A Functor Converting Equivariant Homology to Homotopy

In this paper, we prove an equivariant version of the classical Dold-Thom theorem. Associated to a finite group, a CW-complex on which this group acts and a covariant coefficient system in the sense of Bredon, we functorially construct a topological abelian group by the coend construction. Then we prove that the homotopy groups of this topological abelian group are naturally isomorphic to the Bredon equivariant homology of the CW-complex. At the end we present several examples of this result.Comment: 11 pages. Major style change. The final published versio

Polynomial Optimization with Real Varieties

We consider the optimization problem of minimizing a polynomial f(x) subject to polynomial constraints h(x)=0, g(x)>=0. Lasserre's hierarchy is a sequence of sum of squares relaxations for finding the global minimum. Let K be the feasible set. We prove the following results: i) If the real variety V_R(h) is finite, then Lasserre's hierarchy has finite convergence, no matter the complex variety V_C(h) is finite or not. This solves an open question in Laurent's survey. ii) If K and V_R(h) have the same vanishing ideal, then the finite convergence of Lasserre's hierarchy is independent of the choice of defining polynomials for the real variety V_R(h). iii) When K is finite, a refined version of Lasserre's hierarchy (using the preordering of g) has finite convergence.Comment: 12 page

Subtle Features in Transport Properties: Evidence for a Possible Coexistence of Holes and Electrons in Cuprate Superconductors

Transport properties of high transition temperature (high Tc) cuprate superconductors are investigated within a two-band model. The doping dependent Hall coefficients of La_{2-x}Sr_xCuO_4 (LSCO) and Nd_{2-x}Ce_xCuO_4 (NCCO) are explained by assuming the coexistence of two carriers with opposite charges, loosely speaking electrons (e) and holes (h). Such a possible electron-hole coexistence (EHC) in other p-type cuprates is also inferred from subtle features in the Hall coefficient R_H and thermopower S. The EHC possibly relates to the pseudogap and sign reversals of transport coefficients near Tc. It also corroborates the electronlike Fermi surface revealed in recent photoemission results. An experimental verification is proposed.Comment: 4 pages, 3 EPS figures. RevTe

Entropy degeneration of convex projective surfaces

We show that the volume entropy of the Hilbert metric on a closed convex projective surface tends to zero as the corresponding Pick differential tends to infinity. The proof is based on the theorem, due to Benoist and Hulin, that the Hilbert metric and Blaschke metric are comparable.Comment: 5 page

Solving Toda field theories and related algebraic and differential properties

Toda field theories are important integrable systems. They can be regarded as constrained WZNW models, and this viewpoint helps to give their explicit general solutions, especially when a Drinfeld-Sokolov gauge is used. The main objective of this paper is to carry out this approach of solving the Toda field theories for the classical Lie algebras. In this process, we discover and prove some algebraic identities for principal minors of special matrices. The known elegant solutions of Leznov fit in our scheme in the sense that they are the general solutions to our conditions discovered in this solving process. To prove this, we find and prove some differential identities for iterated integrals. It can be said that altogether our paper gives complete mathematical proofs for Leznov's solutions

Topologically slice (1,1)(1,1)-knots which are not smoothly slice

We prove that there are infinitely many $(1,1)$-knots which are topologically slice, but not smoothly slice, which was a conjecture proposed by B\'ela Andr\'as R\'acz.Comment: 11 pages, 12 figure

Fundamental elements of an affine Weyl group

Fundamental elements are certain special elements of affine Weyl groups introduced by Gortz, Haines, Kottwitz and Reuman. They play an important role in the study of affine Deligne-Lusztig varieties. In this paper, we obtain characterizations of the fundamental elements and their natural generalizations. We also derive an inverse to a version of "Newton-Hodge decomposition" in affine flag varieties. As an application, we obtain a group-theoretic generalization of Oort's results on minimal p-divisible groups, and we show that, in certain good reduction reduction of PEL Shimura datum, each Newton stratum contains a minimal Ekedahl-Oort stratum. This generalizes a result of Viehmann and Wedhorn.Comment: Some applications to good reductions of PEL shimura varieties are adde

Indeterminacy Loci of Iterate Maps

We consider the indeterminacy locus $I(\Phi_n)$ of the iterate map $\Phi_n:\overline{M}_d-rightarrow\overline{M}_{d^n}$, where $\overline{M}_d$ is the GIT compactification of the moduli space $M_d$ of degree $d$ complex rational maps. We give natural conditions on $f$ that imply $[f]\in I(\Phi_n)$. These provide partial answers to a question of Laura DeMarco

Certifying Convergence of Lasserre's Hierarchy via Flat Truncation

This paper studies how to certify the convergence of Lasserre's hierarchy of semidefinite programming relaxations for solving multivariate polynomial optimization. We propose flat truncation as a general certificate for this purpose. Assume the set of global minimizers is nonempty and finite. Our main results are: i) Putinar type Lasserre's hierarchy has finite convergence if and only if flat truncation holds, under some general assumptions, and this is also true for the Schmudgen type one; ii) under the archimedean condition, flat truncation is asymptotically satisfied for Putinar type Lasserre's hierarchy, and similar is true for the Schmudgen type one; iii) for the hierarchy of Jacobian SDP relaxations, flat truncation is always satisfied. The case of unconstrained polynomial optimization is also discussed.Comment: 18 page

Secondary Chern-Euler class for general submanifold

We define and study the secondary Chern-Euler class for a general submanifold of a Riemannian manifold. Using this class, we define and study index for a vector field with non-isolated singularities on a submanifold. As an application, our studies give conceptual proofs of a classical result of Chern.Comment: Section 2 expanded and fixed. Final version to appear in Canadian Mathematical Bulleti