flavor
breaking effects are accounted for in this covariant framework. This article
studies the most general corrections of order within this setting.
Requiring short-distance constraints fixes most of the parameters entering the
form-factors, consistent with previous determinations. The remaining ones are
obtained from a fit of these form-factors to experimental measurements in the
space-like () region of photon momenta. The combination of data,
chiral symmetry relations between form-factors and high-energy constraints
allows us to determine with improved precision the on-shell -pole
contribution to the Hadronic Light-by-Light scattering of the muon anomalous
magnetic moment: we obtain for
our best fit. This result was obtained excluding BaBar data, which our
analysis finds in conflict with the remaining experimental inputs. This study
also allows us to determine the parameters describing the system
in the two-mixing angle scheme and their correlations. Finally, a preliminary
rough estimate of the impact of loop corrections () and higher vector
multiplets (asym) enlarges the uncertainty up to .Comment: 43 pages, 5 figures. Accepted for publication in JHEP. New subsection
involving error analysis and some minor change
Moduli Spaces and Formal Operads
Let overline{M}_{g,n} be the moduli space of stable algebraic curves of genus
g with n marked points. With the operations which relate the different moduli
spaces identifying marked points, the family (overline{M}_{g,n})_{g,n} is a
modular operad of projective smooth Deligne-Mumford stacks, overline{M}. In
this paper we prove that the modular operad of singular chains
C_*(overline{M};Q) is formal; so it is weakly equivalent to the modular operad
of its homology H_*(overline{M};Q). As a consequence, the "up to homotopy"
algebras of these two operads are the same. To obtain this result we prove a
formality theorem for operads analogous to Deligne-Griffiths-Morgan-Sullivan
formality theorem, the existence of minimal models of modular operads, and a
characterization of formality for operads which shows that formality is
independent of the ground field.Comment: 36 pages (v3: some typographical corrections
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