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Lawrence C. Washington

Publications and source records attributed to Lawrence C. Washington.

15 recordsLinked to original sources
arXiv2024

The first level of $\mathbb{Z}_p$-extensions and compatibility of heuristics

Let $K$ be an imaginary quadratic field in which the odd prime $p$ does not split. When the $p$-part of the class group of $K$ is cyclic, we describe the possible structures for the $p$-part of the class group of the first level of the cyclotomic $\mathbb{Z}_p$-extension of $K$. This allows us to show the compatibility of the heuristics of Cohen--Lenstra--Martinet for class groups with the heuristics of Ellenberg--Jain--Venkatesh for how often the cyclotomic Iwasawa invariant $λ$ equals 1.

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arXiv2024

On the Field Isomorphism Problem for the Family of Simplest Quartic Fields

Deciding whether or not two polynomials have isomoprhic splitting fields over the rationals is the Field Isomorphism Problem. We consider polynomials of the form $f_n(x) = x^4-nx^3-6x^2+nx+1$ with $n \neq 3$ a positive integer and we let $K_n$ denote the splitting field of $f_n(x)$; a `simplest quartic field'. Our main theorem states that under certain hypotheses there can be at most one positive integer $m \neq n$ such that $K_m=K_n$. The proof relies on the existence of squares in recurrent sequences and a result of J.H.E. Cohn [3]. These sequences allow us to establish uniqueness of the splitting field under additional hypotheses in Section (5) and to establish a connection with elliptic curves in Section (6).

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arXiv2023

Heuristics for anti-cyclotomic $\mathbb{Z}_p$-extensions

This paper studies Iwasawa invariants in anti-cyclotomic towers. We do this by proposing two heuristics supported by computations. First we propose the Intersection Heuristics: these model `how often' the $p$-Hilbert class field of an imaginary quadratic field intersects the anti-cyclotomic tower and to what extent. Second we propose the Invariants Heuristics: these predict that the Iwasawa invariants $λ$ and $μ$ usually vanish for imaginary quadratic fields where $p$ is non-split.

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arXiv2022

Sums of Powers of Primes II

For a real number $k$, define $π_k(x) = \sum_{p\le x} p^k$. When $k>0$, we prove that $$ π_k(x) - π(x^{k+1}) = Ω_{\pm}\left(\frac{x^{\frac12+k}}{\log x} \log\log\log x\right) $$ as $x\to\infty$, and we prove a similar result when $-1 0$ and usually positive when $-1<k<0$.

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arXiv2022

Relative Ideal Classes of Arbitrary Order

We adapt a known technique for searching for ideal classes of arbitrary order and then apply it to three families of number fields. We show that a family of cyclic sextic number fields has infinitely many fields in it that contain a relative ideal class of order $r,$ where $r$ is a positive integer relatively prime to the degree of the extension. We then show that the same holds true for a family of cyclic quartic number fields. Though the technique is traditionally applied to Galois extensions, we show how it may be adapted to handle a family of non-Galois cubic number fields and prove that this family contains infinitely many fields with an ideal class of arbitrary order relatively prime to three.

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arXiv2021

Dirichlet Series Expansions of p-adic L-Functions

We study $p$-adic $L$-functions $L_p(s,χ)$ for Dirichlet characters $χ$. We show that $L_p(s,χ)$ has a Dirichlet series expansion for each regularization parameter $c$ that is prime to $p$ and the conductor of $χ$. The expansion is proved by transforming a known formula for $p$-adic $L$-functions and by controlling the limiting behavior. A finite number of Euler factors can be factored off in a natural manner from the $p$-adic Dirichlet series. We also provide an alternative proof of the expansion using $p$-adic measures and give an explicit formula for the values of the regularized Bernoulli distribution. The result is particularly simple for $c=2$, where we obtain a Dirichlet series expansion that is similar to the complex case.

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arXiv2021

An Elliptic Curve Analogue of Pillai's Lower Bound on Primitive Roots

Let $E/\mathbb{Q}$ be an elliptic curve. For a prime $p$ of good reduction, let $r(E,p)$ be the smallest non-negative integer that gives the $x$-coordinate of a point of maximal order in the group $E(\mathbb{F}_p)$. We prove unconditionally that $r(E,p)> 0.72\log\log p$ for infinitely many $p$, and $r(E,p) > 0.36 \log p$ under the assumption of the Generalized Riemann Hypothesis. This can be viewed as elliptic curve analogues of classical lower bounds on the least primitive root of a prime.

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arXiv2020

Analogues of the Robin-Lagarias Criteria for the Riemann Hypothesis

Robin's criterion states that the Riemann hypothesis is equivalent to $σ(n) < e^γn \log\log n$ for all integers $n \geq 5041$, where $σ(n)$ is the sum of divisors of $n$ and $γ$ is the Euler-Mascheroni constant. We prove that the Riemann hypothesis is equivalent to the statement that $σ(n) < \frac{e^γ}{2} n \log\log n$ for all odd numbers $n \geq 3^4 \cdot 5^3 \cdot 7^2 \cdot 11 \cdots 67$. Lagarias's criterion for the Riemann hypothesis states that the Riemann hypothesis is equivalent to $σ(n) < H_n + \exp{H_n}\log{H_n}$ for all integers $n \geq 1$, where $H_n$ is the $n$th harmonic number. We establish an analogue to Lagarias's criterion for the Riemann hypothesis by creating a new harmonic series $H^\prime_n = 2H_n - H_{2n}$ and demonstrating that the Riemann hypothesis is equivalent to $σ(n) \leq \frac{3n}{\log{n}} + \exp{H^\prime_n}\log{H^\prime_n}$ for all odd $n \geq 3$. We prove stronger analogues to Robin's inequality for odd squarefree numbers. Furthermore, we find a general formula that studies the effect of the prime factorization of $n$ and its behavior in Robin's inequality.

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arXiv2018

Explicit computations in Iwasawa theory

We give two algorithms to compute layers of the anticyclotomic ${\bf Z}_3$-extension of an imaginary quadratic field. The first is based on complex multiplication techniques for nonmaximal orders; the second is based on Kummer theory. As an illustration of our results, we use the mirroring principle to derive results on the structure of class groups of nonmaximal orders.

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arXiv2017

The Coefficient-Choosing Game

Let $D$ be an integral domain. Two players, Nora and Wanda, alternately choose coefficients from $D$ for a polynomial of degree $d$. When they are done, if the polynomial has a root in the field of fractions of $D$, then Wanda wins. If not, then Nora wins. We determine, for many $D$, who wins this game.

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arXiv2008

Kummer generators and lambda invariants

Let $F_0=\mathbf Q(\sqrt{-d})$ be an imaginary quadratic field with $3\nmid d$ and let $K_0=\mathbf Q(\sqrt{3d})$. Let $\varepsilon_0$ be the fundamental unit of $K_0$ and let $λ$ be the Iwasawa $λ$-invariant for the cyclotomic $\mathbf Z_3$-extension of $F_0$. The theory of 3-adic $L$-functions gives conditions for $λ\ge 2$ in terms of $ε_0$ and the class numbers of $F_0$ and $K_0$. We construct units of $K_1$, the first level of the $\mathbf Z_3$-extension of $K_0$, that potentially occur as Kummer generators of unramified extensions of $F_1(ζ_3)$ and which give an algebraic interpretation of the condition that $λ\ge 2$. We also discuss similar results on $λ\ge 2$ that arise from work of Gross-Koblitz.

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arXiv2008

Visibility of ideal classes

Cremona, Mazur, and others have studied what they call visibility of elements of Shafarevich-Tate groups of elliptic curves. The analogue for an abelian number field $K$ is capitulation of ideal classes of $K$ in the minimal cyclotomic field containing $K$. We develop a new method to study capitulation and use it and classical methods to compute data with the hope of gaining insight into the elliptic curve case. For example, the numerical data for number fields suggests that visibility of nontrivial Shafarevich-Tate elements might be much more common for elliptic curves of positive rank than for curves of rank 0.

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