Noncompact Manifolds Research Articles

Comparison Theorems for 3D Manifolds With Scalar Curvature Bound

Abstract Two sharp comparison results are derived for 3D complete noncompact manifolds with scalar curvature bounded from below. The 1st one concerns the Green’s function. When the scalar curvature is nonnegative, it states that the rate of decay of an energy quantity over the level set is strictly less than that of the Euclidean space unless the manifold itself is isometric to the Euclidean space. The result is in turn converted into a sharp area comparison for the level set of the Green’s function when in addition the Ricci curvature of the manifold is assumed to be asymptotically nonnegative at infinity. The 2nd result provides a sharp upper bound of the bottom spectrum in terms of the scalar curvature lower bound, in contrast to the classical result of Cheng, which involves a Ricci curvature lower bound.

Boundary-value problems for the inhomogeneous Schr"odinger equation with variations of its potential on non-compact Riemannian manifolds

Boundary-value problems for the inhomogeneous Schr"odinger equation with variations of its potential on non-compact Riemannian manifolds

Concentration-Compactness Principle for Trudinger–Moser’s Inequalities on Riemannian Manifolds and Heisenberg Groups: A Completely Symmetrization-Free Argument

Abstract The concentration-compactness principle for the Trudinger–Moser-type inequality in the Euclidean space was established crucially relying on the Pólya–Szegő inequality which allows to adapt the symmetrization argument. As far as we know, the first concentration-compactness principle of Trudinger–Moser type in non-Euclidean settings, such as the Heisenberg (and more general stratified) groups where the Pólya–Szegő inequality fails, was found in [J. Li, G. Lu and M. Zhu, Concentration-compactness principle for Trudinger–Moser inequalities on Heisenberg groups and existence of ground state solutions, Calc. Var. Partial Differential Equations 57 2018, 3, Paper No. 84] by developing a nonsmooth truncation argument. In this paper, we establish the concentration-compactness principle of Trudinger–Moser type on any compact Riemannian manifolds as well as on the entire complete noncompact Riemannian manifolds with Ricci curvature lower bound. Our method is a symmetrization-free argument on Riemannian manifolds where the Pólya–Szegő inequality fails. This method also allows us to give a completely symmetrization-free argument on the entire Heisenberg (or stratified) groups which refines and improves a proof in the paper of Li, Lu and Zhu. Our results also show that the bounds for the suprema in the concentration-compactness principle on compact manifolds are continuous and monotone increasing with respect to the volume of the manifold.

A blow-up result for a nonlinear wave equation on manifolds: the critical case

We consider a inhomogeneous semilinear wave equation on a noncompact complete Riemannian manifold of dimension , without boundary. The reaction exhibits the combined effects of a critical term and of a forcing term. Using a rescaled test function argument together with appropriate estimates, we show that the equation admits no global solution. Moreover, in the special case when , our result improves the existing literature. Namely, our main result is valid without assuming that the initial values are compactly supported.

A CFT distance conjecture

We formulate a series of conjectures relating the geometry of conformal manifolds to the spectrum of local operators in conformal field theories in d > 2 spacetime dimensions. We focus on conformal manifolds with limiting points at infinite distance with respect to the Zamolodchikov metric. Our central conjecture is that all theories at infinite distance possess an emergent higher-spin symmetry, generated by an infinite tower of currents whose anomalous dimensions vanish exponentially in the distance. Stated geometrically, the diameter of a non-compact conformal manifold must diverge logarithmically in the higher-spin gap. In the holographic context our conjectures are related to the Distance Conjecture in the swampland program. Interpreted gravitationally, they imply that approaching infinite distance in moduli space at fixed AdS radius, a tower of higher-spin fields becomes massless at an exponential rate that is bounded from below in Planck units. We discuss further implications for conformal manifolds of superconformal field theories in three and four dimensions.

Gradient estimates for a nonlinear elliptic equation under geometric flow

We investigate the parabolic Allen-Cahn equation ∂u∂t=Δu+(1−u2)u under general geometric flow on complete noncompact manifolds. We first prove a local gradient estimate for the positive solution u to this equation, then we obtain a Harnack inequality as an application.

The Classical and Quantum Photon Field for Non-compact Manifolds with Boundary and in Possibly Inhomogeneous Media

In this article I give a rigorous construction of the classical and quantum photon field on non-compact manifolds with boundary and in possibly inhomogeneous media. Such a construction is complicated by zero-modes that appear in the presence of non-trivial topology of the manifold or the boundary. An important special case is {mathbb {R}}^3 with obstacles. In this case the zero modes have a direct interpretation in terms of the topology of the obstacle. I give a formula for the renormalised stress energy tensor in terms of an integral kernel of an operator defined by spectral calculus of the Laplace Beltrami operator on differential forms with relative boundary conditions.

Asymptotic Properties of Solutions to the Cauchy Problem for Degenerate Parabolic Equations with Inhomogeneous Density on Manifolds

We consider the Cauchy problem for doubly nonlinear degenerate parabolic equations with inhomogeneous density on noncompact Riemannian manifolds. We give a qualitative classification of the behavior of the solutions of the problem depending on the behavior of the density function at infinity and the geometry of the manifold, which is described in terms of its isoperimetric function. We establish for the solutions properties as: stabilization of the solution to zero for large times, finite speed of propagation, universal bounds of the solution, blow up of the interface. Each one of these behaviors of course takes place in a suitable range of parameters, whose definition involves a universal geometrical characteristic function, depending both on the geometry of the manifold and on the asymptotics of the density at infinity.

The sharp lower bound of the first Dirichlet eigenvalue for geodesic balls

On complete noncompact Riemannian manifolds with non-negative Ricci curvature, Li–Schoen proved the uniform Poincaré inequality for any geodesic ball. In this note, we obtain the sharp lower bound of the first Dirichlet eigenvalue of such geodesic balls, which implies the sharp Poincaré inequality for geodesic balls.

The spectrum of simplicial volume of non-compact manifolds

We show that, in dimension at least 4, the set of locally finite simplicial volumes of oriented connected open manifolds is [0,infty ]. Moreover, we consider the case of tame open manifolds and some low-dimensional examples.

The Hitchin–Kobayashi correspondence for holomorphic pairs over non-Kähler manifolds

In this paper, we study holomorphic pairs over a class of non-compact Gauduchon manifolds. We prove that the stability implies the existence of Hermitian–Yang–Mills metric, and the semi-stability implies the existence of approximate Hermitian–Yang–Mills structure. We generalize the result in Bradlow (1991) [7] to the non-compact and non-Kähler case. Our proof is a combination of heat flow method and continuity method.

Narrow equidistribution and counting of closed geodesics on noncompact manifolds

We prove the equidistribution of (weighted) periodic orbits for the geodesic flow on noncompact negatively curved manifolds toward equilibrium states in the narrow topology, i.e. in the dual of bounded continuous functions. We deduce an exact asymptotic counting for periodic orbits (weighted or not), which was previously known only for geometrically finite manifolds.

Navier-Stokes equations on non-compact Einstein manifolds: Stability implies periodicity

For a non-compact Einstein manifold M with negative Ricci curvature tensor we consider the Navier-Stokes Equations (NSE) for vector fields on M and prove the existence and local exponential stability of bounded solutions to NSE. Then, using this local stability property of solutions we show the existence of a time-periodic solution to NSE for vector fields on M under action of a time-periodic external force.

Critical and subcritical Trudinger-Moser inequalities on complete noncompact Riemannian manifolds

Though the sharp Trudinger-Moser inequalities on compact Riemannian manifolds have been known for some times, optimal constants for such inequalities on complete noncompact Riemannian manifolds are still unknown except in some special cases (such as hyperbolic spaces or Hadamard manifolds). In this paper, we will establish the sharp critical and subcritical Trudinger-Moser type inequalities with best constants on any complete and noncompact Riemannian manifold (M,g) whose Ricci curvature and its injectivity radius have lower bounds. (See Theorems 1.3 and 1.4.)More precisely, we will establish the following sharp critical Trudinger-Moser inequality on such manifolds (M,g,dVg):supu∈W1,n(M),||u||1,τ≤1⁡∫Mϕ(αn|u|nn−1)dVg≤C(n,τ), where τ>0, ϕ(t)=∑k=n−1∞tkk!, αn=nωn−11n−1, and ωn−1 is the area of the unit sphere in Rn, ||u||1,τ=(∫Mτ|u|n+|∇u|ndVg)1n. Moreover, we also prove that the following sharp subcritical Trudinger-Moser inequalitysupu∈W1,n(M),||∇u||n≤1⁡1||u||Ln(M)n∫Mϕ(α|u|nn−1)dVg≤C(n,α) in the sense that the supremum is finite for all α<αn, but infinite for α≥αn.The proofs of both the critical and subcritical Trudinger-Moser inequalities rely crucially on the Trudinger-Moser inequality on any compact manifold M with or without boundary, which is of its own interest. The important property we establish in this paper is that the upper bound C(n,M) for the Trudinger-Moser supremum is continuous and monotone increasing with respect to the volume of M. (See Theorems 1.1 and 1.2.) This upper bound property allows us to carry out a symmetrization-free argument from sharp local inequalities on compact manifolds to the optimal global inequalities on complete and noncompact Riemannian manifolds. Our optimal results sharpen substantially the existing ones on such Riemannian manifolds in the literature.

The singular Weinstein conjecture

In this article, we investigate Reeb dynamics on bm-contact manifolds, previously introduced in [37], which are contact away from a hypersurface Z but satisfy certain transversality conditions on Z. The study of these contact structures is motivated by that of contact manifolds with boundary. The search of periodic Reeb orbits on those manifolds thereby starts with a generalization of the well-known Weinstein conjecture. Contrary to the initial expectations, examples of compact bm-contact manifolds without periodic Reeb orbits outside Z are provided. Furthermore, we prove that in dimension 3, there are always infinitely many periodic orbits on the critical set if it is compact. We prove that traps for the bm-Reeb flow exist in any dimension. This investigation goes hand-in-hand with the Weinstein conjecture on non-compact manifolds having compact ends of convex type. In particular, we extend Hofer's arguments to open overtwisted contact manifolds that are R+-invariant in the open ends, obtaining as a corollary the existence of periodic bm-Reeb orbits away from the critical set. The study of bm-Reeb dynamics is motivated by well-known problems in fluid dynamics and celestial mechanics, where those geometric structures naturally appear. In particular, we prove that the dynamics on positive energy level-sets in the restricted planar circular three body problem are described by the Reeb vector field of a b3-contact form that admits an infinite number of periodic orbits at the critical set.

Second Ricci flow on noncompact Hermitian manifolds

In this work, we first establish short time existence and Shi's type estimate of second Ricci flow on complete noncompact Hermitian manifolds. As an application, we use the second Ricci flow to discuss the existence of Kaehler-Einstein metric on complete noncompact Hermitian manifolds.

Compact Sobolev embeddings on non-compact manifolds via orbit expansions of isometry groups

Given a complete non-compact Riemannian manifold (M, g) with certain curvature restrictions, we introduce an expansion condition concerning a group of isometries G of (M, g) that characterizes the coerciveness of G in the sense of Skrzypczak and Tintarev (Arch Math 101(3): 259–268, 2013). Furthermore, under these conditions, compact Sobolev-type embeddings à la Berestycki-Lions are proved for the full range of admissible parameters (Sobolev, Moser-Trudinger and Morrey). We also consider the case of non-compact Randers-type Finsler manifolds with finite reversibility constant inheriting similar embedding properties as their Riemannian companions; sharpness of such constructions are shown by means of the Funk model. As an application, a quasilinear PDE on Randers spaces is studied by using the above compact embeddings and variational arguments.

Fast diffusion on noncompact manifolds: Well-posedness theory and connections with semilinear elliptic equations

We investigate the well-posedness of the fast diffusion equation (FDE) on noncompact Riemannian manifolds. Existence and uniqueness of solutions for L 1 L^1 initial data was established in Bonforte, Grillo, and Vázquez [J. Evol. Equ. 8 (2008), pp. 99–128]. However, in the Euclidean space, it is known from Herrero and Pierre [Trans. Amer. Math. Soc. 291 (1985), pp. 145–158] that the Cauchy problem associated with the FDE is well posed for initial data that are merely in L l o c 1 L^1_{\mathrm {loc}} . We establish here that such data still give rise to global solutions on general manifolds. If, moreover, the radial Ricci curvature satisfies a suitable pointwise bound from below (possibly diverging to − ∞ -\infty at spatial infinity), we prove that also uniqueness holds, for the same type of data, in the class of strong solutions. Besides, assuming in addition that the initial datum is in L l o c 2 L^2_{\mathrm {loc}} and nonnegative, a minimal solution is shown to exist, and we establish uniqueness of purely (nonnegative) distributional solutions, a fact that to our knowledge was not known before even in the Euclidean space. The required curvature bound is sharp, since on model manifolds it is equivalent to stochastic completeness, and it was shown in Grillo, Ishige, and Muratori [J. Math. Pures Appl. (9) 139 (2020), pp. 63–82] that uniqueness for the FDE fails even in the class of bounded solutions when stochastic completeness does not hold. A crucial ingredient of the uniqueness result is the proof of nonexistence of nonnegative, nontrivial distributional subsolutions to certain semilinear elliptic equations with power nonlinearities, of independent interest.

WITTEN DEFORMATION FOR NONCOMPACT MANIFOLDS WITH BOUNDED GEOMETRY

AbstractMotivated by the Landau–Ginzburg model, we study the Witten deformation on a noncompact manifold with bounded geometry, together with some tameness condition on the growth of the Morse function f near infinity. We prove that the cohomology of the Witten deformation $d_{Tf}$ acting on the complex of smooth $L^2$ forms is isomorphic to the cohomology of the Thom–Smale complex of f as well as the relative cohomology of a certain pair $(M, U)$ for sufficiently large T. We establish an Agmon estimate for eigenforms of the Witten Laplacian which plays an essential role in identifying these cohomologies via Witten’s instanton complex, defined in terms of eigenspaces of the Witten Laplacian for small eigenvalues. As an application, we obtain the strong Morse inequalities in this setting.

Dualities in comparison theorems and bundle-valued generalized harmonic forms on noncompact manifolds

We observe, utilize dualities in differential equations and differential inequalities (see Theorem 2.1), dualities between comparison theorems in differential equations (see Theorems E and 2.2), and obtain dualities in ‘swapping’ comparison theorems in differential equations. These dualities generate comparison theorems on differential equations of mixed types I and II (see Theorems 2.3 and 2.4) and lead to comparison theorems in Riemannian geometry (see Theorems 2.5 and 2.8) with analytic, geometric, PDE’s and physical applications. In particular, we prove Hessian comparison theorems (see Theorems 3.1–3.5) and Laplacian comparison theorems (see Theorems 2.6, 2.7 and 3.1–3.5) under varied radial Ricci curvature, radial curvature, Ricci curvature and sectional curvature assumptions, generalizing and extending the work of Han-Li-Ren-Wei (2014) and Wei (2016). We also extend the notion of function or differential form growth to bundle-valued differential form growth of various types and discuss their interrelationship (see Theorem 5.4). These provide tools in extending the notion, integrability and decomposition of generalized harmonic forms to those of bundle-valued generalized harmonic forms, introducing Condition W for bundle-valued differential forms, and proving the duality theorem and the unity theorem, generalizing the work of Andreotti and Vesentini (1965) and Wei (2020). We then apply Hessian and Laplacian comparison theorems to obtain comparison theorems in mean curvature, generalized sharp Caffarelli-Kohn-Nirenberg type inequalities on Riemannian manifolds, the embedding theorem for weighted Sobolev spaces of functions on manifolds, geometric differential-integral inequalities, generalized sharp Hardy type inequalities on Riemannian manifolds, monotonicity formulas and vanishing theorems for differential forms of degree k with values in vector bundles, such as F-Yang-Mills fields (when F is the identity map, they are Yang-Mills fields), generalized Yang-Mills-Born-Infeld fields on manifolds, Liouville type theorems for F - harmonic maps (when $$F\left(t \right) = {1 \over p}{\left({2t} \right)^{{p \over 2}}},p > 1$$ , they become p-harmonic maps or harmonic maps if p = 2), and Dirichlet problems on starlike domains for vector bundle valued differential 1-forms and {tF}-harmonic maps (see Theorems 4.1, 7.3–7.7, 8.1, 9.1–9.3, 10.1, 11.2, 12.1 and 12.2), generalizing the work of Caffarelli et al. (1984) and Costa (2008), in which M = ℝn and its radial curvature K(r) = 0, the work of Wei and Li (2009), Chen et al. (2011, 2014), Dong and Wei (2011), Wei (2020) and Karcher and Wood (1984), etc. The boundary value problem for bundle-valued differential 1-forms is in contrast to the Dirichlet problem for p-harmonic maps to which the solution is due to Hamilton (1975) for the case p = 2 and RiemN ⩽ 0, and Wei (1998) for 1 < p < ∞.