Table Of ContentAffine Jordan cells, logarithmic correlators,
and hamiltonian reduction
Jørgen Rasmussen
6 Department of Mathematics and Statistics, University of Concordia
0 1455 Maisonneuve W, Montr´eal, Qu´ebec, Canada H3G 1M8
0
2 [email protected]
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a
J
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Abstract
3
v WestudyaparticulartypeoflogarithmicextensionofSL(2,R)Wess-Zumino-Wittenmodels. Itisbased
9 on the introduction of affine Jordan cells constructed as multiplets of quasi-primary fields organized in
7
indecomposable representations of the Lie algebra sl(2). We solve the simultaneously imposed set of
1
conformal and SL(2,R) Ward identities for two- and three-point chiral blocks. These correlatorswill in
8
0 generalinvolvelogarithmictermsandmayberepresentedcompactlybyconsideringspinswithnilpotent
5 parts. The chiral blocks are found to exhibit hierarchical structures revealed by computing derivatives
0 with respect to the spins. We modify the Knizhnik-Zamolodchikov equations to cover affine Jordan
/
h cells and show that our chiral blocks satisfy these equations. It is also demonstrated that a simple
t and well-established prescription for hamiltonian reduction at the level of ordinary correlators extends
-
p straightforwardly to the logarithmic correlators as the latter then reduce to the known results for two-
e and three-point conformal blocks in logarithmic conformal field theory.
h
:
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Keywords: Logarithmic conformal field theory, Jordan cell, Wess-Zumino-Witten model, Knizhnik-
i
X Zamolodchikov equations, hamiltonian reduction.
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1 Introduction
In logarithmic conformal field theory (CFT), a primary field may have a so-called logarithmic partner
field onwhichthe Virasoromodes do not allactdiagonally. If only one logarithmicfieldis associatedto
a given primary field, the two fields constitute a so-called conformal Jordan cell of rank two where the
rankindicates the number offields inthe cell. We will be concernedwithconformalJordancells ofrank
two only. The appearance of such cells is known to lead to logarithmic singularities in the correlators.
We refer to [1] for the first systematic study of logarithmic CFT, and to [2, 3, 4] for recent reviews on
the subject. An exposition of links to string theory may be found in [5].
The objective ofthe presentworkis to introduce andstudy a particularlogarithmicextensionof the
SL(2,R) Wess-Zumino-Witten (WZW) model. Alternative extensions have appeared in the literature,
see [6, 7, 8, 4, 9], for example, but all seem to differ significantly from ours in foundation and approach.
Our construction is based on a generalization of the standard multiplets of Virasoro primary fields
organizedasspin-j representation. We findthataninfinite number ofpartnerfields seemto be required
to complete such an indecomposable representation of sl(2), and we refer to these new multiplets as
affine Jordan cells.
We consider the case where the logarithmic fields in the affine Jordan cells are quasi-primary, and
discuss the conformal and SL(2,R) Ward identities which follow. Without making any simplifying
assumptions about the operator-product expansions of the fields, we find the general solutions for two-
and three-point chiral blocks. Our results thus cover all the possible cases based on primary fields not
belonging to affine Jordan cells, primary fields belonging to affine Jordan cells, and the logarithmic
partner fields completing the affine Jordan cells.
Most of our computations are based on the introduction of generating functions for the fields ap-
pearing in the variousrepresentations. This means that the affine correlatorsof the individual fields are
obtained by expanding certain generating-function chiral blocks.
Amodificationofthe Knizhnik-Zamolodchikov(KZ)equations[10]isrequiredto coveraffine Jordan
cells in addition to primary fields. It is demonstrated that the chiral blocks obtained as solutions to the
Ward identities satisfy these generalized KZ equations. This verification is straightforward once it has
been established that the two- and three-point chiral blocks may be expressed compactly in terms of
spinswithnilpotentparts. We showthatthisis possible. Italsofollowsthatatwo-orthree-pointchiral
block factorizes into a ‘conformal‘ part and a ‘group‘ part.
Thechiralblocksarefoundtoexhibithierarchicalstructuresobtainedbycomputingderivativeswith
respecttothespins. Thisextendsanobservationmadein[11,12,13]thatthesetsoftwo-andthree-point
conformal blocks in logarithmic CFT are linked via derivatives with respect to the conformal weights.
ItisnotedthatasimpledistinctionhasbeenintroducedaswerefertochiralcorrelatorsintheWZW
model as chiral blocks, while chiral correlators in logarithmic CFT are referred to as conformal blocks.
This is common practice.
A merit of our construction seems to be that the affine correlators reduce to the conformal ones
when a straightforwardextension of the prescription for hamiltonian reduction introduced in [14, 15] is
employed. The idea is formulatedin the realmof generatingfunctions for the Virasoroprimary fields in
spin-j multiplets,andwefindthatitmaybeextendedtoaffineJordancellsandthuscoverthereduction
of our logarithmic SL(2,R) WZW model to logarithmic CFT.
This paper proceeds as follows. To fix our notation and to prepare for the discussion of hamiltonian
reduction, we first review the recently obtained general solutions to the conformal Ward identities for
two- and three-point conformal blocks in logarithmic CFT [13]. This is followed by a discussion in
Section 3 of generating-function primary fields and their correlators in SL(2,R) WZW models. This
is the framework which we extend in Section 4 and eventually use in our analysis of chiral blocks. In
Section 4, we thus describe the indecomposable sl(2) representations underlying the affine Jordan cells.
ThecorrespondinglymodifiedKZequationsarealsointroduced. Section5concernstheexplicitresultson
two-andthree-pointchiralblocks. Itincludes a discussionofthe factorizationofthe chiralblocks based
on spins with nilpotent parts, as well as a discussion of the hierarchical structures of the chiral blocks.
1
SometechnicaldetailsaredeferredtoAppendixA. Theextendedprescriptionforhamiltonianreduction
is considered in Section 6, where it is demonstrated that our chiral blocks reduce to the conformal ones
reviewed in Section 2. Section 7 contains some concluding remarks.
2 Correlators in logarithmic CFT
2.1 Conformal Jordan cell
AconformalJordancellofranktwoconsistsoftwofields: aprimaryfield, Φ,ofconformalweight∆ˆ and
its non-primary, ‘logarithmic’ partner field, Ψ, on which the Virasoro algebra
cˆ
[L ,L ]=(n−m)L + n(n2−1)δ (1)
n m n+m n+m,0
12
generated by {L } does not act diagonally. The central extension is denoted cˆ. With a conventional
n
relative normalization of the fields, we have
[L ,Φ(z)] = zn+1∂ +∆ˆ(n+1)zn Φ(z)
n z
(cid:16) (cid:17)
[L ,Ψ(z)] = zn+1∂ +∆ˆ(n+1)zn Ψ(z)+(n+1)znΦ(z) (2)
n z
(cid:16) (cid:17)
IthasbeensuggestedbyFlohr[16]todescribethesefieldsinaunifiedwaybyintroducinganilpotent,
yet even, parameter θˆsatisfying θˆ2 =0. We will follow this idea here, though use an approachcloser to
the one employed in [17, 18, 13]. We thus define the field or unified cell
Υ(z;θˆ) = Φ(z)+θˆΨ(z) (3)
which is seen to be ‘primary’ of conformal weight ∆ˆ +θˆas the commutators (2) may be expressed as
L ,Υ(z;θˆ) = zn+1∂ +(∆ˆ +θˆ)(n+1)zn Υ(z;θˆ) (4)
n z
h i (cid:16) (cid:17)
Following[13],aprimaryfieldbelongingtoaconformalJordancellisreferredtoasacellularprimary
field. A primary field not belonging to a conformal Jordan cell may be represented as Υ(z;0), and we
will reserve this notation for these non-cellular primary fields. To avoid ambiguities, we will therefore
refrain from considering unified cells Υ(z;θˆ), as defined in (3), for vanishing θˆ.
2.2 Conformal Ward identities
We considerquasi-primary fieldsonly,ensuring the projectiveinvarianceoftheir correlatorsconstructed
by sandwiching the fields between projectively invariant vacua. This invariance is made manifest qua
the conformal Ward identities which are given here for N-point conformal blocks:
N
0 = ∂ hΥ (z ;θˆ )...Υ (z ;θˆ )i
zi 1 1 1 N N N
i=1
X
N
0 = z ∂ +∆ˆ +θˆ hΥ (z ;θˆ )...Υ (z ;θˆ )i
i zi i i 1 1 1 N N N
Xi=1(cid:16) (cid:17)
N
0 = LN +2 θˆz hΥ (z ;θˆ )...Υ (z ;θˆ )i (5)
i i 1 1 1 N N N
!
i=1
X
2
To simplify the notation, we have introduced the differential operator
N
LN = z2∂ +2∆ˆ z (6)
i zi i i
Xi=1(cid:16) (cid:17)
Information on the individual correlators may be extracted from solutions to the conformal Ward
identities involving unified cells. In the case of
hΥ (z ;θˆ )Υ (z ;0)Υ (z ;θˆ )i (7)
1 1 1 2 2 3 3 3
for example, the third conformal Ward identity (5) reads
0 = L3+2(θˆ z +θˆ z ) hΥ (z ;θˆ )Υ (z ;0)Υ (z ;θˆ )i (8)
1 1 3 3 1 1 1 2 2 3 3 3
(cid:16) (cid:17)
A solution to the complete set of conformal Ward identities is an expression expandable in θˆ and
1
θˆ . The term proportional to θˆ but independent of θˆ , for example, should then be identified with
3 1 3
hΨ (z )Υ (z ;0)Φ (z )i.
1 1 2 2 3 3
Byconstruction,andasillustratedbythisexample,correlatorsinvolvingunifiedcellsandnon-cellular
primaryfieldsmaythusberegardedasgenerating-functioncorrelatorswhoseexpansionsinthenilpotent
parameters give the individual correlatorsinvolving combinations of cellular primary fields, non-cellular
primary fields, and logarithmic fields. Our focus will therefore be on correlators of combinations of
unified cells and non-cellular primary fields.
2.3 Two-point conformal blocks
Based on the ansatz
Aˆ(θˆ ,θˆ )+Bˆ(θˆ ,θˆ )lnz
hΥ (z ;θˆ )Υ (z ;θˆ )i = 1 2 1 2 12 (9)
1 1 1 2 2 2 z2h
12
where
Aˆ(θˆ ,θˆ ) = Aˆ0+Aˆ1θˆ +Aˆ2θˆ +Aˆ12θˆ θˆ (10)
1 2 1 2 1 2
and similarly for Bˆ(θˆ ,θˆ ), the general (generating-function) two-point conformal blocks read
1 2
hΥ (z ;0)Υ (z ;0)i = Aˆ0V
1 1 2 2 2
hΥ (z ;θˆ )Υ (z ;0)i = Aˆ1θˆ V
1 1 1 2 2 1 2
hΥ (z ;0)Υ (z ;θˆ )i = Aˆ2θˆ V
1 1 2 2 2 2 2
hΥ (z ;θˆ )Υ (z ;θˆ )i = Aˆ1θˆ +Aˆ1θˆ + Aˆ12−2Aˆ1lnz θˆ θˆ V (11)
1 1 1 2 2 2 1 2 12 1 2 2
n (cid:16) (cid:17) o
Here we have introduced the shorthand notation
δ
V = ∆ˆ1,∆ˆ2 (12)
2 z∆ˆ1+∆ˆ2
12
To keepthe notation simple, we areusing the standardabbreviationz =z −z . It is understood that
ij i j
an Aˆ1, for example, appearing in one (generating-function) correlator a priori is independent of an Aˆ1
appearing in another. Also, even though Aˆ2 does not appear explicitly in some of these expressions,
it may nevertheless be related to Aˆ1. For the sake of simplicity, the solutions listed here are merely
indicating the general form and the degrees of freedom without reference to the fate of all the various
parameters appearing in the ansatz (9). Similar comments also apply to the results on correlators
discussedin the following. Finally, the solutions for the individual two-pointconformalblocksare easily
extracted [13].
3
By considering θˆ as the nilpotent part of the generalizedconformalweight∆ˆ +θˆ [17, 13], one may
i i i
represent the results (11) as
Aˆ0
hΥ (z ;0)Υ (z ;0)i = δ
1 1 2 2 ∆ˆ1,∆ˆ2z∆ˆ1+∆ˆ2
12
Aˆ1θˆ
hΥ (z ;θˆ )Υ (z ;0)i = δ 1
1 1 1 2 2 ∆ˆ1,∆ˆ2z(∆ˆ1+θˆ1)+∆ˆ2
12
Aˆ1θˆ +Aˆ1θˆ +Aˆ12θˆ θˆ
hΥ (z ;θˆ )Υ (z ;θˆ )i = δ 1 2 1 2 (13)
1 1 1 2 2 2 ∆ˆ1,∆ˆ2 z(∆ˆ1+θˆ1)+(∆ˆ2+θˆ2)
12
The similar expression for the correlatorhΥ (z ;0)Υ (z ;θˆ )i is obtained from the second one by inter-
1 1 2 2 2
changing the indices.
2.4 Three-point conformal blocks
Based on the ansatz
hΥ (z ;θˆ )Υ (z ;θˆ )Υ (z ;θˆ )i
1 1 1 2 2 2 3 3 3
= Aˆ(θˆ ,θˆ ,θˆ )+Bˆ (θˆ ,θˆ ,θˆ )lnz +Bˆ (θˆ ,θˆ ,θˆ )lnz +Bˆ (θˆ ,θˆ ,θˆ )lnz
1 2 3 1 1 2 3 12 2 1 2 3 23 3 1 2 3 13
n+ Dˆ (θˆ ,θˆ ,θˆ )ln2z +Dˆ (θˆ ,θˆ ,θˆ )lnz lnz +Dˆ (θˆ ,θˆ ,θˆ )lnz lnz
11 1 2 3 12 12 1 2 3 12 23 13 1 2 3 12 13
+Dˆ (θˆ ,θˆ ,θˆ )ln2z +Dˆ (θˆ ,θˆ ,θˆ )lnz lnz +Dˆ (θˆ ,θˆ ,θˆ )ln2z z−h1z−h2z−h3
22 1 2 3 23 23 1 2 3 23 13 33 1 2 3 13 12 23 13
o (14)
where
Aˆ(θˆ ,θˆ ,θˆ ) = Aˆ0+Aˆ1θˆ +Aˆ2θˆ +Aˆ3θˆ +Aˆ12θˆ θˆ +Aˆ23θˆ θˆ +Aˆ13θˆ θˆ +Aˆ123θˆ θˆ θˆ (15)
1 2 3 1 2 3 1 2 2 3 1 3 1 2 3
andsimilarlyforBˆ (θˆ ,θˆ ,θˆ )andDˆ (θˆ ,θˆ ,θˆ ),thegeneral(generating-function)three-pointconformal
i 1 2 3 ij 1 2 3
blocks read
hΥ (z ;0)Υ (z ;0)Υ (z ;0)i = Aˆ0V
1 1 2 2 3 3 3
z z
hΥ (z ;θˆ )Υ (z ;0)Υ (z ;0)i = Aˆ0+Aˆ1θˆ −Aˆ0θˆ ln 12 13 V
1 1 1 2 2 3 3 1 1 3
z
(cid:26) 23 (cid:27)
hΥ (z ;θˆ )Υ (z ;θˆ )Υ (z ;0)i
1 1 1 2 2 2 3 3
z z z z
= Aˆ0+Aˆ1θˆ −Aˆ0θˆ ln 12 13 +Aˆ2θˆ −Aˆ0θˆ ln 12 23
1 1 2 2
z z
(cid:26) 23 13
z z z z z z z z
+Aˆ12θˆ θˆ −Aˆ1θˆ θˆ ln 12 23 −Aˆ2θˆ θˆ ln 12 13 +Aˆ0θˆ θˆ ln 12 23 ln 12 13 V
1 2 1 2 1 2 1 2 3
z z z z
13 23 13 23 (cid:27)
hΥ (z ;θˆ )Υ (z ;θˆ )Υ (z ;θˆ )i
1 1 1 2 2 2 3 3 3
z z z z
= Aˆ1θˆ +Aˆ2θˆ +Aˆ3θˆ +Aˆ12θˆ θˆ −Aˆ1θˆ θˆ ln 12 23 −Aˆ2θˆ θˆ ln 12 13
1 2 3 1 2 1 2 1 2
z z
(cid:26) 13 23
z z z z z
+ Aˆ23θˆ θˆ −Aˆ2θˆ θˆ ln 23 13 −Aˆ3θˆ θˆ ln 13 +Aˆ13θˆ θˆ −Aˆ1θˆ θˆ ln 23 13
2 3 2 3 2 3 1 3 1 3
z z z z
12 12 23 12
z z z z
− Aˆ3θˆ θˆ ln 12 13 +Aˆ123θˆ θˆ θˆ −Aˆ12θˆ θˆ θˆ ln 23 13
1 3 1 2 3 1 2 3
z z
23 12
z z z z z z z z
− Aˆ23θˆ θˆ θˆ ln 12 13 −Aˆ13θˆ θˆ θˆ ln 12 23 +Aˆ1θˆ θˆ θˆ ln 23 12 ln 23 13
1 2 3 1 2 3 1 2 3
z z z z
23 13 13 12
4
z z z z z z z z
+ Aˆ2θˆ θˆ θˆ ln 12 13 ln 23 13 + Aˆ3θˆ θˆ θˆ ln 12 23 ln 12 13 V (16)
1 2 3 1 2 3 3
z z z z
23 12 13 23 (cid:27)
Here we have introduced the abbreviation
1
V = (17)
3 z∆ˆ1+∆ˆ2−∆ˆ3z−∆ˆ1+∆ˆ2+∆ˆ3z∆ˆ1−∆ˆ2+∆ˆ3
12 23 13
The remaining correlators are obtained by appropriate permutations in the indices.
As in the case of two-point conformal blocks, the three-point conformal blocks may be represented
in terms of generalized conformal weights, ∆ˆ +θˆ:
i i
Aˆ0
hΥ (z ;0)Υ (z ;0)Υ (z ;0)i =
1 1 2 2 3 3 z∆ˆ1+∆ˆ2−∆ˆ3z−∆ˆ1+∆ˆ2+∆ˆ3z∆ˆ1−∆ˆ2+∆ˆ3
12 23 13
Aˆ0+Aˆ1θˆ
hΥ (z ;θˆ )Υ (z ;0)Υ (z ;0)i = 1
1 1 1 2 2 3 3 z(∆ˆ1+θˆ1)+∆ˆ2−∆ˆ3z−(∆ˆ1+θˆ1)+∆ˆ2+∆ˆ3z(∆ˆ1+θˆ1)−∆ˆ2+∆ˆ3
12 23 13
hΥ (z ;θˆ )Υ (z ;θˆ )Υ (z ;0)i
1 1 1 2 2 2 3 3
Aˆ0+Aˆ1θˆ +Aˆ2θˆ +Aˆ12θˆ θˆ
1 2 1 2
=
z(∆ˆ1+θˆ1)+(∆ˆ2+θˆ2)−∆ˆ3z−(∆ˆ1+θˆ1)+(∆ˆ2+θˆ2)+∆ˆ3z(∆ˆ1+θˆ1)−(∆ˆ2+θˆ2)+∆ˆ3
12 23 13
hΥ (z ;θˆ )Υ (z ;θˆ )Υ (z ;θˆ )i
1 1 1 2 2 2 3 3 3
Aˆ1θˆ +Aˆ2θˆ +Aˆ3θˆ +Aˆ12θˆ θˆ +Aˆ23θˆ θˆ +Aˆ13θˆ θˆ +Aˆ123θˆ θˆ θˆ
1 2 3 1 2 2 3 1 3 1 2 3
= (18)
z(∆ˆ1+θˆ1)+(∆ˆ2+θˆ2)−(∆ˆ3+θˆ3)z−(∆ˆ1+θˆ1)+(∆ˆ2+θˆ2)+(∆ˆ3+θˆ3)z(∆ˆ1+θˆ1)−(∆ˆ2+θˆ2)+(∆ˆ3+θˆ3)
12 23 13
The remaining four combinations are obtained by appropriate permutations in the indices.
2.5 Hierarchical structures for conformal blocks
Basedon ideas discussedin [12, 11], it was found in [13] that the correlatorsinvolving logarithmic fields
may be represented as follows:
hΨ (z )Υ (z ;0)i = Aˆ1V
1 1 2 2 2
hΨ (z )Φ (z )i = Aˆ1V
1 1 2 2 2
hΨ (z )Ψ (z )i = Aˆ12+Aˆ2∂ +Aˆ1∂ V
1 1 2 2 ∆ˆ1 ∆ˆ2 2
(cid:16) (cid:17)
hΨ (z )Υ (z ;0)Υ (z ;0)i = Aˆ1+Aˆ0∂ V
1 1 2 2 3 3 ∆ˆ1 3
(cid:16) (cid:17)
hΨ (z )Φ (z )Υ (z ;0)i = Aˆ1+Aˆ0∂ V
1 1 2 2 3 3 ∆ˆ1 3
(cid:16) (cid:17)
hΨ (z )Ψ (z )Υ (z ;0)i = Aˆ12+Aˆ1∂ +Aˆ2∂ +A0∂ ∂ V
1 1 2 2 3 3 ∆ˆ2 ∆ˆ1 ∆ˆ1 ∆ˆ2 3
hΨ (z )Φ (z )Φ (z )i = A(cid:16)ˆ1V (cid:17)
1 1 2 2 3 3 3
hΨ (z )Ψ (z )Φ (z )i = Aˆ12+Aˆ2∂ +Aˆ1∂ V
1 1 2 2 3 3 ∆ˆ1 ∆ˆ2 3
(cid:16) (cid:17)
hΨ (z )Ψ (z )Ψ (z )i = Aˆ123+Aˆ23∂ +Aˆ13∂ +Aˆ12∂
1 1 2 2 3 3 ∆ˆ1 ∆ˆ2 ∆ˆ3
(cid:16)
+Aˆ3∂ ∂ +Aˆ1∂ ∂ +Aˆ2∂ ∂ V (19)
∆ˆ1 ∆ˆ2 ∆ˆ2 ∆ˆ3 ∆ˆ1 ∆ˆ3 3
(cid:17)
inadditiontoexpressionsobtainedbyappropriatelypermutingtheindices. Onemaythereforerepresent
the correlators hierarchically as
hΨ (z )Υ (z ;0)i = Aˆ1V +∂ hΦ (z )Υ (z ;0)i
1 1 2 2 2 ∆ˆ1 1 1 2 2
5
hΨ (z )Φ (z )i = Aˆ1V +∂ hΦ (z )Φ (z )i
1 1 2 2 2 ∆ˆ1 1 1 2 2
hΨ (z )Ψ (z )i = Aˆ12V +∂ hΦ (z )Ψ (z )i+∂ hΨ (z )Φ (z )i−∂ ∂ hΦ (z )Φ (z )i
1 1 2 2 2 ∆ˆ1 1 1 2 2 ∆ˆ2 1 1 2 2 ∆ˆ1 ∆ˆ2 1 1 2 2
(20)
in the case of two-point conformal blocks, and
hΨ (z )Υ (z ;0)Υ (z ;0)i = Aˆ1V +∂ hΦ (z )Υ (z ;0)Υ (z ;0)i
1 1 2 2 3 3 3 ∆ˆ1 1 1 2 2 3 3
hΨ (z )Φ (z )Υ (z ;0)i = Aˆ1V +∂ hΦ (z )Φ (z )Υ (z ;0)i
1 1 2 2 3 3 3 ∆ˆ1 1 1 2 2 3 3
hΨ (z )Ψ (z )Υ (z ;0)i = Aˆ12V +∂ hΦ (z )Ψ (z )Υ (z ;0)i+∂ hΨ (z )Φ (z )Υ (z ;0)i
1 1 2 2 3 3 3 ∆ˆ1 1 1 2 2 3 3 ∆ˆ2 1 1 2 2 3 3
− ∂ ∂ hΦ (z )Φ (z )Υ (z ;0)i
∆ˆ1 ∆ˆ2 1 1 2 2 3 3
hΨ (z )Φ (z )Φ (z )i = Aˆ1V +∂ hΦ (z )Φ (z )Φ (z )i
1 1 2 2 3 3 3 ∆ˆ1 1 1 2 2 3 3
hΨ (z )Ψ (z )Φ (z )i = Aˆ12V +∂ hΦ (z )Ψ (z )Φ (z )i+∂ hΨ (z )Φ (z )Φ (z )i
1 1 2 2 3 3 3 ∆ˆ1 1 1 2 2 3 3 ∆ˆ2 1 1 2 2 3 3
− ∂ ∂ hΦ (z )Φ (z )Φ (z )i
∆ˆ1 ∆ˆ2 1 1 2 2 3 3
hΨ (z )Ψ (z )Ψ (z )i = Aˆ123V +∂ hΦ (z )Ψ (z )Ψ (z )i+∂ hΨ (z )Φ (z )Ψ (z )i
1 1 2 2 3 3 3 ∆ˆ1 1 1 2 2 3 3 ∆ˆ2 1 1 2 2 3 3
+ ∂ hΨ (z )Ψ (z )Φ (z )i−∂ ∂ hΦ (z )Φ (z )Ψ (z )i
∆ˆ3 1 1 2 2 3 3 ∆ˆ1 ∆ˆ2 1 1 2 2 3 3
− ∂ ∂ hΨ (z )Φ (z )Φ (z )i−∂ ∂ hΦ (z )Ψ (z )Φ (z )i
∆ˆ2 ∆ˆ3 1 1 2 2 3 3 ∆ˆ1 ∆ˆ3 1 1 2 2 3 3
+ ∂ ∂ ∂ hΦ (z )Φ (z )Φ (z )i (21)
∆ˆ1 ∆ˆ2 ∆ˆ3 1 1 2 2 3 3
in the case of three-point conformal blocks. As above, the remaining correlators may be obtained by
appropriately permuting the indices.
3 On SL(2,R) WZW models
The affine sl(2) Lie algebra,including the commutators with the Virasoro modes, reads
k
[J ,J ] = 2J +knδ
+,n −,m 0,n+m n+m,0
[J ,J ] = ±J
0,n ±,m ±,n+m
k
[J ,J ] = nδ
0,n 0,m n+m,0
2
[L ,J ] = −mJ (22)
n a,m a,n+m
Another conventional notation is obtained by replacing {J ,2J ,J } by {E ,H ,F }. The level
+,n 0,n −,n n n n
ofthe algebraisindicatedbyk andisrelatedtothecentralchargeasc=3k/(k+2). Thenon-vanishing
entries of the Cartan-Killing form of sl(2) are given by
1
κ = , κ =κ =1 (23)
00 +− −+
2
and appear as coefficients to the central terms in (22). Its inverse is given by
κ00 =2, κ+− =κ−+ =1 (24)
and comes into play when discussing the affine Sugawara construction below. We will be concerned
mainly with the ‘horizontal’ part of the affine Lie algebra, the sl(2) Lie algebra generated by the zero
modes {J :=J }.
a a,0
We will assume that the Virasoro primary fields of a given conformal weight ∆ may be organized in
multiplets corresponding to spin-j representations of the sl(2) algebra, where
j(j+1)
∆= (25)
k+2
6
In the following, j is takento be real even though the generalformalism is amenable to treat j complex
as well. If 2j is a non-negative integer, we may label the 2j+1 members of the associated multiplet as
in
φ (z), φ (z), ..., φ (z), φ (z) (26)
−j −j+1 j−1 j
where the dependence on j, often indicated by φ , is suppressed. A finite-dimensional representation
j,m
like (26) is often referredto as an integrablerepresentation. The field φ has J eigenvalue m, while we
m 0
will use the following convenient choice of relative normalizations of the fields:
[J ,φ (z)] = (j+m+1)φ (z)
+ m m+1
[J ,φ (z)] = mφ (z)
0 m m
[J ,φ (z)] = (j−m+1)φ (z) (27)
− m m−1
If 2j is not a non-negative integer, the associated primary fields may in general be organized in an
infinite-dimensional multiplet corresponding to an sl(2) representation.
3.1 Generating-function primary fields
A generating function for the 2j + 1 Virasoro primary fields in an integrable representation may be
written [19]
j
φ(z,x) = φ (z)xj−m (28)
m
m=−j
X
To keep the notation simple here and in the following, we do not indicate explicitly whether the sum
is over integers or half-integers as this should be obvious from the integer or half-integer nature of the
spin itself. For general spin and associated infinite-dimensional multiplet, the generating function for a
so-called highest-weight representation, for example, reads
φ(z,x) = φ (z)xj−m (29)
m
m∈X(j+Z≤)
The adjoint action of the affine generators on the generating-function primary field reads
[J ,φ(z,x)] = −znD (x)φ(z,x) (30)
a,n a
where the differential operators D (x) are defined by
a
D (x) = x2∂ −2jx
+ x
D (x) = x∂ −j
0 x
D (x) = −∂ (31)
− x
They generate the Lie algebra sl(2), and one recovers (27) from (30).
A correlatorlike the N-point chiral block
hφ (z ,x )...φ (z ,x )i (32)
1 1 1 N N N
is seen to correspond to a generating function for the individual correlators based on fields, φ (z ),
i,mi i
appearing in expansions like (28) (or (29), for example). That is, the N-point chiral block
hφ (z )...φ (z )i (33)
1,m1 1 N,mN N
appears as the coefficient to N xji−mi in an expansion of (32). The general expansion thus reads
i=1 i
hφ (z ,x )...φ (zQ,x )i = hφ (z )...φ (z )ixj1−m1...xjN−mN (34)
1 1 1 N N N 1,m1 1 N,mN N 1 N
m1,X...,mN
where the ranges of the summation variables depend on the individual spin-j representations.
i
7
3.2 The KZ equations
In a WZW model, the Virasoro generators are realized as bilinear expressions in the affine generators.
This is referred to as the affine Sugawara construction which is here written in terms of modes
1
L = κab J J + J J (35)
N a,n b,N−n a,N−n b,n
2(k+2)
n≤−1 n≥0
X X
Here and in the following, we will use the convention of summing over appropriately repeated group
indices, a = ±,0. Acting on a highest-weight state, the affine Sugawara construction gives rise to
singular vectors of the combined algebra. The decoupling of these is trivial for N > 0. For N = 0, it
reproduces the relation (25) as the eigenvalue of L is equated with the eigenvalue of the normalized
0
quadratic Casimir:
κabD (x)D (x) j(j+1)
a b
∆ = = (36)
2(k+2) k+2
The condition correspondingto N =−1 leads to the celebratedKZ equations [10] which are written
here for an N-point chiral block of generating-function primary fields
0 = KZ hφ (z ,x )...φ (z ,x )i, i=1,...,N (37)
i 1 1 1 N N N
where
κabD (x )D (x )
a i b j
KZ = (k+2)∂ − (38)
i zi z −z
i j
j6=i
X
These N differential equations associated to a given N-point chiral block are not all independent. This
is easily illustrated by considering the sum
N N
KZ = (k+2) ∂ (39)
i zi
i=1 i=1
X X
which merely induces translationalinvariance alreadyimposed by the first conformalWard identity (5).
As we will discuss below, a simple modification of the KZ equations (37), (38) apply to correlators
involving certain logarithmic fields to be introduced in the following.
4 Affine Jordan cells
WewishtoconsiderthesituationwhereeveryVirasoroprimaryfieldinagivensl(2)representationmay
have a logarithmic partner. The resulting multiplet of fields is comprised of primary fields as well as
so-called logarithmic fields and will be referred to as an affine Jordan cell. A priori, the hosting model
may consist of a family of affine Jordan cells in coexistence with an independent family of multiplets
of primary fields without logarithmic partners. We will refer loosely to such a model as a logarithmic
WZW model. Primary fields not appearing in an affine Jordan cell will be called non-cellular primary
fields. It is found that the affine Jordan cells relevant to our studies contain primary fields not having
logarithmic partners. These primary fields are naturally included in the generating functions for the
logarithmic fields rather than in the generating functions for the primary fields comprising the original
spin-j representationwe are extending. To reachthis appreciationof the affine Jordancells, we initially
consider an extension of the differential-operatorrealization(31) and its role in a generalizationof (30).
8
4.1 Generating-function unified cells
The differential-operator realization
D (x;θ) = x2∂ −2(j+θ)x
+ x
D (x;θ) = x∂ −(j+θ)
0 x
D (x;θ) = −∂ (40)
− x
of the Lie algebra sl(2) is designed to act on a representation of (generalized) spin j +θ, where θ is a
nilpotent, yet even, parameter satisfying θ2 = 0. Extending the idea of organizing fields in generating
functions as in (28) satisfying (30), we introduce the formal generating-function unified cell Υ(z,x;θ)
satisfying
[J ,Υ(z,x;θ)] = −D (x;θ)Υ(z,x;θ) (41)
a a
Wenotethatthisalsoappliestogenerating-functionprimaryfieldsasitreducesto(30)(forn=0)when
we set θ = 0. Here and in the following, focus is on the sl(2) Lie algebra part of the affine generators.
An expansion of the generating-function unified cell with respect to θ may be written
Υ(z,x;θ) = Φ(z,x)+θΨ(z,x) (42)
resembling the definition of the unified cell (3) in logarithmic CFT. In terms of the new generating
functions, Φ(z,x) and Ψ(z,x), the commutators (41) read
[J ,Φ(z,x)] = −D (x)Φ(z,x)
+ +
[J ,Ψ(z,x)] = −D (x)Ψ(z,x)+2xΦ(z,x)
+ +
[J ,Φ(z,x)] = −D (x)Φ(z,x)
0 0
[J ,Ψ(z,x)] = −D (x)Ψ(z,x)+Φ(z,x)
0 0
[J ,Φ(z,x)] = −D (x)Φ(z,x)
− −
[J ,Ψ(z,x)] = −D (x)Ψ(z,x) (43)
− −
where the differential operators,D (x), are given in (31).
a
These commutators severely restrict the set of sl(2) representations for which the two fields Φ(z,x)
and Ψ(z,x) can be considered generating functions. It is beyond the scope of the present work,though,
to classify these representations, even in the simple case where Φ(z,x) is the generating function for a
finite-dimensional representation as in (28). We hope to address this classification elsewhere. Here we
merely wish to demonstrate the existence of representations corresponding to the generating functions
(42), (43) and to illustrate their complexity. We will do so by considering a particular logarithmic
extensionofa finite-dimensionalspin-j representation. Moregeneralexamples areconsideredinSection
4.2.
We thus introduce the following expansions of the generating functions Φ(z,x) and Ψ(z,x):
j j
Φ(z,x) = Φ (z)xj−m, Ψ(z,x) = Ψ (z)xj−m (44)
m m
m=−j m=−∞
X X
The remark following (28) about m taking on integer or half-integer values also applies when one (or
even both) of the summation bounds is (either plus or minus) infinity. As already mentioned, we are
concernedwithJordancellswhoseprincipalpartscorrespondtofinite-dimensionalspin-jrepresentations,
here governed by the generating function Φ(z,x). It is noted that the logarithmic part, on the other
hand, consists of infinitely many fields.
With the understanding that Φ (z) only exists for m = −j,...,j while Ψ (z) only exists for m =
m m
−∞,...,j, the adjoint actionof the sl(2)Lie algebraon the modes of the two generatingfunctions (44)
9
