arXiv subjects

Ken Ono

Publications and source records attributed to Ken Ono.

At least 91 records · Page 5Linked to original sources

arXiv2020

Elliptic curves and lower bounds for class numbers

Ideal class pairings map the rational points of rank $r\geq 1$ elliptic curves $E/\Q$ to the ideal class groups $\CL(-D)$ of certain imaginary quadratic fields. These pairings imply that $$h(-D) \geq \frac{1}{2}(c(E)-\varepsilon)(\log D)^{\frac{r}{2}} $$ for sufficiently large discriminants $-D$ in certain families, where $c(E)$ is a natural constant. These bounds are effective, and they offer improvements to known lower bounds for many discriminants.

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arXiv2019

Higher Width Moonshine

\textit{Weak moonshine} for a finite group $G$ is the phenomenon where an infinite dimensional graded $G$-module $$V_G=\bigoplus_{n\gg-\infty}V_G(n)$$ has the property that its trace functions, known as McKay-Thompson series, are modular functions. Recent work by DeHority, Gonzalez, Vafa, and Van Peski established that weak moonshine holds for every finite group. Since weak moonshine only relies on character tables, which are not isomorphism class invariants, non-isomorphic groups can have the same McKay-Thompson series. We address this problem by extending weak moonshine to arbitrary width $s\in\mathbb{Z}^+$. For each $1\leq r\leq s$ and each irreducible character $χ_i$, we employ Frobenius' $r$-character extension $χ_i^{(r)} \colon G^{(r)}\rightarrow\mathbb{C}$ to define \textit{width $r$ McKay-Thompson series} for $V_G^{(r)}:=V_G\times\cdots\times V_G$ ($r$ copies) for each $r$-tuple in $G^{(r)}:=G\times\cdots\times G$ ($r$ copies). These series are modular functions which then reflect differences between $r$-character values. Furthermore, we establish orthogonality relations for the Frobenius $r$-characters, which dictate the compatibility of the extension of weak moonshine for $V_G$ to width $s$ weak moonshine.

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arXiv2019

Class Numbers and Self-Conjugate 7-Cores

We investigate $sc_7(n)$, the number of self-conjugate $7$-core partitions of size $n$. It turns out that $sc_7(n)=0$ for $n\equiv 7\pmod 8$. For $n\equiv 1, 3, 5\pmod 8$, with $n\not \equiv 5\pmod 7,$ we find that $sc_7(n)$ is essentially a Hurwitz class number. Using recent work of Gao and Qin, we show that $$ sc_7(n) = 2^{-\varepsilon(n)-1}\cdot H(-D_n), $$ where $-D_n:=-4^{\varepsilon(n)}(7n+14)$ and $\varepsilon(n):=\frac{1}{2}\cdot(1+(-1)^{\frac{n-1}{2}})$. This fact implies several corollaries which are of interest. For example, if $-D_n$ is a fundamental discriminant and $p\not \in \{2, 7\}$ is a prime with $ord_p(-D_n)\leq 1$, then for every positive integer $k$ we have $$ sc_7\left((n+2)p^{2k}-2\right)=sc_7(n)\cdot \left(1+\frac{p^{k+1}-p}{p-1}-\frac{p^k-1}{p-1}.\left(\frac{-D_n}{p}\right)\right), $$ where $\left(\frac{-D_n}{p}\right)$ is the Legendre symbol.

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arXiv2019

From partitions to Hodge numbers of Hilbert Schemes of Surfaces

We celebrate the 100th anniversary of Srinivasa Ramanujan's election as a Fellow of the Royal Society, which was largely based on his work with G. H. Hardy on the asymptotic properties of the partition function. After recalling this revolutionary work, marking the birth of the "circle method", we present a contemporary example of its legacy in topology. We deduce the equidistribution of Hodge numbers for Hilbert schemes of suitable smooth projective surfaces.

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arXiv2019

Multiquadratic fields generated by characters of $A_n$

For a finite group $G$, let $K(G)$ denote the field generated over $\mathbb{Q}$ by its character values. For $n>24$, G. R. Robinson and J. G. Thompson proved that $$K(A_n)=\mathbb{Q}\left (\{ \sqrt{p^*} \ : \ p\leq n \ {\text{ an odd prime with } p\neq n-2}\}\right),$$ where $p^*:=(-1)^{\frac{p-1}{2}}p$. Confirming a speculation of Thompson, we show that arbitrary suitable multiquadratic fields are similarly generated by the values of $A_n$-characters restricted to elements whose orders are only divisible by ramified primes. To be more precise, we say that a $π$-number is a positive integer whose prime factors belong to a set of odd primes $π:= \{p_1, p_2,\dots, p_t\}$. Let $K_π(A_n)$ be the field generated by the values of $A_n$-characters for even permutations whose orders are $π$-numbers. If $t\geq 2$, then we determine a constant $N_π$ with the property that for all $n> N_π$, we have $$K_π(A_n)=\mathbb{Q}\left(\sqrt{p_1^*}, \sqrt{p_2^*},\dots, \sqrt{p_t^*}\right).$$

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arXiv2019

On Witten's extremal partition functions

In his famous 2007 paper on three dimensional quantum gravity, Witten defined candidates for the partition functions $$Z_k(q)=\sum_{n=-k}^{\infty}w_k(n)q^n$$ of potential extremal CFTs with central charges of the form $c=24k$. Although such CFTs remain elusive, he proved that these modular functions are well-defined. In this note, we point out several explicit representations of these functions. These involve the partition function $p(n)$, Faber polynomials, traces of singular moduli, and Rademacher sums. Furthermore, for each prime $p\leq 11$, the $p$ series $Z_k(q)$, where $k\in \{1, \dots, p-1\} \cup \{p+1\},$ possess a Ramanujan congruence. More precisely, for every non-zero integer $n$ we have that $$ w_k(pn) \equiv 0\begin{cases} \pmod{2^{11}}\ \ \ \ &{\text {\rm if}}\ p=2, \pmod{3^5} \ \ \ \ &{\text {\rm if}}\ p=3, \pmod{5^2}\ \ \ \ &{\text {\rm if}}\ p=5, \pmod{p} \ \ \ \ &{\text {\rm if}}\ p=7, 11. \end{cases} $$

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arXiv2019

Jensen polynomials for the Riemann zeta function and other sequences

In 1927 Pólya proved that the Riemann Hypothesis is equivalent to the hyperbolicity of Jensen polynomials for the Riemann zeta function $ζ(s)$ at its point of symmetry. This hyperbolicity has been proved for degrees $d\leq 3$. We obtain an asymptotic formula for the central derivatives $ζ^{(2n)}(1/2)$ that is accurate to all orders, which allows us to prove the hyperbolicity of a density $1$ subset of the Jensen polynomials of each degree. Moreover, we establish hyperbolicity for all $d\leq 8$. These results follow from a general theorem which models such polynomials by Hermite polynomials. In the case of the Riemann zeta function, this proves the GUE random matrix model prediction in derivative aspect. The general theorem also allows us to prove a conjecture of Chen, Jia, and Wang on the partition function.

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arXiv2019

O'Nan moonshine and arithmetic

Answering a question posed by Conway and Norton in their seminal 1979 paper on moonshine, we prove the existence of a graded infinite-dimensional module for the sporadic simple group of O'Nan, for which the McKay--Thompson series are weight $3/2$ modular forms. The coefficients of these series may be expressed in terms of class numbers, traces of singular moduli, and central critical values of quadratic twists of weight 2 modular $L$-functions. As a consequence, for primes $p$ dividing the order of the O'Nan group we obtain congruences between O'Nan group character values and class numbers, $p$-parts of Selmer groups, and Tate--Shafarevich groups of certain elliptic curves. This work represents the first example of moonshine involving arithmetic invariants of this type.

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arXiv2018

Black holes and class groups

The theory of quadratic forms and class numbers has connections to many classical problems in number theory. Recently, class numbers have appeared in the study of black holes in string theory. We describe this connection and raise questions in the hope of inspiring new collaborations between number theorists and physicists.

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arXiv2018

CM Evaluations of the Goswami-Sun Series

In recent work, Sun constructed two $q$-series, and he showed that their limits as $q\rightarrow1$ give new derivations of the Riemann-zeta values $ζ(2)=π^2/6$ and $ζ(4)=π^4/90$. Goswami extended these series to an infinite family of $q$-series, which he analogously used to obtain new derivations of the evaluations of $ζ(2k)\in\mathbb{Q}\cdotπ^{2k}$ for every positive integer $k$. Since it is well known that $Γ\left(\frac{1}{2}\right)=\sqrtπ$, it is natural to seek further specializations of these series which involve special values of the $Γ$-function. Thanks to the theory of complex multiplication, we show that the values of these series at all CM points $τ$, where $q:=e^{2πiτ}$, are algebraic multiples of specific ratios of $Γ$-values. In particular, classical formulas of Ramanujan allow us to explicitly evaluate these series as algebraic multiples of powers of $Γ\left(\frac{1}{4}\right)^4/π^3$ when $q=e^{-π}$, $e^{-2π}$.

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arXiv2017

Pariah moonshine

Finite simple groups are the building blocks of finite symmetry. The effort to classify them precipitated the discovery of new examples, including the monster, and six pariah groups which do not belong to any of the natural families, and are not involved in the monster. It also precipitated monstrous moonshine, which is an appearance of monster symmetry in number theory that catalysed developments in mathematics and physics. Forty years ago the pioneers of moonshine asked if there is anything similar for pariahs. Here we report on a solution to this problem that reveals the O'Nan pariah group as a source of hidden symmetry in quadratic forms and elliptic curves. Using this we prove congruences for class numbers, and Selmer groups and Tate--Shafarevich groups of elliptic curves. This demonstrates that pariah groups play a role in some of the deepest problems in mathematics, and represents an appearance of pariah groups in nature.

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arXiv2017

Number-theoretic generalization of the Monster denominator formula

The denominator formula for the Monster Lie algebra is the product expansion for the modular function $j(z)-j(τ)$ in terms of the Hecke system of $\operatorname{SL}_2(\mathbb{Z})$-modular functions $j_n(τ)$. This formula can be reformulated entirely number-theoretically. Namely, it is equivalent to the description of the generating function for the $j_n(z)$ as a weight 2 modular form in $τ$ with a pole at $z$. Although these results rely on the fact that $X_0(1)$ has genus 0, here we obtain a generalization, framed in terms of polar harmonic Maass forms, for all of the $X_0(N)$ modular curves. In this survey we discuss this generalization, and we offer an introduction to the theory of polar harmonic Maass forms. We conclude with applications to formulas of Ramanujan and Green's functions.

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arXiv2017

Partition-theoretic formulas for arithmetic densities

If $\gcd(r,t)=1$, then a theorem of Alladi offers the Möbius sum identity $$-\sum_{\substack{ n \geq 2 \\ p_{\rm{min}}(n) \equiv r \pmod{t}}} μ(n)n^{-1}= \frac{1}{φ(t)}. $$ Here $p_{\rm{min}}(n)$ is the smallest prime divisor of $n$. The right-hand side represents the proportion of primes in a fixed arithmetic progression modulo $t$. Locus generalized this to Chebotarev densities for Galois extensions. Answering a question of Alladi, we obtain analogs of these results to arithmetic densities of subsets of positive integers using $q$-series and integer partitions. For suitable subsets $§$ of the positive integers with density $d_§$, we prove that \[- \lim_{q \to 1} \sum_{\substack{ λ\in \mathcal{P} \\ \rm{sm}(λ) \in §}} μ_{\mathcal{P}} (λ)q^{\vert λ\vert} = d_§,\] where the sum is taken over integer partitions $λ$, $μ_{\mathcal{P}}(λ)$ is a partition-theoretic Möbius function, $\vert λ\vert$ is the size of partition $λ$, and $\rm{sm}(λ)$ is the smallest part of $λ$. In particular, we obtain partition-theoretic formulas for even powers of $π$ when considering power-free integers.

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arXiv2017

On Divisors of Modular Forms

The denominator formula for the Monster Lie algebra is the product expansion for the modular function $j(z)-j(τ)$ given in terms of the Hecke system of $\operatorname{SL}_2(\mathbb Z)$-modular functions $j_n(τ)$. It is prominent in Zagier's seminal paper on traces of singular moduli, and in the Duncan-Frenkel work on Moonshine. The formula is equivalent to the description of the generating function for the $j_n(z)$ as a weight 2 modular form with a pole at $z$. Although these results rely on the fact that $X_0(1)$ has genus 0, here we obtain a generalization, framed in terms of polar harmonic Maass forms, for all of the $X_0(N)$ modular curves. We use these functions to study divisors of modular forms.

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arXiv2016

Zeta-polynomials for modular form periods

Answering problems of Manin, we use the critical $L$-values of even weight $k\geq 4$ newforms $f\in S_k(Γ_0(N))$ to define zeta-polynomials $Z_f(s)$ which satisfy the functional equation $Z_f(s)=\pm Z_f(1-s)$, and which obey the Riemann Hypothesis: if $Z_f(ρ)=0$, then $\operatorname{Re}(ρ)=1/2$. The zeros of the $Z_f(s)$ on the critical line in $t$-aspect are distributed in a manner which is somewhat analogous to those of classical zeta-functions. These polynomials are assembled using (signed) Stirling numbers and "weighted moments" of critical values $L$-values. In analogy with Ehrhart polynomials which keep track of integer points in polytopes, the $Z_f(s)$ keep track of arithmetic information. Assuming the Bloch--Kato Tamagawa Number Conjecture, they encode the arithmetic of a combinatorial arithmetic-geometric object which we call the "Bloch-Kato complex" for $f$. Loosely speaking, these are graded sums of weighted moments of orders of Šafarevič-Tate groups associated to the Tate twists of the modular motives.

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arXiv2016

The 1729 K3 Surface

We revisit the mathematics that Ramanujan developed in connection with the famous "taxi-cab" number $1729$. A study of his writings reveals that he had been studying Euler's diophantine equation $$ a^3+b^3=c^3+d^3. $$ It turns out that Ramanujan's work anticipated deep structures and phenomena which have become fundamental objects in arithmetic geometry and number theory. We find that he discovered a $K3$ surface with Picard number $18$, one which can be used to obtain infinitely many cubic twists over $\mathbb{Q}$ with rank $\geq 2$.

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arXiv2016

Explorations in the theory of partition zeta functions

We introduce and survey results on two families of zeta functions connected to the multiplicative and additive theories of integer partitions. In the case of the multiplicative theory, we provide specialization formulas and results on the analytic continuations of these "partition zeta functions", find unusual formulas for the Riemann zeta function, prove identities for multiple zeta values, and see that some of the formulas allow for $p$-adic interpolation. The second family we study was anticipated by Manin and makes use of modular forms, functions which are intimately related to integer partitions by universal polynomial recurrence relations. We survey recent work on these zeta polynomials, including the proof of their Riemann Hypothesis.

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arXiv2016

A framework of Rogers-Ramanujan identities and their arithmetic properties

The two Rogers-Ramanujan $q$-series \[ \sum_{n=0}^{\infty}\frac{q^{n(n+σ)}}{(1-q)\cdots (1-q^n)}, \] where $σ=0,1$, play many roles in mathematics and physics. By the Rogers-Ramanujan identities, they are essentially modular functions. Their quotient, the Rogers-Ramanujan continued fraction, has the special property that its singular values are algebraic integral units. We find a framework which extends the Rogers-Ramanujan identities to doubly-infinite families of $q$-series identities. If $a\in\{1,2\}$ and $m,n\geq 1$, then we have \[ \sum_{\substack{λλ_1\leq m}} q^{a|λ|} P_{2λ}(1,q,q^2,\dots;q^n) =\textrm{"infinite product modular function"}, \] where the $P_λ(x_1,x_2,\dots;q)$ are Hall-Littlewood polynomials. These $q$-series are specialized characters of affine Kac--Moody algebras. Generalizing the Rogers-Ramanujan continued fraction, we prove in the case of $\textrm{A}_{2n}^{(2)}$ that the relevant $q$-series quotients are integral units.

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