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Jeffrey S. Case

Publications and source records attributed to Jeffrey S. Case.

At least 19 recordsLinked to original sources
arXiv2026

Sharp weighted Sobolev trace inequalities and fractional powers of the Laplacian

We establish a family of sharp Sobolev trace inequalities involving the $W^{k,2}(\mathbb{R}_+^{n+1},y^a)$-norm. These inequalities are closely related to the realization of fractional powers of the Laplacian on $\mathbb{R}^n=\partial\mathbb{R}_+^{n+1}$ as generalized Dirichlet-to-Neumann operators associated to powers of the weighted Laplacian in upper half space, generalizing observations of Caffarelli--Silvestre and of Yang.

math.AP↗
arXiv2026

Computing renormalized curvature integrals on Poincaré-Einstein manifolds

We describe a general procedure for computing renormalized curvature integrals on Poincaré-Einstein manifolds. In particular, we explain the connection between the Gauss-Bonnet-type formulas of Albin and Chang-Qing-Yang for the renormalized volume, and explicitly identify a scalar conformal invariant in the latter formula. Our approach constructs scalar conformal invariants of weight $-n$ on $n$-manifolds, $n \geq 8$, that are natural divergences; these imply that the scalar invariant in the Chang-Qing-Yang formula is not unique in dimension $n \geq 8$. Our procedure also produces explicit conformally invariant Gauss--Bonnet-type formulas for compact Einstein manifolds.

math.DG↗
arXiv2026

Local and global conformal invariants of submanifolds

We develop methods for constructing and computing conformal invariants of submanifolds, with a particular emphasis on conformal submanifold scalars and conformally invariant integrals of natural submanifold scalars. These methods include a direct construction of the extrinsic ambient space, a construction of global invariants of conformally compact minimal submanifolds of conformally compact Einstein manifolds via renormalized extrinsic curvature integrals, and the introduction of a large class of conformal submanifold scalars that are easily computed at minimal submanifolds of Einstein manifolds. As an application, we derive an explicit Gauss--Bonnet--Chern-type formula relating the renormalized area of a conformally compact $k$-dimensional minimal submanifold of a conformally compact Einstein manifold to its Euler characteristic and the integral of a conformal submanifold scalar of weight $-k$. As another application, we prove a rigidity result for conformally compact minimal submanifolds of conformally compact hyperbolic manifolds.

math.DG↗
arXiv2026

Yamabe problems for formally self-adjoint, conformally covariant, polydifferential operators

Formally self-adjoint, conformally covariant, polydifferential operators provide a general framework for studying variational problems, such as prescribing the scalar, $Q$-, or $σ_2$-curvatures, within a conformal class. We describe recent progress on Yamabe problems for such operators, including uniqueness results on the sphere and nonuniqueness results in general. We also highlight a number of open questions related to these operators, some of which constitute a possible blueprint for the general solution of the Yamabe problem for polydifferential operators.

math.DG↗
arXiv2026

Non-homothetic complete periodic contact forms with constant Tanaka--Webster scalar curvature

We study the existence problem for complete contact forms with constant Tanaka--Webster scalar curvature on non-compact strictly pseudoconvex CR manifolds. We prove that, under mild assumptions, the universal cover of a compact strictly pseudoconvex CR manifold admits infinitely many non-homothetic such contact forms whenever its fundamental group has infinite profinite completion. As applications, we treat complements of real or complex spheres in the standard CR sphere, as well as circle bundles over compact Kähler manifolds and the boundary of a Reinhardt domain.

math.DG↗
arXiv2025

A general construction of conformally covariant tridifferential operators

We construct a large family of conformally covariant tridifferential operators as tangential operators in the Fefferman--Graham ambient space. Our construction is analogous to the linear and bilinear constructions of Graham--Jenne--Mason--Sparling and Case--Lin--Yuan, respectively. We also show that the symmetrization of our ambient operators are formally self-adjoint when acting on densities of the correct weight.

math.DG↗
arXiv2025

A general nonuniqueness result for Yamabe-type problems for conformally variational Riemannian invariants

Given a conformally variational scalar Riemannian invariant $I$, we identify a sufficient condition for a compact Riemannian manifold to admit finite regular coverings with many nonhomothetic conformal rescalings with $I$ constant. We also identify a sufficient condition for the universal cover to admit infinitely many geometrically distinct periodic conformal rescalings with $I$ constant. Using these conditions, we improve known nonuniqueness results for the $Q$-curvatures of orders two, four, and six, and establish nonuniqueness results for higher-order $Q$-curvatures and renormalized volume coefficients.

math.DG↗
arXiv2025

Nonhomothetic complete periodic metrics with constant scalar curvature

We show that there are infinitely many pairwise nonhomothetic, complete, periodic metrics with constant scalar curvature that are conformal to the round metric on $S^n\setminus S^k$, where $k < \frac{n-2}{2}$. These metrics are obtained by pulling back Yamabe metrics defined on products of $S^{n-k-1}$ and compact hyperbolic $(k+1)$-manifolds. Our main result proves that these solutions are generically distinct up to homothety. The core of our argument relies on classical rigidity theorems due to Obata and Ferrand, which characterize the round sphere by its conformal group.

math.DG↗
arXiv2025

The GJMS operators in geometry, analysis, and physics

The GJMS operators, introduced by Graham, Jenne, Mason, and Sparling, are a family of conformally invariant linear differential operators with leading term a power of the Laplacian. These operators and their method of construction have had a major impact in geometry, analysis, and physics. We describe the GJMS operators and their construction, and briefly survey their importance and impact.

math.DG↗
arXiv2025

A Gauss-Bonnet formula for the renormalized area of minimal submanifolds of Poincaré-Einstein manifolds

Assuming the extrinsic $Q$-curvature admits a decomposition into the Pfaffian, a scalar conformal submanifold invariant, and a tangential divergence, we prove that the renormalized area of an even-dimensional minimal submanifold of a Poincaré-Einstein manifold can be expressed as a linear combination of its Euler characteristic and the integral of a scalar conformal submanifold invariant. We derive such a decomposition of the extrinsic $Q$-curvature in dimensions two and four, thereby recovering and generalizing results of Alexakis-Mazzeo and Tyrrell, respectively. We also conjecture such a decomposition for general natural submanifold scalars whose integral over compact submanifolds is conformally invariant, and verify our conjecture in dimensions two and four. Our results also apply to the area of a compact even-dimensional minimal submanifold of an Einstein manifold.

math.DG↗
arXiv2024

Deformations of the scalar curvature of a partially integrable pseudohermitian manifold

We consider deformations of the scalar curvature of a partially integrable pseudohermitian manifold, in analogy with the work of Fischer and Marsden on Riemannian manifolds. In particular, we introduce and discuss $R$-singular spaces, give sufficient conditions for the stability of the scalar curvature, and give a partial infinitesimal rigidity result for the scalar curvature of a compact, torsion-free, scalar-flat, integrable pseudohermitian manifold.

math.DG↗
arXiv2024

Extrinsic GJMS operators for submanifolds

We derive extrinsic GJMS operators and $Q$-curvatures associated to a submanifold of a conformal manifold. The operators are conformally covariant scalar differential operators on the submanifold with leading part a power of the Laplacian in the induced metric. Upon realizing the conformal manifold as the conformal infinity of an asymptotically Poincaré--Einstein space and the submanifold as the boundary of an asymptotically minimal submanifold thereof, these operators arise as obstructions to smooth extension as eigenfunctions of the Laplacian of the induced metric on the minimal submanifold. We derive explicit formulas for the operators of orders 2 and 4. We prove factorization formulas when the original submanifold is a minimal submanifold of an Einstein manifold. We also show how to reformulate the construction in terms of the ambient metric for the conformal manifold, and use this to prove that the operators defined by the factorization formulas are conformally invariant for all orders in all dimensions.

math.DG↗
arXiv2023

A factorization of the GJMS operators of special Einstein products and applications

We show that the GJMS operators of a special Einstein product factor as a composition of second- and fourth-order differential operators. In particular, our formula applies to the Riemannian product $H^{\ell} \times S^{d-\ell}$. We also show that there is an integer $D = D(k,\ell)$ such that if $d \geq D$, then for any special Einstein product $N^\ell \times M^{d-\ell}$, the Green's function for the GJMS operator of order $2k$ is positive. As a result, these products give new examples of closed Riemannian manifolds for which the $Q_{2k}$-Yamabe problem is solvable.

math.DG↗
arXiv2023

The Obata-Vétois argument and its applications

We simplify Vétois' Obata-type argument and use it to identify a closed interval $I_n$, $n \geq 3$, containing zero such that if $a \in I_n$ and $(M^n,g)$ is a closed conformally Einstein manifold with nonnegative scalar curvature and $Q_4 + aσ_2$ constant, then it is Einstein. We also relax the scalar curvature assumption to the nonnegativity of the Yamabe constant under a more restrictive assumption on $a$. Our results allow us to compute many Yamabe-type constants and prove sharp Sobolev inequalities on closed Einstein manifolds with nonnegative scalar curvature. In particular, we show that closed locally symmetric Einstein four-manifolds with nonnegative scalar curvature extremize the functional determinant of the conformal Laplacian, partially answering a question of Branson and Ørsted.

math.DG↗
arXiv2023

A Sharp Inequality for Trace-Free Matrices with Applications to Hypersurfaces

We derive a sharp inequality relating the second and fourth elementary symmetric functions of the eigenvalues of a trace-free matrix and give two applications. First, we give a new proof of the classification of conformally flat hypersurfaces in spaceforms. Second, we construct a functional which characterizes rotational hypersurfaces and catenoids.

math.DG↗
arXiv2023

The Neumann problem on the Clifford torus in $\mathbb{S}^3$

We discuss the solution of the Neumann problem associated with the CR Yamabe operator on a subset $Ω$ of the CR manifold $\mathbb{S}^3$ bounded by the Clifford torus $Σ$. We also discuss the Yamabe-type problem of finding a contact form on $Ω$ which has zero Tanaka--Webster scalar curvature and for which $Σ$ has constant $p$-mean curvature.

math.AP↗