arXiv subjects
Publications and source records attributed to Dimitrios Chatzakos.
For arbitrary $m\geq 2$ and $d\geq 1$, we establish square-root cancellation for sums of Fourier coefficients of $\mathrm{GL}(m)$-automorphic forms averaged over values of random degree-$d$ polynomials.
For the full modular group, we obtain a logarithmic improvement on Selberg's long-standing bound for the error term of the counting function in the hyperbolic circle problem over Heegner points of different discriminants. The main ingredients in our method are Waldspurger's formula, twisted first moments of certain Rankin-Selberg convolutions, and a new fractional moment estimate.
We investigate the mean value of the inner product of squared $\mathrm{GL}_{n}$ degenerate maximal parabolic Eisenstein series against a smooth compactly supported function lying in a restricted space of incomplete Eisenstein series induced from a $\mathrm{SL}_{2}(\mathbb{Z})$ Hecke-Maass cusp form $\varphi$. Our result breaks the fundamental threshold with a polynomial power-saving beyond the pointwise implications of the generalised Lindel\"{o}f hypothesis for $L$-functions attached to $\varphi$. Furthermore, we evaluate the archimedean quantum variance and establish approximate orthogonality, expanding upon Zhang's (2019) work on quantum unique ergodicity for $\mathrm{GL}_{n}$ degenerate maximal parabolic Eisenstein series as well as Huang's (2021) work on quantum variance for $\mathrm{GL}_{2}$ Eisenstein series. Despite the theoretical strength of these manifestations, our argument relies exclusively on the Watson-Ichino-type formula for incomplete Eisenstein series of type $(2, 1, \ldots, 1)$ and Jutila's (1996) asymptotic formula for the second moment of $L$-functions attached to $\varphi$ in long intervals, supplemented by a standard analytical toolbox.
We address the prime geodesic theorem in arithmetic progressions, and resolve conjectures of Golovchanski\u{\i}-Smotrov (1999). In particular, we prove that the traces of closed geodesics on the modular surface do not equidistribute in the reduced residue classes of a given modulus.
We study a refinement of the quantum unique ergodicity conjecture for shrinking balls on arithmetic hyperbolic manifolds, with a focus on dimensions $ 2 $ and $ 3 $. For the Eisenstein series for the modular surface $\mathrm{PSL}_2( {\mathbb Z}) \backslash \mathbb{H}^2$ we prove failure of quantum unique ergodicity close to the Planck-scale and an improved bound for its quantum variance. For arithmetic $ 3 $-manifolds we show that quantum unique ergodicity of Hecke-Maaß forms fails on shrinking balls centered on an arithmetic point and radius $ R \asymp t_j^{-δ} $ with $ δ> 3/4 $. For $ \mathrm{PSL}_2(\mathcal{O}_K) \setminus \mathbb{H}^3 $ with $ \mathcal{O}_K $ being the ring of integers of an imaginary quadratic number field of class number one, we prove, conditionally on the generalized Lindelöf hypothesis, that equidistribution holds for Hecke-Maa{ss} forms if $ δ< 2/5 $. Furthermore, we prove that equidistribution holds unconditionally for the Eisenstein series if $ δ< (1-2θ)/(34+4θ) $ where $ θ$ is the exponent towards the Ramanujan-Petersson conjecture. For $ \mathrm{PSL}_2(\mathbb{Z}[i]) $ we improve the last exponent to $ δ< (1-2θ)/(27+2θ) $. Studying mean Lindelöf estimates for $ L $-functions of Hecke-Maaß forms we improve the last exponent on average to $ δ< 2/5$. Finally, we study massive irregularities for Laplace eigenfunctions on $ n $-dimensional compact arithmetic hyperbolic manifolds for $ n \geq 4 $. We observe that quantum unique ergodicity fails on shrinking balls of radii $ R \asymp t^{-δ_n+ε} $ away from the Planck-scale, with $ δ_n = 5/(n+1) $ for $ n \geq 5 $.
We study the fine distribution of lattice points lying on expanding circles in the hyperbolic plane $\mathbb{H}$. The angles of lattice points arising from the orbit of the modular group $PSL_{2}(\mathbb{Z})$, and lying on hyperbolic circles, are shown to be equidistributed for generic radii. However, the angles fail to equidistribute on a thin set of exceptional radii, even in the presence of growing multiplicity. Surprisingly, the distribution of angles on hyperbolic circles turns out to be related to the angular distribution of $\mathbb{Z}^2$-lattice points (with certain parity conditions) lying on circles in $\mathbb{R}^2$, along a thin subsequence of radii. A notable difference is that measures in the hyperbolic setting can break symmetry - on very thin subsequences they are not invariant under rotation by $\fracπ{2}$, unlike the Euclidean setting where all measures have this invariance property.
Let $X(D,1) =Γ(D,1) \backslash \mathbb{H}$ denote the Shimura curve of level $N=1$ arising from an indefinite quaternion algebra of fixed discriminant $D$. We study the discrete average of the error term in the hyperbolic circle problem over Heegner points of discriminant $d <0$ on $X(D,1)$ as $d \to -\infty$. We prove that if $|d|$ is sufficiently large compared to the radius $r \approx \log X$ of the circle, we can improve on the classical $O(X^{2/3})$-bound of Selberg. Our result extends the result of Petridis and Risager for the modular surface to arithmetic compact Riemann surfaces.
The remainder $E_Γ(X)$ in the Prime Geodesic Theorem for the Picard group $Γ= \mathrm{PSL}(2,\mathbb{Z}[i])$ is known to be bounded by $O(X^{3/2+ε})$ under the assumption of the Lindelöf hypothesis for quadratic Dirichlet $L$-functions over Gaussian integers. By studying the second moment of $E_Γ(X)$, we show that on average the same bound holds unconditionally.
For $Γ$ a cofinite Kleinian group acting on $\mathbb{H}^3$, we study the Prime Geodesic Theorem on $M=Γ\backslash \mathbb{H}^3$, which asks about the asymptotic behaviour of lengths of primitive closed geodesics (prime geodesics) on $M$. Let $E_Γ(X)$ be the error in the counting of prime geodesics with length at most $\log X$. For the Picard manifold, $Γ=\mathrm{PSL}(2,\mathbb{Z}[i])$, we improve the classical bound of Sarnak, $E_Γ(X)=O(X^{5/3+ε})$, to $E_Γ(X)=O(X^{13/8+ε})$. In the process we obtain a mean subconvexity estimate for the Rankin-Selberg $L$-function attached to Maass-Hecke cusp forms. We also investigate the second moment of $E_Γ(X)$ for a general cofinite group $Γ$, and show that it is bounded by $O(X^{16/5+ε})$.
For $Γ$ a Fuchsian group of finite covolume, we study the lattice point problem in conjugacy classes on the Riemann surface $Γ\backslash \mathbb{H}$. Let $\mathcal{H}$ be a hyperbolic conjugacy class in $Γ$ and $\ell$ the $\mathcal{H}$-invariant closed geodesic on the surface. The main asymptotic for the counting function of the orbit $\mathcal{H} \cdot z$ inside a circle of radius $t$ centered at $z$ grows like $c_{\mathcal{H}} \cdot e^{t/2}$. This problem is also related with counting distances of the orbit of $z$ from the geodesic $\ell$. For $X \sim e^{t/2}$ we study mean value and $Ω$-results for the error term $e(\mathcal{H}, X ;z)$ of the counting function. We prove that a normalized version of the error $e(\mathcal{H}, X ;z)$ has finite mean value in the parameter $t$. Further, we prove that if $Γ$ is cocompact then \begin{eqnarray*} \int_{\ell} e(\mathcal{H}, X;z) d s(z) = Ω\left( X^{1/2} \log \log \log X \right). \end{eqnarray*} We prove that the same $Ω$-result holds for $Γ= {\hbox{PSL}_2( {\mathbb Z})}$ if we assume a subconvexity bound for the Epstein zeta function associated to an indefinite quadratic form in four variables. We also study pointwise $Ω_{\pm}$-results for the error term. Our results extend the work of Phillips and Rudnick for the classical lattice problem to the conjugacy class problem.
For $Γ$ a cocompact or cofinite Fuchsian group, we study the lattice point problem on the Riemann surface $Γ\backslash\mathbb{H}$. The main asymptotic for the counting of the orbit $Γz$ inside a circle of radius $r$ centered at $z$ grows like $c e^r$. Phillips and Rudnick studied $Ω$-results for the error term and mean results in $r$ for the normalized error term. We investigate the normalized error term in the natural parameter $X=2 \cosh r$ and prove $Ω_{\pm}$-results for the orbit $Γw$ and circle centered at $z$, even for $z \neq w$.
For $Γ$ a cocompact or cofinite Fuchsian group, we study the hyperbolic lattice point problem in conjugacy classes, which is a modification of the classical hyperbolic lattice point problem. We use large sieve inequalities for the Riemann surfaces $Γ\backslash \mathbb H$ to obtain average results for the error term, which are conjecturally optimal. We give a new proof of the error bound $O(X^{2/3})$, due to A. Good. For $\hbox{SL}(2,{\mathbb Z})$ we interpret our results in terms of indefinite quadratic forms.