PhyslibAlpha.ProbabilisticTheory.JordanOrderUnit.Examples.SpinFactor
Spin factors
i. Overview
A spin factor is `V × ℝ` with the Jordan product `(x, a) ∘ (y, b) = (a y + b x, B x y + a b)` for a symmetric bilinear form `B`. It is the basic non-associative Jordan algebra; for a positive definite form it carries the Lorentz cone. Only the algebraic structure is built here.
ii. Key results
- `JordanAlgebra.SpinFactor` : the spin factor of a bilinear form. - `JordanAlgebra.SpinFactor.isCommJordan` : it is a Jordan algebra. - `JordanAlgebra.SpinFactor.mul_self_sub_two_smul_snd_mul_add_determinant_smul_one` : every element satisfies a quadratic equation.
iii. References
- Adapted from Cobord, `Jordan/SpinFactor.lean`.
30 declarations
Spin factor of a bilinear form
Given a module over a commutative ring and a bilinear form , the spin factor is the type . This structure is designed to be equipped with the Jordan product defined by , where and . The definition is implemented as a type synonym to ensure that Jordan algebra structures associated with different bilinear forms remain distinct.
The spin factor is an additive abelian group
The spin factor , associated with a module over a commutative ring and a bilinear form , is an additive abelian group.
-module structure on the spin factor
Given a commutative ring , a module over , and a bilinear form , the spin factor (associated with ) is a module over . This structure inherits the standard component-wise scalar multiplication from the product .
in a spin factor if their components are equal
Let be a module over a commutative ring , and let be a bilinear form on . For any two elements in the spin factor associated with , if their first components (in ) are equal and their second components (in ) are equal, then .
in a spin factor
Let be a module over a commutative ring , and let be a bilinear form on . For any two elements in the spin factor associated with , the first component of their sum is the sum of their first components, i.e., .
in a spin factor
In the spin factor defined by a bilinear form on a module over a commutative ring , for any two elements and , the second component of their sum is equal to the sum of their individual second components, i.e., .
The first component of in a spin factor is
In the spin factor defined by a bilinear form on a module over a commutative ring , the first component of the additive identity element is the zero vector .
The second component of in a spin factor is
In the spin factor defined by a bilinear form on a module over a commutative ring , the second component of the additive identity element is the zero element .
for spin factors
Let be a commutative ring, be an -module, and be a bilinear form on . For any element in the spin factor associated with , the first component of the additive inverse is equal to the additive inverse of the first component of . That is, , where denotes the first component of the pair .
for spin factors
Let be a commutative ring, be an -module, and be a bilinear form on . For any element in the spin factor associated with , the second component of the additive inverse is equal to the additive inverse of the second component of . That is, , where the subscript denotes the second component of the pair.
for spin factors
Let be a commutative ring, be an -module, and be a bilinear form on . For any scalar and any element in the spin factor associated with , the first component of the scalar multiplication is equal to the scalar multiplication of with the first component of . That is, , where denotes the first component of the pair .
for a spin factor
Let be a module over a commutative ring and be a bilinear form on . For any scalar and any element in the spin factor (defined as the product ), the second component of the scalar multiplication is equal to multiplied by the second component of . That is, .
Constructor of an element in the spin factor
Given a module over a commutative ring and a bilinear form on , the function maps a vector and a scalar to the corresponding element in the spin factor .
for a spin factor
Let be a module over a commutative ring and be a bilinear form on . For any vector and scalar , the first component of the element in the spin factor is equal to . That is, .
The second component of in the spin factor is
Let be a commutative ring and be an -module equipped with a bilinear form . For any vector and scalar , the second component of the element constructed in the spin factor is equal to .
Multiplication on the spin factor
Given a module over a commutative ring and a bilinear form on , the multiplication operation on the spin factor is defined such that for any two elements and (where and ), their product is given by .
The first component of the product in the spin factor equals
Let be a commutative ring and be an -module equipped with a bilinear form . For any two elements and in the spin factor , let denote their vector components and denote their scalar components. Then the first component (the vector part) of their Jordan product is given by .
The second component of the product in a spin factor is
Let be a module over a commutative ring and be a bilinear form on . For any two elements in the spin factor , the second component of their Jordan product is given by , where and are the first and second components of and , respectively.
Identity element of the spin factor
Given a module over a commutative ring and a bilinear form , the identity element in the spin factor is defined as the element , where is the zero vector in and is the multiplicative identity in . This element acts as the unit with respect to the Jordan product .
The first component of the identity element in the spin factor is
Let be a module over a commutative ring , and let be a bilinear form on . In the spin factor , the first component of the identity element is the zero vector .
The second component of the identity element in the spin factor is
Let be a module over a commutative ring , and let be a bilinear form on . In the spin factor , the second component of the identity element is .
The spin factor is a non-associative ring
Given a module over a commutative ring and a bilinear form , the spin factor is a non-associative ring. The multiplication is defined by the Jordan product , and the identity element is . This structure satisfies the left and right distributive laws of multiplication over addition, as well as the identity laws and .
Commutativity of the multiplication in a spin factor
Let be a commutative ring and be a module over . Let be a symmetric bilinear form. For any elements in the spin factor associated with , the Jordan product is commutative, i.e., .
in spin factors
Let be a module over a commutative ring , and let be a bilinear form on . The spin factor associated with is the set equipped with the Jordan product defined by . For any scalar and elements , the scalar multiplication and Jordan product satisfy the compatibility condition .
Scalar multiplication and Jordan product commute in the spin factor:
Let be a commutative ring, be an -module, and be a bilinear form. In the spin factor equipped with the Jordan product , the scalar multiplication by and the Jordan product commute. That is, for any and any elements , it holds that .
Non-associative commutative ring structure on the spin factor of a symmetric form
Let be a commutative ring and be a module over . Given a symmetric bilinear form , the spin factor forms a non-associative commutative ring. The multiplication (the Jordan product) is defined by for and , and the multiplicative identity is .
The Spin Factor of a Symmetric Bilinear Form is a Commutative Jordan Algebra
Let be a commutative ring and be a module over . If is a symmetric bilinear form, then the spin factor , equipped with the Jordan product , is a commutative Jordan algebra. This implies that the product is commutative and satisfies the Jordan identity for all elements in the spin factor.
Determinant of a spin factor
For a spin factor associated with a module over a commutative ring and a bilinear form , the determinant is a quadratic map from the spin factor to . For any element , where is the vector component and is the scalar component, the determinant is defined as .
Determinant of in a spin factor is
Let be a commutative ring, a module over , and a bilinear form. For any element in the spin factor associated with , where is the vector component and is the scalar component, the determinant of is given by .
Cayley–Hamilton identity for spin factors
Let be a commutative ring, a module over , and a symmetric bilinear form. Let be the spin factor associated with , equipped with the identity element and the multiplication . For any element (where and ), the following quadratic Cayley–Hamilton identity holds: where and .
