Hostname: page-component-669899f699-7tmb6 Total loading time: 0 Render date: 2025-04-30T02:39:10.571Z Has data issue: false hasContentIssue false

NEAR OPTIMAL THRESHOLDS FOR EXISTENCE OF DILATED CONFIGURATIONS IN $\mathbb {F}_q^d$

Published online by Cambridge University Press:  26 January 2024

PABLO BHOWMIK
Affiliation:
Department of Mathematics, University of Rochester, Rochester, NY, USA e-mail: [email protected]
FIRDAVS RAKHMONOV*
Affiliation:
Department of Mathematics, University of Rochester, Rochester, NY, USA

Abstract

Let $\mathbb {F}_q^d$ denote the d-dimensional vector space over the finite field $\mathbb {F}_q$ with q elements. Define for $\alpha = (\alpha _1, \dots , \alpha _d) \in \mathbb {F}_q^d$. Let $k\in \mathbb {N}$, A be a nonempty subset of $\{(i, j): 1 \leq i < j \leq k + 1\}$ and $r\in (\mathbb {F}_q)^2\setminus {0}$, where $(\mathbb {F}_q)^2=\{a^2:a\in \mathbb {F}_q\}$. If $E\subset \mathbb {F}_q^d$, our main result demonstrates that when the size of the set E satisfies $|E| \geq C_k q^{d/2}$, where $C_k$ is a constant depending solely on k, it is possible to find two $(k+1)$-tuples in E such that one of them is dilated by r with respect to the other, but only along $|A|$ edges. To be more precise, we establish the existence of $(x_1, \dots , x_{k+1}) \in E^{k+1}$ and $(y_1, \dots , y_{k+1}) \in E^{k+1}$ such that, for $(i, j) \in A$, we have $\lVert y_i - y_j \rVert = r \lVert x_i - x_j \rVert $, with the conditions that $x_i \neq x_j$ and $y_i \neq y_j$ for $1 \leq i < j \leq k + 1$, provided that $|E| \geq C_k q^{d/2}$ and $r\in (\mathbb {F}_q)^2\setminus \{0\}$. We provide two distinct proofs of this result. The first uses the technique of group actions, a powerful method for addressing such problems, while the second is based on elementary combinatorial reasoning. Additionally, we establish that in dimension 2, the threshold $d/2$ is sharp when $q \equiv 3 \pmod 4$. As a corollary of the main result, by varying the underlying set A, we determine thresholds for the existence of dilated k-cycles, k-paths and k-stars (where $k \geq 3$) with a dilation ratio of $r\in (\mathbb {F}_q)^2\setminus \{0\}$. These results improve and generalise the findings of Xie and Ge [‘Some results on similar configurations in subsets of $\mathbb {F}_q^d$’, Finite Fields Appl. 91 (2023), Article no. 102252, 20 pages].

Type
Research Article
Copyright
© The Author(s), 2024. Published by Cambridge University Press on behalf of Australian Mathematical Publishing Association Inc.

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Article purchase

Temporarily unavailable

References

Bennett, M., Hart, D., Iosevich, A., Pakianathan, J. and Rudnev, M., ‘Group actions and geometric combinatorics in ${F}_{q^d}$ ’, Forum Math. 29(1) (2017), 91110.10.1515/forum-2015-0251CrossRefGoogle Scholar
Bourgain, J., Katz, N. and Tao, T., ‘A sum-product estimate in finite fields, and applications’, Geom. Funct. Anal. 14(1) (2004), 2757.10.1007/s00039-004-0451-1CrossRefGoogle Scholar
Chapman, J., Burak Erdoğan, M., Hart, D., Iosevich, A. and Koh, D., ‘Pinned distance sets, $k$ -simplices, Wolff’s exponent in finite fields and sum-product estimates’, Math. Z. 271(1–2) (2012), 6393.10.1007/s00209-011-0852-4CrossRefGoogle Scholar
Hart, D., Iosevich, A., Koh, D. and Rudnev, M., ‘Averages over hyperplanes, sum-product theory in vector spaces over finite fields and the Erdős–Falconer distance conjecture’, Trans. Amer. Math. Soc. 363(6) (2011), 32553275.10.1090/S0002-9947-2010-05232-8CrossRefGoogle Scholar
Iosevich, A., Koh, D. and Parshall, H., ‘On the quotient set of the distance set’, Mosc. J. Comb. Number Theory 8(2) (2019), 103115.10.2140/moscow.2019.8.103CrossRefGoogle Scholar
Iosevich, A., Koh, D. and Rakhmonov, F., ‘The quotient set of the quadratic distance set over finite fields’, Forum Math. to appear, doi:10.1515/forum-2023-0313.CrossRefGoogle Scholar
Iosevich, A. and Rudnev, M., ‘Erdős distance problem in vector spaces over finite fields’, Trans. Amer. Math. Soc. 359(12) (2007), 61276142.10.1090/S0002-9947-07-04265-1CrossRefGoogle Scholar
Murphy, B. and Petridis, G., ‘An example related to the Erdős–Falconer question over arbitrary finite fields’, Bull. Hellenic Math. Soc. 63 (2019), 3839.Google Scholar
Murphy, B., Petridis, G., Pham, T., Rudnev, M. and Stevens, S., ‘On the pinned distances problem in positive characteristic’, J. Lond. Math. Soc. (2) 105(1) (2022), 469499.10.1112/jlms.12524CrossRefGoogle Scholar
Rakhmonov, F., ‘Distribution of similar configurations in subsets of ${F}_{q^d}$ ’, Discrete Math. 346(10) (2023), Article no. 113571, 21 pages.10.1016/j.disc.2023.113571CrossRefGoogle Scholar
Xie, C. and Ge, G., ‘Some results on similar configurations in subsets of ${F}_{q^d}$ ’, Finite Fields Appl. 91 (2023), Article no. 102252, 20 pages.10.1016/j.ffa.2023.102252CrossRefGoogle Scholar