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Sagun Chanillo

Publications and source records attributed to Sagun Chanillo.

29 records · Page 2Linked to original sources
arXiv2010

Embeddability for Three-Dimensional Cauchy-Riemann Manifolds and CR Yamabe Invariants

Let M^3 be a closed CR 3-manifold. In this paper we derive a Bochner formula for the Kohn Laplacian in which the pseudo-hermitian torsion plays no role. By means of this formula we show that the non-zero eigenvalues of the Kohn Laplacian are bounded below by a positive constant provided the CR Paneitz operator is non-negative and the Webster curvature is positive. Our lower bound for the non-zero eigenvalues is sharp and is attained on S^3. A consequence of our lower bound is that all compact CR 3-manifolds with non-negative CR Paneitz operator and positive CR Yamabe constant are embeddable. Non-negativity of the CR Paneitz operator and positivity of the CR Yamabe constant are both CR invariant conditions and do not depend on conformal changes of the contact form. In addition we show that under the sufficient conditions above for embeddability, the embedding is stable in the sense of Burns and Epstein. We also show that for the Rossi example for non-embedability, the CR Paneitz operator is negative. For CR structures close to the standard structure on $S^3$ we show the CR Paneitz operator is positive on the space of pluriharmonic functions with respect to the standard CR structure on $S^3$.

math.CV↗
arXiv2008

Regularity of the minimizers in the composite membrane problem in R^2

We study the regularity of minimizers to the composite membrane problem in the plane (ie given a domain omega and a positive number A, smaller than the measure of omega, minimize the first Dirichlet eigenvalue for the Schrodinger operator with potential equal to a fixed multiple of the characteristic function of a subset D of omega, with measure A). We show that for minimizers, the boundary of D is analytic.

math.AP↗
arXiv2008

Subelliptic Bourgain-Brezis Estimates on Groups

We show that divergence free vector fields which belong to L^1 on stratified, nilpotent groups are in the dual space of functions whose sub-gradient are L^Q integrable where Q is the homogeneous dimension of the group. This was first obtained on Euclidean space by Bourgain and Brezis.

math.AP↗
arXiv2007

Sharp Global Bounds for the Hessian on Pseudo-Hermitian Manifolds

We find sharp bounds for the norm inequality on a Pseudo-hermitian manifold, where the L^2 norm of all second derivatives of the function involving horizontal derivatives is controlled by the L^2 norm of the sub-Laplacian. Perturbation allows us to get a-priori bounds for solutions to sub-elliptic PDE in non-divergence form with bounded measurable coefficients. The method of proof is through a Bochner technique. The Heisenberg group is seen to be en extremal manifold for our inequality in the class of manifolds whose Ricci curvature is non-negative.

math.AP↗
arXiv2006

Uniqueness of Solutions to Schrodinger Equations on Complex Semi-simple Lie Groups

We consider the time dependent Schrodinger equation on a complex semi-simple Lie group. We consider initial data a bi-invariant function. We prove that if the initial data decays fast enough, and the solution decays fast enough at one time slice, then the solution hs to vanish identically for all time. The hypothesis for decay we impose is shown to be optimal, uniqueness fails otherwise. We also consider the Heisenberg roup. There we show that the presence of closed loops that arise as the projection of geodesics to the contact plane at the origin precludes writing down a solution operator.

math.RT↗
arXiv2002

Non-Linear Eigenvalues and Analytic Hypoellipticity

Motivated by the problems of analytic hypoellipticity, we show that a special family of compact non self-adjoint operators has a non-zero eigenvalue. We recover old results by Christ,Hanges, Himonas, Pham-The-Lai and Robert proved by using ordinary differential equations. We show our method applies to higher dimensional cases, giving in particular a new class of hypoelliptic but not analytic hypoelliptic operators.

math.AP↗
arXiv2001

The conformal plate buckling equation

We study the conformal plate buckling equation (Laplace--Beltrami)^2 u =1, where the L-B operator is for the metric g = e^{2u}g_0, with $g_0$ the standard Euclidean metric on R^2. This conformal elliptic PDE of fourth order is equivalent to the nonlinear system of elliptic PDEs of second order, Delta u +K_g e^(2u)=0, Delta K_g + e^(2u)=0, with x in R^2, describing a conformally flat surface with a Gauss curvature function K_g that is generated self-consistently through the metric's conformal factor.

math.AP↗
arXiv2000

Surfaces with radially symmetric prescribed Gauss curvature

We study conformally flat surfaces with prescribed Gaussian curvature, described by solutions $u$ of the PDE: $Δu(x)+K(x)\exp(2u(x))=0$, with $K(x)$ the Gauss curvature function at $x\in\RR^2$. We assume that the integral curvature is finite. For radially symmetric $K$ we introduce the notion of a least integrally curved surface, and also the notion of when such a surface is critical. With respect to these notions we analyze the radial symmetry of $u$ for the whole spectrum of possible integral curvature values. Under a mild integrability condition which rules out harmonic non-radial behavior near infinity, we prove that $u$ is radially symmetric and decreasing in the following categories: (1) $K$ is decreasing, $u$ a classical solution, and the integral curvature of the surface is above critical; (2) $K$ is decreasing, $u$ a classical solution, the integral curvature of the surface is critical, and the surface satisfies an additional integrability condition which is mildly stronger than finite integral curvature; (3) $K$ is non-positive. In categories 1 and 2, $K$ is allowed to diverge logarithmically or as power law to $-\infty$ at spatial infinity. Examples of nonradial solutions which violate one or more of our conditions are discussed as well. In particular, for non-positive and non-negative $K$ that satisfy appropriate integrability conditions and otherwise are fairly arbitrary, we introduce probabilistic methods to construct surfaces with finite integral curvature and entire harmonic asymptotics at infinity. For radial symmetric $K$ these surfaces are examples of broken symmetry.

math.AP↗
arXiv1998

Curl-Free Ginzburg-Landau Vortices

For certain nonlinear elliptic PDE problems in two dimensions, the classical isoperimetric inequality produces a sharp inequality that violates a Pohozaev identity except for radial symmetric, decreasing solutions. A generalized version of this technique is used here to prove radial symmetry of curl-free Ginzburg-Landau vortices.

math.AP↗