9. GAUGE THEORIES 25
the renormalization group flow. In addition, one requires that the effective
actions
Seff
[Λ] satisfy a locality axiom, as before.
This picture also solves the problem that the low energy gauge symme-
tries are not a group. The energy Λ effective action
Seff
[Λ], satisfying the
energy Λ quantum master equation, gives the extended space of low-energy
fields a certain homotopical algebraic structure, which has the following in-
terpretation:
(1) The space of low-energy infinitesimal gauge symmetries has a Lie
bracket.
(2) This Lie algebra acts on the space of low-energy fields.
(3) The space of low-energy fields has a functional, invariant under the
bracket.
(4) The action of the Lie algebra on the space of fields, and on itself,
preserves the Lebesgue measure.
However, these axioms don’t hold on the nose, but hold up to a sequence of
coherent higher homotopies.
9.5. Let us now formalize our definition of a gauge theory. As we have
seen, whenever we have the data of a classical gauge theory, we get an
extended space of fields, that we will denote by E . This is always the space
of sections of a graded vector bundle on the manifold M. As before, let E≤Λ
denote the space of low-energy extended fields.
Definition 9.5.1. A theory in the BV formalism consists of a set of
low-energy effective actions
Seff
[Λ] : E≤Λ R[[ ]],
which is a formal series both in E≤Λ and , and which is such that:
(1) The renormalization group equation is satisfied.
(2) Each
Seff
[Λ] satisfies the energy Λ quantum master equation.
(3) The same locality axiom as before holds.
(4) There is one more technical restriction : modulo , each
Seff
[Λ] is
of the form
Seff
[Λ](e) = e, Qe + cubic and higher terms
where −, is a certain canonical pairing on E , and Q : E E
satisfies certain ellipticity conditions.
As before, the locality axiom needs to be expressed in length-scale terms.
The main theorem holds in this context also, but in a slightly modified
form. If we remove the requirement that the effective actions satisfy the
quantum master equation, we find a bijection between theories and local
action functionals, depending on the choice of a renormalization scheme,
as before. Requiring that the effective actions satisfy the QME leads to a
constraint on the corresponding local action functional, which is called the
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