Generalizations of the image conjecture and the Mathieu conjecture

We first propose a generalization of the image conjecture Zhao (submitted for publication) [31] for the commuting differential operators related with classical orthogonal polynomials. We then show that the non-trivial case of this generalized image conjecture is equivalent to a variation of the Mathieu conjecture Mathieu (1997) [21] from integrals of G-finite functions over reductive Lie groups G to integrals of polynomials over open subsets of Rⁿ with any positive measures. Via this equivalence, the generalized image conjecture can also be viewed as a natural variation of the Duistermaat and van der Kallen theorem Duistermaat and van der Kallen (1998) [14] on Laurent polynomials with no constant terms. To put all the conjectures above in a common setting, we introduce what we call the Mathieu subspaces of associative algebras. We also discuss some examples of Mathieu subspaces from other sources and derive some general results on this newly introduced notion.     

Power functions with low uniformity on odd characteristic finite fields

In this paper, we give some new low differential uniformity of some power functions defined on finite fields with odd characteristic. As corollaries of the uniformity, we obtain two families of almost perfect nonlinear functions in GF(3 ⁿ ) and GF(5 ⁿ ) separately. Our results can be used to prove the Dobbertin et al.’s conjecture.     

On the Gray index conjecture for phantom maps

We study the Gray index, a numerical invariant for phantom maps. It has been conjectured that the only phantom map between finite-type spaces with infinite Gray index is the constant map. We disprove this conjecture by constructing a counter example. We also prove that this conjecture is valid if the target spaces of the phantom maps are restricted to being simply connected finite complexes.As a result of the counter example, we can show that SNT^∞(X) can be non-trivial for some space X of finite type.     

Spectral geometry for almost isospectral hermitian manifolds

The following question was posed by M. Berger: Is it possible to determine from the spectrum of the real Laplacian whether or not a manifold is Kähler? The Kähler condition for Hermitian manifolds is found out from the invariants of the spectrum of some differential operators acting on forms of type (p, q). P. Gilkey and H. Donnelly proved the Berger conjecture for the complex Laplacian and the reduced complex Laplacian respectively. In this paper we consider the Berger conjecture of almost isospectral Hermitian manifolds about the complex Laplacian acting on forms of type (p, q). Then we can show that a closed complexm(≥ 3)-dimensional Hermitian manifold which is strongly (?2/m)-isospectral to the complex projective space CP ^m with the Fubini-Study metric is holomorphically isometric to CP ^m .     

Contre-exemple à une caractérisation conjecturée de la sphère

It has long been conjectured that a closed convex surface of class C₊² whose principal curvatures K₁, K₂ satisfy the inequality (K₁−c)(K₂−c)≤0 with some constant c, must be a sphere. Partial results have been obtained by A.D. Aleksandrov, H.F. Münzner and D. Koutroufiotis.We reformulate the conjecture in terms of hedgehogs and we give a counter-example. Besides, we prove the conjecture for surfaces of constant width and give a new proof for analytic surfaces.     

Regularity of Kähler–Ricci flows on Fano manifolds

In this paper, we will establish a regularity theory for the Kähler–Ricci flow on Fano n-manifolds with Ricci curvature bounded in L^p-norm for some \({p > n}\). Using this regularity theory, we will also solve a long-standing conjecture for dimension 3. As an application, we give a new proof of the Yau–Tian–Donaldson conjecture for Fano 3-manifolds. The results have been announced in [45].     

Arithmetical properties of a sequence arising from an arctangent sum

The sequence {xn} defined by xn=(n+xn−1)/(1−nxn−1), with x₁=1, appeared in the context of some arctangent sums. We establish the fact that xn≠0 for n?4 and conjecture that xn is not an integer for n?5. This conjecture is given a combinatorial interpretation in terms of Stirling numbers via the elementary symmetric functions. The problem features linkage with a well-known conjecture on the existence of infinitely many primes of the form n²+1, as well as our conjecture that (1+¹²)(1+²²)?(1+n²) is not a square for n>3. We present an algorithm that verifies the latter for n?¹⁰³²⁰⁰.     

The Tate conjecture for K3 surfaces over finite fields

Artin’s conjecture states that supersingular K3 surfaces over finite fields have Picard number 22. In this paper, we prove Artin’s conjecture over fields of characteristic p≥5. This implies Tate’s conjecture for K3 surfaces over finite fields of characteristic p≥5. Our results also yield the Tate conjecture for divisors on certain holomorphic symplectic varieties over finite fields, with some restrictions on the characteristic. As a consequence, we prove the Tate conjecture for cycles of codimension 2 on cubic fourfolds over finite fields of characteristic p≥5.     

Atiyah’s L 2-index theorem,Kan-Thurston construction,and weak Bass conjecture

We conjecture that for a group G of type FP, the L ²-Euler characteristic of a group G is the same as the ordinary Euler characteristic of G, and show that this conjecture is closely related with the weak Bass conjecture. We also present a class of groups satisfying this conjecture. Ourmethod combines the Kan-Thurston construction, Atiyah’s L ²-index theorem, and a result of Berrick, Chatterji, and Mislin.     

An improved list decoding algorithm for the second order Reed–Muller codes and its applications

We propose an algorithm which is an improved version of the Kabatiansky–Tavernier list decoding algorithm for the second order Reed–Muller code RM(2, m), of length n = 2 ^m , and we analyse its theoretical and practical complexity. This improvement allows a better theoretical complexity. Moreover, we conjecture another complexity which corresponds to the results of our simulations. This algorithm has the strong property of being deterministic and this fact drives us to consider some applications, like determining some lower bounds concerning the covering radius of the RM(2, m) code.     

On the isoperimetric problem for radial log-convex densities

Given a smooth, radial, uniformly log-convex density e ^V on ${\mathbb{R}^n}$ , n ≥ 2, we characterize isoperimetric sets E with respect to weighted perimeter ${\int_{\partial E}e^{V} d \mathcal{H}^{n-1}}$ and weighted volume m = ∫ _E e ^V as balls centered at the origin, provided ${m \in [0, m_0)}$ for some (potentially computable) m ₀>0; this affirmatively answers conjecture (Rosales et al. Calc Var Part Differ Equat 31(1):27–46, 2008, Conjecture 3.12) for such values of the weighted volume parameter. We also prove that the set of weighted volumes such that this characterization holds true is open, thus reducing the proof of the full conjecture to excluding the possibility of bifurcation values of the weighted volume parameter. Finally, we show the validity of the conjecture when V belongs to a C ²-neighborhood of c|x|² (c> 0).     

Continued fractions for quadratic elements in formal power series

There exist certain quadratic elements α∈?((t ^?1)) over the rational function field ?(t) having nonperiodic continued fraction expansion, see W.M. Schmidt in (Acta Arith. 95(2):139–166, 2000). Hence we need a modification of Lagrange’s theorem with regard to function fields instead of number fields. In this paper, we introduce a class of continued fractions and describe Lagrange’s theorem as a conjecture related to quadratic elements over ?(t). We give some examples which support our conjecture.     

Characterization of some finite groups by order and length of one conjugacy class

We study the possibility of characterizing S ∈ {²D_n(2), ²D_n+1(2)} by simple conditions when 2ⁿ⁺¹ > 5 is a prime. Furthermore, we will show that Thompson’s conjecture is valid under some weak condition for these groups.     

L 1-approximation rate of certain trigonometric series

By employing new ideas and techniques, we will refigure out the whole frame of L ¹-approximation. First, except generalizing the coefficients from monotonicity to a wider condition, Logarithm Rest Bounded Variation condition, we will also drop the prior requirement f∈L _2π but directly consider the sine or cosine series. Secondly, to achieve nontrivial generalizations in complex spaces, we use a one-sided condition with some kind of balance conditions. In addition, a conjecture raised in [9] is disproved in Section?3.     

The Atiyah-Jones conjecture for rational surfaces

We show that if the Atiyah-Jones conjecture holds for a surface X, then it also holds for the blow-up of X at a point. Since the conjecture is known to hold for P² and for ruled surfaces, it follows that the conjecture is true for all rational surfaces.     

Small, nm-stable compact G-groups

We prove that if (H, G) is a small, nm-stable compact G-group, then H is nilpotent-by-finite, and if additionally NM(H) < ω or NM(H) = ω ^α for some ordinal α, then H is abelian-by-finite. Both results are significant steps towards the proof of the conjecture that each small, nm-stable compact G-group is abelian-by-finite. We provide counter-examples to the NM-gap conjecture, that is we give examples of small, nm-stable compact G-groups of infinite ordinal NM-rank.     

New Beauville surfaces and finite simple groups

In this paper we construct new Beauville surfaces with group either PSL(2, p ^e ), or belonging to some other families of finite simple groups of Lie type of low Lie rank, or an alternating group, or a symmetric group, proving a conjecture of Bauer, Catanese and Grunewald. The proofs rely on probabilistic group theoretical results of Liebeck and Shalev, on classical results of Macbeath and on recent results of Marion.     

A note on Potter’s theorem for quasi-commutative matrices

We discuss the converse of a theorem of Potter stating that if the matrix equation AB=ωBA is satisfied with ω a primitive qth root of unity, then A^q+B^q=(A+B)^q. We show that both conditions have to be modified to get a converse statement and we present a characterization when the converse holds for these modified conditions and q=3 and a conjecture for the general case. We also present some further partial results and conjectures.     

Tactical decompositions and orbits of projective groups

We consider decompositions of the incidence structure of points and lines of PG(n, q) (n?3) with equally many point and line classes. Such a decomposition, if line-tactical, must also be point-tactical. (This holds more generally in any 2-design.) We conjecture that such a tactical decomposition with more than one class has either a singleton point class, or just two point classes, one of which is a hyperplane. Using the previously mentioned result, we reduce the conjecture to the case n=3, and prove it when q²+q+1 is prime and for very small values of q. The truth of the conjecture would imply that an irreducible collineation group of PG(n, q) (n?3) with equally many point and line orbits is line-transitive (and hence known).