All a b c d e f g h i j k l m n o p q r s t u v w x y z Other

Previous Page 3 Next

Displaying 41 – 60 of 101

Showing per page

Non-Archimedean integrals and stringy Euler numbers of log-terminal pairs

Victor V. Batyrev (1999)

Journal of the European Mathematical Society

Using non-Archimedian integration over spaces of arcs of algebraic varieties, we define stringy Euler numbers associated with arbitrary Kawamata log-terminal pairs. There is a natural Kawamata log-terminal pair corresponding to an algebraic variety V having a regular action of a finite group G . In this situation we show that the stringy Euler number of this pair coincides with the physicists’ orbifold Euler number defined by the Dixon-Harvey-Vafa-Witten formula. As an application, we prove a conjecture...

Non-embeddable 1 -convex manifolds

Jan Stevens (2014)

Annales de l’institut Fourier

We show that every small resolution of a 3-dimensional terminal hypersurface singularity can occur on a non-embeddable 1 -convex manifold.We give an explicit example of a non-embeddable manifold containing an irreducible exceptional rational curve with normal bundle of type ( 1 , - 3 ) . To this end we study small resolutions of c D 4 -singularities.

Numerical character of the effectivity of adjoint line bundles

Frédéric Campana, Vincent Koziarz, Mihai Păun (2012)

Annales de l’institut Fourier

In this note we show that, for any log-canonical pair ( X , Δ ) , K X + Δ is ℚ -effective if its Chern class contains an effective ℚ -divisor. Then, we derive some direct corollaries.

On a question of Demailly-Peternell-Schneider

Meng Chen, Qi Zhang (2013)

Journal of the European Mathematical Society

We give an affirmative answer to an open question posed by Demailly-Peternell-Schneider in 2001 and recently by Peternell. Let f : X → Y be a surjective morphism from a log canonical pair ( X , D ) onto a ℚ -Gorenstein variety Y . If - ( K X + D ) is nef, we show that − K Y is pseudo-effective.

On covering and quasi-unsplit families of curves

Laurent Bonavero, Cinzia Casagrande, Stéphane Druel (2007)

Journal of the European Mathematical Society

Given a covering family V of effective 1-cycles on a complex projective variety X , we find conditions allowing one to construct a geometric quotient q : X → Y , with q regular on the whole of X , such that every fiber of q is an equivalence class for the equivalence relation naturally defined by V . Among other results, we show that on a normal and ℚ -factorial projective variety X with canonical singularities and dim X ≤ 4 , every covering and quasi-unsplit family V of rational curves generates a geometric extremal...

On log canonical divisors that are log quasi-numerically positive

Shigetaka Fukuda (2004)

Open Mathematics

Let (X Δ) be a four-dimensional log variety that is projective over the field of complex numbers. Assume that (X, Δ) is not Kawamata log terminal (klt) but divisorial log terminal (dlt). First we introduce the notion of “log quasi-numerically positive”, by relaxing that of “numerically positive”. Next we prove that, if the log canonical divisorK X+Δ is log quasi-numerically positive on (X, Δ) then it is semi-ample.

On some numerical properties of Fano varieties

Cinzia Casagrande (2004)

Bollettino dell'Unione Matematica Italiana

This is the text of a talk given at the XVII Convegno dell’Unione Matematica Italiana held at Milano, September 8-13, 2003. I would like to thank Angelo Lopez and Ciro Ciliberto for the kind invitation to the conference. I survey some numerical conjectures and theorems concerning relations between the index, the pseudo-index and the Picard number of a Fano variety. The results I refer to are contained in the paper [3], wrote in collaboration with Bonavero, Debarre and Druel.

Currently displaying 41 – 60 of 101