We show that Rabinowitz Floer homology and cohomology carry the structure of a graded Frobenius algebra for both closed and open strings. We prove a Poincaré duality theorem between homology and cohomology that preserves this structure. This lifts to a duality theorem between graded open–closed topological quantum field theories (TQFTs). We use in a systematic way the formalism of Tate vector spaces. Specializing to the case of cotangent bundles, we define Rabinowitz loop homology and cohomology and explain from a unified perspective pairs of dual results that have been observed over the years in the context of the search for closed geodesics. These concern critical levels, relations to the based loop space, manifolds all of whose geodesics are closed, Bott index iteration, and level potency. Moreover, the graded Frobenius algebra structure gives meaning and proof to a relation conjectured by Sullivan between the loop product and coproduct.

Consider a quadratic polynomial $Q(\xi_{1},\ldots,\xi_{n})$ of independent Rademacher random variables $\xi_{1},\ldots,\xi_{n}$. To what extent can $Q(\xi_{1},\ldots,\xi_{n})$ concentrate on a single value? This quadratic version of the classical Littlewood–Offord problem was popularised by Costello, Tao and Vu in their study of symmetric random matrices. In this paper, we obtain an essentially optimal bound for this problem, as conjectured by Nguyen and Vu. Specifically, if $Q(\xi_{1},\ldots,\xi_{n})$ ‘robustly depends on at least m of the $\xi_{i}$’ in the sense that there is no way to pin down the value of $Q(\xi_{1},\ldots,\xi_{n})$ by fixing values for fewer than m of the variables $\xi_{i}$, then we have $\mathrm{Pr}[Q(\xi_{1},\ldots,\xi_{n})=0]\le O(1/\sqrt{m})$. This also implies a similar result in the case where $\xi_{1},\ldots,\xi_{n}$ have arbitrary distributions. Our proof combines a number of ideas that may be of independent interest, including an inductive decoupling scheme that reduces quadratic anticoncentration problems to high-dimensional linear anticoncentration problems. Also, one application of our main result is the resolution of a conjecture of Alon, Hefetz, Krivelevich and Tyomkyn related to graph inducibility.

For log canonical (lc) algebraically integrable foliations on Kawamata log terminal (klt) varieties, we prove the base-point-freeness theorem, the contraction theorem, and the existence of flips. The first result resolves a conjecture of Cascini and Spicer, while the latter two results strengthen a result of Cascini and Spicer by removing their assumption on the termination of flips. Moreover, we prove the existence of the minimal model program for lc algebraically integrable foliations on klt varieties and the existence of good minimal models or Mori fiber spaces for lc algebraically integrable foliations polarized by ample divisors on klt varieties. As a consequence, we show that $\mathbb{Q}$-factorial klt varieties with lc algebraically integrable Fano foliation structures are Mori dream spaces. We also show the existence of a Shokurov-type polytope for lc algebraically integrable foliations.

This work concerns representations of a finite flat group scheme G defined over a noetherian commutative ring R. The focus is on lattices, namely, finitely generated G-modules that are projective as R-modules, and on the full subcategory of all G-modules projective over R generated by the lattices. The stable category of such G-modules is a rigidly-compactly generated, tensor triangulated category. The main result is that this stable category is stratified and costratified by the natural action of the cohomology ring of G. Applications include formulas for computing the support and cosupport of tensor products and the module of homomorphisms, and a classification of the thick ideals in the stable category of lattices.

A classical argument was introduced by Khintchine in 1926 in order to exhibit the existence of totally irrational singular linear forms in two variables. This argument was subsequently revisited and extended by many authors. For instance, in 1959 Jarník used it to show that for $n \geqslant 2$ and for any non-increasing positive f there are totally irrational matrices $A \in M_{m,n}(\mathbb{R})$ such that for all large enough t there are $\mathbf{p} \in \mathbb{Z}^m, \mathbf{q} \in \mathbb{Z}^n \smallsetminus \{0\}$ with $\|\mathbf{q}\| \leqslant t$ and $\|A \mathbf{q} - \mathbf{p}\| \leqslant f(t)$. We denote the collection of such matrices by $\operatorname{UA}^*_{m,n}(f)$. We adapt Khintchine’s argument to show that the sets $\operatorname{UA}^*_{m,n}(f)$, and their weighted analogues $\operatorname{UA}^*_{m,n}(f, {\boldsymbol{\omega}})$, intersect many manifolds and fractals, and have strong intersection properties. For example, we show that: (i) when $n \geqslant 2$, the set $\bigcap_{{\boldsymbol{\omega}}} \operatorname{UA}^*(f, {\boldsymbol{\omega}}) $, where the intersection is over all weights ${\boldsymbol{\omega}}$, is non-empty, and moreover intersects many manifolds and fractals; (ii) for $n \geqslant 2$, there are vectors in $\mathbb{R}^n$ which are simultaneously k-singular for every k, in the sense of Yu; and (iii) when $n \geqslant 3$, $\operatorname{UA}^*_{1,n}(f) + \operatorname{UA}^*_{1,n}(f) =\mathbb{R}^n$. We also obtain new bounds on the rate of singularity which can be attained by column vectors in analytic submanifolds of dimension at least 2 in $\mathbb{R}^n$.

We prove the geometric Satake equivalence for mixed Tate motives over the integral motivic cohomology spectrum. This refines previous versions of the geometric Satake equivalence for split reductive groups. Our new geometric results include Whitney–Tate stratifications of Beilinson–Drinfeld Grassmannians and cellular decompositions of semi-infinite orbits. With future global applications in mind, we also achieve an equivalence relative to a power of the affine line. Finally, we use our equivalence to give Tannakian constructions of Deligne’s modification of the dual group and a modified form of Vinberg’s monoid over the integers.

We study the space of traces associated with arbitrary full free products of unital, separable $C^*$-algebras. We show that, unless certain basic obstructions (which we fully characterize) occur, the space of traces always results in the same object: the Poulsen simplex, that is, the unique infinite-dimensional metrizable Choquet simplex whose extreme points are dense. Moreover, we show that whenever such a trace space is the Poulsen simplex, the extreme points are dense in the Wasserstein topology. Concretely for the case of groups, we find that, unless the trivial character is isolated in the space of characters, the space of traces of any free product of non-trivial countable groups is the Poulsen simplex. Our main technical contribution is a new perturbation result for pairs of von Neumann subalgebras $(M_{1},M_{2})$ of a tracial von Neumann algebra M, providing necessary conditions under which $M_{1}$ and a small unitary perturbation of $M_{2}$ generate a II$_{1}$ factor.

We study functions f on $\mathbb{Q}$ which satisfy a ‘quantum modularity’ relation of the shape $ f(x+1)=f(x)$ and $f(x) - {| {x} |}^{-k} f(-1/x) = h(x)$, where $h:\mathbb{R}_{\neq 0} \to \mathbb{C}$ is a function satisfying various regularity conditions. We study the case $\operatorname{Re}(k)\neq 0$. We prove the existence of a limiting function, denoted by $f^\triangleleft$ or $f^\triangleright$, depending on the sign of $\operatorname{Re}(k)$, which extends continuously f to $\mathbb{R}$ in some sense. This means, in particular, that in the $\operatorname{Re}(k)\neq0$ case, the quantum modular form itself has to have at least a certain level of regularity. We deduce that the values $\{f(a/q), 1\leqslant a<q, (a, q)=1\}$, appropriately normalized, tend to equidistribute along the graph of $f^\triangleleft$ or $f^\triangleright$, and we prove that, under natural hypotheses, the limiting measure is diffuse. We apply these results to obtain limiting distributions of values and continuity results for several arithmetic functions known to satisfy the above quantum modularity: higher weight modular symbols associated to holomorphic cusp forms; Eichler integral associated to Maaß forms; a function of Kontsevich and Zagier related to the Dedekind $\eta$-function; and generalized cotangent sums.

We establish a version of Seiberg–Witten Floer K-theory for knots, as well as a version of Seiberg–Witten Floer K-theory for 3-manifolds with involution. The main theorems are 10/8-type inequalities for knots and for involutions. The 10/8-inequality for knots yields numerous applications to knots, such as lower bounds on stabilizing numbers and relative genera. We also give obstructions to extending involutions on 3-manifolds to 4-manifolds, and detect non-smoothable involutions on 4-manifolds with boundary.

We prove cohomological vanishing criteria for the Ceresa cycle of a curve C embedded in its Jacobian J: (A) if $\mathrm{H}^3(J)^{\mathrm{Aut}(C)} = 0$, then the Ceresa cycle is torsion modulo rational equivalence; (B) if $\mathrm{H}^0(J, \Omega_J^3)^{\mathrm{Aut}(C)} = 0$, then the Ceresa cycle is torsion modulo algebraic equivalence, with criterion (B) conditional on the Hodge conjecture. We then use these criteria to study the simplest family of curves where (B) holds but (A) does not, namely the family of Picard curves $C \colon y^3 = x^4 + ax^2 + bx + c$. Criterion (B) and work of Schoen combine to show that the Ceresa cycle of a Picard curve is torsion in the Griffiths group. We furthermore determine exactly when it is torsion in the Chow group. As a byproduct, we deduce that there exist one-parameter families of plane quartic curves with torsion Ceresa Chow class; that the torsion locus in $\mathcal{M}_3$ of the Ceresa Chow class contains infinitely many components; and that the order of a torsion Ceresa Chow class of a Picard curve over a number field K is bounded, with the bound depending only on $[K\colon \mathbb{Q}]$. Finally, we determine which automorphism group strata are contained in the vanishing locus of the universal Ceresa cycle over $\mathcal{M}_3$.

While the splinter property is a local property for Noetherian schemes in characteristic zero, Bhatt observed that it imposes strong conditions on the global geometry of proper schemes in positive characteristic. We show that if a proper scheme over a field of positive characteristic is a splinter, then its Nori fundamental group scheme is trivial and its Kodaira dimension is negative. In another direction, Bhatt also showed that any splinter in positive characteristic is a derived splinter. We ask whether the splinter property is a derived invariant for projective varieties in positive characteristic and give a positive answer for normal Gorenstein projective varieties with big anticanonical divisor. We also show that global F-regularity is a derived invariant for normal Gorenstein projective varieties in positive characteristic.

We consider the Harder–Narasimhan formalism on the category of normed isocrystals and show that the Harder–Narasimhan filtration is compatible with tensor products which generalizes a result of Cornut. As an application of this result, we are able to define a (weak) Harder–Narasimhan stratification on the $B_{\mathrm{dR}}^+$-affine Grassmannian for arbitrary $(G, b, \mu)$. When $\mu$ is minuscule, it corresponds to the Harder–Narasimhan stratification on the flag varieties defined by Dat, Orlik and Rapoport. Moreover, when b is basic, it has been studied by Nguyen and Viehmann, and Shen. We study the basic geometric properties of the Harder–Narasimhan stratification, such as non-emptiness, dimension and its relation with other stratifications.

We improve, by a factor of 2, known homology stability ranges for the integral homology of symplectic groups over commutative local rings with infinite residue field and show that the obstruction to further stability is bounded below by Milnor–Witt K-theory. In particular, our stability range is optimal in many cases.

We give an interpretation of the semi-infinite intersection cohomology sheaf associated with a semisimple simply connected algebraic group in terms of finite-dimensional geometry. Specifically, we describe a procedure for building factorization spaces over moduli spaces of finite subsets of a curve from factorization spaces over moduli spaces of divisors, and show that, under this procedure, the compactified Zastava space is sent to the support of the semi-infinite intersection cohomology (IC) sheaf in the factorizable Grassmannian. We define ‘semi-infinite t-structures’ for a large class of schemes with an action of the multiplicative group, and show that, for the Zastava, the limit of these t-structures recovers the infinite-dimensional version. As an application, we also construct factorizable parabolic semi-infinite IC sheaves and a generalization (of the principal case) to Kac–Moody algebras.

In this paper, we give a complete topological and smooth classification of non-invertible Anosov maps on torus. We show that two non-invertible Anosov maps on torus are topologically conjugate if and only if their corresponding periodic points have the same Lyapunov exponents on the stable bundles. As a corollary, if two $C^r$ non-invertible Anosov maps on torus are topologically conjugate, then the conjugacy is $C^r$-smooth along the stable foliation. Moreover, we show that the smooth conjugacy class of a non-invertible Anosov map on torus is completely determined by the Jacobians of return maps at periodic points.

Given a symplectic class $$\left[ \omega \right]$$ on a four torus $${T^4}$$ (or a $$K3$$ surface), a folklore problem in symplectic geometry is whether symplectic forms in $$\left[ \omega \right]$$ are isotopic to each other. We introduce a family of nonlinear Hodge heat flows on compact symplectic four manifolds to approach this problem, which is an adaption of nonlinear Hodge theory in symplectic geometry. As a particular example, we study a conformal Hodge heat flow in detail. We prove a stability result of the flow near an almost Kähler structure $$\left( {M,\omega ,g} \right)$$. We also prove that, if $$\left| {\nabla {\rm{log}}u} \right|$$ stays bounded along the flow, then the flow exists for all time for any initial symplectic form $$\rho \in \left[ \omega \right]$$ and it converges to $$\omega $$ smoothly along the flow with uniform control, where $$u$$ is the volume potential of $$\rho $$.