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| Main Authors: | , |
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| Format: | Preprint |
| Published: |
2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2506.16547 |
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| _version_ | 1866912442102054912 |
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| author | Giblin, Peter Wettig, Alexander |
| author_facet | Giblin, Peter Wettig, Alexander |
| contents | We generalise the well-known ``embroidery'' envelopes of chords joining points at angles $t$ and $mt$ of a single circle in several ways. Firstly we allow $m$ to be rational (possibly negative) instead of integral, finding formulas for the number of cusps, points at infinity and self-intersections of these envelopes. Secondly we use two concentric circles instead of one, taking the chords to join a point of one circle to a point of the other. This construction allows the formation of different (higher) singularities -- not just simple cusps -- which however do not reveal their full inner structure when changing the radius of one of the circles. For this we need to break some of the symmetry and move the center of one of the circles as well as its radius. This permits the higher singularities, including swallowtails and butterflies,
to be ``versally unfolded'' in the language of singularity theory. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2506_16547 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Envelopes of lines, unfoldings and breaking symmetry Giblin, Peter Wettig, Alexander Differential Geometry 58K35, 51M15, 58K60 We generalise the well-known ``embroidery'' envelopes of chords joining points at angles $t$ and $mt$ of a single circle in several ways. Firstly we allow $m$ to be rational (possibly negative) instead of integral, finding formulas for the number of cusps, points at infinity and self-intersections of these envelopes. Secondly we use two concentric circles instead of one, taking the chords to join a point of one circle to a point of the other. This construction allows the formation of different (higher) singularities -- not just simple cusps -- which however do not reveal their full inner structure when changing the radius of one of the circles. For this we need to break some of the symmetry and move the center of one of the circles as well as its radius. This permits the higher singularities, including swallowtails and butterflies, to be ``versally unfolded'' in the language of singularity theory. |
| title | Envelopes of lines, unfoldings and breaking symmetry |
| topic | Differential Geometry 58K35, 51M15, 58K60 |
| url | https://arxiv.org/abs/2506.16547 |