# Restriction of 3D arithmetic Laplace eigenfunctions to a plane

## TL;DR

This paper studies the expected length of intersections between random Laplace eigenfunctions on a 3D torus and a surface, revealing universal proportionality and arithmetic-dependent variance bounds.

## Contribution

It provides a universal formula for the expected intersection length and introduces bounds on variance for planar surfaces based on lattice point estimates.

## Key findings

- Expected intersection length proportional to surface area and wavenumber
- Variance bounds depend on the arithmetic properties of the plane
- Lattice point estimates are used to derive variance bounds

## Abstract

We consider a random Gaussian ensemble of Laplace eigenfunctions on the 3D torus, and investigate the 1-dimensional Hausdorff measure (`length') of nodal intersections against a smooth 2-dimensional toral sub-manifold (`surface'). The expected length is universally proportional to the area of the reference surface, times the wavenumber, independent of the geometry. For surfaces contained in a plane, we give an upper bound for the nodal intersection length variance, depending on the arithmetic properties of the plane. The bound is established via estimates on the number of lattice points in specific regions of the sphere.