Nonperturbative Corrections to Adler Function and Hypothesis of Vacuum Dominance

We check the range of values of four-quark condensate, relying on the processing of experimental data on e+e− annihilation into even number of pions (BaBar, CMD-2, OLYA) and extracting from them the values of the nonperturbative corrections. According to the hypothesis of vacuum dominance, the vacuum average of the four-quark condensate is expressed in terms of quark condensate while only vacuum intermediate states contribution is taken into account. However, assuming a possible non-zero effect of non-vacuum intermediate states, we check its influence on the four-quark condensate, or coefficient C6 in operator product expansion. Moreover, we explore how other nonperturbative corrections, C2 (operator with dimension 2), and C4 (which includes gluon condensate), are changed when assuming this effect. It is shown that values of four-quark condensate, or coefficient C6, can vary not more than 15-20%. Other parameters (C2 and C4) take values close to the currently available ones.