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Yotam Svoray

Publications and source records attributed to Yotam Svoray.

12 recordsLinked to original sources

Bounds on the F-Pure Threshold of Isolated Hypersurface Singularities

In this note, we obtain bounds for the $F$-pure threshold of isolated hypersurface singularities over an algebraically closed field of positive characteristic in terms of classical singularity invariants, notably the Milnor and Tjurina numbers. We also compare the $F$-pure threshold of a power series with that of its weighted initial form. For irreducible plane curves, this gives bounds in terms of the first two generators of the value semigroup, together with an equality criterion and an example showing that higher weighted-order terms can change the $F$-pure threshold. As applications, we derive bounds on the log canonical threshold and the Brian{ç}on--Skoda exponent of complex isolated hypersurface singularities.

math.AG

The Algebraicity Problem for Hard-Core Entropy Constants on the Discrete Hypertori

We use tools and techniques from $p$-adic analysis and algebraic number theory to study the algebraicity of the hard square entropy constant and its high dimensional analogues. Specifically, we study arithmetic properties of $a_d(n)$, the number of independent sets in the $d$-dimensional discrete torus, and the associated entropy constants $κ_d=\lim_{n\to\infty}a_d(n)^{1/n^d}$. It is not known whether $κ_d$ is algebraic or transcendental for $d>1$. Using the fact that the sequence $a_d(p^k)$ converges $p$-adically for every prime $p$ and other arithmetic facts, we present a collection of criteria for the algebraicity of $κ_d$ and bound the number of possible values of prime powers $p^k$ for which $a_d(p^k)=κ_d^{p^{kd}}$.

math.NT

The fundamental group of surfaces parametrizing cuboids

We prove that an irreducible projective complete intersection of dimension at least two with isolated singularities has trivial fundamental group. As an application, the surface $Υ$ parametrizing cuboids and its minimal resolution of singularities are simply connected. By an independent argument we also show that the surface $V$ parametrizing face cuboids and its resolution are simply connected as well. We then introduce two smooth open subvarieties $S_{1}$ and $S_{2}$ of the surface parametrizing face cuboids, show that each has fundamental group isomorphic to $\mathbb{F}_{3}\ltimes \mathbb{Z}^{2}$, and prove that their Malcev completions reduce to the free pro-unipotent group on three generators. In an appendix we treat the corresponding real loci, whose fundamental groups, in contrast, are far from trivial.

math.AG

Onion De Bruijn Sequences: Fixed-Window Counting by Growing the Alphabet

We study a fixed-window counting system in which integers are represented by words of constant length while the alphabet grows as needed. This viewpoint arises from De Bruijn sequences: for fixed order $n$, the reverse prefer-max sequence is compatible with alphabet growth, since for each $k$ its restriction to $[k]^n$ is a De Bruijn sequence, yielding an infinite sequence over $\mathbb{N}$. We formalize this through the notion of an onion De Bruijn sequence, prove the resulting structural properties, and count compatible finite onion prefixes by an explicit product formula. For orders $n=2,3$, we give explicit rank and unrank formulas and describe addition and multiplication via finite normalization, with exact carry counts and linear carry complexity in the input layers.

cs.DM

Detecting and Quantifying Isolated Singularities over Discrete Valuation Rings

This paper develops a theory of isolated hypersurface singularities in mixed characteristic $(0,p)$, focusing on quotient rings over a Discrete Valuation Ring (DVR). We introduce and study analogues of the classical Tjurina and Milnor numbers for this setting, prove a generalized analogue of the determinacy theorem and the Mather-Yau Theorem for complete Noetherian local rings, and define numerical invariants that provide distinct criteria for detecting isolated singularities in the unramified and ramified cases.

math.AC

The Milnor Number of One Dimensional Local Rings

In this paper we present an analogue of the Milnor number for one dimensional local ring, and we show that it satisfies analogous properties to those of the Milnor number of plane curves over a field. In addition, we present two analogues of the semi-group of values for a one dimensional ring and show how they relate to our Milnor number. Finally, we use these tools and techniques to show we can relate these semigroups of one dimensional rings of finite Cohen-Macaulay type to those of the classical ADE singularities.

math.AC

ADE Classification of Hypersurface Singularities over Local Rings

In this paper we present an ADE-type classification of hypersurfaces of complete regular local rings based on their Cohen-Macaulay type. In order to preform this classification, we show how we can generalize the classical result regarding finite and countable Cohen-Macaulay type to larger cardinalities, depending on the cardinality of the residue field.

math.AC

Completely Syndetic Sets in Discrete Groups

We study completely syndetic (CS) sets in discrete groups - subsets that for every natural n admit finitely many left translates that jointly cover every n-tuple of group elements. While for finitely-generated groups, the non-virtually nilpotent ones admit a partition into two CS sets, we show that virtually abelian groups do not. We also characterize CS subsets of the group of integers Z, and as a result characterize subsets of Z whose closure in the Stone-Cech compactification contains the smallest two sided ideal. Finally, we show that CS sets can have an arbitrarily small density.

math.GR

Invariants of Non-Isolated Singularities of Hypersurfaces

In this paper we generalize some results by Siersma, Pellikaan, and de Jong regarding morsifications of singular hypersurfaces whose singular locus is a smooth curve, and present some applications to the study of Yomdin-type isolated singularities. In order to prove these results, we discuss the transversal discriminant of such singularities and how it relates to other algebraic and topological invariants.

math.AG

Rings of Bounded Continuous Functions

We examine several classical concepts from topology and functional analysis, using methods of commutative algebra. We show that these various concepts are all controlled by BC R-rings and their maximal spectra. A BC R-ring is a ring A that is isomorphic to the ring of bounded continuous R-valued functions on some compact topological space X. These rings are not topologized. We prove that the category of BC R-rings is dual to the category of compact topological spaces. Next we prove that for every topological space X the ring of bounded continuous functions on it is a BC R-ring. These theorems combined yield an algebraic construction of the Stone-Cech Compactification of an arbitrary topological space. There is a similar notion of BC C-ring. Every BC C-ring A has a canonical involution. The canonical hermitian subring of A is a BC R-ring, and this is an equivalence of categories from BC C-rings to BC R-rings. Let K be either R or C. We prove that a BC K-ring A has a canonical norm on it, making it into a Banach K-ring. We then prove that the forgetful functor is an equivalence from Banach^* K-rings (better known as commutative unital C^* K-algebras) to BC K-rings. The quasi-inverse of the forgetful functor endows a BC K-ring with its canonical norm, and the canonical involution when K = C. Stone topological spaces, also known as profinite topological spaces, are traditionally related to boolean rings - this is Stone Duality. We give a BC ring characterization of Stone spaces. From that we obtain a very easy proof of the fact that the Stone-Cech Compactification of a discrete space is a Stone space. Most of the results in this paper are not new. However, most of our proofs seem to be new - and our methods could potentially lead to genuine progress related to these classical topics.

math.AC

De Bruijn Sequences: From Games to Shift-Rules to a Proof of the Fredricksen-Kessler-Maiorana Theorem

We present a combinatorial game and propose efficiently computable optimal strategies. We then show how these strategies can be translated to efficiently computable shift-rules for the well known prefer-max and prefer-min De Bruijn sequences, in both forward and backward directions. Using these shift-rules, we provide a new proof of the well known theorem by Fredricksen, Kessler, and Maiorana on De Bruijn sequences and Lyndon words.

cs.DM

An Efficient Shift Rule for the Prefer-Max De Bruijn Sequence

A shift rule for the prefer-max De Bruijn sequence is formulated, for all sequence orders, and over any finite alphabet. An efficient algorithm for this shift rule is presented, which has linear (in the sequence order) time and memory complexity.

cs.DM