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Amitai Regev

Publications and source records attributed to Amitai Regev.

At least 19 recordsLinked to original sources
arXiv2015

Surprising Relations Between Sums-Of-Squares of Characters of the Symmetric Group Over Two-Rowed Shapes and Over Hook Shapes

In a recent article (arXiv:1507.03499) (joint with Alon Regev) we studied sums of squares of characters Chi(L,M) of the Symmetric Group over shapes L that are two-rowed, and shapes L that are hook shapes, and M is an arbitrary shape that mostly consists of ones, and designed algorithms for closed-form evaluations of each of these. We noted (and proved) that when M is the shape with n cells consisting of 3 followed by n-3 ones, the former sum equals one half time the analogous sum over hook shapes with n+2 cells and M is the partition consisting of 3,2, followed by n-3 ones. Here we show that this is just a tip of an iceberg, and prove (alas, by purely human means) that the former sum with M consisting of all odd parts, and (possibly) a consecutive string of powers of 2, starting at 2, equals one half of the latter sum where M is replaced by a partition where all the odd parts are retained but the consecutive string of powers of 2: 2,4, ..., $2^{t-1}$ is replaced by $2^t$.

math.CO↗
arXiv2015

Identities in character tables of $S_n$

In the classic "Concrete Math", by Graham, Patashnik and Knuth, it is stated that "The numbers in Pascal's triangle satisfy, practically speaking, infinitely many identities, so it is not too surprising that we can find some surprising relationships by looking closely." The aim of this note is to indicate that a similar statement seems to hold for the character tables of the symmetric groups $S_n$. Just as important, it is a case-study in using a computer algebra system to prove deep identities, way beyond the ability of mere humans. This article is accomanied by a Maple pacgage, Sn, and ample output, avaialble from the webpage http://www.math.rutgers.edu/~zeilberg/mamarim/mamarimhtml/sn.html .

math.CO↗
arXiv2015

Growth for the central polynomials

We study the growth of the central polynomials for the algebras $G$ and $M_k(F)$, the infinite dimensional Grassmann algebra and the $k\times k$ matrices over a field $F$ of characteristic zero. In particular it follows that $M_k(F)$ satisfy many proper central polynomials.

math.RT↗
arXiv2010

Kronecker multiplicities in the $(k,\ell)$ hook are polynomially bounded

The problem of decomposing the Kronecker product of $S_n$ characters is one of the last major open problems in the ordinary representation theory of the symmetric group $S_n$. Here we prove upper and lower polynomial bounds for the multiplicities of the Kronecker product $χ^\lm\otimesχ^μ$, where for some fixed $k$ and $\ell$ both partitions $\lm$ and $μ$ are in the $(k,\ell)$ hook, $\lm$ and $μ$ are partitions of $n$, and $n$ goes to infinity.

math.RT↗
arXiv2010

Refined Asymptotics and Explicit Recurrences for the numbers of Young tableaux in the (k,l) hook for k+l less than six

This is an etude in experimental semi-rigorous (rigorizable!) mathematics. The leading asymptotics was brilliantly derived by Allan Berele and Amitai Regev for general hooks H(k,l) and general powers z, but what about more refined asymptotics? For small k and l, one can "guess" a linear recurrence (since we live in the holonomic ansatz) and using the Birkhoff-Trjitzinsky method, beautifully implemented in Doron Zeilberger's Maple package AsyRec (that has been incorporated into the present Maple package), we computed amazing refined asymptotics, that confirm, with a vengeance, the Berele-Regev asymptotic formula, and especially the impressive constant in front!

math.CO↗
arXiv2010

Identities for the number of standard Young tableaux in some $(k,\ell)$ hooks

Closed formulas are known for $S(k,0;n)$, the number of standard Young tableaux of size $n$ and with at most $k$ parts, where $1\le k\le 5$. Here we study the analogue problem for $S(k,\ell;n)$, the number of standard Young tableaux of size $n$ which are contained in the $(k,\ell)$ hook. We deduce some formulas for the cases $k+\ell\le 4$.

math.CO↗
arXiv2010

Bijections for an identity of Young Tableaux

We present an elegant bijection between standard Young tableaux with 2n cells and at most two rows, and pairs of standard Young tableaux of the same shape, with n+1 cells, where only the top row can have more than one cell.

math.CO↗
arXiv2009

A Multi-Set Identity for Partitions

We prove that the multiset {(RightArmLength,LeftArmLength)} ranging over all cells of all Ferrers diagrams with n cells equals the multiset {(RightArmLength,LegLength)} ranging over all cells of all Ferrers diagrams with n cells, thereby refining a multi-set identity proved by C. Bessenrodt and by Bacher and L. Manivel. Added In revised version: Guo-Niu Han kindly pointed out to us that our main result is contained in reference [B.H] of the present article.

math.CO↗
arXiv2009

The Golod Shafarevich counter-example without Hilbert series

Let $F$ be an arbitrary field. The Golod-Shafarevich example of a finitely generated nil $F$-algebra which is infinite dimensional -- is revisited. Here we offer a rather elementary treatment of that example, in which induction replaces Hilbert series techniques. This note also contains a detailed exposition of the construction of that example.

math.RA↗
arXiv2005

Expected lengths and distribution functions for Young diagrams in the hook

We consider $β$--Plancherel measures \cite{Ba.Ra.} on subsets of partitions -- and their asymptotics. These subsets are the Young diagrams contained in a $(k,\ell)$--hook, and we calculate the asymptotics of the expected shape of these diagrams, relative to such measures. We also calculate the asymptotics of the distribution function of the lengths of the rows and the columns for these diagrams. This might be considered as the restriction to the $(k,\ell)$--hook of the fundamental work of Baik, Deift and Johansson \cite{B.D.J.1}. The above asymptotics are given here by ratios of certain Selberg-type multi--integrals.

math.CO↗
arXiv2005

A Foata bijection for the alternating group and for q analogues

The Foata bijection $Φ: S_n \to S_n$ is extended to the bijections $Ψ: A_{n+1} \to A_{n+1}$ and $Ψ_q : S_{n+q-1} \to S_{n+q-1}$, where S_m, A_m are the symmetric and the alternating groups. These bijections imply bijective proofs for recent equidistribution theorems, by Regev and Roichman, for A_{n+1} and for S_{n+q-1}.

math.CO↗
arXiv2004

Statistics on Wreath Products and Generalized Binomial-Stirling Numbers

Various statistics on wreath products are defined via canonical words, "colored" right to left minima and "colored" descents. It is shown that refined counts with respect to these statistics have nice recurrence formulas of binomial-Stirling type. These extended Stirling numbers determine (via matrix inversion) dual systems, which are also shown to have combinatorial realizations within the wreath product. The above setting also gives rise to MacMahon type equi-distribution theorem over subsets with prescribed statistics.

math.CO↗
arXiv2003

q Statistics on $S_n$ and Pattern Avoidance

Natural q analogues of classical statistics on the symmetric groups $S_n$ are introduced; parameters like: the q-length, the q-inversion number, the q-descent number and the q-major index. MacMahon's theorem about the equi-distribution of the inversion number and the reverse major index is generalized to all positive integers q. It is also shown that the q-inversion number and the q-reverse major index are equi-distributed over subsets of permutations avoiding certain patterns. Natural q analogues of the Bell and the Stirling numbers are related to these q statistics -- through the counting of the above pattern-avoiding permutations.

math.CO↗
arXiv2003

Permutation Statistics on the Alternating Group

Let $A_n\subseteq S_n$ denote the alternating and the symmetric groups on $1,...,n$. MacMahaon's theorem, about the equi-distribution of the length and the major indices in $S_n$, has received far reaching refinements and generalizations, by Foata, Carlitz, Foata-Schutzenberger, Garsia-Gessel and followers. Our main goal is to find analogous statistics and identities for the alternating group $A_{n}$. A new statistic for $S_n$, {\it the delent number}, is introduced. This new statistic is involved with new $S_n$ equi-distribution identities, refining some of the results of Foata-Schutzenberger and Garsia-Gessel. By a certain covering map $f:A_{n+1}\to S_n$, such $S_n$ identities are `lifted' to $A_{n+1}$, yielding the corresponding $A_{n+1}$ equi-distribution identities.

math.CO↗
arXiv2001

Frobenius-Schur functions

The present paper is a detailed version of math/0003031. We introduce and study a new basis in the algebra of symmetric functions. The elements of this basis are called the Frobenius-Schur functions (FS-functions, for short). Our main motivation for studying the FS-functions is the fact that they enter a formula expressing the combinatorial dimension of a skew Young diagram in terms of the Frobenius coordinates. This formula plays a key role in the asymptotic character theory of the symmetric groups. The FS-functions are inhomogeneous, and their top homogeneous components coincide with the conventional Schur functions. The FS-functions are best described in the super realization of the algebra of symmetric functions. As supersymmetric functions, the FS-functions can be characterized as a solution to an interpolation problem. Our main result is a simple determinantal formula for the transition coefficients between the FS-functions and the Schur functions. We also establish the FS analogs for a number of basic facts concerning the Schur functions: Jacobi-Trudi formula together with its dual form; combinatorial formula (expression in terms of tableaux); Giambelli formula and the Sergeev-Pragacz formula. All these results hold for a large family of bases interpolating between the FS-functions and the ordinary Schur functions.

math.CO↗