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András Biró

Publications and source records attributed to András Biró.

10 recordsLinked to original sources
arXiv2026

Local square mean in the hyperbolic circle problem and sums of Salié sums

Let $Γ\subseteq PSL(2, \mathbb R)$ be a finite volume Fuchsian group. The hyperbolic circle problem is the estimation of the number of elements of the $Γ$-orbit of $z$ in a hyperbolic circle around $w$ of radius $R$, where $z$ and $w$ are given points of the upper half plane and $R$ is a large number. An estimate with error term $e^{\frac 23R}$ is known, and this has not been improved for any group. Recently, taking $ z=w$ and considering $Γ= PSL(2, \mathbb Z)$, we have shown the estimate $ e^{\left(\frac 9{14}+ε\right)R}$ for the local $L^2$-norm of the error term, which is better than the pointwise bound. Here we improve the exponent $\frac 9{14}$, conditionally on a twisted Linnik-Selberg-type conjecture for sums of Salié sums.

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arXiv2025

Cusp forms of weight 1/2 and pairs of quadratic forms

We prove a spectral summation formula for the product of four Fourier coefficients of half-integral weight cusp forms in Kohnen's subspace. The other side of the formula involves certain generalized class numbers of pairs of quadratic forms with integer coefficients.

math.NT↗
arXiv2025

Local square mean in the hyperbolic circle problem

Let $Γ\subseteq PSL_2({\bf R})$ be a finite volume Fuchsian group. The hyperbolic circle problem is the estimation of the number of elements of the $Γ$-orbit of $z$ in a hyperbolic circle around $w$ of radius $R$, where $z$ and $w$ are given points of the upper half plane and $R$ is a large number. An estimate with error term $e^{{2\over 3}R}$ is known, and this has not been improved for any group. Petridis and Risager proved that in the special case $Γ=PSL_2({\bf Z})$ taking $z=w$ and averaging over $z$ locally the error term can be improved to $e^{\left({7\over {12}}+ε\right)R}$. Here we show such an improvement for the local $L^2$-norm of the error term. Our estimate is $e^{\left({9\over {14}}+ε\right)R}$, which is better than the pointwise bound $e^{{2\over 3}R}$ but weaker than the bound of Petridis and Risager for the local average.

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arXiv2025

Triple product integrals and Rankin-Selberg L-functions

We prove a reciprocity formula that relates a spectral average of products of triple product integrals involving automorphic forms of weights $0$ and $1/2$ to the classical Rankin-Selberg integrals for automorphic forms of weight $0$.

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arXiv2023

On the geometric trace of a generalized Selberg trace formula

A certain generalization of the Selberg trace formula was proved by the first named author in 1999. In this generalization instead of considering the integral of $K(z,z)$ (where $K(z,w)$ is an automorphic kernel function) over the fundamental domain, one considers the integral of $K(z,z)u(z)$, where $u(z)$ is a fixed automorphic eigenfunction of the Laplace operator. This formula was proved for discrete subgroups of $PSL(2,\mathbb{R})$, and just as in the case of the classical Selberg trace formula it was obtained by evaluating in two different ways ("geometrically" and "spectrally") the integral of $K(z,z)u(z)$. In the present paper we work out the geometric side of a further generalization of this generalized trace formula: we consider the case of discrete subgroups of $PSL(2,\mathbb{R})^n$ where $n>1$. Many new difficulties arise in the case of these groups due to the fact that the classification of conjugacy classes is much more complicated for $n>1$ than in the case $n=1$.

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arXiv2019

Bykovskii-type theorem for the Picard manifold

We generalise a result of Bykovskii to the Gaussian integers and prove an asymptotic formula for the prime geodesic theorem in short intervals on the Picard manifold. Previous works show that individually the remainder is bounded by $O(X^{13/8+ε})$ and $O(X^{3/2+θ+ε})$, where $θ$ is the subconvexity exponent for quadratic Dirichlet $L$-functions over $\mathbb{Q}(i)$. By combining arithmetic methods with estimates for a spectral exponential sum and a smooth explicit formula, we obtain an improvement for both of these exponents. Moreover, by assuming two standard conjectures on $L$-functions, we show that it is possible to reduce the exponent below the barrier $3/2$ and get $O(X^{34/23+ε})$ conditionally. We also demonstrate a dependence of the remainder in the short interval estimate on the classical Gauss circle problem for shifted centres.

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arXiv2018

The prime geodesic theorem in square mean

We strengthen the recent result of Cherubini and Guerreiro on the square mean of the error term in the prime geodesic theorem for $\mathrm{PSL}_2(\mathbb{Z})$. We also develop a short interval version of this result.

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arXiv2017

Local average of the hyperbolic circle problem for Fuchsian groups

Let $Γ\subseteq PSL(2,{\bf R})$ be a finite volume Fuchsian group. The hyperbolic circle problem is the estimation of the number of elements of the $Γ$-orbit of $z$ in a hyperbolic circle around $w$ of radius $R$, where $z$ and $w$ are given points of the upper half plane and $R$ is a large number. An estimate with error term $e^{{2\over 3}R}$ is known, and this has not been improved for any group. Recently Risager and Petridis proved that in the special case $Γ=PSL(2,{\bf Z})$ taking $z=w$ and averaging over $z$ in a certain way the error term can be improved to $e^{\left({7\over {12}}+ε\right)R}$. Here we show such an improvement for a general $Γ$, our error term is $e^{\left({5\over 8}+ε\right)R}$ (which is better that $e^{{2\over 3}R}$ but weaker than the estimate of Risager and Petridis in the case $Γ=PSL(2,{\bf Z})$). Our main tool is our generalization of the Selberg trace formula proved earlier.

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arXiv2017

Some integrals of hypergeometric functions

We consider a certain definite integral involving the product of two classical hypergeometric functions having complicated arguments. We show in this paper the surprising fact that this integral does not depend on the parameters of the hypergeometric functions.

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