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Twistor forms on Kähler manifolds

Andrei Moroianu, Uwe Semmelmann (2003)

Annali della Scuola Normale Superiore di Pisa - Classe di Scienze

Twistor forms are a natural generalization of conformal vector fields on riemannian manifolds. They are defined as sections in the kernel of a conformally invariant first order differential operator. We study twistor forms on compact Kähler manifolds and give a complete description up to special forms in the middle dimension. In particular, we show that they are closely related to hamiltonian 2-forms. This provides the first examples of compact Kähler manifolds with non–parallel twistor forms in...

Two examples of fattening for the curvature flow with a driving force

Giovanni Bellettini, Maurizio Paolini (1994)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

We provide two examples of a regular curve evolving by curvature with a forcing term, which degenerates in a set having an interior part after a finite time.

Two new estimates for eigenvalues of Dirac operators

Wenmin Gong, Guangcun Lu (2016)

Annales Polonici Mathematici

We establish lower and upper eigenvalue estimates for Dirac operators in different settings, a new Kirchberg type estimate for the first eigenvalue of the Dirac operator on a compact Kähler spin manifold in terms of the energy momentum tensor, and an upper bound for the smallest eigenvalues of the twisted Dirac operator on Legendrian submanifolds of Sasakian manifolds. The sharpness of those estimates is also discussed.

Two remarks on Riemann surfaces.

José M. Rodriguez (1994)

Publicacions Matemàtiques

We study the relationship between linear isoperimetric inequalities and the existence of non-constant positive harmonic functions on Riemann surfaces.We also study the relationship between growth conditions of length of spheres and the existence and the existence of Green's function on Riemann surfaces.

Un nouveau regard sur l’estimation de Mourre

Sylvain Golénia (2006)

Journées Équations aux dérivées partielles

La théorie de Mourre est un outil puissant pour étudier le spectre continu d’opérateurs auto-adjoints et pour développer une théorie de la diffusion. Dans cet exposé nous proposons d’un nouveau regard sur la théorie de Mourre en donnant une nouvelle approche du résultat principal de la théorie  : le principe d’aborption limite (PAL) obtenu à partir de l’estimation de Mourre. Nous donnons alors une nouvelle interprétation de ce résultat. Cet exposé a aussi pour but d’être une introduction à la théorie....

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