English

Surfaces containing two isotropic circles through each point

Differential Geometry 2022-09-08 v2 Algebraic Geometry

Abstract

We prove (under some technical assumptions) that each surface in R3\mathbb R^3 containing two arcs of parabolas with axes parallel to OzOz through each point has a parametrization (P(u,v)R(u,v),Q(u,v)R(u,v),Z(u,v)R2(u,v))\left(\frac{P(u,v)}{R(u,v)},\frac{Q(u,v)}{R(u,v)},\frac{Z(u,v)}{R^2(u,v)}\right) for some P,Q,R,ZR[u,v]P,Q,R,Z\in\mathbb R[u,v] such that P,Q,RP,Q,R have degree at most 1 in uu and vv, and ZZ has degree at most 2 in uu and vv. The proof is based on the observation that one can consider a parabola with vertical axis as an isotropic circle; this allows us to use methods of the recent work by M. Skopenkov and R. Krasauskas in which all surfaces containing two Euclidean circles through each point are classified. Such approach also allows us to find a similar parametrization for surfaces in R3\mathbb R^3 containing two arbitrary isotropic circles through each point (under the same technical assumptions). Finally, we get some results concerning the top view (the projection along the OzOz axis) of the surfaces in question.

Keywords

Cite

@article{arxiv.2002.01355,
  title  = {Surfaces containing two isotropic circles through each point},
  author = {Egor Morozov},
  journal= {arXiv preprint arXiv:2002.01355},
  year   = {2022}
}

Comments

17 pages, 8 figures; v2: title changed, new figures added, appendix replaced by a reference to arXiv:1512.09062v3. Many minor additions and improvements

R2 v1 2026-06-23T13:30:55.317Z