Publications

Using singular perturbation theory and family blow-up we prove that nilpotent contact points in deformations of slow-fast Darboux integrable systems have finite cyclicity. The deformations are smooth or analytic depending on the region in the parameter space. This paper is a natural continuation of [3, 1] where one studies limit cycles in polynomial deformations of slow-fast Darboux integrable systems, around the "integrable" direction in the ...

In this short article, given a smooth diagonalizable group scheme G of finite type acting on a smooth quasi-compact separated scheme X, we prove that (after inverting some elements of representation ring of G) all the information concerning the additive invariants of the quotient stack [X/G] is "concentrated" in the subscheme of G-fixed points X-G. Moreover, in the particular case where G is connected and the action has finite stabilizers, we ...

In this paper, we study tensor (or monoidal) categories of finite rank over an algebraically closed field F. Given a tensor category C, we have two structure invariants of C: the Green ring (or the representation ring) r(C) and the Auslander algebra A(C) of C. We show that a Krull-Schmit abelian tensor category C of finite rank is uniquely determined (up to tensor equivalences) by its two structure invariants and the associated associator system ...

The isotropic matroid M[IAS(G)] of a looped simple graph G is a binary matroid equivalent to the isotropic system of G. In general, M[IAS(G)] is not regular, so it cannot be represented over fields of characteristic not equal 2. The ground set of M[IAS(G)] is denoted W(G); it is partitioned into 3-element subsets corresponding to the vertices of G. When the rank function of M[IAS(G)] is restricted to subtransversals of this partition, the ...

Smoothing (and decay) spacetime estimates are discussed for evolution groups of self-adjoint operators in an abstract setting. The basic assumption is the existence (and weak continuity) of the spectral density in a functional setting. Spectral identities for the time evolution of such operators are derived, enabling results concerning U+201Cbest constantsU+201D for smoothing estimates. When combined with suitable U+201Ccomparison ...

In 1956, Tutte showed that every planar 4-connected graph is hamiltonian. In this article, we will generalize this result and prove that polyhedra with at most three 3-cuts are hamiltonian. In 2002 Jackson and Yu have shown this result for the subclass of triangulations. We also prove that polyhedra with at most four 3-cuts have a hamiltonian path. It is well known that for each k U+2265 6 non-hamiltonian polyhedra with k 3-cuts exist. We give ...

In this paper, we prove that there is a canonical homotopy (n+1)-algebra structure on the shifted operadic deformation complex $\Def(e_n\to\mathcal{P})[-n]$ for any operad $\mathcal{P}$ and a map of operads $f\colon e_n\to\mathcal{P}$. This result generalizes a result of Tamarkin, who considered the case $\mathcal{P}=\End_\Op(X)$. Another more computational proof of the same result was recently sketched by Calaque and Willwacher. Our method ...

The conjecture of Graham and Lovasz that the (normalized) coefficients of the distance characteristic polynomial of a tree are unimodal is proved; it is also shown that the (normalized) coefficients are log-concave. Upper and lower bounds on the location of the peak are established.