On an analogue of BRK-type sets in finite fields
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866917064592064512 |
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| author | Forbes, Madeline |
| author_facet | Forbes, Madeline |
| contents | A Besicovitch-Rado-Kinney (BRK) set in $\mathbb{R}^n$ contains a hypersphere of every radius. In $\mathbb{F}_q^n$, BRK-type sets of degree $\ell$ analogously contain a family of $(n-1)$-dimensional surfaces, parametrized by a dilation factor and determined by a fixed homogeneous polynomial of degree $\ell$. We define $(n,d)$-BRK-type sets of degree $\ell$, which contain a family of $d$-dimensional sets parametrized by an $(n-d)$-dimensional dilation factor and determined by fixed homogeneous polynomials of degree $\ell$. We use the polynomial method to obtain a lower bound $|S| \gtrsim_{n, \ell} q^n$ on $(n,d)$-BRK-type sets $S$ of degree $\ell$. We obtain an improved lower bound $|S| \geq \frac{(q-1)^n}{(\ell + 1 - 2\ell/q)^n}$ by implementing the method of multiplicities; this is the same bound obtained by Trainor on BRK-type sets of degree $\ell$, and we obtain this bound independently of $d$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_04113 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | On an analogue of BRK-type sets in finite fields Forbes, Madeline Combinatorics 05B25, 11T99 A Besicovitch-Rado-Kinney (BRK) set in $\mathbb{R}^n$ contains a hypersphere of every radius. In $\mathbb{F}_q^n$, BRK-type sets of degree $\ell$ analogously contain a family of $(n-1)$-dimensional surfaces, parametrized by a dilation factor and determined by a fixed homogeneous polynomial of degree $\ell$. We define $(n,d)$-BRK-type sets of degree $\ell$, which contain a family of $d$-dimensional sets parametrized by an $(n-d)$-dimensional dilation factor and determined by fixed homogeneous polynomials of degree $\ell$. We use the polynomial method to obtain a lower bound $|S| \gtrsim_{n, \ell} q^n$ on $(n,d)$-BRK-type sets $S$ of degree $\ell$. We obtain an improved lower bound $|S| \geq \frac{(q-1)^n}{(\ell + 1 - 2\ell/q)^n}$ by implementing the method of multiplicities; this is the same bound obtained by Trainor on BRK-type sets of degree $\ell$, and we obtain this bound independently of $d$. |
| title | On an analogue of BRK-type sets in finite fields |
| topic | Combinatorics 05B25, 11T99 |
| url | https://arxiv.org/abs/2511.04113 |