Physlib

Physlib.QFT.AnomalyCancellation.Basic

Anomaly cancellation conditions

i. Overview

Anomaly cancellation conditions (ACCs) are consistency conditions which arise in gauge field theories. They correspond to a set of homogeneous diophantine equations in the rational charges assigned to fermions under `u(1)` contributions to the gauge group.

These formally arise from triangle Feynman diagrams, but can otherwise be got from index theorems.

ii. Key results

There are four different types related to the underlying structure of the ACCs: - `ACCSystemCharges`: the structure carrying the number of charges present. - `ACCSystemLinear`: the structure extending `ACCSystemCharges` with linear anomaly cancellation conditions. - `ACCSystemQuad`: the structure extending `ACCSystemLinear` with quadratic anomaly cancellation conditions. - `ACCSystem`: the structure extending `ACCSystemQuad` with the cubic anomaly cancellation condition.

Related to these are the different types of spaces of charges: - `Charges`: the module of all possible charge allocations. - `LinSols`: the module of solutions to the linear ACCs. - `QuadSols`: the solutions to the linear and quadratic ACCs. - `Sols`: the solutions to the full ACCs.

iii. Table of contents

- A. The module of charges - A.1. A constructor for `ACCSystemCharges` - B. The module of charges - B.1. The `ℚ`-module structure on the type `Charges` - B.2. The finiteness of the `ℚ`-module structure on `Charges` - C. The linear anomaly cancellation conditions - D. The module of solutions to the linear ACCs - D.1. Extensionality of solutions to the linear ACCs - D.2. Module structure on the solutions to the linear ACCs - D.3. Embedding of the solutions to the linear ACCs into the module of charges - E. The quadratic anomaly cancellation conditions - F. The solutions to the quadratic and linear anomaly cancellation conditions - F.1. Extensionality of solutions to the quadratic and linear ACCs - F.2. MulAction of rationals on the solutions to the quadratic and linear ACCs - F.3. Embeddings of quadratic solutions into linear solutions - F.4. Embeddings of solutions to linear ACCs into quadratic solutions when no quadratics - F.5. Embeddings of quadratic solutions into all charges - G. The full anomaly cancellation conditions - H. The solutions to the full anomaly cancellation conditions - H.1. Extensionality of solutions to the ACCs - H.2. The `IsSolution` predicate - H.3. MulAction of `ℚ` on the solutions to the ACCs - H.4. Embeddings of solutions to the ACCs into quadratic solutions - H.5. Embeddings of solutions to the ACCs into linear solutions - H.6. Embeddings of solutions to the ACCs into charges - I. Morphisms between ACC systems - I.1. Composition of morphisms between ACC systems - J. Open TODO items

iv. References

Some references on anomaly cancellation conditions are: - Alvarez-Gaume, L. and Ginsparg, P. H. (1985). The Structure of Gauge and Gravitational Anomalies. - Bilal, A. (2008). Lectures on Anomalies. arXiv preprint. - Nash, C. (1991). Differential topology and quantum field theory. Elsevier.

A. The module of charges

We define the type `ACCSystemCharges`, this carries the charges of the specification of the number of charges present in a theory.

For example for the standard model without right-handed neutrinos, this is `15` charges, whilst with right handed neutrinos it is `18` charges.

We can think of `Fin χ.numberCharges` as an indexing type for the representations present in the theory where `χ : ACCSystemCharges`.

A.1. A constructor for `ACCSystemCharges`

We provide a constructor `ACCSystemChargesMk` for `ACCSystemCharges` given the number of charges.

B. The module of charges

Given an `ACCSystemCharges` object `χ`, we define the type of charges `χ.Charges` as functions from `Fin χ.numberCharges → ℚ`.

That is, for each representation in the theory, indexed by an element of `Fin χ.numberCharges`, we assign a rational charge.

B.1. The `ℚ`-module structure on the type `Charges`

The type `χ.Charges` has the structure of a module over the field `ℚ`.

B.2. The finiteness of the `ℚ`-module structure on `Charges`

The type `χ.Charges` is a finite module.

C. The linear anomaly cancellation conditions

We define the type `ACCSystemLinear` which extends `ACCSystemCharges` by adding a finite number (determined by `numberLinear`) of linear equations in the rational charges.

D. The module of solutions to the linear ACCs

We define the type `LinSols` of solutions to the linear ACCs. That is the submodule of `χ.Charges` which satisfy all the linear ACCs.

D.1. Extensionality of solutions to the linear ACCs

We prove a lemma relating to the equality of two elements of `LinSols`.

D.2. Module structure on the solutions to the linear ACCs

we now give a module structure to `LinSols`.

D.3. Embedding of the solutions to the linear ACCs into the module of charges

We give the linear embedding of solutions to the linear ACCs `LinSols` into the module of all `charges`.

E. The quadratic anomaly cancellation conditions

We extend `ACCSystemLinear` to `ACCSystemQuad` by adding a finite number (determined by `numberQuadratic`) of quadratic equations in the rational charges.

These quadratic anomaly cancellation conditions correspond to the interaction of the `u(1)` part of the gauge group of interest with another abelian part.

F. The solutions to the quadratic and linear anomaly cancellation conditions

We define the type `QuadSols` of solutions to the linear and quadratic ACCs.

F.1. Extensionality of solutions to the quadratic and linear ACCs

We prove a lemma relating to the equality of two elements of `QuadSols`.

F.2. MulAction of rationals on the solutions to the quadratic and linear ACCs

The type `QuadSols` does not carry the structure of a module over `ℚ` as the quadratic ACCs are not linear. However it does carry the structure of a `MulAction` of `ℚ`.

F.3. Embeddings of quadratic solutions into linear solutions

We give the equivariant of solutions to the quadratic and linear ACCs `QuadSols` into the solutions to the linear ACCs `LinSols`.

F.4. Embeddings of solutions to linear ACCs into quadratic solutions when no quadratics

When there are no quadratic ACCs, the solutions to the linear ACCs embed into the solutions to the quadratic and linear ACCs.

F.5. Embeddings of quadratic solutions into all charges

We give the equivariant embedding of solutions to the quadratic and linear ACCs `QuadSols` into the module of all charges `Charges`.

G. The full anomaly cancellation conditions

We extend `ACCSystemQuad` to `ACCSystem` by adding the single cubic equation in the rational charges. This corresponds to the `u(1)^3` anomaly.

H. The solutions to the full anomaly cancellation conditions

We define the type `Sols` of solutions to the full ACCs.

H.1. Extensionality of solutions to the ACCs

We prove a lemma relating to the equality of two elements of `Sols`.

H.2. The `IsSolution` predicate

we define a predicate on charges which is true if they correspond to a solution.

H.3. MulAction of `ℚ` on the solutions to the ACCs

Like with `QuadSols`, the type `Sols` does not carry the structure of a module over `ℚ` as the cubic nor quadratic ACC is not linear. However it does carry the structure of a `MulAction` of `ℚ`.

H.4. Embeddings of solutions to the ACCs into quadratic solutions

H.5. Embeddings of solutions to the ACCs into linear solutions

H.6. Embeddings of solutions to the ACCs into charges

I. Morphisms between ACC systems

We define a morphisms between two `ACCSystem` objects. as a linear map between their spaces of charges and a map between their spaces of solutions such that mapping solutions and then including in the module of charges is the same as including in the module of charges and then mapping charges.

I.1. Composition of morphisms between ACC systems

J. Open TODO items

We give some open TODO items for future work.

One natural direction is to formalize how the anomaly cancellation conditions defining an `ACCSystem` arise from gauge-theoretic data (a gauge group together with fermionic representations). Physically these arise from triangle Feynman diagrams, and can also be described via index-theoretic or characteristic-class constructions (e.g. through an anomaly polynomial). At present we do not formalize this derivation in Lean, and instead take the resulting homogeneous forms as data.

(To view these you may need to go to the GitHub source code for the file.)

29 declarations

definition

Constructor for an ACC system with nn charges

Given a natural number nn, this function constructs an `ACCSystemCharges` object which specifies that a gauge theory has nn fermion representations. The resulting object defines the dimension of the charge space as nn.

definition

The module of charges Qn\mathbb{Q}^n for an ACC system

For an anomaly cancellation system χ\chi with nn charges, the type of charges is defined as the space of functions from the finite index set {0,1,,n1}\{0, 1, \dots, n-1\} to the rational numbers Q\mathbb{Q}. This space represents the assignment of a rational charge qiQq_i \in \mathbb{Q} to each of the nn fermion representations in the theory, effectively forming the vector space Qn\mathbb{Q}^n.

instance

Additive commutative monoid of charges χ.Charges\chi.\text{Charges}

For an anomaly cancellation system χ\chi, the space of charges χ.Charges\chi.\text{Charges} (which represents the rational charges qQnq \in \mathbb{Q}^n assigned to nn fermions) is equipped with the structure of an additive commutative monoid. This structure defines a zero element (where all charges are 00) and a binary addition operation (the pointwise sum of charges) that is both associative and commutative.

instance

Q\mathbb{Q}-module structure on the space of charges χ.Charges\chi.\text{Charges}

For an anomaly cancellation system χ\chi, the space of charges χ.Charges\chi.\text{Charges} (which represents vectors of rational charges qQnq \in \mathbb{Q}^n) is equipped with the structure of a module over the field of rational numbers Q\mathbb{Q}. This structure defines the standard pointwise addition of charge vectors and their scalar multiplication by rational numbers.

instance

Additive commutative group of charges χ.Charges\chi.\text{Charges}

For an anomaly cancellation system χ\chi, the space of charges χ.Charges\chi.\text{Charges} (representing vectors of rational charges qQnq \in \mathbb{Q}^n) is equipped with the structure of an additive commutative group. This structure defines vector addition, the additive identity (the zero charge vector), and the existence of additive inverses (negation of charges).

instance

The space of charges χ.Charges\chi.\text{Charges} is a finite Q\mathbb{Q}-module

For an anomaly cancellation system χ\chi, the space of charges χ.Charges\chi.\text{Charges} (representing the rational charge assignments qQnq \in \mathbb{Q}^n for the nn fermion representations in the theory) is a finitely generated module over the field of rational numbers Q\mathbb{Q}.

theorem

S.val=T.val    S=TS.\text{val} = T.\text{val} \implies S = T for solutions to linear ACCs

For a linear anomaly cancellation system χ\chi, let SS and TT be two solutions in the space of linear solutions χ.LinSols\chi.\text{LinSols}. If their underlying rational charge assignments in the module of charges χ.Charges\chi.\text{Charges} are equal (that is, S.val=T.valS.\text{val} = T.\text{val}), then the solutions SS and TT are equal.

instance

Additive commutative monoid of linear ACC solutions χ.LinSols\chi.\text{LinSols}

For a linear anomaly cancellation system χ\chi, the set of solutions to the linear constraints, denoted χ.LinSols\chi.\text{LinSols}, forms an additive commutative monoid. The addition of two solutions SS and TT is defined as the pointwise sum of their rational charges, and the identity element is the zero charge vector (where all charges are 00). This structure inherits the properties of associativity and commutativity from the underlying space of rational charges Qn\mathbb{Q}^n.

instance

Q\mathbb{Q}-module structure on the space of linear ACC solutions χ.LinSols\chi.\text{LinSols}

For a linear anomaly cancellation system χ\chi, the set of solutions to the linear constraints, denoted by χ.LinSols\chi.\text{LinSols}, is equipped with the structure of a module over the field of rational numbers Q\mathbb{Q}. This structure is inherited from the underlying space of charges χ.ChargesQn\chi.\text{Charges} \cong \mathbb{Q}^n, such that for any rational scalar aQa \in \mathbb{Q} and any solution vector Sχ.LinSolsS \in \chi.\text{LinSols}, the scalar product aSa \cdot S also satisfies the linear anomaly cancellation conditions.

instance

Additive commutative group of linear ACC solutions χ.LinSols\chi.\text{LinSols}

For a linear anomaly cancellation system χ\chi, the set of solutions to the linear constraints, denoted χ.LinSols\chi.\text{LinSols}, forms an additive commutative group. This structure is inherited from its Q\mathbb{Q}-module structure, meaning that for any two solutions S,Tχ.LinSolsS, T \in \chi.\text{LinSols}, their pointwise sum S+TS + T is a solution, and for every solution SS, there exists an additive inverse S-S in χ.LinSols\chi.\text{LinSols} such that S+(S)=0S + (-S) = 0.

definition

Q\mathbb{Q}-linear inclusion of linear ACC solutions χ.LinSolsχ.Charges\chi.\text{LinSols} \hookrightarrow \chi.\text{Charges}

For a linear anomaly cancellation system χ\chi, the map linSolsIncl\text{linSolsIncl} is the canonical Q\mathbb{Q}-linear inclusion from the space of solutions χ.LinSols\chi.\text{LinSols} into the space of all charges χ.ChargesQn\chi.\text{Charges} \cong \mathbb{Q}^n. This map takes a solution vector SS and returns its underlying vector of rational charges.

theorem

The inclusion map linSolsIncl\text{linSolsIncl} is injective

For any linear anomaly cancellation system χ\chi, the canonical Q\mathbb{Q}-linear inclusion map linSolsIncl:χ.LinSolsχ.Charges\text{linSolsIncl} : \chi.\text{LinSols} \to \chi.\text{Charges}, which maps a solution to the linear anomaly cancellation conditions to its underlying vector of rational charges in Qn\mathbb{Q}^n, is injective.

theorem

S.val=T.val    S=TS.\text{val} = T.\text{val} \implies S = T for solutions to quadratic and linear ACCs

For an anomaly cancellation system χ\chi with linear and quadratic conditions, let SS and TT be two solutions in the space of quadratic solutions χ.QuadSols\chi.\text{QuadSols}. If their underlying rational charge assignments in the module of charges χ.Charges\chi.\text{Charges} are equal (that is, S.val=T.valS.\text{val} = T.\text{val}), then the solutions SS and TT are equal.

instance

Scalar action of Q\mathbb{Q} on the space of quadratic ACC solutions χ.QuadSols\chi.\text{QuadSols}

For a quadratic anomaly cancellation system χ\chi, the set of solutions to both the linear and quadratic constraints, denoted by χ.QuadSols\chi.\text{QuadSols}, is equipped with a scalar multiplication action (a `MulAction`) by the rational numbers Q\mathbb{Q}. This means that for any rational scalar aQa \in \mathbb{Q} and any solution Sχ.QuadSolsS \in \chi.\text{QuadSols}, the pointwise product aSa \cdot S also satisfies the linear and quadratic anomaly cancellation conditions, making it an element of χ.QuadSols\chi.\text{QuadSols}.

definition

Inclusion of quadratic solutions into linear solutions χ.QuadSolsχ.LinSols\chi.\text{QuadSols} \to \chi.\text{LinSols}

For a quadratic anomaly cancellation system χ\chi, the function χ.quadSolsInclLinSols\chi.\text{quadSolsInclLinSols} is the Q\mathbb{Q}-equivariant inclusion map from the set of solutions satisfying both linear and quadratic constraints, χ.QuadSols\chi.\text{QuadSols}, into the set of solutions satisfying only the linear constraints, χ.LinSols\chi.\text{LinSols}. This map sends a solution sχ.QuadSolss \in \chi.\text{QuadSols} to itself viewed as an element of χ.LinSols\chi.\text{LinSols}, and it commutes with scalar multiplication by rational numbers qQq \in \mathbb{Q}.

theorem

The inclusion map χ.quadSolsInclLinSols\chi.\text{quadSolsInclLinSols} is injective

For a quadratic anomaly cancellation system χ\chi, the inclusion map χ.quadSolsInclLinSols\chi.\text{quadSolsInclLinSols} that embeds the set of quadratic solutions χ.QuadSols\chi.\text{QuadSols} into the space of linear solutions χ.LinSols\chi.\text{LinSols} is injective.

definition

Inclusion χ.LinSolsχ.QuadSols\chi.\text{LinSols} \hookrightarrow \chi.\text{QuadSols} when χ.numberQuadratic=0\chi.\text{numberQuadratic} = 0

For a quadratic anomaly cancellation system χ\chi, if the number of quadratic equations is zero (χ.numberQuadratic=0\chi.\text{numberQuadratic} = 0), this definition provides the Q\mathbb{Q}-equivariant inclusion map from the space of linear solutions χ.LinSols\chi.\text{LinSols} to the space of solutions satisfying both linear and quadratic conditions χ.QuadSols\chi.\text{QuadSols}. Since the set of quadratic constraints is empty when χ.numberQuadratic=0\chi.\text{numberQuadratic} = 0, every vector in the Q\mathbb{Q}-module χ.LinSols\chi.\text{LinSols} vacuously satisfies the quadratic anomaly cancellation conditions.

definition

Q\mathbb{Q}-equivariant inclusion χ.QuadSolsχ.Charges\chi.\text{QuadSols} \hookrightarrow \chi.\text{Charges}

For a quadratic anomaly cancellation system χ\chi, the map quadSolsIncl\text{quadSolsIncl} is the Q\mathbb{Q}-equivariant inclusion from the space of quadratic solutions χ.QuadSols\chi.\text{QuadSols} into the space of all charges χ.ChargesQn\chi.\text{Charges} \cong \mathbb{Q}^n. This map is defined by composing the inclusion of solutions satisfying both linear and quadratic constraints into the space of linear solutions (χ.LinSols\chi.\text{LinSols}) with the canonical inclusion of linear solutions into the full space of rational charges. The map preserves scalar multiplication by rational numbers qQq \in \mathbb{Q}.

theorem

The inclusion map χ.quadSolsIncl:χ.QuadSolsχ.Charges\chi.\text{quadSolsIncl} : \chi.\text{QuadSols} \to \chi.\text{Charges} is injective

For a quadratic anomaly cancellation system χ\chi, the inclusion map χ.quadSolsIncl:χ.QuadSolsχ.Charges\chi.\text{quadSolsIncl} : \chi.\text{QuadSols} \to \chi.\text{Charges}, which maps each solution satisfying both linear and quadratic anomaly cancellation conditions to its corresponding vector of rational charges in Qn\mathbb{Q}^n, is injective.

theorem

S.val=T.val    S=TS.\text{val} = T.\text{val} \implies S = T for solutions to full ACCs

For an anomaly cancellation system χ\chi, let SS and TT be two solutions in the space of full solutions χ.Sols\chi.\text{Sols} (satisfying the linear, quadratic, and cubic conditions). If their underlying rational charge assignments in the module of charges χ.Charges\chi.\text{Charges} are equal (that is, S.val=T.valS.\text{val} = T.\text{val}), then the solutions SS and TT are equal.

definition

SS is a solution to the ACC system χ\chi

Given an anomaly cancellation system χ\chi and a charge assignment Sχ.ChargesS \in \chi.\text{Charges}, the predicate IsSolution(χ,S)\text{IsSolution}(\chi, S) holds if SS satisfies the full set of anomaly cancellation conditions (linear, quadratic, and cubic). Formally, this is defined by the existence of an element solsol in the space of solutions χ.Sols\chi.\text{Sols} such that its underlying value in the module of charges is equal to SS.

instance

Scalar action of Q\mathbb{Q} on the space of ACC solutions χ.Sols\chi.\text{Sols}

For an anomaly cancellation system χ\chi, the set of solutions χ.Sols\chi.\text{Sols} to the full set of conditions (linear, quadratic, and cubic) is equipped with a scalar multiplication action (a `MulAction`) by the rational numbers Q\mathbb{Q}. Given a rational number aQa \in \mathbb{Q} and a solution Sχ.SolsS \in \chi.\text{Sols}, the product aSa \cdot S is also a solution. This is well-defined because the linear, quadratic, and cubic anomaly cancellation conditions are homogeneous; specifically, the cubic part of the action is verified by the fact that if SS satisfies the cubic condition, then aSa \cdot S satisfies it as the cubic form scales by a3a^3.

definition

Inclusion map χ.Solsχ.QuadSols\chi.\text{Sols} \to \chi.\text{QuadSols}

For an anomaly cancellation system χ\chi, this is the equivariant inclusion map from the set of solutions χ.Sols\chi.\text{Sols} (which satisfy the full set of linear, quadratic, and cubic conditions) to the set of solutions χ.QuadSols\chi.\text{QuadSols} (which satisfy the linear and quadratic conditions). The map commutes with the scalar multiplication action of the rational numbers Q\mathbb{Q}.

theorem

The inclusion χ.Solsχ.QuadSols\chi.\text{Sols} \to \chi.\text{QuadSols} is injective

For an anomaly cancellation system χ\chi, the inclusion map χ.solsInclQuadSols:χ.Solsχ.QuadSols\chi.\text{solsInclQuadSols} : \chi.\text{Sols} \to \chi.\text{QuadSols}, which maps solutions satisfying the full set of (linear, quadratic, and cubic) conditions to the space of solutions satisfying only the linear and quadratic conditions, is injective.

definition

Inclusion of full solutions into linear solutions χ.Solsχ.LinSols\chi.\text{Sols} \to \chi.\text{LinSols}

For an anomaly cancellation system χ\chi, this is the Q\mathbb{Q}-equivariant inclusion map from the set of full solutions χ.Sols\chi.\text{Sols} (which satisfy the linear, quadratic, and cubic conditions) to the set of solutions χ.LinSols\chi.\text{LinSols} (which satisfy only the linear conditions). This map is defined by the composition of the inclusion χ.Solsχ.QuadSols\chi.\text{Sols} \to \chi.\text{QuadSols} and the inclusion χ.QuadSolsχ.LinSols\chi.\text{QuadSols} \to \chi.\text{LinSols}.

theorem

The inclusion χ.Solsχ.LinSols\chi.\text{Sols} \to \chi.\text{LinSols} is injective

For an anomaly cancellation system χ\chi, the inclusion map χ.solsInclLinSols:χ.Solsχ.LinSols\chi.\text{solsInclLinSols} : \chi.\text{Sols} \to \chi.\text{LinSols}, which maps solutions satisfying the full set of (linear, quadratic, and cubic) conditions to the set of solutions satisfying only the linear conditions, is injective.

definition

Q\mathbb{Q}-equivariant inclusion χ.Solsχ.Charges\chi.\text{Sols} \hookrightarrow \chi.\text{Charges}

For an anomaly cancellation system χ\chi, this is the Q\mathbb{Q}-equivariant inclusion map from the space of solutions χ.Sols\chi.\text{Sols} into the space of all charges χ.ChargesQn\chi.\text{Charges} \cong \mathbb{Q}^n. The set χ.Sols\chi.\text{Sols} consists of the rational charge allocations that satisfy the complete set of linear, quadratic, and cubic anomaly cancellation conditions. The map is defined by the composition of the inclusion of full solutions into the space of quadratic solutions (χ.QuadSols\chi.\text{QuadSols}) and the inclusion of quadratic solutions into the space of charges. It preserves scalar multiplication by rational numbers aQa \in \mathbb{Q}.

theorem

The inclusion map χ.Solsχ.Charges\chi.\text{Sols} \to \chi.\text{Charges} is injective

For an anomaly cancellation system χ\chi, the inclusion map χ.solsIncl:χ.Solsχ.Charges\chi.\text{solsIncl} : \chi.\text{Sols} \to \chi.\text{Charges}, which maps the set of rational charge allocations satisfying the full set of linear, quadratic, and cubic anomaly cancellation conditions into the space of all possible charges, is injective.

definition

Composition of ACC system morphisms gfg \circ f

Given three anomaly cancellation systems χ,η,\chi, \eta, and ε\varepsilon, and two morphisms f:χηf: \chi \to \eta and g:ηεg: \eta \to \varepsilon, their composition gf:χεg \circ f: \chi \to \varepsilon is defined as the morphism whose: 1. Linear map on the space of charges is the composition of the linear maps of the individual morphisms, g.chargesf.chargesg.\text{charges} \circ f.\text{charges}. 2. Map between the solution spaces is the composition of the maps g.anomalyFreef.anomalyFreeg.\text{anomalyFree} \circ f.\text{anomalyFree}. The resulting map satisfies the required commutativity condition for morphisms between anomaly cancellation systems.