Update on pion weak decay constants in nuclear matter

摘要

The QCD sum rule calculation of the in-medium pion decay constants using pseudoscalar-axial-vector correlation function, i integral d(4)xe(ip.x) is revisited. In particular, we argue that the dimension 5 condensate, <(q) over bar (iD(0))(2)q>(N) + 1/8<(q) over barg(s)sigma . G(q)>(N), which is crucial for splitting the time (f(t)) and space (f(s)) components of the decay constant, is not necessarily restricted to be positive. Its positive value is found to yield a tachyonic pion mass. Using the in-medium pion mass as an input, we fix the dimension 5 condensate to be around -0.025 GeV2 similar to -0.019 GeV2. The role of the N and Delta intermediate states in the correlation function is also investigated. The N intermediate state is found not to contribute to the sum rules. For the A intermediate state, we either treat it as a part of the continuum or propose a way to subtract explicitly from the sum rules. With (and without) explicit A subtraction while allowing the in-medium pion mass to vary within 139 MeV less than or equal to m(pi)* less than or equal to 159 MeV, we obtain f(s)/f(pi) = 0.37 similar to 0.78 and f(t)/f(pi) = 0.63 similar to 0.79. (C) 2003 Elsevier Science B.V. All rights reserved. [References: 28]