arXiv subjects

Kaya Lakein

Publications and source records attributed to Kaya Lakein.

4 recordsLinked to original sources

arXiv2022

Supersingular Loci from Traces of Hecke Operators

A classical observation of Deligne shows that, for any prime $p \geq 5$, the divisor polynomial of the Eisenstein series $E_{p-1}(z)$ mod $p$ is closely related to the supersingular polynomial at $p$, $$S_p(x) := \prod_{E/\bar{\mathbb{F}}_p \text{ supersingular}}(x-j(E)) \in \mathbb{F}_p[x].$$ Deuring, Hasse, and Kaneko and Zagier found other families of modular forms which also give the supersingular polynomial at $p$. In a new approach, we prove an analogue of Deligne's result for the Hecke trace forms $T_k(z)$ defined by the Hecke action on the space of cusp forms $S_k$. We use the Eichler-Selberg trace formula to identify congruences between trace forms of different weights mod $p$, and then relate their divisor polynomials to $S_p(x)$ using Deligne's observation.

math.NT↗

arXiv2021

Some Remarks on Small Values of $τ(n)$

A natural variant of Lehmer's conjecture that the Ramanujan $τ$-function never vanishes asks whether, for any given integer $α$, there exist any $n \in \mathbb{Z}^+$ such that $τ(n) = α$. A series of recent papers excludes many integers as possible values of the $τ$-function using the theory of primitive divisors of Lucas numbers, computations of integer points on curves, and congruences for $τ(n)$. We synthesize these results and methods to prove that if $0 < |α| < 100$ and $α\notin T := \{2^k, -24,-48, -70,-90, 92, -96\}$, then $τ(n) \neq α$ for all $n > 1$. Moreover, if $α\in T$ and $τ(n) = α$, then $n$ is square-free with prescribed prime factorization. Finally, we show that a strong form of the Atkin-Serre conjecture implies that $|τ(n)| > 100$ for all $n > 2$.

math.NT↗

arXiv2021

A Proof of Merca's Conjectures on Sums of Odd Divisor Functions

In a recent paper, Merca posed three conjectures on congruences for specific convolutions of a sum of odd divisor functions with a generating function for generalized $m$-gonal numbers. Extending Merca's work, we complete the proof of these conjectures.

math.NT↗

arXiv2021

On Class Numbers, Torsion Subgroups, and Quadratic Twists of Elliptic Curves

The Mordell-Weil groups $E(\mathbb{Q})$ of elliptic curves influence the structures of their quadratic twists $E_{-D}(\mathbb{Q})$ and the ideal class groups $\mathrm{CL}(-D)$ of imaginary quadratic fields. For appropriate $(u,v) \in \mathbb{Z}^2$, we define a family of homomorphisms $Φ_{u,v}: E(\mathbb{Q}) \rightarrow \mathrm{CL}(-D)$ for particular negative fundamental discriminants $-D:=-D_E(u,v)$, which we use to simultaneously address questions related to lower bounds for class numbers, the structures of class groups, and ranks of quadratic twists. Specifically, given an elliptic curve $E$ of rank $r$, let $Ψ_E$ be the set of suitable fundamental discriminants $-D<0$ satisfying the following three conditions: the quadratic twist $E_{-D}$ has rank at least 1; $E_{\text{tor}}(\mathbb{Q})$ is a subgroup of $\mathrm{CL}(-D)$; and $h(-D)$ satisfies an effective lower bound which grows asymptotically like $c(E) \log (D)^{\frac{r}{2}}$ as $D \to \infty$. Then for any $\varepsilon > 0$, we show that as $X \to \infty$, we have $$\#\, \left\{-X < -D < 0: -D \in Ψ_E \right \} \, \gg_{\varepsilon} X^{\frac{1}{2}-\varepsilon}.$$ In particular, if $\ell \in \{3,5,7\}$ and $\ell \mid |E_{\mathrm{tor}}(\mathbb{Q})|$, then the number of such discriminants $-D$ for which $\ell \mid h(-D)$ is $\gg_{\varepsilon} X^{\frac{1}{2}-\varepsilon}.$ Moreover, assuming the Parity Conjecture, our results hold with the additional condition that the quadratic twist $E_{-D}$ has rank at least 2.

math.NT↗