An entire solution of the Allen–Cahn equation
,
where
is an odd function and has exactly three zeros at
and
, for example,
, is called a
-end solution if its nodal
set is asymptotic to
half lines, and if along each of these half lines the function
looks like the one-dimensional, heteroclinic solution. In this paper we
consider the family of four-end solutions whose ends are almost parallel at
. We
show that this family can be parametrized by the family of solutions of the Toda
system. As a result we obtain the uniqueness of four-end solutions with almost
parallel ends. Combining this result with the classification of connected components
in the moduli space of the four-end solutions, we can classify all such solutions. Thus
we show that four-end solutions form, up to rigid motions, a one parameter family.
This family contains the saddle solution, for which the angle between the nodal lines
is
, as
well as solutions for which the angle between the asymptotic half lines of the nodal set is
any
.
Keywords
Allen–Cahn equation, entire solutions, moduli space, Toda
system, four-end solutions