. 7
( 8)


where S(x, y, z) is 4 times the symplectic area of the triangle with vertices x, y and
The von Neumann integral formula gives a well-de¬ned product on various
spaces of functions, including Schwartz functions, smooth functions whose par-
tial derivatives of all orders are bounded, and Λ-periodic smooth functions on E

where Λ is a lattice, i.e. smooth functions on a torus E/Λ. This product does not
extend to continuous functions on E/Λ, but it is possible to complete C ∞ (E/Λ)
to a noncommutative C — algebra called “the continuous functions on a quantum
torus” [144].

20.3 A¬ne Invariance of the Weyl Product

The Weyl product on a Poisson vector space (E, Π) is invariant under a¬ne Poisson
maps, i.e. if A : E ’ E is an a¬ne symplectic map, then the induced pull-back
A— : C ∞ (E)[[ ]] ’’ C ∞ (E)[[ ]]
is an algebra automorphism for the Weyl product.
By a¬ne invariance, the Weyl product (on the Weyl algebra or any of the
other related spaces of functions mentioned at the end of the previous section)
passes to any Poisson manifold locally modeled on E, as long as we only allow
a¬ne coordinate changes. This condition on E amounts to the existence of a
¬‚at connection without torsion, for which parallel transport preserves the Poisson
The in¬nitesimal counterpart of a¬ne invariance is that, for every polynomial
function k on E of degree less than or equal to 2,

{f {g, k} + {f, k}
g, k} = f g.

In words, {·, k} is a derivation not just of the pointwise product (Leibniz identity)
and of the Poisson bracket (Jacobi identity), but of the whole -product.
Remark. Dirac™s [44] quantum Poisson bracket

f f
[f, g] :=
satis¬es the derivation law

[f g, k] = f [g, k] + [f, k] g

just as a consequence of associativity. The similar property for {·, k} is explained
by the fact that, for a polynomial k on E of degree ¤ 2, we have [·, k] = {·, k}.
In particular, for k1 and k2 polynomials of degree ¤ 2, we have [k1 , k2 ] =
{k1 , k2 }, which shows that polynomials of degree ¤ 2 form a Lie algebra. ™¦

20.4 Derivations of Formal Weyl Algebras

Let F (E)[[ ]] be the space of formal power series on the vector space E, thought
as an algebra over C[[ ]].
A theorem of E. Borel states that every formal power series is the Taylor ex-
pansion of some function. This implies that the space F (E) of formal power series
on the vector space E is isomorphic to C ∞ (E) modulo the functions which vanish
to in¬nite order at 0.
20.5 Weyl Algebra Bundles 153

Theorem 20.1 Suppose that Π is a non-degenerate Poisson structure on E. Then
every derivation D of F (E)[[ ]] such that D = 0 is of the form [·, f ] for some
f ∈ F (E)[[ ]].

Exercise 78
Prove this theorem. Hints:
A derivation D is determined by its e¬ect on generators of the algebra
q1 , . . . , qn , p1 , . . . , pn . Notice that qi , pi have degree ¤ 2. Suppose that
D = [·, f ] were a inner derivation. Then
{qi , f }
Dqi = [qi , f ] = = ‚pi
{pi , f } ’ ‚q
Dpi = [pi , f ] = =

To ¬nd the element f , we must solve
df = (Dqi )dpi ’ (Dpi )dqi
for f . If the right-hand side is closed, then the left-hand side will be determined
up to an element in the center C[[ ]] of C ∞ (E)[[ ]]. Let us check that the right-
hand side is closed:
‚ ‚
’{pj , Dqi } + {qi , Dpj }
(Dqi ) + (Dpj ) =
‚qj ‚pi
= [Dqi , pj ] + [qi , Dpj ]
= D[qi , pj ] = D(δi,j ) = 0 .
To ¬nish the proof that D = [·, f ] , consider the ¬ltration of F (E) by ideals
Ak generated by the homogeneous polynomials of degree k. Show that, if D is
a derivation, then DAk ⊆ Ak’1 [[ ]].

Let (E, Π) be a Poisson vector space, and let • be an automorphism of the Weyl
algebra C ∞ (E)[[ ]] as a C[[ ]]-algebra..
The term in • of 0-th order in shows that • induces an automorphism of

C (E), hence a di¬eomorphism of E.
The term in • of ¬rst order in shows that this di¬eomorphism is a Poisson
automorphism of (E, Π).
We hence obtain an exact sequence
E Aut(C ∞ (E)[[ ]]) E P(E, Π)
1 E1

where P(E, Π) is the set of Poisson automorphisms of (E, Π). The kernel I of the
third arrow is the group of inner automorphisms of C ∞ (E)[[ ]] corresponding to
invertible elements of C ∞ (E)[[ ]] [59].

20.5 Weyl Algebra Bundles

Let (E, ρ, [·, ·]E ) be a Lie algebroid over a manifold M , with symplectic structure ω ∈
“(§2 E — ). The symplectic E-2-form ω is non-degenerate and dE ω = 0; it determines
an E-Poisson structure Π (see Section 18.3) by Π = ω ’1 , and an ordinary Poisson
structure ρ(Π) on T M .
Let W E be the Weyl algebra bundle over M whose ¬ber at x ∈ M is the
formal Weyl algebra of the symplectic (hence Poisson) vector space Ex . The smooth
sections of W E are those for which the coe¬cient of each term is a smooth function
on M ; they form an algebra under ¬berwise multiplication. We think of “(W E)
as “functions on the quantized E”. Locally, we write a typical section as f (x, y, ),
where x ∈ M , y is a formal variable in Ex , and is another formal parameter. (The

constant is taken the same on each ¬ber, just as Planck™s constant is a universal
From now on, to simplify, we will analyze the case where E = T M is the tangent
bundle of M . Everything works for the general Lie algebroid case [126].
Interpret “(W T M ) as the space of smooth functions on the “quantized tangent
“(W T M ) = C ∞ (Q T M ) .
The zero section is the map

C ∞ (Q T M ) E C ∞ (M )[[ ]]

given by evaluation at y = 0. We may think of Q T M as an in¬nitesimal neighbor-
hood of the zero section.
In the next chapter, we will describe the quantization method of Fedosov, in
which C ∞ (M )[[ ]] is identi¬ed with a subalgebra of “(W T M ). The Weyl product
is then carried back to C ∞ (M )[[ ]] to give a deformation quantization.
Geometrically, a subalgebra of “(W T M ) annihilated by a Lie algebra of deriva-
tions corresponds to a “foliation” of Q T M . The foliation is transverse to the ¬bers
when the derivations are of the form X as X ranges over the vector ¬elds on M ,
de¬ning a ¬‚at connection on the bundle W T M itself.
When the foliation is transverse to the zero section as well, parallel sections of
W T M are in one-to-one correspondence with elements of C ∞ (M )[[ ]]. Notice that
a ¬‚at linear connection on T M would not work: parallel sections of a ¬‚at connection
on C ∞ (T M ) correspond to functions on a tangent ¬ber, not C ∞ (M )[[ ]] as we need.
Example. Let (M, ω) be a symplectic vector space with coordinates x. De¬ne
the connection by
‚ ‚

= ,

‚xi ‚yi

where y are the tangent coordinates induced by x. Lift functions u(x) and v(x) on
M to u(x + y) and v(x + y) on T M . To evaluate (u v)(x0 ), freeze the x variable
at x0 , take the Weyl product with respect to y, and then set y = 0 to obtain a
function on M . This recipe reproduces the usual Weyl product.
21 Deformation Quantization
On a general Poisson manifold, if the rank of the Poisson tensor Π is constant, then
by a theorem of Lie the Poisson manifold is locally isomorphic to a vector space
with constant Poisson structure (see Section 3.4). Such Poisson manifolds, which
are called regular, are always locally deformation quantizable using the Moyal-
Weyl product in canonical coordinates; the problem is to patch together the local
deformations to produce a global -product.

21.1 Fedosov™s Connection

There is one case in which the patching together of local quantizations is easy.
Since the Moyal-Weyl product on a vector space V with constant Poisson structure
is invariant under all the a¬ne automorphisms of V , we can construct a global
quantization of any Poisson manifold (M, Π) covered by canonical coordinate sys-
tems in the general case for which the transition maps are a¬ne. Such a covering
exists when M admits a ¬‚at torsionless linear connection for which the covariant
derivative of Π is zero.
Fedosov overcomes the di¬culty of patching together local Weyl structures by
making the canonical coordinate neighborhoods “in¬nitely small”. To understand
his idea, we should ¬rst think of elements of the deformed algebra C ∞ (T M )[[ ]] as
sections of the bundle W T M over M whose ¬ber at x ∈ M is W Tx M .
Of course we are most interested in dealing with the case where (M, Π) does
not admit a ¬‚at Poisson connection, and this is where the most interesting part of
Fedosov™s proof comes in. He shows (in other terms) that the tangent bundle of
every symplectic (or regular Poisson) manifold does admit a ¬‚at Poisson connection,
if one gives the appropriate extended meaning to that concept, namely admitting
“nonlinear quantum maps” as the structure group.
Fedosov™s connection is constructed on the bundle W T M of Weyl algebras.
The “structure Lie algebra” of this connection, in which the connection forms take
values, is W R2n acting on itself by the adjoint representation of its Lie algebra
structure. Since the full Weyl algebra is used, and not just the quadratic functions
which generate linear symplectic transformations, the structure group allows non-
linear transformations of the (quantized) tangent spaces. Since linear generating
functions are included, the structure group even allows translations.
In fact (this idea was also used in [133]), it is not the full Weyl algebra of
R which serves as the typical ¬ber, but only the formal Weyl algebra F (W R2n ),

consisting of formal Taylor expansions at the origin. Geometrically, one can think
of this step as the replacement of the (quantized) tangent bundle by a formal
neighborhood of the zero section T M .
Remark. Since T M is an in¬nitesimal neighborhood of the zero section, parallel
transport does not go anywhere. This step may hence appear to be inconsistent
with the inclusion of translations in the structure group, since these do not leave
the origin ¬xed. In fact, the e¬ect is to force us to forget the group and to work only
with the structure Lie algebra. A bene¬cial, and somewhat surprising, result of this
e¬ect is that a parallel section with respect to a ¬‚at connection is not determined by
its value at a single point. This situation is very close to that in formal di¬erential
geometry, where the bundle of in¬nite jets of functions on a manifold M has a ¬‚at


connection whose sections are the lifts of functions on M . (See [160, Section 1] for
a nice exposition with references.)
Fedosov uses an iterative method for “¬‚attening” a connection which is similar
to that used in many di¬erential geometric problems. (See [119] for an example,
and [147] for a recent survey.) Over the domain of a local trivialization of a principal
G-bundle, a connection is given by a 1-form φ with values in the Lie algebra g; the
curvature of the connection is the Lie algebra valued 2-form
„¦φ = dφ + [φ, φ] .
If the curvature is not zero, we may try to “improve” the connection by adding
another Lie algebra valued 1-form ±. The curvature zero condition for φ + ± is the
quadratic equation
d± + [φ, ±] = ’„¦φ ’ [±, ±] .
Rather than trying to solve this equation exactly, we linearize it by dropping the
term ’ 1 [±, ±]. The operator d + [φ, ·] is the covariant exterior derivative Dφ , so
our linearized equation has the form

Dφ ± = ’„¦φ .

From the Bianchi identity, Dφ „¦φ = 0, it appears that the obstruction to solving
the equation above for ± lies in a cohomology space. This is not quite correct, since
Dφ = [„¦φ , ·], which is not zero because the connection φ is not yet ¬‚at.
Up to now, we have essentially been following Newton™s method for solving
nonlinear equations. At this point, we add an idea similar to one often attributed
to Nash and Moser. (See [155, Section III.6] for an exposition of this method with
original references.) Since the linear di¬erential equation we are trying to solve
is only an approximation to the nonlinear one which we really want to solve, we
do not have to solve it precisely. It is enough to solve it approximately and to
compensate for the error in the later iterations which will in any case be necessary
to take care of the neglected quadratic term ’ 2 [±, ±]. Such approximate solutions
are constructed by some version of the Hodge decomposition. In the di¬erential
geometric applications mentioned above, the full story involves elliptic di¬erential
operators, Sobolev spaces, and so on, but in the case at hand, it turns out that the
“Hodge theory” is purely algebraic and quite trivial.

21.2 Preparing the Connection

We now start the construction of a ¬‚at connection on the bundle of Weyl algebras
by an iteration procedure. All the constructions are intrinsic, but for simplicity we
will describe them in local canonical coordinates.

Step 1 We begin with an arbitrary (linear) Poisson connection on the tangent
bundle of the symplectic manifold M .
The connection induces a covariant di¬erentiation operator on the dual
bundle, i.e. on the linear functions on ¬bers. In coordinates (x1 , . . . , xm )
on M :
‚ ‚
= “ijk ωk .

‚xi ‚x ‚x
21.2 Preparing the Connection 157

We introduce the coe¬cients (ωk ) of the symplectic form to lower the
last index. For convenience, we assume that ωk is constant (i.e. the xi ™s
are Darboux coordinates).
If the connection has torsion, we can make it torsion-free by symmetriza-
tion [59]
“ijk + “jik
“ijk .
Because this is a symplectic connection, symmetry in the last two indices
comes for free: “ijk = “ikj .

Step 2 The connection form is a 1-form with values in the Lie algebra of the
symplectic group sp(m). The elements of sp(m) may be identi¬ed with
linear hamiltonian vector ¬elds on the manifold and hence with quadratic
functions. Thus the connection form can be written as
“ijk yi yj — dxk ,
φ’1 =
where (y1 , . . . , ym ) is a basis of linear functions on the ¬bers correspond-
ing to the coordinates (x1 , . . . , xm ) on M .

Step 3 The symplectic connection lifts to the Weyl algebra bundle. A co-
variant di¬erentiation D on the Weyl algebra bundle is described with
respect to a local trivialization by

Du = du + ψu

for a local section u, where ψ is a 1-form with values in Der(W T M ). We
can rewrite this local expression in the form

Du = du + [φ, u] ,

where now φ is a 1-form with values in W T M itself, and [·, ·] is (1/i )
times the commutator bracket; the bracket [·, ·] is the quantum Poisson
bracket of Dirac [44]de¬ned in Section 20.3. The generator φ of this
“inner derivation” is determined up to a 1-form on M with values in the
center C[[ ]] of the Weyl algebra.

Step 4 If we consider the form φ’1 (with the yi ™s now interpreted as formal
variables) as taking values in the bundle F W (T M ),

φ’1 ∈ “(T — M — F W (T M ))

becomes the connection form for the associated connection on that bun-
dle. Even if this connection were ¬‚at, it would not be the correct one to
use for quantization, since its parallel sections would not be identi¬able
in any reasonable way with functions on M . Instead we must use for our
¬rst approximation

“ijk yi yj ) — dxk .
φ0 = ( ωkj yj + 2

Step 5 To start the recursion, one calculates, using the fact that the connection
is symplectic and torsion free (see [57]), that its curvature is

dφ0 + 1 [φ0 , φ0 ]
„¦0 = 2
’1 1
ωir — dxi § dxr + Rijkl yi yj — dxk § dxl
= 2 4
’1 — ω + R ,

where R is the curvature of the original linear symplectic connection,
considered as a 2-form with values in the Lie algebra of quadratic func-
tions. The term linear in y vanishes because the torsion is zero. The
term ’1—ω appears even when the linear connection is ¬‚at, but it causes
no trouble because it is a central element of the Weyl Lie algebra and
therefore acts trivially in the adjoint representation.

21.3 A Derivation and Filtration of the Weyl Algebra

The coe¬cients of the connection forms which we are using are sections of the bun-
dle F W (T M ). Rather than measuring the size of these forms by the usual Sobolev
norms involving derivatives, we shall use a pointwise algebraic measurement.
In the formal Weyl algebra F W (V ) of a Poisson vector space V , we assign
degree 2 to the variable and degree 1 to each linear function on V . We denote
by F Wr (V ) the ideal generated by the monomials of degree r. Because the kth
term in the expansion of the -product involves 2k derivatives and multiplication
by k , we obtain a ¬ltration of the algebra F W (V ). We will also occasionally use
the classical grading, compatible with the commutative multiplication but not with
the -product, which assigns degree 0 to and 1 to each linear function on V .
The Lie algebra structure which we use for the formal Weyl algebra is the
quantum Poisson bracket of Dirac [44] de¬ned in Section 20.3. The factor (1/i )
makes the quantum bracket reduce to the classical one (rather than to zero) when
’ 0. In addition, the quantum and classical brackets are equal when one of the
entries contains only terms linear or quadratic in the variable on V , and they share
the property
[F Wr (V ), F Ws (V )] ⊆ F Wr+s’2 (V ) ,
so that the adjoint action of any element of F W2 (V ) preserves the ¬ltration.
We introduce the algebra

W(V ) = F W (V ) — §— (V )

whose elements may be regarded as di¬erential forms on the “quantum space whose
algebra of functions is F W (V )”. The algebra W(V ) inherits a ¬ltration by sub-
spaces Wr (V ) from the formal Weyl algebra, and a grading from the exterior al-
gebra. We can also consider W(V ) as the algebra of in¬nite jets at the origin of
di¬erential forms on the classical space V , in which case we generally use the classi-
cal grading. In this way, W(V ) inherits the exterior derivative operator, which we
denote by δ. Remarkably, δ is also a derivation for the quantized algebra structure
on W(V ).
We may describe the operator δ in terms of linear coordinates (x1 , . . . , xm )
on V . With an eye toward the case where V is a tangent space, we denote the
corresponding formal generators of F W (V ) by (y1 , ..., ym , ) and the generators of
21.3 A Derivation and Filtration of the Weyl Algebra 159

§— (V ) by (dx1 , . . . , dxm ). Then W(V ) is formally generated by the elements yi — 1,
— 1, and 1 — dxi , and we have

δ(yi — 1) = 1 — dxi , δ( — 1) = 0 , and δ(1 — dxi ) = 0 .

Notice that δ decreases the Weyl algebra ¬ltration degree by 1 while it increases
the exterior algebra grading by 1.
Since δ is essentially the de Rham operator on a contractible space, we expect
the cohomology of the complex which it de¬nes to be trivial. Fedosov makes this
explicit by introducing the dual operator δ — of contraction with the Euler vector
¬eld i yi — ‚xi . More precisely, δ — maps the monomial yi1 · · · yip — dxj1 § · · · § dxjq

(’1)k’1 yi1 · · · yip yjk — dxj1 § · · · § dxjk § · · · § dxjq .

(This operator is not a derivation for the quantized algebra structure.) A simple
computation (or the Cartan formula for the Lie derivative by the Euler vector ¬eld)
shows that, on the monomial above, we have

δδ — + δ — δ = (p + q)id ,

so that if we de¬ne the operator δ ’1 to be p+q δ — on the monomial above, and 0 on

1 — 1, we ¬nd that each element u of W(V ) has the decomposition

u = δδ ’1 u + δ ’1 δu + Hu ,

where the “harmonic” part Hu of u is the part involving only powers of and
no yi ™s or dxi ™s, i.e. the pullback of u by the constant map from V to the origin.
In other words, we have reproduced the usual proof of the Poincar´ lemma via a
homotopy operator δ from H to the identity.
When the Poisson vector space V is symplectic, the operator δ has another
description. For any a ∈ F W (V ), [yi , a] = {yi , a} = j πij (‚a/‚yj ). If (ωij ) is the
matrix of the symplectic structure, inverse to (πij ), we get ‚a/‚yi = [ j ωij yj , a],
and hence

δ(a — 1) = (‚a/‚yi ) — dxi = [ ωij yj — dxi , a — 1] .
i ij

It follows from the derivation property that a similar equation holds for any element
of W(V ); i.e. the operator δ is equal to the adjoint action of the element ij ωij yj —
dxi (which is just the symplectic structure itself).
Of course, all the considerations above apply when V is replaced by a symplectic
vector bundle E and W(V ) by the space of sections of the associated bundle

W(E) = F W (E) — §— (E) .

In particular, when E is the tangent bundle of a symplectic manifold M , the op-
erator δ and its relatives act on the algebra of di¬erential forms on M with values
in F W (T M ). These operators are purely algebraic with respect to the variable in
M , with δ being just the adjoint action of the symplectic structure viewed as an
F W (T M )-valued 1-form.

21.4 Flattening the Connection
Following Section 21.2, we next try to construct a convergent (with respect to
the ¬ltration) sequence φn of connections whose curvatures „¦n tend to the central
element ’1 — ω. Fedosov calls this central element the Weyl curvature of the
limit connection; to simplify notation, we will write „¦ = „¦ + 1 — ω for the form
which should be zero, and we call this the e¬ective curvature.

Step 6 As suggested in Section 21.1, we let

φn+1 = φn + ±n+1 ,

where ±n+1 is a section of W(T M ).
The corresponding curvature is

dφn+1 + 1 [φn+1 , φn+1 ]
„¦n+1 = 2
„¦n + d±n+1 + [φn , ±n+1 ] + 1 [±n+1 , ±n+1 ]
= 2
Dn ±n+1

where Dn = Dφn = d + [φn , ·]. Instead of solving
Dn ±n+1 = ’„¦n ’ 2 [±n+1 , ±n+1 ] ’ 1 — ω ,

we drop the quadratic term and look at the simpler equation

Dn ±n+1 = ’„¦n ’ 1 — ω .

This would solve approximately the linearized equation for zero e¬ective
Dn ±n+1 + „¦n = 0 .

The operator Dn = Dφn will have the form d + δ + [cn , ·], where cn
Step 7
is an F W (T M )-valued 1-form. We will try to arrange for cn to lie in
F W2 (T M ) so that the operator [cn , ·], like d, is ¬ltration preserving.
Since δ lowers the ¬ltration degree by 1, the principal part of the di¬er-
ential operator Dn will actually be the algebraic operator δ (and not d
as it would be if we measured forms by the size of their derivatives.)
We cannot even solve
δ±n+1 + „¦n = 0
exactly, because the Bianchi identity gives Dn „¦n = 0 instead of δ „¦n = 0.
(The term 1 — ω is killed by both operators.) Nevertheless, we de¬ne

±n+1 = ’δ ’1 („¦n ) ,

and take care of the errors later.
Step 8 From the recursion relation
„¦n+1 = „¦n + Dn ±n+1 + 2 [±n+1 , ±n+1 ] ,

we ¬nd after a straightforward calculation using the decompositions

u = δδ ’1 u + δ ’1 δu + Hu
Dn = d + δ + [cn , ·] and
21.5 Classi¬cation of Deformation Quantizations 161


δ ’1 δ „¦n
„¦n+1 =
+H„¦n + d±n+1 + [cn , ±n+1 ] + 1 [±n+1 , ±n+1 ] .

Using Dn = d + δ + [cn , ·] again, we can rewrite this as

δ ’1 Dn „¦n ’ δ ’1 d„¦n ’ δ ’1 [cn , „¦n ]
„¦n+1 =
+H„¦n + d±n+1 + [cn , ±n+1 ] + 1 [±n+1 , ±n+1 ] .

By the Bianchi identity Dn „¦n = 0, we get

„¦n+1 = H„¦n ’δ ’1 d„¦n ’δ ’1 [cn , „¦n ]+d±n+1 +[cn , ±n+1 ]+ 1 [±n+1 , ±n+1 ] .

Suppose now that „¦n ∈ Wr (T M ) with r ≥ 1. Then H„¦n = 0 and
±n+1 ∈ Wr+1 (T M ), so that cn ∈ W2 (T M ) and hence all the terms on
the right hand side of the equation above belong to Wr+1 (T M ).

Step 9 Since „¦0 = R has ¬ltration-degree 2, we conclude that „¦n has degree
at least n + 2, and ±n+1 has degree at least n + 3, so the sequence φn
converges to a connection form

φ = φ0 + ±1 + ±2 + . . .

for which the curvature is „¦ = ’1 — ω. This curvature is a central
section, so the connection on F W (T M ) associated to φ by the adjoint
representation F W (T M ) is ¬‚at. Since the adjoint action is by deriva-
tions of the multiplicative structure, the space of parallel sections is a
subalgebra of the space of all sections.

Step 10 The last step in Fedosov™s construction is to show by a recursive con-
struction, similar to the one above, that each element of C ∞ (M )[[ ]]
is the harmonic part of a unique parallel section of F W (T M ), so that
C ∞ (M )[[ ]] is identi¬ed with the space of parallel sections and thus
inherits from it an algebra structure, which is easily shown to be a de-
formation quantization associated with the symplectic structure ω.

21.5 Classi¬cation of Deformation Quantizations

Fedosov [59] showed that his iterative construction of a connection on F W (T M )
—ωj , for any sequence of closed
can be modi¬ed so that the curvature becomes
2-forms ωj such that ω0 is the original symplectic structure ω. He also showed that
the isomorphism class of the resulting -product depends precisely on the sequence
of de Rham cohomology classes [ωj ] ∈ H 2 (M, R) and in particular is independent
of the initial choice of connection φ0 .
In summary, the relevant data for an equivalence class of deformation quanti-
zations on a manifold M is
ω , [ω1 ] , [ω2 ] , . . .
A representative of such an equivalence class is called a Fedosov quantization of

This left open the question of whether every -product is isomorphic to one ob-
tained by Fedosov™s construction. A positive answer to this question has been given
by Nest and Tsygan. Using a noncommutative version of Gel™fand-Fuks cohomol-
ogy, they construct in [124] for each deformation quantization a characteristic class
in H 2 (M, R)[[ ]] with constant term ω. In [125], they show that this class deter-
mines the -product up to isomorphism and that it agrees with Fedosov™s curvature
for the -products constructed by his method. By Moser™s classi¬cation [121] of
nearby symplectic structures by their cohomology classes, the isomorphism classes
of -products on a symplectic manifold are thus in one-to-one correspondence with
isomorphism classes of formal deformations of the symplectic structure. Other ref-
erences concerning this classi¬cation are Bertelson-Cahen-Gutt [15] Kontsevich [97],
and Weinstein-Xu [173].
One consequence of this classi¬cation is that there is (up to isomorphism) a
unique deformation quantization whose characteristic class is independent of .
Although one might think that this special quantization is somehow the natural
one, there is considerable evidence that the others are important as well. For
instance, [54] suggests that -products with nonconstant characteristic classes may
be related to geometric phases and deformations of symplectic forms which arise in
the analysis of coupled wave equations [107].
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ee a
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action Baer groupoid, 91
Baer, A., 91
coadjoint, 39
Berezin, F. A., 81, 82
e¬ective, 8
bisection, 106, 107
free, 8
bivector ¬eld, 12
groupoid, 90, 101
Borel groupoid, 93
groupoid algebra action, 103
Borel, E., 152
hamiltonian, 39
linear action, 102
cobracket, 132
of a groupoid bisection, 107
commutator, 150
of a Lie algebra, 8
Dirac™s quantum Poisson, 152, 157
right, 8
E-Gerstenhaber bracket, 133
Gerstenhaber, 141
operation, 47
Gerstenhaber bracket on Hochschild
representation of C ∞ (M ), 14
cohomology, 143
admissible section, 106
Lie-Poisson, 11
Albert, C., 108
on alternating multilinear maps,
center, 50
Poisson, 149
dual pair, 50
properties of [·, ·]E , 133
factor, 50
Schouten-Nijenhuis, 12, 135, 144
von Neumann, 49
Brandt groupoid, 87
Weyl, 149
Brandt, W., 87, 89
Almeida, R., 118
of groups, 93
commutativity of the universal en-
of Lie algebras, 114, 116
veloping algebra, 5
of Lie groups, 116
complex structure, 120
Lie algebra, 7 canonical
Poisson structure, 12 coordinate, 14
symplectic manifold, 20 1-form, 36
±-density, 77 Poisson relation, 14
anchor map symplectic structure on a cotan-
de¬nition, 113 gent bundle, 36, 119
image, 113 Cartan™s magic formula, 21, 126, 159
injective, 115 ´
Cartan, E., 9
kernel, 113 Casimir function, 14, 16, 136
surjective, 123 Cauchy-Riemann structure, 121
antipode, 69 center, 50
Arnold, V., 26 Chevalley cohomology, 132, 142
associativity Chevalley complex, 142
associative structure, 142 Chevalley-Eilenberg cohomology, 142
coassociativity, 70 classical observables, 151
of the cup product, 142 classical Yang-Baxter equation, 135
Atiyah algebra, 123 co-commutativity of the coproduct, 82
Atiyah sequence, 123 co-unit or coidentity, 69
Atiyah, M., 121, 123 coadjoint


action, 39 form, 124
orbit, 39 iterative construction, 156, 160
coarse groupoid, 87 on a Lie algebroid, 124
coboundary, 43 on a transitive Lie algebroid, 124
cobracket, 132 torsionless ¬‚at Poisson, 155
cochain, 43 Connes, A., 89
cocycle, 43 conormal space, 25
cohomology convolution
Chevalley, 132, 142 of functions, 75
Chevalley-Eilenberg, 142 of measures, 73, 98
de Rham, 23 coproduct
E-cohomology, 132 co-commutativity, 82
E-Π-cohomology, 136 de¬nition, 69
Gel™fand-Fuks, 162 CR-functions, 121
Harrison, 142 CR-structure, 121
C — -algebra
Hochschild, 142
Lie algebra, 132, 142 de¬nition, 47
Lie algebroid, 132, 136 groupoid, 98
Poisson, 16 cup product
Poisson cohomology on a Lie al- associativity, 142
gebroid, 136 of multilinear maps, 142
squaring map, 139 on Hochschild cohomology, 143
coisotropic, 34 supercommutativity, 143
collective function, 66 curvature
commutant e¬ective, 160
de¬nition, 49 form, 124
double, 50 Lie algebroid, 124
double commutant theorem, 50 Weyl, 160
Poisson geometry, 51
Darboux™s theorem, 20, 21
commutative Hopf algebra, 72
Dazord, P., 108, 117
compact operator, 48
compatible equivalence relation, 34
Lie algebra, 2
obstructions, 143
Poisson map, 31
of products, 144
symplectically complete foliation,
of products of functions, 144, 146
quantization, 6, 144, 146, 155
quantization of R2n , 151
coordinates in symplectic geom-
theory, 141
etry, 62
degenerate Lie algebra, 26
Lie algebroid, 120
structure, 120
multilinear map, 141
of [·, ·]E , 133
Chevalley, 142
of dE , 131
Hochschild, 142
of an E-di¬erential form, 131
complexi¬ed tangent bundle, 62


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