# King's College London

## On the distribution of lattice points on hyperbolic circles

Research output: Contribution to journalArticlepeer-review

Dimitrios Chatzakos, Par Kurlberg, Stephen Lester, Igor Wigman

Original language English 23 Algebra and Number Theory 28 Feb 2021

### Documents

• On_the_distribution_of_CHATZAKOS_Accepted28February2021_GREEN_AAM.pdf, 489 KB, application/pdf

We study the fine distribution of lattice points lying on expanding circles in the hyperbolic plane $\mathbb{H}$. The angles of lattice points arising from the orbit of the modular group $\pslz$, and lying on hyperbolic circles, are shown to be equidistributed for {\em generic} radii. However, the angles fail to equidistribute on a thin set of exceptional radii, even in the presence of growing multiplicity. Surprisingly, the distribution of angles on hyperbolic circles turns out to be related to the angular distribution of $\mathbb{Z}^2$-lattice points (with certain parity conditions) lying on circles in $\mathbb{R}^2$, along a thin subsequence of radii. A notable difference is that measures in the hyperbolic setting can break symmetry --- on very thin subsequences they are not invariant under rotation by $\frac{\pi}{2}$, unlike the Euclidean setting where all measures have this invariance property.