arXiv subjects

Dmitry Jakobson

Publications and source records attributed to Dmitry Jakobson.

At least 19 recordsLinked to original sources

arXiv2026

Flexibility of eigenvalues for graph Laplacians arising from genus 3 surfaces

It is known that the small eigenvalues of the Laplacian of a Riemann surface close to the boundary of the modular space can be well approximated by the eigenvalues of the discrete Laplacian on a certain graph coming from the pair of pants decomposition of the surface. In this paper, we provide a complete description of the sets of eigenvalues of the weighted graph Laplacian for all graphs on four vertices that correspond to a valid pair of pants decomposition of a surface of genus 3.

math.SP↗

arXiv2019

Conformal invariants from nodal sets II. Manifolds with boundary

In this paper, we study conformal invariants that arise from nodal sets and negative eigenvalues of conformally covariant operators on manifolds with boundary. We also consider applications to curvature prescription problems on manifolds with boundary. We relate Dirichlet and Neumann eigenvalues and put the results developed here for the Escobar problem into the more general framework of boundary operators of arbitrary order.

math.AP↗

arXiv2017

Large covers and sharp resonances of hyperbolic surfaces

Let $Γ$ be a convex co-compact discrete group of isometries of the hyperbolic plane $\mathbb{H}^2$, and $X=Γ\backslash \mathbb{H}^2$ the associated surface. In this paper we investigate the behaviour of resonances of the Laplacian for large degree covers of $X$ given by a finite index normal subgroup of $Γ$. Using various techniques of thermodynamical formalism and representation theory, we prove two new existence results of "sharp non-trivial resonances" close to $\Re(s)=δ_Γ$, both in the large degree limit, for abelian covers and also infinite index congruence subgroups of $SL2(\mathbb{Z})$.

math.SP↗

arXiv2017

L-functions and sharp resonances of infinite index congruence subgroups of $SL_2(\mathbb{Z})$

For convex co-compact subgroups of SL2(Z) we consider the "congruence subgroups" for p prime. We prove a factorization formula for the Selberg zeta function in term of L-functions related to irreducible representations of the Galois group SL2(Fp) of the covering, together with a priori bounds and analytic continuation. We use this factorization property combined with an averaging technique over representations to prove a new existence result of non-trivial resonances in an effective low frequency strip.

math.SP↗

arXiv2016

Zero and negative eigenvalues of the conformal Laplacian

We show that zero is not an eigenvalue of the conformal Laplacian for generic Riemannian metrics. We also discuss non-compactness for sequences of metrics with growing number of negative eigenvalues of the conformal Laplacian.

math.DG↗

arXiv2016

On Small Gaps in the Length Spectrum

We discuss upper and lower bounds for the size of gaps in the length spectrum of negatively curved manifolds. For manifolds with algebraic generators for the fundamental group, we establish the existence of exponential lower bounds for the gaps. On the other hand, we show that the existence of arbitrary small gaps is topologically generic: this is established both for surfaces of constant negative curvature (Theorem 3.1), and for the space of negatively curved metrics (Theorem 4.1). While arbitrary small gaps are topologically generic, it is plausible that the gaps are not too small for almost every metric. One result in this direction is presented in Section 5.

math.DS↗

arXiv2015

Gaussian measures on the of space of Riemannian metrics

We introduce Gaussian-type measures on the manifold of all metrics with a fixed volume form on a compact Riemannian manifold of dimension $\geq 3$. For this random model we compute the characteristic function for the $L^2$ (Ebin) distance to the reference metric. In the Appendix, we study Lipschitz-type distance between Riemannian metrics and give applications to the diameter, eigenvalue and volume entropy functionals.

math.DG↗

arXiv2015

An extremal eigenvalue problem in Kähler geometry

We study Laplace eigenvalues $λ_k$ on Kähler manifolds as functionals on the space of Kähler metrics with cohomologous Kähler forms. We introduce a natural notion of a $λ_k$-extremal Kähler metric and obtain necessary and sufficient conditions for it. A particular attention is paid to the $λ_1$-extremal properties of Kähler-Einstein metrics of positive scalar curvature on manifolds with non-trivial holomorphic vector fields.

math.DG↗

arXiv2014

Conformally Covariant Operators and Conformal Invariants on Weighted Graphs

Let G be a finite connected simple graph. We define the moduli space of conformal structures on G. We propose a definition of conformally covariant operators on graphs, motivated by [25]. We provide examples of conformally covariant operators, which include the edge Laplacian and the adjacency matrix on graphs. In the case where such an operator has a nontrivial kernel, we construct conformal invariants, providing discrete counterparts of several results in [11,12] established for Riemannian manifolds. In particular, we show that the nodal sets and nodal domains of null eigenvectors are conformal invariants.

math.CO↗

arXiv2014

Resonances and convex co-compact congruence subgroups of PSL2(Z)

This papers deals with congruence subgroups of convex cocompact subgroups of PSL2(Z). We examine the behaviour of the resonance spectrum when the congruence parameter q goes to infinity: we show a lower bound for the counting function in discs and an upper bound in vertical strips. These results show drastically different behaviour on both sides of the critical line $\Re(s)=δ/2$.

math.SP↗

arXiv2014

The semiclassical theory of discontinuous systems and ray-splitting billiards

We analyze the semiclassical limit of spectral theory on manifolds whose metrics have jump-like discontinuities. Such systems are quite different from manifolds with smooth Riemannian metrics because the semiclassical limit does not relate to a classical flow but rather to branching (ray-splitting) billiard dynamics. In order to describe this system we introduce a dynamical system on the space of functions on phase space. To identify the quantum dynamics in the semiclassical limit we compute the principal symbols of the Fourier integral operators associated to reflected and refracted geodesic rays and identify the relation between classical and quantum dynamics. In particular we prove a quantum ergodicity theorem for discontinuous systems. In order to do this we introduce a new notion of ergodicity for the ray-splitting dynamics. The paper contains an Appendix written by Yves Colin de Verdiere in which a non-trivial class of examples is constructed.

math.AP↗

arXiv2013

On the distribution of perturbations of propagated Schrödinger eigenfunctions

Let $(M,g_0)$ be a compact Riemmanian manifold of dimension $n$. Let $P_0 (\h) := -\h^2Δ_{g}+V$ be the semiclassical Schrödinger operator for $\h \in (0,\h_0]$, and let $E$ be a regular value of its principal symbol $p_0(x,ξ)=|ξ|^2_{g_0(x)} +V(x)$. Write $φ_\h$ for an $L^2$-normalized eigenfunction of $P(\h)$, $P_0(\h)φ_\h =E(\h)φ_\h$ and $E(\h) \in [E-o(1),E+ o(1)]$. Consider a smooth family of perturbations $g_u$ of $g_0$ with $u$ in the ball $\mathcal B^k(\varepsilon) \subset \mathbb R^k$ of radius $\varepsilon>0$. For $P_{u}(\h) := -\h^2 Δ_{g_u} +V$ and small $|t|$, we define the propagated perturbed eigenfunctions $$φ_\h^{(u)}:=e^{-\frac{i}{\h}t P_u(\h)} φ_\h.$$ We study the distribution of the real part of the perturbed eigenfunctions regarded as random variables $$\Re (φ^{(\cdot)}_\h(x)):\mathcal B^{k}(\varepsilon) \to \mathbb R \quad \quad \text{for}\;\, x\in M.$$ In particular, when $(M,g)$ is ergodic, we compute the $h \to 0^+$ asymptotics of the variance $\text{Var} [\Re (φ^{(\cdot)}_\h(x))] $ and show that all odd moments vanish as $h \to 0^+.$

math.SP↗

arXiv2012

Conformal invariants from nodal sets. I. Negative Eigenvalues and Curvature Prescription

In this paper, we study conformal invariants that arise from nodal sets and negative eigenvalues of conformally covariant operators; more specifically, the GJMS operators, which include the Yamabe and Paneitz operators. We give several applications to curvature prescription problems. We establish a version in conformal geometry of Courant's Nodal Domain Theorem. We also show that on any manifold of dimension $n\geq 3$, there exist many metrics for which our invariants are nontrivial. We prove that the Yamabe operator can have an arbitrarily large number of negative eigenvalues on any manifold of dimension $n\geq 3$. We obtain similar results for some higher order GJMS operators on some Einstein and Heisenberg manifolds. We describe the invariants arising from the Yamabe and Paneitz operators associated to left-invariant metrics on Heisenberg manifolds. Finally, in the appendix, the 2nd named author and Andrea Malchiodi study the $Q$-curvature prescription problems for non-critical $Q$-curvatures.

math.DG↗

arXiv2012

Gaussian Free Fields and KPZ Relation in R^4

This work aims to extend part of the two dimensional results of Duplantier and Sheffield on Liouville quantum gravity to four dimensions, and indicate possible extensions to other even-dimensional spaces R^(2n) as well as Riemannian manifolds. Let "Θ" be the Gaussian free field on R^4 with the underlying Hilbert space being the Sobolev space H^2 witb the inner product determined by the operator (I-Δ)^2. Assume "θ" is a generic element from Θ. We consider a sequence of random Borel measures on R^4, each of which is absolutely continuous with respect to the Lebesgue measure dx and the density function is given by the exponential of a centered Gaussian family parametrized by x in R^4. We show that with probability 1, this sequence of measures weakly converges to a limit random measure which can be "formally" written as "exp(2γθ(x)dx". In this setting, we also prove a KPZ relation, which is the quadratic relation between the scaling exponent of a bounded Borel set on R^4 under the Lebesgue measure and its counterpart under the random measure obtained above. Our approach is similar to the one used by Duplantier and Sheffield in 2D but with adaptations to R^4.

math.PR↗

arXiv2012

Nullspaces of Conformally Invariant Operators. Applications to $Q_{k}$-curvature

We study conformal invariants that arise from functions in the nullspace of conformally covariant differential operators. The invariants include nodal sets and the topology of nodal domains of eigenfunctions in the kernel of GJMS operators. We establish that on any manifold of dimension $n\geq 3$, there exist many metrics for which our invariants are nontrivial. We discuss new applications to curvature prescription problems.

math.DG↗

arXiv2012

Uniform estimates for the solutions of the Schrödinger equation on the torus and regularity of semiclassical measures

We establish uniform bounds for the solutions $e^{itΔ}u$ of the Schrödinger equation on arithmetic flat tori, generalising earlier results by J. Bourgain. We also study the regularity properties of weak-* limits of sequences of densities of the form $|e^{itΔ}u_{n}|^{2}$ corresponding to highly oscillating sequences of initial data $(u_{n})$. We obtain improved regularity properties of those limits using previous results by N. Anantharaman and F. Macià on the structure of semiclassical measures for solutions to the Schrödinger equation on the torus.

math.AP↗

arXiv2010

Scalar curvature and $Q$-curvature of random metrics

We study Gauss curvature for random Riemannian metrics on a compact surface, lying in a fixed conformal class; our questions are motivated by comparison geometry. Next, analogous questions are considered for the scalar curvature in dimension $n>2$, and for the $Q$-curvature of random Riemannian metrics.

math.DG↗

arXiv2010

On the resonances of convex co-compact subgroups of arithmetic groups

Let $Λ$ be a non-elementary convex co-compact fuchsian group which is a subgroup of an arithmetic fuchsian group. We prove that the Laplace operator of the hyperbolic surface $X=Λ\backslash\H$ has infinitely many resonances in an effective strip depending on the dimension of the limit set $δ$. Applications to lower bounds for the hyperbolic lattice point counting problem are derived.

math.SP↗