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Abstract |
Employing the Bethe-Salpeter formalism, we present a computation of the space-like baryonic form factor for the pion and kaon. In the exact isospin-symmetric limit this observable is forbidden by G-parity, so that any nonzero signal constitutes a direct probe of the quark mass difference m(d) – m(u). The form factors are evaluated in the impulse approximation using fully dressed quark propagators, meson Bethe-Salpeter amplitudes, and a dressed baryon-current vertex constrained by the vector Ward-Takahashi identity. The baryonic radius computed with this method for the pion is given by < r(B)(2)>(1/2)(pi+) = 0.043(2) fm, and is consistent with the available dispersive benchmarks. Our predictions for the kaons, namely < r(B)(2)>(1/2)(K+) = 0.265(7)fm and < r(B)(2)>(1/2)(K0) = 0.262(7) fm, indicate a larger spatial extent than in the pion case; these results have no dispersive counterparts, and are compatible with chiral QCD models. |
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