1305.6839 (H. Leutwyler)

The mass of the two lightest quarks    [PDF]

H. Leutwyler

The problems encountered in the determination of m_u and m_d are discussed. While their sum is known quite well, the difference m_d-m_u, which measures the breaking of isospin symmetry in the QCD Lagrangian, is still subject to significant uncertainties. I focus on recent work based on the dispersive analysis of the decay eta -> 3 pi, which offers a good handle on isospin breaking, because in that transition, the contributions from the e.m. interaction are suppressed.

View original: http://arxiv.org/abs/1305.6839