Table Of ContentPARTITION IDENTITIES ARISING FROM THE
(2)
STANDARD A -MODULES OF LEVEL 4
2
BY DEBAJYOTI NANDI
A dissertation submitted to the
Graduate School—New Brunswick
Rutgers, The State University of New Jersey
in partial fulfillment of the requirements
for the degree of
Doctor of Philosophy
Graduate Program in Mathematics
Written under the direction of
Robert L. Wilson
and approved by
New Brunswick, New Jersey
October, 2014
ABSTRACT OF THE DISSERTATION
Partition Identities Arising from the Standard
(2)
A -Modules of Level 4
2
by Debajyoti Nandi
Dissertation Director: Robert L. Wilson
In this dissertation, we propose a set of new partition identities, arising from a twisted
vertex operator construction of the level 4 standard modules for the affine Kac-Moody
(2)
algebra of type A . These identities have an interesting new feature, absent from
2
previously known examples of this type.
Thisworkisacontinuationofalonglineofresearchofconstructingstandardmodules
for affine Kac-Moody algebras via vertex operators, and the associated combinatorial
identities. The interplay between representation theory and combinatorial identities
was exemplified by the vertex-algebraic proof of the famous Rogers-Ramanujan-type
(1)
identities using standard A -modules by J. Lepowsky and R. Wilson. In his Ph.D.
1
thesis, S. Capparelli proposed new combinatorial identities using a twisted vertex
(2)
operator construction of the standard A -modules of level 3, which were later proved
2
independently by G. Andrews, S. Capparelli, and M. Tamba-C. Xie.
We begin with an obvious spanning set for each of the level 4 standard modules for
(2)
A , and reduce this spanning set using various relations. Most of these relations come
2
from certain product generating function identities which are valid for all the level 4
modules. There are also other ad-hoc relations specific to a particular module of level 4.
In this way, we reduce our spanning sets to match with the graded dimensions of the
ii
said modules as closely as possible. We conjecture and present strong evidence for three
(2)
partition identities based on the spanning sets for the three standard A -modules of
2
level 4.
One surprising result of our work is the discovery of relations of arbitrary length.
Consequently, the partitions corresponding to these spanning sets cannot be described
by difference conditions of finite length.
The spanning set result proves one inequality of the proposed identities. There is
strong evidence for the validity of the conjecture (i.e., the opposite inequality), since it
has been verified to hold for partitions of n ≤ 170, and n = 180,190 and 200.
iii
Acknowledgements
This work would not have been possible without the support and encouragement of
many people. But, foremost, I wish to express my sincerest gratitude to my adviser,
Prof. Robert Wilson, for his continued support, patience and valuable guidance. I would
also like to thank Prof. James Lepowsky his guidance and insightful comments during
the review of this thesis. I would like to thank my colleague and friend Shashank Kanade
for reading this thesis and suggesting improvements, and Matthew Russell for his help
with the Maple codes for computations in noncommutative algebras.
I am also grateful to my friends Amit, Aravind, Bibhash, Chitra, Moulik, Samreen,
Supriya, Swathi, Yevgen, and many others for all their support, patience and the fun
times together.
I am specially indebted to my family—my mother Sulata Nandi, my sister, Soumi
Nandi, and my brother-in-law Anirban Biswas—for their unwavering love, support,
understanding and encouragement.
iv
Dedication
To my loving mother
Sulata Nandi,
my lovely sister
Soumi Nandi,
and in memory of my father
Late Joydeb Nandi.
v
Table of Contents
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
Dedication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Preliminaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1. Formal Calculus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2. Vertex Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
(2)
2.3. The Algebra A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2
3. Standard Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.1. Basic Notions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.2. The Graded Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4. The Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.1. Tuples and Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.2. Standard Monomials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.3. Structure of the Standard Modules . . . . . . . . . . . . . . . . . . . . . 48
4.4. Tools and Techniques for Working with Relations . . . . . . . . . . . . . 55
5. Generating Function Identities . . . . . . . . . . . . . . . . . . . . . . . . 67
5.1. Definitions: The Product Generating Functions . . . . . . . . . . . . . . 68
5.2. Identities on the Basic Module . . . . . . . . . . . . . . . . . . . . . . . 70
5.3. Identities on the Level 4 Standard Modules . . . . . . . . . . . . . . . . 73
5.4. Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
vi
6. Forbidden Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
6.1. Forbidden Pairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
6.2. Regular Forbidden Triplets . . . . . . . . . . . . . . . . . . . . . . . . . 86
6.3. Exceptional Forbidden Triplets . . . . . . . . . . . . . . . . . . . . . . . 92
6.4. Exceptional Forbidden Partitions of Arbitrary Length . . . . . . . . . . 99
6.5. Summary of Forbidden Partitions for Level 4 Modules . . . . . . . . . . 103
7. Initial Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
7.1. Initial Condition for the (4,0)-module . . . . . . . . . . . . . . . . . . . 105
7.2. Initial Conditions for the (2,1)-Module . . . . . . . . . . . . . . . . . . . 106
7.3. Initial Conditions for the (0,2)-Module . . . . . . . . . . . . . . . . . . . 109
8. Partition Identities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
8.1. The Main Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Appendix A. Computation of the Relations . . . . . . . . . . . . . . . . . 116
A.1. Maple Worksheet for Computing Relations . . . . . . . . . . . . . . . . 116
A.2. Maple Codes to Generate Partitions . . . . . . . . . . . . . . . . . . . . 123
A.3. Maple Codes to Compute the Coefficients . . . . . . . . . . . . . . . . . 126
A.4. Other Codes Used in the Maple Worksheet . . . . . . . . . . . . . . . . 129
Appendix B. Computation in Noncommutative Algebra . . . . . . . . . 133
B.1. Verification of the Isomorphism . . . . . . . . . . . . . . . . . . . . . . . 134
B.2. Computations for the Proofs of the Initial Conditions . . . . . . . . . . 137
B.3. Maple Codes for Noncommutative Polynomials . . . . . . . . . . . . . . 144
B.4. Substitution Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
B.5. Other Miscellaneous Maple Codes Used . . . . . . . . . . . . . . . . . . 175
Appendix C. Verification of the Partition Identities . . . . . . . . . . . . 179
C.1. File: verify.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
C.2. File: data.h. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
vii
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
viii
1
Chapter 1
Introduction
In this work, we conjecture and present strong evidence for possible partition identities
(2)
arisingfromthestandardmodulesoflevel4fortheaffineLiealgebraA usingatwisted
2
vertex operator construction. Historically, the discovery of vertex operator constructions
ofrepresentationsofaffineLiealgebraswasmotivatedbyaconjecturedinterplaybetween
classical partition identities and standard modules for affine Kac-Moody Lie algebras.
The first famous example of such interplay arises from the Rogers-Ramanujan
identities, which may be stated as follows:
(i) The number of partitions of a nonnegative integer n in which the differ-
ence between any two successive parts is at least 2 is the same as the number
of partitions of n into parts congruent to 1 or 4 modulo 5.
(ii) The number of partitions of a nonnegative integer n in which the
difference between any two successive parts is at least 2 and such that the
smallest part is at least 2 is the same as the number of partitions of n into
parts congruent to 2 or 3 modulo 5.
(1)
A connection between the congruence conditions and standard modules for A was dis-
1
covered by J. Lepowsky and S. Milne [LM78]. A vertex operator theoretic interpretation
and proof of the Rogers-Ramanujan identities, “explaining” the difference conditions,
was given by Lepowsky and R. Wilson in [LW82, LW84]. They used monomials, acting
on a highest weight vector, in certain new operators whose indices reflected the difference
(1)
conditions. They extended their work to all the standard A -modules in [LW82, LW84,
1
LW85], giving a vertex-algebraic interpretation of a family of Rogers-Ramanujan-type
identities, discovered by B. Gordon, G. Andrews and D. Bressoud. The case for the
2
(1)
level 2 standard A -modules was described by certain “difference-one” conditions
1
(where adjacent parts have difference at least one). For level 3 it was described by
“difference-two” conditions (where adjacent parts have difference at least two). For levels
greater than 3, the description changed into “difference-two-at-a-distance” and parity
conditions, reflecting the sum sides of the Gordon-Andrews-Bressoud identities.
The linear independence of the relevant monomials (applied to a highest weight
(1)
vector) for standard A -modules of level greater than 3 was not proved in the sequel
1
[LW82, LW84, LW85]. This problem was solved by A. Meurman and M. Primc [MP87],
providing a vertex-algebraic proof of the Gordon-Andrews-Bressoud identities beyond
the case of Rogers-Ramanujan identities.
In his Ph.D. thesis [Cap88], S. Capparelli proposed a pair of combinatorial iden-
(2)
tities based on the standard A -modules of level 3. He also demonstrated that the
2
(2)
construction of the level 2 standard modules for A in this way gives rise to another
2
vertex operator theoretic interpretation of the classical Rogers-Ramanujan identities
(see also [Cap92, Cap93]). It was believed that once a few low level cases for standard
(2)
A -modules had been successfully analyzed in this way, a general construction for all
2
(2)
levels would emerge. However, the cases for A turned out to be much harder and
2
(1)
subtler than those for A which had been extensively studied. One of Capparelli’s
1
(2)
identities, arising from the level 3 standard A -modules, may be stated as follows:
2
The number of partitions of a nonnegative integer n into parts different
from 1 and such that the difference of two successive parts is at least 2, and
is exactly 2 or 3 only if their sum is a multiple of 3, is the same as the
number of partitions of n into parts congruent to ±2,±3 modulo 12.
Aq-seriesproofofthisidentitywasgivenbyG.Andrews[And94],provingCapparelli’s
conjecture. Capparelli also provided a direct vertex operator theoretic proof of his
identities by proving the linear independence of his spanning sets in [Cap96]. M. Tamba
and C. Xie [TX95] independently gave another vertex operator theoretic proof of
Capparelli’s identities. See [Lep07] for more details.
In this work, we give combinatorial interpretations of the graded dimensions of the
