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Mathematics Analysis of PDEs

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Tuesday 29 September

Analysis of PDEs

Boundary Layers and Initial-Boundary Corner Asymptotics for the 2D Navier-Stokes Equations with Vanishing Vertical Viscosity

Motivated by anisotropic viscosity in geophysical fluid dynamics, where vertical momentum diffusion is often much weaker than horizontal diffusion and may be negligible in the interior yet remains essential near a solid wall, we study the vanishing vertical viscosity limit for the two-dimensional incompressible Navier–Stokes equations in the upper half-plane, with horizontal viscosity fixed at one and vertical viscosity \(\varepsilon^2\). For arbitrary divergence-free \(H^4\) no-slip initial data, with no time-differentiated compatibility conditions required, we construct the limiting horizontally viscous flow and the boundary-layer profiles on every prescribed finite interval \([0,T]\). The leading-order corrected approximation has \(O(\varepsilon)\) error in \(L^\infty\), and the full finite-order expansion reduces this error to \(O(\varepsilon^{3/2})\), uniformly down to \(t=0\). We further describe the development of the layer from data that vanish initially at the wall. At the initial–boundary corner, we determine the first two self-similar coefficients and characterize matching through exact profile tails, thereby separating the fixed-time scale \(\varepsilon\) from the short-time scale \(\varepsilon\sqrt t\). When the initial wall acceleration is nonzero, both the leading correction rate and the first normalized corner remainder are sharp. Finally, continuity estimates for fixed data yield joint small-time and small-viscosity limits for the exact solution, as well as finite-\(L^p\) asymptotics.
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Analysis of PDEs

Finite-Time Vanishing of Vacuum and Large-Time Behavior of the Multi-Dimensional Degenerate Compressible Navier-Stokes Equations with Large Spherically Symmetric Initial Data

In this paper, we study the two- and three-dimensional barotropic compressible Navier-Stokes equations with degenerate density-dependent viscosity coefficients in the whole space or in a ball for arbitrarily large spherically symmetric initial data. For initial data allowing vacuum, we establish the global existence of weak solutions and derive uniform-in-time a priori estimates. As a consequence, we prove that the vacuum state of weak solutions will vanish in finite time. The key ingredients include a treatment of the pressure terms based on separate estimates in the low- and high-density regions, the Bresch-Desjardins entropy estimates, weighted radial estimates, and a coupled control of the velocity and effective velocity. In the three-dimensional case, this approach also allows us to treat the endpoint case of the adiabatic exponent. For sufficiently regular initial data with strictly positive density, we establish the global existence and large-time behavior of classical solutions.
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Analysis of PDEs

Optimal regularity of optimal transport and degenerations of convex cones

If $T$ is an optimal transport map between bounded convex domains $\Omega$ and $\Omega'$, we characterize the regularity/singularity dichotomy for $DT$ at $(x,T(x)) \in \partial \Omega \times \partial \Omega'$. This is obtained through a new approach to the regularity theory based on affine degenerations of the tangent cones to $(\Omega, \Omega')$ at $(x,T(x))$. We formulate a general principle relating the optimal boundary regularity to a stability criterion and an $\mathrm{SL}(n)$ moduli space of pairs of convex cones. Among other results, we establish geometric criteria for existence and non-existence of homogeneous optimal transport maps between convex cones.
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Analysis of PDEs

An advanced hybrid-dimensional Stokes-Darcy model for fractured porous media

Thin fluid-filled channels in porous media are prevalent in a wide range of environmental settings including fractures in geological formations. Transport of fluid in such multi-domain systems is commonly described by Darcy's law and formulated either in a fully dimensional framework or through a hybrid-dimensional approach, where fractures are represented as inclusions of co-dimension one enclosed in the porous matrix. These mixed-dimensional models enable accurate representation of the corresponding full-dimensional systems while significantly reducing computational complexity. Models available in literature usually do not properly account for channel-wall roughness while applying coupling conditions on the fracture-matrix interface and are usually developed for flow directions parallel to the fracture. The goal of this work is to advance and study the hybrid-dimensional Stokes-Darcy model developed by the authors in their previous work. We consider a thin open channel embedded within a porous matrix, where the channel walls are in contact with porous regions of distinct permeabilities. We incorporate channel-wall roughness effects into the model and improve it to accommodate arbitrary flow directions. We prove existence and uniqueness of the weak solution for the new model and demonstrate its advantages over existing hybrid-dimensional Stokes-Darcy models using pore-scale resolved simulations.
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Analysis of PDEs

Global theory for NLS in the weighted spaces II: final data problem

In this paper, we study the final data problem for the defocusing nonlinear Schrödinger equation (NLS) $$ i\partial_t u + \frac12\Delta u = |u|^p u $$ in weighted spaces $\dot\Sigma^s(\mathbb R^d):=L_x^2(\mathbb R^d;|x|^{2s}\mathrm{d} x)$. Let $s_c=\frac d2-\frac2p$. Under the scaling of the NLS, $\dot{\Sigma}^{-s_c}(\mathbb R^d)$ is the scaling-critical weighted space. In three dimensions, within the range of exponents considered in this paper, we show that the final data problem is locally well-posed for $s\geq -s_c$ and ill-posed for $s<-s_c$. This is opposite to the corresponding initial data problem, which is locally well-posed for $s\leq -s_c$ and ill-posed for $s>-s_c$. For the three-dimensional quadratic equation, we further obtain a unique global solution for every radial final datum in the critical space $\dot\Sigma^{\frac12}(\mathbb R^3)$.
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All authors Yujin Guo, Jia Shen, Yifei Wu, Changping Yang

Analysis of PDEs · Cross-listed from math.DG

On filtration formula and nodal sets in min-max theory

Let $(M^{n+1},g)$ be a closed smooth Riemannian manifold, and let \[ 0=\lambda_0\leq\lambda_1\leq\ldots \] be the spectrum of the Laplace-Beltrami operator, with corresponding real eigenfunctions $\{\phi_j\}_{j\geq0}$. Let $\{\omega_p(M,g)\}_{p\geq1}$ denote Gromov's volume spectrum. In 2014, Marques-Neves conjectured that the sweepout generated by the nodal sets of $\phi_0,\ldots,\phi_p$ is asymptotically optimal for $\omega_p(M,g)$ as $p\to\infty$. We show that this conjecture is false in every dimension, even for positively curved real-analytic metrics. Nevertheless, we show that a less rigid notion of nodal sweepouts recovers the volume spectrum. Let \[ E_N(M,g):=\operatorname{span}\{\phi_0,\ldots,\phi_N\}, \qquad a_N\in H^1\bigl(\mathbb P(E_N(g));\mathbb Z_2\bigr) \] be the generator, and for $p\geq1$ define \[ \mathcal N_p^N(g) := \left\{ \Psi \mid X\text{ is a finite complex},\ \Psi\in C\bigl(X,\mathbb P(E_N(g))\bigr),\ \Psi^*(a_N^p)\neq0 \right\}. \] We define the nodal $(p,N)$-width by \[ \nu_p^N(M,g) := \inf_{\Psi\in\mathcal N_p^N(g)} \sup_{x\in\operatorname{dmn}(\Psi)} \mathcal H_g^{n}\bigl(\{\Psi_x=0\}\bigr). \] We prove the following filtration formula \[ \omega_p(M,g) = \lim_{N\to\infty}\nu_p^N(M,g) \] for every $p\geq1$. We state several questions on nodal geometry and min-max theory.
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Analysis of PDEs

Global theory for NLS in the weighted spaces I: finite pseudo conformal energy

We intend to prove that for defocusing nonlinear Schrödinger equations, solutions with finite pseudo conformal energy must be global and scatter. This fact is first proved by Bourgain when $0<s_c<1$: the equation is locally well-posed in $H_x^{s_c}$, and if one further assumes that the initial data satisfies $xu_0\in L_x^2$, then the solution is global and scatters. The $s_c<0$ case remains not studied, and the best result is given by Beceanu, Deng, Soffer, and Wu: If the initial data is in $H_x^{s_c}$, radial, and compactly supported, then the solution is globally well-posed. In this paper, we extend Bourgain's result to the $s_c<0$ case. We prove that if the initial data satisfies $|x|^{-s_c}u_0\in L_x^2$ and $xu_0\in L_x^2$, or if the radial initial data satisfies $u_0\in \dot{H}_x^{s_c}$ and $xu_0\in L_x^2$, then the solution is global and scatters. Bourgain's result is based on the subcritical a priori control on $L_x^{p+2}$, while our argument relies on the supercritical bound on $\mathcal{F}\dot H_x^1$.
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Analysis of PDEs

Explicit Robin Green's Functions and Resonance Spectra for the Helmholtz Equation on Balls in All Dimensions

This work constructs explicit closed-form Green's functions for the Helmholtz equation with Robin boundary conditions on balls in all dimensions $d\ge 2$. Despite the canonical geometry, such kernels have remained unavailable because the Robin condition couples the field and its normal derivative, preventing the method of images and obstructing standard eigenfunction expansions. By a decomposition–expansion method, the free-space fundamental solution is expanded via Graf's addition theorem in two dimensions and the hyperspherical addition theorem in higher dimensions; the regular correction is then determined algebraically by matching Robin boundary data mode by mode. The resulting series converge absolutely on compact interior subsets and are computable to machine precision. These explicit kernels yield a complete characterisation of the resonance spectra: each spectral branch increases strictly with the impedance parameter, interpolating between Neumann and Dirichlet eigenvalues. We establish a low-frequency spectral gap with an explicit cutoff estimate, and a universal high-frequency mode spacing with a second-order correction that distinguishes the Robin condition from the Dirichlet and Neumann extremes. The closed-form expressions furnish exact benchmark solutions for wave simulations in impedance-matched cavities, eliminating geometric discretisation error and providing reference data for the validation of finite-element and boundary-element algorithms in acoustics, electromagnetism and quantum mechanics.
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Analysis of PDEs · Cross-listed from math.DG

A geometric rigidity estimate for codimension-1 immersions into spheres

We establish a quantitative stability estimate for codimension-one immersions into a round sphere. Let $(M,g)$ be an oriented Riemannian manifold and suppose that a prescribed shape operator is realised by a smooth isometric immersion $\theta:(M,g)\to\mathbb S^{n+1}$. We prove that, on every relatively compact strongly Lipschitz domain and for every $1<p<\infty$, any Sobolev immersion $\phi$ is close to $\theta$ modulo an ambient rotation, with the $W^{1,p}$-distances between both the immersions and their Gauss maps controlled by the $L^p$ stretching-plus-bending energies of $\phi$. No a priori bounds on the fundamental forms of $\phi$ are required. The proof proceeds by extending the immersions along normal geodesics and reducing the problem to an equidimensional geometric rigidity estimate on the sphere. A finite localisation and patching argument handles the possible non-injectivity of the normal extension of the reference immersion.
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Analysis of PDEs

Sharp decay rate and asymptotic simplification for a quasilinear heat equation

We study the decay rate for a quasilinear heat equation of the form $ \dot u-\Delta u = \operatorname{div B}(\nabla u)$. The term on the right-hand-side is interpreted as a nonlinear perturbation of the ordinary heat equation and we will prove an optimal decay rate for the solution. More precisely, under natural conditions on the operator $B \colon \R^d \to \R^d$, we show that for sufficiently regular initial data the solution decays as $t^{-d/4}$ and its gradient as $t^{-d/4 - 1/2}$ for large times, that is at the same rates as for the free heat equation. Furthermore, we prove that the difference between the quasilinear and the linear solution decays strictly faster than the solution of either equation generically does, that is that there is asymptotic simplification. All estimates are completely explicit and rely on variations of Fourier splitting techniques, originally introduced by Schonbek.
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Analysis of PDEs

Asymptotic spreading speeds of a road-field reaction-diffusion predator-prey model

This paper is devoted to studying asymptotic spreading speeds of a road-field reaction-diffusion predator-prey system, in which predators diffuse faster on the straight line $\R\times \{0\}$ than in the half plane $\R\times (0,+\infty)$. We give a sharp characterization of the spreading properties of solutions of the system with compactly supported initial values by appealing to the invasion speed of the prey when predators are absent, and the invasion speed of predators when the prey is saturated. Notably, since the line may accelerate the expansion of predators in a cone of directions, the invasion speed of predators varies with the direction. To overcome the difficulty arising from the coupling between the predator-prey interaction and the road-field interaction, we first derive pointwise comparisons between predators and the prey and then reduce the components of predators in the system to a truncated field-road system depending on the invasion speed of the prey. By using known results for the single-species field-road model, we further show the propagation properties of the truncated system. This step is very crucial. Once the propagation properties of the truncated system are established, we can obtain the expected spreading properties of solutions to the original system by applying the comparison principle and contradiction arguments, and constructing appropriate Lyapunov functionals.
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Analysis of PDEs · Cross-listed from math.NT

On minima of theta and Epstein zeta functions in dimension four

Let the theta and Epstein zeta functions be $\Theta(\alpha,L)=\sum_{v\in L}e^{-\pi\alpha|v|^2}$ for $\alpha>0$ and $E(L,s)=\sum_{v\in L\setminus\{0\}}{|v|^{-2s}}$ for $s>2$, respectively. We consider full-rank lattices $L\subset\mathbb R^4$. Let the covolume of $L$ be one, and let $\mathcal D_4=2^{-1/4}D_4$ be the root lattice $D_4$ rescaled to covolume one. We prove that, up to orthogonal transformations, \begin{equation}\nonumber arg\,min_{covol(L)=1}\Theta(\alpha,L)=\mathcal D_4 \qquad\text{if}\quad \alpha>0, \end{equation} and this implies that \begin{equation}\nonumber arg\,min_{covol(L)=1}E(L,s)=\mathcal D_4 \qquad\text{if}\quad s>2. \end{equation} This proves that the root lattice minimizes the theta and Epstein zeta functions among all lattices in dimension four, as conjectured by Sarnak-Strömbergsson (\cite{SS}, 2006), who established the local minimality of $\mathcal D_4$. Thereby, this resolves the Rankin-Sobolev problem in dimension four dating back to Éndibaev (\cite{End1978}, 1978) and Shushbaev (\cite{Shu1978}, 1978).
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Analysis of PDEs

Long time strong Sobolev instability for quasilinear NLS

We prove long-time strong Sobolev instability for a class of quasilinear Schrödinger equations on $\mathbb T^2$ arising, via the Madelung transform, in the description of Euler-Korteweg capillary fluids. More precisely, for every $s\ge 7$, arbitrarily small $\mu>0$, and arbitrarily large $\mathcal K>0$, we construct a solution such that $$ \|u(0)\|_{H^s}<\mu, \qquad \|u(T)\|_{H^s}>\mathcal K $$ at some finite time $T$, for which we provide an explicit exponential upper bound. The instability mechanism is generated by a finite-dimensional resonant Toy Model associated with the cubic semilinear part of the equation, in the spirit of Colliander-Keel-Staffilani-Takaoka-Tao. The main technical difficulty is to justify this dynamics over the long time scale of the energy transfer in the presence of quasilinear derivative losses. We achieve this by combining a weak Birkhoff normal form with paradifferential calculus, microlocal symmetrization, and modified energy estimates. Our result provides a rigorous quasilinear realization of a resonant energy-transfer mechanism, and suggests a connection with weakly turbulent dynamics in capillary fluids.
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All authors Yuri Cacchiò, Filippo Giuliani, Felice Iandoli, Raffaele Scandone

Analysis of PDEs

Formation of shear bands through discrete localized plastic increments

We study rate-independent systems in which the evolution is obtained by incremental minimization of elastic energy and one-homogeneous dissipation under constraints on the admissible inelastic increments. Such constraints arise naturally in several models of inelastic materials, including shear-transformation-zone models, intermittent plasticity, and quantized plasticity, where evolution proceeds through prescribed elementary activation events rather than arbitrary plastic increments. We establish the existence of a continuous-time limit for the corresponding constrained incremental scheme under suitable assumptions. As an application, we formulate a simplified shear-transformation-zone model consisting of localized activation events on a lattice embedded in a two-dimensional elastic medium. We prove that this model generates shear-band formation through the successive activation of neighboring transformation zones. More precisely, we show that every admissible evolution remains localized on a growing line segment in the infinite-domain setting and that the same mechanism persists on sufficiently large bounded domains. These results provide a rigorous mathematical framework for constrained activation models and show that restrictions on admissible elementary events alone constitute a mechanism for localization in rate-independent systems.
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Analysis of PDEs · Cross-listed from nlin.SI

Asymptotic behavior analysis of solutions to the Heisenberg ferromagnet equation with the Schwartz initial data

This work aims to investigate the long-time asymptotic behavior of solutions to the Cauchy problem for the Heisenberg ferromagnet equation with the Schwartz initial data. Utilizing the gauge transformations, spectral analysis and the inverse scattering method, we prove that the solutions to the Heisenberg ferromagnet equation can be expressed in terms of the solutions to a matrix Riemann-Hilbert problem formulated in the complex $k$-plane. Various Deift-Zhou contour deformations and the motivation behind them are given. By applying the nonlinear steepest descent method to the associated matrix-valued Riemann-Hilbert problem, we obtain the exact leading-order asymptotic formulas and uniform error estimates for solutions to the Cauchy problem of the Heisenberg ferromagnet equation.
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Analysis of PDEs · Cross-listed from math.DG

Smoothing polyhedral spaces via Ricci flow

We prove Petrunin's smoothing conjecture in all dimensions: every compact Euclidean polyhedral space without boundary and with nonnegative Alexandrov curvature is a Gromov-Hausdorff limit of smooth Riemannian orbifolds with geometrically nonnegative curvature. More strongly, the approximating metrics are positive-time slices of a single orbifold Ricci flow whose metric initial condition is the given polyhedral space. The proof rests on a new short-time existence and regularization theory for Ricci flow that, under two-sided volume bounds and a generalized segment inequality, replaces pointwise lower curvature control by small scale-invariant integral control of the defect from a preserved curvature cone. Although it allows arbitrarily large pointwise violations, this theory yields an existence time and positive-time curvature estimates independent of the initial upper curvature bound. As a further application, it gives rigidity consequences for manifolds with small integral curvature defect.
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Analysis of PDEs

Global well-posedness and scattering for energy-critical Schrodinger equations with conservative Marcus noise

This work establishes global well-posedness for the three-dimensional defocusing energy-critical nonlinear Schrödinger equation with conservative linear Marcus noise. For arbitrary deterministic energy-space data, we construct a probabilistically strong solution, unique in the critical spacetime class, and prove convergence of finite-activity approximations. The spatial profiles need only be bounded and Lipschitz, while the centered pure-jump Lévy noise is assumed to have finite second moment. If the temporal noise coefficient is square integrable on the half-line, the solution scatters almost surely, with uniform mean-square tail convergence and no smallness restriction. The solution conserves mass and satisfies an exact energy balance. The proof combines deterministic energy-critical stability with Poisson Strichartz estimates; convergence of the interaction-representation martingale gives the critical spacetime control needed for continuation and scattering.
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All authors Bin Liu, Fan Xu, Bo Yang, Lei Zhang

Analysis of PDEs

Interface-Shifted Minnaert Resonances

We develop a unified asymptotic theory for Minnaert resonances generated by a small bubble $D_\varepsilon$ placed near an interface $\Gamma$ of material discontinuity in an acoustic background. The bubble has characteristic size $\varepsilon>0$, with its density and bulk modulus depending on the same small parameter through the Minnaert high-contrast scaling. The analysis is organized by the scaled separation \[ \Theta_\varepsilon := \frac{\operatorname{dist}(D_\varepsilon,\Gamma)}{\varepsilon}, \] and covers the three natural regimes \[ \Theta_\varepsilon\to+\infty, \qquad \Theta_\varepsilon\to\Theta_*\in(0,\infty), \qquad \Theta_\varepsilon\to0: \] 1) In the far-separation regime, the interface is invisible at leading order and the classical full-space Minnaert law is recovered. 2) In the critical regime, the rescaled geometry retains both the bubble and the interface at finite separation, and the Newtonian capacitance is replaced by a flat-interface capacitance determined by the limiting tangent transmission problem. 3) In the near-contact regime, this family converges to a contact-limiting capacitance, yielding the same leading-order Minnaert resonance for all gap scalings satisfying $\operatorname{dist}(D_\varepsilon,\Gamma) = o(\varepsilon)$. These three regimes provide a unified description of how the resonance frequency changes as the bubble approaches the interface, from the classical isolated-bubble limit to the contact limit. The analysis relies on a uniform reduction of the resonance problem to a scalar equation and on a variational characterization of the interface-dependent capacitances; in particular, Mosco convergence of the associated transmission energies yields convergence of the capacitary potentials and minimum energies up to the singular contact configuration.
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Analysis of PDEs

Sharp stability and instability of stratified steady states for the incompressible porous media equation

We study the stability and instability of stratified steady states $\rho_s=\rho_s(y)$ for the two-dimensional incompressible porous media equation on $\mathbb{T}\times(-1,1)$ and $\mathbb{T}\times\mathbb{R}$. On the periodic channel, uniformly decreasing steady states satisfying natural boundary-compatibility conditions are nonlinearly stable under small $H^m$ perturbations, for every integer $m>2$. The solutions converge in $L^2$ to the measure-preserving stratification of the initial density at the rate $t^{-m/2}$. Conversely, every steady state with $\sup\rho_s'>0$ is nonlinearly unstable in $H^m$. On the infinite cylinder, we prove nonlinear instability under the additional gap condition \[ \sup_{\mathbb{R}}\rho_s' >\limsup_{|y|\to\infty}\rho_s'(y). \] In both settings, the instability is generated by positive eigenvalues of the linearized operator converging to $\sup\rho_s'$, which equals both its spectral bound and semigroup growth bound.
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Analysis of PDEs

The compactness of Moser-Trudinger type inequalities in the unit ball

In this paper, we employ the concentration-compactness principle to show that if the Dirichlet norm is replaced by the standard Sobolev norm, then the supremum of $$ \int_{\mathbb{B}} |x|^{N \epsilon} \Phi \left( \alpha_N \left( 1+ \epsilon \right) |u|^{ \frac{N}{N-1} } \right) dx $$ over all such functions is uniformly bounded. Furthermore, we also prove the existence of extremals. Finally, we consider the compactness of the sequence of extremals of the inequalities and the limit of this sequence is the extremal of $$ \int_{\mathbb{B}} \Phi \left( \alpha_N |u|^{ \frac{N}{N-1} } \right) dx $$ in $C^1 \left( \mathbb{B} \right)$, where $\alpha_N = N \omega_{N-1}^{ \frac{1}{N-1} } $, $\Phi \left( t \right) := e^t - \sum_{j=0}^{N-2} \frac{t^j}{j!} $ and $\omega_{N-1}$ is the surface of the unit ball in $\mathbb{R}^N$.
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Analysis of PDEs

Optimal Hardy Inequalities for Fractional $p$-Laplacians on the Integers

We obtain optimal Hardy inequalities for fractional powers of the $p$-Laplacian $\Delta_p^\sigma$ on $\mathbb{Z}$, $p\in (1,\infty)$, $\sigma \in (0, 1/p)$. Asymptotically, the optimal weights behave like $|x|^{-p\sigma}$ as $|x|\to \infty$. We show a similar result for the Riesz fractional $p$-Laplacian. In an appendix, we show that for general $p$-Laplace operators on locally summable graphs, $p$-null-criticality implies $p$-optimality at infinity.
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Analysis of PDEs

Spectral geometry of the magnetic $p$-Laplacian

We investigate the interplay between the geometry of a planar domain and the spectrum of the nonlinear $p$-Laplacian, subject to a homogeneous magnetic field and Dirichlet boundary conditions. First, we establish a lower bound for the bottom of the spectrum on the whole plane, extending the classical Landau-level estimate to the nonlinear regime. Second, we prove Pólya-type bounds for the first eigenvalue on bounded convex planar domains in terms of the area, perimeter, minimal width and magnetic field strength, and show that they are asymptotically sharp along sequences of suitable thinning domains. Finally, we post some remarks with open problems.
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Analysis of PDEs

Sharp Decay estimates for the discrete Fourth-Order Schrödinger Equation

We establish sharp time-decay estimates for the discrete fourth-order Schrödinger equation on lattices of arbitrary dimension, extending the author's previous work \cite{C24}. In higher dimensions, scalar Fourier factorization reduces the analysis to product estimates for one-dimensional oscillatory integrals. Since this method does not yield the sharp decay exponents in low dimensions, we also use Newton polyhedra to obtain the required uniform estimates. In particular, the sharp decay rate for the biharmonic Schrödinger propagator is $|t|^{-d/4}$.
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Analysis of PDEs

Boundary Value Problems for the $SU(\infty)$-Toda Equation via the Onofri Inequality

We formulate and solve a degenerate elliptic boundary value problem for the $SU(\infty)$-Toda equation on $[0,\frac12)\times\mathbb{S}^2$. This constructs anti-self-dual Poincaré–Einstein metrics with circle symmetry on the $4$-ball and on complex line bundles over $\mathbb{S}^2$.
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Analysis of PDEs

Existence of three solutions for parametric $p$-Laplacian equations in $\mathbb{R}^N$

In this paper we deal with a nonlinear elliptic problem in the whole space $\mathbb{R}^N$ involving the $p$-Laplacian operator with $p>N$. Under suitable assumptions on the potential term and on the nonlinearity, we establish the existence of at least three distinct weak solutions. Our approach is variational and relies on two different three critical points theorems. The results extend to higher dimensions some recent multiplicity theorems for one-dimensional $p$-Laplacian equations on the real line, and provide explicit ranges for the parameter $\lambda > 0$ ensuring the existence of multiple solutions, which are nonnegative under additional sign conditions. The nontriviality of the solutions is also discussed. Finally, applications to problems whose nonlinearities have separated variables are presented.
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Analysis of PDEs · Cross-listed from math.DG

The capillary $L_{p}$ dual Christoffel-Minkowski problem for $1<p<q\leq k+1$ with $1\leq k\leq n$

This paper is concerned with a capillary $L_p$ Christoffel–Minkowski-type problem involving the prescription of a class of $L_p$ geometric measures formed by the $k$-th capillary area measure and the $q$-th dual curvature measure. By establishing a gradient estimate, we prove the existence of an even, smooth, strictly convex solution in the parameter range $1<p<q\leq k+1$, where $1\leq k\leq n$.
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Analysis of PDEs

Uniform $W^{2,m}$ approximation of almost isometric maps

This paper shows that an almost-isometric Sobolev map from a Lipschitz subset of an oriented manifold $M$ into another oriented manifold $N$ can be approximated by a map of class $C^{1,\alpha}$, with a universal bound on the $W^{2,m}$ norm, for any $m\in(1,\infty)$. This, in turn, implies a universal bound on the $C^{1,\alpha}$ seminorm. The $W^{1,p}$ distance of the approximation from the original map is controlled in terms of the $L^p$-deviation from being an isometry, with the optimal scaling. The manifolds $M$ and $N$ are assumed to be compact, oriented and have equal dimension; $M$ may have a boundary.
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Analysis of PDEs

Hölder estimates up to the singular time for the Córdoba-Córdoba-Fontelos equation

We prove that the solution to the Córdoba-Córdoba-Fontelos equation $\theta_t-u\theta_x=0$, $u=H\theta$, on the real line with analytic initial datum $\theta_0(x)=(1+x^2)^{-1}$ develops a finite-time singularity while remaining uniformly bounded in $C^{2/5}$. We also prove that, as the solution approaches the singular time, the $C^{2/3}$ seminorms of both $\theta$ and $u$ diverge. The main ingredient is an integral representation in terms of a probability measure that is preserved by the nonlinear evolution. From this representation we derive a pointwise quadratic estimate for the key nonlinear term in the equation for $u$, using a comparison of positive kernels. Together with evolution identities for the moments of the measure, this estimate yields both the uniform Hölder bound and the divergence of the higher seminorms.
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Analysis of PDEs

Dynamical stability for the periodic modified Mullins-Sekerka flow

We prove dynamical stability in arbitrary dimension for the modified Mullins–Sekerka flow, the gradient flow of the sharp-interface Ohta–Kawasaki energy on the flat torus. Specifically, we show that if an initial set has the same volume as a strictly stable critical set for the energy and is sufficiently close to it in $C^{3,\alpha}$, then the flow exists for all times and converges exponentially fast, in every $C^k$ norm, to a translate of that critical set. The proof relies on a quantitative Alexandrov-type estimate for strictly stable critical sets of the energy.
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Analysis of PDEs

Sequences of generalized moments and their applications to some moment partial differential equations

We introduce sequences of generalized moments that are a generalization of sequences preserving summability and sequences of moments from Balser's theory of moment summability. We construct extensions of Laplace and Borel integral operators for these new sequences. We find integral representations of moment derivatives for generalized moments. We show the characterization of summable solutions of moment-PDEs with generalized moments. We describe singular directions for summable solutions of moment-PDEs with generalized moments and we express jumps across these singular directions in terms of hyperfunctions and in terms of kernel functions associated with sequences preserving summability, which are connected with given sequences of generalized moments.
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