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In this note, we prove a sharp lower bound for the log canonical threshold of a plurisubharmonic function with an isolated singularity at 0 in an open subset of . This threshold is defined as the supremum of constants c > 0 such that is integrable on a neighborhood of 0. We relate to the intermediate multiplicity numbers , defined as the Lelong numbers of at 0 (so that in particular ). Our main result is that . This inequality is shown to be sharp; it simultaneously improves the classical result due to Skoda, as well as the lower estimate which has received crucial applications to birational geometry in recent years. The proof consists in a reduction to the toric case, i.e. singularities arising from monomial ideals.
We establish an analytic interpretation for the index of certain transversally elliptic symbols on non-compact manifolds. By using this interpretation, we establish a geometric quantization formula for a Hamiltonian action of a compact Lie group acting on a non-compact symplectic manifold with proper moment map. In particular, we present a solution to a conjecture of Michèle Vergne in her ICM 2006 plenary lecture.
We consider the quintic generalized Korteweg–de Vries equation (gKdV) which is a canonical mass critical problem, for initial data in H1 close to the soliton. In earlier works on this problem, finite- or infinite-time blow up was proved for non-positive energy solutions, and the solitary wave was shown to be the universal blow-up profile, see ,  and . For well-localized initial data, finite-time blow up with an upper bound on blow-up rate was obtained in .
In this paper, we fully revisit the analysis close to the soliton for gKdV in light of the recent progress on the study of critical dispersive blow-up problems (see , ,  and , for example). For a class of initial data close to the soliton, we prove that three scenarios only can occur: (i) the solution leaves any small neighborhood of the modulated family of solitons in the scale invariant L2 norm; (ii) the solution is global and converges to a soliton as t → ∞; (iii) the solution blows up in finite time T with speed Moreover, the regimes (i) and (iii) are stable. We also show that non-positive energy yields blow up in finite time, and obtain the characterization of the solitary wave at the zero-energy level as was done for the mass critical non-linear Schrödinger equation in .
We prove that for any free ergodic probability measure-preserving action of a free group on n generators , the associated group measure space II1 factor has L∞(X) as its unique Cartan subalgebra, up to unitary conjugacy. We deduce that group measure space II1 factors arising from actions of free groups with different number of generators are never isomorphic. We actually prove unique Cartan decomposition results for II1 factors arising from arbitrary actions of a much larger family of groups, including all free products of amenable groups and their direct products.