A.A. Bytsenko, M. Chaichian / Nuclear Physics B 907 (2016) 258–285 263
P
sl
N
;R
1
,...,R
(q, t) :=
k,j∈Z
q
k
t
j
dim H
sl
N
;R
1
,...,R
k,j
(L). (2.4)
By definition, it is a polynomial in q
±1
and t
±1
with integer non-negative coefficients. In addi-
tion, evaluating (2.4) at t =−1gives (2.3). In the case R
a
= 2 for all a = 1, ..., , the homology
H
sl
N
;2,...,2
k,j
(L) is known as the Khovanov–Rozansky homology,
(KR)
H
N
k,j
(L). The further phys-
ical interpretation of homological link invariants via Hilbert spaces of BPS states leads to certain
predictions regarding the behavior of link homologies with rank N (for more discussion see
[35,37]).
In the case when dimensions of homologies of appropriate topological spaces are precisely
known the procedure of the calculation can be appreciably simplified. Such a situation hap-
pends, for example, if asymptotic behavior the total dimension of H
sl
N
;R
1
,··· ,R
∗,∗
(L) grows as
[34]: dimH
sl
N
;R
1
,··· ,R
∗,∗
(L)|
N→∞
→ N
d
, d =
j=1
dim R
j
.
3. Hopf algebraic approach and group theory
Usually the Euler–Poincaré formula applies to chain complexes of finite dimensional Lie
algebras. In the infinite dimensional case matters can be fixed up by considering polygraded
Lie algebras. Thus the partition functions can indeed be converted into product expressions. The
expression on the right-hand side of (2.1) looks like counting the states in the Hilbert space of a
second quantized theory
. Certain formulas for the partition functions or Poincaré polynomials
n
1
,...,n
k
1 − q
n
1
1
···q
n
k
k
dim g
n
1
,...,n
k
,
n
1
,...,n
k
1 − q
n
1
1
···q
n
k
k
rank g
n
1
,...,n
k
(3.1)
are associated with dimensions of homologies of appropriate topological spaces and linked to
generating functions and elliptic genera. Note that this conclusively explains the sequence of
dimensions (distinguished powers) of the simple Lie algebras.
Before e
xamine a ring of formal power series (of type (3.1)) we provide a short discussion
on the theory of a higher-weight modules over Lie algebra. We start with very well known Lie
algebra gl(n, k).
1
Results for gl(n, k) survive the passage to the limit n →∞, if one assumes that
gl(∞, k) is the Lie algebra of infinite finitary matrices, which means
n
gl(n, k). In this remark
we deal with the Lie algebra gl
J
(k) of generalized Jacobian matrices.
2
The algebra gl
J
(k) can
be considered as a nontrivial one-dimensional central extension of the Lie algebra gl
J
(k) (for
details, see [38]). It is obvious that gl
J
(k) ⊃ gl
J
(∞, k). The importance of this Lie algebra
stems from the following facts:
• Man
y of the classical constructions of the theory of representations of the Lie algebra gl
J
(k)
can be also applied to the algebra gl
J
(k). This creates a sizable supply of gl
J
(k)-modules.
• Important infinite-dimensional Lie algebras can be embedded in gl
J
(k). Thus, the already
mentioned representations of gl
J
(k) become representations of these algebras.
1
The symbol k denotes the field of real numbers R or the field C of complex numbers. In particular, gl(n, C) is the
Lie algebra of all complex n × n matrices with the operation A, B → [A, B] = AB − BA.
2
The bilateral matrix a
ij
i,j∈Z
is called a generalized Jacobian matrix if it has a finite number of nonzero diagonals
(that is, if there exists a positive N such that a
ij
= 0for |j − i| >N). It is clear that the set of generalized Jacobian
matrices constitutes a Lie algebra, with respect to the usual commutation rule.