nLab quantum anomaly




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There are at least two things that are called quantum anomalies in the context of quantum field theory


Anomalous action functional

There are two major kinds of action functionals that may be anomalous in that they are not actually functions/functionals on the configuration space of fields, but just sections of some line bundle:

Fermionic anomalies

The path integral for a quantum field theory with fermions can be decomposed into a fermionic path integral (see there for more details) over the fermionic fields followed by that over the bosonic fields. The former, a Berezin integral, is typically well defined for a fixed configuration of the bosonic fields, but does not produce a well defined function on the space of all bosonic fields: but a twisted function, a section of some line bundle called a determinant line bundle or, in 8k+28k+2 dimensions, its square root, the Pfaffian line bundle.

So to even start making sense of the remaining path integral over the bosonic degree of freedom, this determinant line bundle or the corresponding Pfaffian line bundle has to be trivializable. Its non-trivializability is the fermionic anomaly .

More in detail (Freed 86), the path integral over an Lagrangian of the form (ϕ¯,Dϕ)(\overline \phi, D \phi) for

D:VW D \;\colon\; V \longrightarrow W

a Fredholm operator computes the determinant of that operator. Formally this is a section of the determinant line bundle over the remaining fields

(detV) *(detW)(detkerD) *(detcokerD), (det V)^\ast \otimes (det W) \simeq (det ker D)^\ast \otimes (det coker D) \,,

where the left hand side makes sense and the equivalence holds for VV and WW finite dimensional, and where the right hand side is the definition of the expression for general Fredholm operators. ((Freed 86, 1.))

In more detail this determinant line bundle also carries a connection on a bundle. To make the formal path integral, which is a section of this bundle, into an actual function, one this bundle with connection needs to be trivializable and trivialized. The obstruction to this is the anomaly.

Higher gauge-theoretic anomalies

For the moment see Green-Schwarz mechanism for more.

Anomalous symmetry

under construction


S:C S : C \to \mathbb{R}

be a (well defined) action functional. Write PP for its resolved covariant phase space in dg-geometry and

S BV:P S^{BV} : P \to \mathbb{R}

for the BV-action functional, both as given by BRST-BV formalism.

If the action functional is local (comes from a Lagrangian on a jet bundle) the covariant phase space PP a priori only carries a presymplectic structure. But by BV-theory there exists an equivalent (homotopical) derived action functional S Ψ BV:PS_\Psi^{BV} : P \to \mathbb{R} such that S Ψ BVS_\Psi^{BV} does induce a genuine symplectic structure on the derived space PP.

For ordinary Poisson manifolds and hence symplectic manifolds Maxim Kontsevich‘s theorem says that their deformation quantization always exist. But if SS is the action functional of a gauge theory then PP is in general a nontrivial derived infinity-Lie algebroid (its function algebra has “ghosts” and “ghosts of ghost”: the Chevalley-Eilenberg algebra generators) and the theorem does not apply. Instead, the quantization of the derived symplectic space PP exists only if the first and second infinity-Lie algebroid cohomology of PP vanishes:

These two cohomology groups

Anom gauge=H 1(CE(P))H 2(CE(P)) Anom_{gauge} = H^1(CE(P)) \oplus H^2(CE(P))

are called the gauge anomaly of the system. Only if they vanish does the quantization of the gauge theory encoded by SS exist.

More concretely, the function algebra on PP is a graded-commutative dg-algebra equipped with a graded Poisson bracket {,} BV\{-,-\}_{BV} and an element QC (P)Q \in C^\infty(P) (the BV-BRST charge) whose Hamiltonian vector field is the derivation that is the differential of the dg-algebra C (X)C^\infty(X). If the gauge anomaly does not vanish, then, while the deformation quantization of the graded algebra C (P)C^\infty(P) to a non commutative graded algebra with commutator [,][-,-] will exist, it may happen that the image SS of QQ under the quantization no longer satisfies the quantum master equation [S,S]=ΔS[S,S] = \hbar \Delta S.

Therefore the derivation [S,][S,-] will not define a quantized differential and therefore the quantization of the graded-commutative dg-algebra C (P)C^\infty(P) will only be a noncommutative algebra, not a non-commutative dg-algebra, hence will not be functions on a non-commutative space in derived geometry.


Anomalous action functional

Spinning particles and super-branes

The sigma-model for a supersymmetric fundamental brane on a target space XX has an anomaly coming from the nontriviality of Pfaffian line bundles associated with the fermionic fields on the worldvolume. These anomalies disappear (i.e. these bundles are trivializable) when the structure group of the tangent bundle of XX has a sufficiently high lift through the Whitehead tower of O(n)O(n).

  • Spin structure the worldline anomaly for the spinning particle/superparticle vanishes when XX has Spin structure

    This is a classical result. A concrete derivation is in

    • Edward Witten, Global anomalies in String theory in Symposium on anomalies, geometry, topology , World Scientific Publishing, Singapore (1985)
  • String structure the worldsheet anomaly for the spinning string/superstring in heterotic string theory vanishes (essentially) when XX has String structure

    This is originally due to Killingback and Witten. A commented list of literature is here. Recently Ulrich Bunke gave the rigorous proof

    • Ulrich Bunke, String structures and trivialisations of a Pfaffian line bundle (arXiv)

in terms of differential cohomology in general and differential string structures in particular.

Gravitational anomaly

Axial anomaly

Conformal anomaly of the string

The 2d CFT on the worldsheet of the bosonic string (in flat space, without further background fields) has an anomaly unless the dimensional target space is d=26d = 26.

This is discussed as a condition of trivialization of a bundle in (Freed 86, section 2). A brief summary is stated this comment on MO.

For more see at conformal anomaly for more.

Freed-Witten anomaly

see at Freed-Witten anomaly.

Diaconescu-Moore-Witten anomaly

see at Diaconescu-Moore-Witten anomaly

M5-Brane anomaly

see at M5-brane anomaly

Anomalous symmetry

Conformal anomaly

For the moment see Liouville cocycle.



Anomalies originate in the 1949 article by Steinberger:

  • J. Steinberger, On the Use of Subtraction Fields and the Lifetimes of Some Types of Meson Decay, Phys. Rev. 76, 1180 – Published 15 October 1949. doi.

Another early reference is

  • Stephen L. Adler, Axial-Vector Vertex in Spinor Electrodynamics, Phys. Rev. 177, 2426 – Published 25 January 1969. doi.

Anomalous action functional

The original articles on anomalous action functionals are


The mathematical formulation of this in terms of index theory is due to

and a clear comprehensive account of the situation (topological anomaly, geometric anomaly) is in

Slick formulation of these anomalies as invertible topological field theories is discussed in

A physicists’ monograph is

  • Reinhold A. Bertlmann, Anomalies in quantum field theory, Oxford Science Publ., 1996, 2000


A clear description of the quantum anomalies for higher gauge theories is in

As an application of this, a detailed discussion of the cancellation of the anomaly of the supergravity C-field in 11-dimensional supergravity is in

The role of spin structures as the anomaly cancellation condition for the spinning particle is discussed in

  • Edward Witten, Global anomalies in String theory in Symposium on anomalies, geometry, topology , World Scientific Publishing, Singapore (1985)

Gauge anomaly

The original work on the chiral anomaly is due to

  • Stephen Adler. Axial-Vector Vertex in Spinor Electrodynamics Physical Review 177 (5): 2426. (1969)

  • John Bell, Roman Jackiw, A PCAC puzzle: π0→γγ in the σ-model“. Il Nuovo Cimento A 60: 47. (1969)

See also

  • L. Faddeev and S. Shatashvili, “Algebraic and Hamiltonian Methods in the theory of Nonabelian Anomalies,” Theor. Math. Fiz., 60 (1984) 206; english transl. Theor. Math. Phys. 60 (1984) 770.

  • B. Zumino, “Chiral anomalies and differential geometry,” in Relativity, Groups and Topology II, proceedings of the Les Houches summer school, B.S. DeWitt and R. Stora, eds. North-Holland, 1984.

  • Mikio Nakahara, Chapter 13 of: Geometry, Topology and Physics, IOP 2003 (doi:10.1201/9781315275826, pdf)

In BV-BRST formulation

General discussion in the context of BRST-BV formalism (breaking of the quantum master equation by quantum corrections) is discussed in

  • W. Troost, P. van Nieuwenhuizen, A. van Proeyen, Anomalies and the Batalin-Vilkovisky lagrangian formalism (web)

  • Paul Howe, Ulf Lindström, P. White, Anomalies And Renormalization In The BRST-BV Framework , Phys. Lett. B246 (1990) 430.

  • J. Paris, W. Troost, Higher loop anomalies and their consistency conditions in nonlocal regularization , Nucl. Phys. B482 (1996) 373 (arXiv:hep-th/9607215)

  • Glenn Barnich, Classical and quantum aspects of the

    extended antifield formalism_ (arXiv:hep-th/0011120)

The fact that the anomaly sits in degree-1 BRST cohomology corresponds to the consistency condition discussed in

  • Julius Wess and B. Zumino, Consequences of anomalous Ward identities , Phys. Lett. B37 (1971) 95 doi
  • R. Stora, The Wess Zumino consistency condition: a paradigm in renormalized perturbation theory, Fortsch. Phys. 54:175-182 (2006) doi

Discussion of special applications in

  • F. De Jonghe, J. Paris and W. Troost, The BPHZ renormalised BV master equation and Two-loop Anomalies in Chiral Gravities , Nucl. Phys. B476 (1996) 559 arXiv:hep-th/9603012

  • J. Paris, Nonlocally regularized antibracket - antifield formalism and anomalies in chiral W(3)W(3) gravity , Nucl. Phys. B450 (1995) 357 (arXiv:hep-th/9502140)

  • R. Amorim, N.R.F.Braga, R. Thibes, Axial and gauge anomalies in the field antifield quantization of the generalized Schwinger model (arXiv:hep-th/9712014)

Discussion in the context of AQFT with functional analysis taken into account is in


An interpretation of gauge anomalies as failures of Hamiltonians to have self-adjoint extensions is in

Anomaly inflow

In finite-dimensional quantum mechanics

  • A. P. Balachandran, Amilcar R. de Queiroz, Mixed states from anomalies, Phys. Rev. D85 (2012) 025017 arxiv/1108.3898 doi
  • Carlos Alcalde, Daniel Sternheimer, Analytic vectors, anomalies and star representations, Lett. Math. Phys. 17 (1989), no. 2, 117–127. MR90h:22012, doi (the last section has also the field theory case)

Last revised on August 6, 2023 at 19:23:47. See the history of this page for a list of all contributions to it.