Annals of Global Analysis and Geometry最新文献

Let ((M,H,g_H;g)) be a sub-Riemannian manifold and (N, h) be a Riemannian manifold. For a smooth map (u: M rightarrow N), we consider the energy functional (E_G(u) = frac{1}{2} int _M[|textrm{d}u_text {H}|^2 - 2,G(u)] textrm{d}V_M), where (textrm{d}u_text {H}) is the horizontal differential of u, (G:Nrightarrow mathbb {R}) is a smooth function on N. The critical maps of (E_G(u)) are referred to as subelliptic harmonic maps with potential G. In this paper, we investigate the existence problem for subelliptic harmonic maps with potentials by a subelliptic heat flow. Assuming that the target Riemannian manifold has nonpositive sectional curvature and the potential G satisfies various suitable conditions, we prove some Eells–Sampson-type existence results when the source manifold is either a step-2 sub-Riemannian manifold or a step-r sub-Riemannian manifold whose sub-Riemannian structure comes from a tense Riemannian foliation.

In this paper, we deal with a strongly pseudoconvex almost CR manifold with a CR contraction. We will prove that the stable manifold of the CR contraction is CR equivalent to the Heisenberg group model.

The radial map u(x) (=) (frac{x}{Vert xVert }) is a well-known example of a harmonic map from ({mathbb {R}}^m,-,{0}) into the spheres ({mathbb {S}}^{m-1}) with a point singularity at x (=) 0. In Nakauchi (Examples Counterexamples 3:100107, 2023), the author constructed recursively a family of harmonic maps (u^{(n)}) into ({mathbb {S}}^{m^n-1}) with a point singularity at the origin ((n = 1,,2,ldots )), such that (u^{(1)}) is the above radial map. It is known that for m (ge ) 3, the radial map (u^{(1)}) is not only stable as a harmonic map but also a minimizer of the energy of harmonic maps. In this paper, we show that for n (ge ) 2, (u^{(n)}) may be unstable as a harmonic map. Indeed we prove that under the assumption n > ({displaystyle frac{sqrt{3}-1}{2},(m-1)}) ((m ge 3), (n ge 2)), the map (u^{(n)}) is unstable as a harmonic map. It is remarkable that they are unstable and our result gives many examples of unstable harmonic maps into the spheres with a point singularity at the origin.

We continue our investigation of the interplay between causal structures on symmetric spaces and geometric aspects of Algebraic Quantum Field Theory. We adopt the perspective that the geometric implementation of the modular group is given by the flow generated by an Euler element of the Lie algebra (an element defining a 3-grading). Since any Euler element of a semisimple Lie algebra specifies a canonical non-compactly causal symmetric space (M = G/H), we turn in this paper to the geometry of this flow. Our main results concern the positivity region W of the flow (the corresponding wedge region): If G has trivial center, then W is connected, it coincides with the so-called observer domain, specified by a trajectory of the modular flow which at the same time is a causal geodesic. It can also be characterized in terms of a geometric KMS condition, and it has a natural structure of an equivariant fiber bundle over a Riemannian symmetric space that exhibits it as a real form of the crown domain of G/K. Among the tools that we need for these results are two observations of independent interest: a polar decomposition of the positivity domain and a convexity theorem for G-translates of open H-orbits in the minimal flag manifold specified by the 3-grading.

We discuss local Sasakian immersion of Sasaki–Ricci solitons (SRS) into fiber products of homogeneous Sasakian manifolds. In particular, we prove that SRS locally induced by a large class of fiber products of homogeneous Sasakian manifolds are, in fact, (eta )-Einstein. The results are stronger for immersions into Sasakian space forms. Moreover, we show an example of a Kähler–Ricci soliton on (mathbb C^n) which admits no local holomorphic isometry into products of homogeneous bounded domains with flat Kähler manifolds and generalized flag manifolds.

We generalize McCann’s theorem of optimal transport to a submanifold setting and use it to prove Michael–Simon–Sobolev inequalities for submanifolds in manifolds with lower bounds on intermediate Ricci curvatures. The results include a variant of the sharp Michael–Simon–Sobolev inequality in Brendle’s (arXiv:2009.13717) when the intermediate Ricci curvatures are nonnegative.

We prove that every complex contact structure gives rise to a distinguished type of almost contact metric 3-structure. As an application, we provide several new examples of manifolds which admit taut contact circles, taut and round almost cosymplectic 2-spheres, and almost hypercontact (metric) structures. These examples generalize the well-known examples of contact circles defined by the Liouville-Cartan forms on the unit cotangent bundle of Riemann surfaces. Further, we provide sufficient conditions for a compact complex contact manifold to be the twistor space of a positive quaternionic Kähler manifold.

We provide the first example of continuous families of Poincaré–Einstein metrics developing cusps on the trivial topology (mathbb {R}^4). We also exhibit families of metrics with unexpected degenerations in their conformal infinity only. These are obtained from the Riemannian version of an ansatz of Debever and Plebański–Demiański. We additionally indicate how to construct similar examples on more complicated topologies.

We define conic reductions (X^{textrm{red}}_{nu }) for torus actions on the boundary X of a strictly pseudo-convex domain and for a given weight (nu ) labeling a unitary irreducible representation. There is a natural residual circle action on (X^{textrm{red}}_{nu }). We have two natural decompositions of the corresponding Hardy spaces H(X) and (H(X^{textrm{red}}_{nu })). The first one is given by the ladder of isotypes (H(X)_{knu }), (kin {mathbb {Z}}); the second one is given by the k-th Fourier components (H(X^{textrm{red}}_{nu })_k) induced by the residual circle action. The aim of this paper is to prove that they are isomorphic for k sufficiently large. The result is given for spaces of (0, q)-forms with (L^2)-coefficient when X is a CR manifold with non-degenerate Levi form.

We study the homology groups of certain 2-connected 7-manifolds admitting quasi-regular Sasaki–Einstein metrics, among them, we found 52 new examples of Sasaki–Einstein rational homology 7-spheres, extending the list given by Boyer et al. (Ann Inst Fourier 52(5):1569–1584, 2002). As a consequence, we exhibit new families of positive Sasakian homotopy 9-spheres given as cyclic branched covers, determine their diffeomorphism types and find out which elements do not admit extremal Sasaki metrics. We also improve previous results given by Boyer (Note Mat 28:63–105, 2008) showing new examples of Sasaki–Einstein 2-connected 7-manifolds homeomorphic to connected sums of (S^3times S^4). Actually, we show that manifolds of the form (#kleft( S^{3} times S^{4}right) ) admit Sasaki–Einstein metrics for 22 different values of k. All these links arise as Thom–Sebastiani sums of chain type singularities and cycle type singularities where Orlik’s conjecture holds due to a recent result by Hertling and Mase (J Algebra Number Theory 16(4):955–1024, 2022).