Weak solution

In particle physics, the pion decay constant is the square root of the coefficient in front of the kinetic term for the pion in the low-energy effective action. It is dimensionally an energy scale and it determines the strength of the chiral symmetry breaking. The values are:

$f_{\pi ^{\pm }}=130.41\pm 0.03\pm 0.20~{\mbox{MeV}}$

$f_{\pi ^{0}}=130\pm 5~{\mbox{MeV}}$

Beware: There are several conventions which differ by powers of $\scriptstyle {\sqrt {2}}$. The textbook by Weinberg uses the value 184 MeV. The textbook by Peskin and Schroeder uses the value 93 MeV.

References

1. Particle Data Group: W.-M. Yao et al., J. Phys. G 33, 1 (2006).
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3. Particle Data Group: Decay constants of charged pseudoscalar mesons

External links

1. Particle Data Group & WWW edition of Review of Particle Physics

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