S.A. Akimenko et al. [43] have investigated
the general form of the matrix element for 
decays,
obtained by adding scalar and tensor
couplings to
the standard V-A interaction. Analyzing the
Dalitz-plot
distribution of 
events, they
find that the presence of scalar and tensor couplings or nonlinearities in the
form factor 
cannot be excluded.
DA
NE may be
an ideal place to check this claim (
events in
one year). However, the same proviso as in the case
of radiative 
decays should be made
(see subsection 1.6): before any firm conclusion
can
be drawn, one has to estimate the effect of higher-order terms in the chiral
calculation. In the present case this may be less difficult to achieve than in
radiative kaon decays,
as only one form factor comes into play, which, in addition, depends on
one kinematical variable only.