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A lagrangian of the u and d quarks where they don't have a mass, shares chiral SU(2) and U(1) symmetries.

In the vacuum, we write

[itex] <0| \bar{Q} Q | 0 > = \eta [/itex]

where Q is the douplet of u and d quarks. In such a way we break chiral symmetries.

The current associated with the three axial broken symmetries creates three goldstone bosons, the pions, and in the approximation where d and u are massless, the pions are massless too.

Now I just don't understand the following point: breaking the symmetry, we give a mass to u and d quarks, as Peskin says in pag. 669.

How can these quarks and their relative antiquarks form the pions, which we said to be massless?

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# Quarks effective masses and the pions

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