2,228 research outputs found

    Renormalization of chiral perturbation theory to order p^6

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    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

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    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

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    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

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    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.

    Private Labeling and Competition between Retailers

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

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    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

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    We analyze the supersymmetric contributions to direct-CP-violating observables in Kâ†’Ï€Ï€ÎłK \to \pi\pi\gamma decays induced by gluino-mediated magnetic-penguin operators. We find that \epsp_{+-\gamma} and the differential width asymmetry of K±→π±π0ÎłK^\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 ∣ΔS∣=1|\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.