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Vigleik Angeltveit

Publications and source records attributed to Vigleik Angeltveit.

At least 19 recordsLinked to original sources
arXiv2026

An improved algorithm for checking the Collatz conjecture for all n < 2^N

We describe a new algorithm for verifying the Collatz conjecture for all n < 2^N for some fixed N. The algorithm takes less than twice as long to verify convergence for all n < 2^{N+1} as it does to verify convergence for all n < 2^N. We also discuss verification of the analogue of the Collatz conjecture for negative numbers.

math.NT↗
arXiv2024

$R(5,5)\le 46$

We prove that the Ramsey number $R(5,5)$ is less than or equal to~$46$. The proof uses a combination of linear programming and checking a large number of cases by computer. All of the computations were independently implemented by both authors, with consistent results.

math.CO↗
arXiv2023

R(3,10) <= 41

We improve the upper bound on the Ramsey number R(3,10) from 42 to 41. Hence R(3,10) is equal to 40 or 41.

math.CO↗
arXiv2022

Recovering a cohomological Mackey Functor from its restriction to Sylow subgroups

We explain how to recover the top level of a cohomological G-Mackey functor $\underline{M}$ from the restriction of $\underline{M}$ to each of the Sylow subgroups of G. As an application, we compute the Mackey functor valued G-equivariant homology groups of a point with constant $\mathbb{Z}$-coefficients when G has order pq for odd primes p<q. We also indicate how the calculation goes for $G=A_4$.

math.AT↗
arXiv2021

The Picard group of the category of $C_n$-equivariant stable homotopy theory

For a finite group $G$, there is a map $RO(G) \to {\rm Pic}(Sp^G)$ from the real representation ring of $G$ to the Picard group of $G$-spectra. This map is not known to be surjective in general, but we prove that when $G$ is cyclic this map is indeed surjective and in that case we describe ${\rm Pic}(Sp^G)$ explicitly. We also show that for an arbitrary finite group $G$ homology and cohomology with coefficients in a cohomological Mackey functor do not see the part of ${\rm Pic}(Sp^G)$ coming from the Picard group of the Burnside ring. Hence these homology and cohomology calculations can be graded on a smaller group.

math.AT↗
arXiv2019

Picard groups and the K-theory of curves with cuspidal singularities

We calculate the algebraic $K$-theory of the coordinate ring of a planar cuspidal curve over a regular $\mathbb{F}_p$-algebra, thereby verifying a conjecture due to Hesselholt. In the course of the proof we compute the Picard group of the homotopy category of $p$-complete genuine $C_{p^n}$-spectra.

math.AT↗
arXiv2017

$R(5,5) \le 48$

We improve the upper bound on the Ramsey number $R(5,5)$ from $R(5,5) \le 49$ to $R(5,5) \le 48$. We also complete the catalogue of extremal graphs for $R(4,5)$.

math.CO↗
arXiv2017

Witt vectors and truncation posets

One way to define Witt vectors starts with a truncation poset $S \subset \mathbb{N}$. We generalize Witt vectors to truncation posets, and show how three types of maps of truncation posets can be used to encode the following six structure maps on Witt vectors: addition, multiplication, restriction, Frobenius, Verschiebung and norm.

math.AC↗
arXiv2017

Graded Tambara Functors

We define the notion of an $\mathcal{RO}(G)$-graded Tambara functor and prove that any $G$-spectrum with norm multiplication gives rise to such an $\mathcal{RO}(G)$-graded Tambara functor.

math.AT↗
arXiv2015

On the algebraic K-theory of Witt vectors of finite length

Let k be a perfect field of characteristic p and let $W_n(k)$ denote the p-typical Witt vectors of length n. For example, $W_n(\mathbb{F}_p)=\mathbb{Z}/p^n$. We study the algebraic K-theory of $W_n(k)$, and prove that $K(W_n(k))$ satisfies "Galois descent". We also compute the K-groups through a range of degrees, and show that the first p-torsion element in the stable homotopy groups of spheres is detected in $K_{2p-3}(W_n(k))$ for all $n \geq 2$.

math.AT↗
arXiv2015

Enriched Reedy categories

We define the notion of an enriched Reedy category, and show that if A is a C-Reedy category for some symmetric monoidal model category C and M is a C-model category, the category of C-functors and C-natural transformations from A to M is again a model category.

math.AT↗
arXiv2015

Uniqueness of BP

Fix a prime number p and a non-negative integer n. We prove that if a p-complete spectrum X satisfying a mild finiteness condition has the same mod p cohomology as BP as a module over the Steenrod algebra, then X is weak homotopy equivalent to the p-completion of BP .

math.AT↗
arXiv2013

On the algebraic K-theory of truncated polynomial algebras in several variables

We consider the algebraic K-theory of a truncated polynomial algebra in several commuting variables, K(k[x_1, ..., x_n]/(x_1^a_1, ..., x_n^a_n)). This naturally leads to a new generalization of the big Witt vectors. If k is a perfect field of positive characteristic we describe the K-theory computation in terms of a cube of these Witt vectors on N^n. If the characteristic of k does not divide any of the a_i we compute the K-groups explicitly. We also compute the K-groups modulo torsion for k=Z. To understand this K-theory spectrum we use the cyclotomic trace map to topological cyclic homology, and write TC(k[x_1, ..., x_n]/(x_1^a_1, ..., x_n^a_n)) as the iterated homotopy cofiber of an n-cube of spectra, each of which is easier to understand. Updated: This is a substantial revision. We corrected several errors in the description of the Witt vectors on a truncation set on N^n and modified the key proofs accordingly. We also replaces several topological statement with purely algebraic ones. Most arguments have been reworked and streamlined.

math.AT↗