We study Euclidean designs from the viewpoint of the potential energy. For a
finite set in Euclidean space, We formulate a linear programming bound for the
potential energy by applying harmonic analysis on a sphere. We also introduce
the concept of strong Euclidean designs from the viewpoint of the linear
programming bound, and we give a Fisher type inequality for strong Euclidean
designs. A finite set on Euclidean space is called a Euclidean a-code if any
distinct two points in the set are separated at least by a.
In the previous paper, we studied the "Toy models for D. H. Lehmer's
conjecture". Namely, we showed that the m-th Fourier coefficient of the
weighted theta series of the $\mathbb{Z}^2$-lattice and the $A_{2}$-lattice
does not vanish, when the shell of norm $m$ of those lattices is not the empty
set. In other words, the spherical 4 (resp. 6)-design does not exist among the
nonempty shells in the $\mathbb{Z}^2$-lattice (resp. $A_{2}$-lattice). This
paper is the sequel to the previous paper.
Let $L$ be any integral lattice in the 2-dimensional Euclidean space.
Generalizing the earlier works of Hiroshi Maehara and others, we prove that for
every integer $n>0$, there is a circle in the plane $\mathbb{R}^{2}$ that
passes through exactly $n$ points of $L$.
In this paper, we show that an extremal Type II $\ZZ_{2k}$-code of length $n$
dose not exist for all sufficiently large $n$ when $k=2,3,4,5,6$.