On the size of the chiral condensate, generalized chiral perturbation theory and the DIRAC experiment

In the near future, the DIRAC collaboration will measure pi pi scattering l engths with great precision. Those measurements are likely to shed some lig ht on the problem of the size of the chiral [0\(q) over bar q\0] condensate . Although it is usually assumed to be as large as similar to (-225 MeV)(3) , in the last years a more general approach has been developed to accommoda te either a large or a small alternative similar to (-100 MeV)(3). Such a l ow value would also modify the standard temperature estimate at which the c hiral phase transition occurs. In this work we briefly review the basic the oretical ideas related to this issue as well as the experiment that could h elp to establish any of the two scenarios.