Further Results on the Riemann Hypothesis for Angular Lattice Sums

We present further results on a class of sums which involve complex powers of the distance to points in a two-dimensional square lattice and trigonometric functions of their angle, supplementing those in a previous paper (McPhedran et al, Porc. Roy. Soc., 2008). We give a general expression which permits numerical evaluation of members of the class of sums to arbitrary order. We use this to illustrate numerically the properties of trajectories along which the real and imaginary parts of the sums are zero, and we show results for the first two of a particular set of angular sums which indicate their density of zeros on the critical line of the complex exponent is the same as that for the product of the Riemann zeta function and the Catalan beta function.