1,621 research outputs found
The Vector and Scalar Form Factors of the Pion to Two Loops
We calculate the vector and scalar form factors of the pion to two loops in
Chiral Perturbation Theory. We estimate the unknown O(p^6) constants using
resonance exchange. We make a careful comparison to the available data and
determine two O(p^4) constants rather precisely, and two O(p^6) constants less
precisely. We also use Chiral Perturbation Theory to two loops to extract in a
model--independent manner the charge radius of the pion from the available
data, and obtain \rpiV=0.437\pm 0.016 fm^2.Comment: Latex2e, JHEP.cls, 30 pages 5 figure
Matching the Heavy Vector Meson Theory
We show how to obtain a ``heavy'' meson effective lagrangian for the case
where the number of heavy particles is not conserved. We apply the method in a
simple example at tree level and perform then the reduction for the case of
vector mesons in Chiral Perturbation Theory in a manifestly chiral invariant
fashion. Some examples showing that ``heavy'' meson effective theory also works
at the one-loop level are included.Comment: 11 pages, 2 figures, revte
Low Energy Constants from Kl4 Form-Factors
We have calculated the form-factors F and G in K ---> pi pi e nu decays (Kl4)
to two-loop order in Chiral Perturbation Theory (ChPT). Combining this together
with earlier two-loop calculations an updated set of values for the L's, the
ChPT constants at p^4, is obtained. We discuss the uncertainties in the
determination and the changes compared to previous estimates.Comment: 6 pages, uses axodraw.sty, 2 figures, bug in program corrected, new
numerical result
Conformal and Nonconformal Symmetries in 2d Dilaton gravity
We study finite-dimensional extra symmetries of generic 2D dilaton gravity
models. Using a non-linear sigma model formulation we show that the unique
theories admitting an extra (conformal) symmetry are the models with an
exponential potential (), which include the CGHS
model as a particular though limiting () case. These models give rise
to black hole solutions with a mass-dependent temperature. The underlying extra
symmetry can be maintained in a natural way in the one-loop effective action,
thus implying the exact solubility of the semiclassical theory including
back-reaction. Moreover, we also introduce three different classes of
(non-conformal) transformations which are extra symmetries for generic 2D
dilaton gravity models. Special linear combinations of these transformations
turn out to be the (conformal) symmetries of the CGHS and models. We show that one of the non-conformal extra symmetries
can be converted into a conformal one by means of adequate field redefinitions
involving the metric and the derivatives of the dilaton. Finally, by expressing
the Polyakov-Liouville effective action in terms of an invariant metric, we are
able to provide semiclassical models which are also invariant. This generalizes
the solvable semiclassical model of Bose, Parker and Peleg (BPP) for a generic
2D dilaton gravity model.Comment: Latex, no figures. Revised version published i
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