Growth Series of the Braid Monoid <svg xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg" style="vertical-align:-4.3442pt" id="M1" height="15.5972pt" version="1.1" viewBox="-0.0657574 -11.253 32.1356 15.5972" width="32.1356pt"><g transform="matrix(.017,0,0,-0.017,0,0)"><path id="g190-78" d="M861 0V28C774 35 771 41 768 147L759 509C756 612 762 614 851 622V650H681L449 149L221 650H57V622C148 613 153 609 144 479L130 271C123 166 117 123 111 88C104 46 85 34 26 28V0H259V28C192 35 169 42 167 90C166 130 166 173 170 256L185 541H187L411 7H431L675 555H679L683 147C683 41 680 35 598 28V0H861Z"/></g><g transform="matrix(.017,0,0,-0.017,15.346,0)"><path id="g190-67" d="M372 352C427 368 507 407 507 502C507 548 486 592 451 616C420 638 376 650 301 650H44V622C124 616 128 610 128 527V123C128 40 122 34 36 28V0H257C336 0 402 12 453 40C512 72 548 124 548 191C548 291 471 335 372 350V352ZM213 362V558C213 591 216 602 226 608C235 614 258 618 282 618C377 618 415 558 415 490C415 406 369 362 260 362H213ZM213 328H258C380 328 450 283 450 181C450 76 377 35 296 34C231 34 213 53 213 125V328Z"/></g><g transform="matrix(.012,0,0,-0.012,25.475,4.134)"><path id="g50-54" d="M158 548H390L417 615L410 623H122L83 318C105 326 143 337 185 337C296 337 350 275 350 188C350 116 308 42 225 42C164 42 122 74 100 93C90 101 82 99 72 92C60 82 51 68 50 59C48 46 52 38 66 24C82 9 125 -12 172 -12C225 -11 292 15 346 59C408 108 437 166 437 226C437 309 371 397 242 397C214 397 170 382 133 369L158 548Z"/></g></svg> in Band Generators

Khan, Muhammad Haleem; Iqbal, Zaffar

doi:https://doi.org/10.1155/2022/9108480

Advances in Mathematical Physics

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Abstract Introduction Materials and Methods Results and Discussion Conclusion Data Availability Conflicts of Interest References Copyright Related Articles

Research Article | Open Access

Volume 2022 | Article ID 9108480 | https://doi.org/10.1155/2022/9108480

Growth Series of the Braid Monoid in Band Generators

Muhammad Haleem Khan¹and Zaffar Iqbal¹

Academic Editor: Dimitrios Tsimpis

Received12 Apr 2022

Accepted24 May 2022

Published07 Jun 2022

Abstract

Growth series is an important invariant associated with group or monoid which classifies all the words of group or monoid. Therefore, the growth series of braid monoids and Hecke algebras in Artin’s generators is presented in many scholarly published articles. The growth series of braid monoids and in band generators is known. In this work, we compute the complete presentation of braid monoid in band generators by solving all the ambiguities of . The words on the left-hand of each relation are reducible words, and the words on the right-hand side are canonical words. We partially find the growth series of reducible words. Then, we construct a linear system for canonical words of in band presentation and compute the corresponding growth series. We also find the growth rate of growth series of in band generators.

1. Introduction

The growth series also known as Hilbert series is an important invariant in the study of modern geometry. In physics, growth series have recently become a power full tool in high energy theory, appearing, for example in the study of Bogomol’nyi-Prasad-Sommerfield operators of supersymmetric gauge theories [1, 2]; supersymmetric quantum chromodynamics [3, 4], and instanton moduli space [5, 6]. In [7], Hilbert series was used to construct an operator basis in 1/m expansion of a theory with a nonrelativistic heavy fermion in an electromagnetic (NRQED) or color gauge field (NRQCD/HQET).

The braid group admits the presentation given by Artin [8].

The braid group admits other presentations such as Sergiescu graph-presentation and Birman-Ko-Lee presentation or band presentation. The last presentation is given by

Growth series of braid monoid and is computed in [9]. In [10], growth series of the finite dimensional Hecke algebra is presented. Growth series for graded S-module was computed by Haider in [11]. The growth series of binomial edge ideals was computed by Kumar and Sarkar in [12]. In [13], growth series of the graded algebra of real regular functions on the symplectic quotient associated to an -module is computed and given an explicit expression for the first nonzero coefficient of the Laurent expansion of the growth series at Growth series and the coefficient of Laurent expansion of growth series of special linear group of matrices are computed in [14]. In [15], Saito proved that the growth functions associated with Artin monoids of finite type are rational functions whose nominator is 1 and the denominator is polynomial having distinct roots. Growth series of symplectic quotients by 2-torus is computed in [16]. In [17], the Laurent coefficients of the growth series of a Gorenstein algebra is presented. In the growth series of (for ) for Artin generators, the degrees of the polynomials are 3, 4, 10, 15, respectively (for detail see [18]). Universal upper bound for the growth of Artin monoid is computed in [19]. Growth series of braid monoid and in band generators is computed in [9]. The degrees of polynomial in case of band generators are 2 and 3 (for and 4). In this paper, we compute the growth series of braid monoid using band presentation, and we see that the degree of the polynomial is 4. We note that growth rate of in band generators is much slower than that of Artin generators.

2. Materials and Methods

In , we fix a total order on the generators. In the monoid, the relation will be written as in the length-lexicographic order. Let and ; then the word of the form is said to be ambiguity (for detail see [20]). If as a relation as well as in the length-lexicographic order, then, we say that the ambiguity is solvable. A presentation is complete if and only if all the ambiguities are solvable (for detail see [21, 22]). Corresponding to the relations the changes give a rewriting system. A presentation will be called a complete presentation if and only if all the ambiguities are solvable.

In a complete presentation (or in the general presentation) of if a word contains, then is called a reducible word and we denote it by in general. If word does not contain, then is called canonical word or canonical form. Let and be nonempty words; then, the word will be denoted as .

Definition 1 (see [23]). Let be a finitely generated group and be a finite set of generators of . Then, the word length of an element is the smallest integer for which there exist such that

Definition 2 (see [23]). Let be a finitely generated group and be a finite set of generators of . Then, the growth function of the pair associates to an integer the number of the element such that , and the corresponding growth series is given by .

In 2008, Bokut [22] gave the Grbner-shirshov basis (GSB) of in band generators. The notion of this basis is in [14, 20, 24–27] under different names: complete presentation, presentations with solvable ambiguities, Grbner-shirshov basis, rewriting system, and so on. In [28], we proved the subset of GSB of given by Bokut [26] is a GSB of Using the notation (used in [28]) for generator and or for the words in such that , we have.

Theorem 3 (see [28]). A GSB of braid monoid consist of following relations: where

Proposition 4 (see [9]). Solution of linear system for canonical words of braid monoid is given by And the growth series of in band generators is given as

3. Results and Discussion

In this paper, we compute the growth series of (in band presentation). From Equation (2), we have the following band-presentation of : where are given basic relations.

For the braid monoid , we have given another form of Theorem 3 that is directly used to compute the growth series of . This form is obtained by solving all the ambiguities in the band presentation of .

Proposition 5. A complete presentation of for band presentation is given by where the new relations … are given as follows where and are positive integers, a canonical word in starting with and (i): is a canonical word in starting with (ii): and (as mentioned in Theorem 3)

Proof. We denote the ambiguity formed by left sides of the relation and in by - (say). If in the ambiguity and are different lexicographically, then we get a new relation in the complete presentation of , and if and are reduced to an identical word, then we say the ambiguity is solvable and no new relation is formed. The above relations are formed by solving the ambiguities involving basic relations and new relations.
For an ambiguity (say), we have Hence, we have a new relation . Again, by solving new ambiguity (say), we have Hence, we have another relation Now by solving ambiguity (say), we have Hence, we have a relation . By continuing the same process, we have the general relation For an ambiguity (say), we have Hence, we have a new relation . Again, by solving new ambiguity (say), we have which give another relation Now by solving ambiguity (say), we have Hence, . By continuing the same process, we have the general relation For an ambiguity (say), we have where are reduced to identical word, so ambiguity is solvable and no new relation is formed. Using a similar procedure, we obtained all above new relations in complete presentation of Hence the proof is omitted.

As defined above, denotes the set of canonical words and the set of reducible words in in general. In particular, , where denote the set of reducible words starting with and ending on In this notation is a generator in : , denotes the canonical word (possibly empty) in starting with , denotes the canonical word (possibly empty) in starting with and denotes the canonical word (possibly empty) in starting with We will denote the empty word by We denote the set all reducible words starting with and ending on by . Hence, is a subset of

We are using other notions as follows: (i)We denote the set by (ii) denotes the set of canonical words starting with in (iii) denotes the set of all the word in such that the index of each generator is increased by . Hence, , i.e., the cardinality remains unchanged. In particular for the set , we have (iv) denotes the set of canonical words starting with in (v)The growth series of , and is denoted by and , respectively

Note that growth series of is

Proposition 6. The following equalities hold for the reducible words in :

Proof. Using simple decomposition of words and denotes the disjoint union of sets then, we have (1)Since = , hence , (2) == implies (3) implies Using similar procedure, we obtained all above of Hence, the proof is omitted.

Next, we construct linear system for canonical form in

Proposition 7. The following equalities hold for the canonical words in :

Proof. We compute the growth series inductively. By using decomposition of words, we have (1) gives (2) implies (3)