2,228 research outputs found

### Renormalization of chiral perturbation theory to order p^6

The renormalization of chiral perturbation theory is carried out to
next-to-next-to-leading order in the meson sector. We calculate the divergent
part of the generating functional of Green functions of quark currents to
O(p^6) for chiral SU(n), involving one- and two-loop diagrams. The
renormalization group equations for the renormalized low-energy constants of
O(p^6) are derived. We compare our results with previous two-loop calculations
in chiral perturbation theory.Comment: 43 pages, LaTeX2e, 1 figur

### 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

### The quark condensate from K_{e_4} decays

We show that, independently of the size of the quark condensate, chiral
symmetry correlates the two S-wave \pi\pi scattering lengths. In view of this
constraint, the new precision data on K_{e_4} decay allow a remarkably accurate
determination of these quantities. The result confirms the hypothesis that the
quark condensate is the leading order parameter.Comment: 4 pages (LaTex), 3 figure

### Quenched chiral perturbation theory to one loop

We calculate the divergences of the generating functional of quenched chiral perturbation theory at one loop, and renormalize the theory by an appropriate definition of the counterterms. We show that the quenched chiral logarithms can be accounted for by defining a renormalized B0 parameter which, at lowest order, is proportional to the vacuum expectation value of the scalar quark density. Finally, we calculate several quantities at one loop to better analyze the modifications induced by quenching in the ultraviolet finite part of the one-loop corrections. We point out that some of the finite loop corrections may diverge in the chiral limit.

### Una valutazione dell'attivit\ue0 dell'antitrust italiano dopo venti anni

Si ripercorre l'attivit\ue0 svolta dalla autorit\ue0 antitrust italiana nei venti anni individuando successi e insuccessi ed esprimendo una valutazione complessiva

### Supersymmetric contributions to direct CP violation in K -> pi pi gamma decays

We analyze the supersymmetric contributions to direct-CP-violating
observables in $K \to \pi\pi\gamma$ decays induced by gluino-mediated
magnetic-penguin operators. We find that \epsp_{+-\gamma} and the
differential width asymmetry of $K^\pm \to \pi^\pm \pi^0 \gamma$ decays could
be substantially enhanced with respect to their Standard Model values,
especially in the scenario where \epsp/\eps is dominated by supersymmetric
contributions. These observables could therefore provide a useful tool to
search for New Physics effects in $|\Delta S|=1$ transitions, complementary to
\epsp/\eps and rare decays.Comment: 14 pages, Latex. Numerical error in Eq.(36) corrected, conclusions
unchanged; version to appear in Phys. Lett.

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