Physlib

Physlib.Relativity.LorentzGroup.Proper

The Proper Lorentz Group

The proper Lorentz group is the subgroup of the Lorentz group with determinant `1`.

We define the give a series of lemmas related to the determinant of the Lorentz group.

20 declarations

theorem

det(Λ)=±1\det(\Lambda) = \pm 1 for ΛLd\Lambda \in \mathcal{L}_d

Let Ld\mathcal{L}_d denote the Lorentz group acting on a (1+d)(1+d)-dimensional Minkowski space. For any element ΛLd\Lambda \in \mathcal{L}_d, the determinant of its matrix representation is either 11 or 1-1. That is, det(Λ)=1ordet(Λ)=1.\det(\Lambda) = 1 \quad \text{or} \quad \det(\Lambda) = -1.

instance

Discrete topology on Z2\mathbb{Z}_2

The definition provides a topological space structure on the group Z2\mathbb{Z}_2 (the cyclic group of order 2), where the topology assigned is the discrete topology.

instance

Z2\mathbb{Z}_2 is a discrete space

The topological space defined on the group Z2\mathbb{Z}_2 (the cyclic group of order 2) is a discrete space.

instance

Z2\mathbb{Z}_2 is a topological group

The cyclic group of order 2, Z2\mathbb{Z}_2, is a topological group when equipped with the discrete topology. This implies that the group multiplication and inversion operations are continuous maps.

definition

Continuous map from {1,1}\{-1, 1\} to Z2\mathbb{Z}_2

The function is a continuous map f:{1,1}Z2f: \{-1, 1\} \to \mathbb{Z}_2, where the domain {1,1}\{-1, 1\} is a subset of the real numbers R\mathbb{R} and Z2\mathbb{Z}_2 is the cyclic group of order 2. The map is defined such that f(1)f(1) is the identity element of Z2\mathbb{Z}_2 (corresponding to 0Z/2Z0 \in \mathbb{Z}/2\mathbb{Z}) and f(1)f(-1) is the non-identity element of Z2\mathbb{Z}_2 (corresponding to 1Z/2Z1 \in \mathbb{Z}/2\mathbb{Z}).

definition

Continuous determinant map det:LdZ2\det: \mathcal{L}_d \to \mathbb{Z}_2

The continuous map det:LdZ2\det: \mathcal{L}_d \to \mathbb{Z}_2 from the Lorentz group Ld\mathcal{L}_d to the cyclic group of order 2. For a Lorentz matrix Λ\Lambda, it maps the determinant det(Λ){1,1}\det(\Lambda) \in \{-1, 1\} to the corresponding element in Z2\mathbb{Z}_2, where det(Λ)=1\det(\Lambda) = 1 corresponds to the identity element and det(Λ)=1\det(\Lambda) = -1 corresponds to the non-identity element.

theorem

detcont(Λ)=1    det(Λ)=1\det_{\text{cont}}(\Lambda) = 1 \iff \det(\Lambda) = 1

For any element Λ\Lambda in the Lorentz group Ld\mathcal{L}_d, the continuous determinant map det:LdZ2\det: \mathcal{L}_d \to \mathbb{Z}_2 evaluates to the identity element of Z2\mathbb{Z}_2 if and only if the determinant of the matrix Λ\Lambda is 11.

theorem

detcont(Λ)=1    det(Λ)=1\det_{\text{cont}}(\Lambda) = -1 \iff \det(\Lambda) = -1

For any element Λ\Lambda in the Lorentz group Ld\mathcal{L}_d acting on (1+d)(1+d)-dimensional Minkowski space, the continuous determinant map detcont:LdZ2\det_{\text{cont}}: \mathcal{L}_d \to \mathbb{Z}_2 evaluates to the non-identity element of Z2\mathbb{Z}_2 if and only if the determinant of the matrix representation of Λ\Lambda is 1-1.

theorem

detcont(Λ)=detcont(Λ)    det(Λ)=det(Λ)\det_{\text{cont}}(\Lambda) = \det_{\text{cont}}(\Lambda') \iff \det(\Lambda) = \det(\Lambda')

For any elements Λ\Lambda and Λ\Lambda' in the Lorentz group Ld\mathcal{L}_d, the values of the continuous determinant map detcont:LdZ2\det_{\text{cont}}: \mathcal{L}_d \to \mathbb{Z}_2 are equal if and only if the determinants of their matrix representations are equal. That is, detcont(Λ)=detcont(Λ)    det(Λ)=det(Λ).\det_{\text{cont}}(\Lambda) = \det_{\text{cont}}(\Lambda') \iff \det(\Lambda) = \det(\Lambda').

definition

Determinant representation det:LdZ2\det: \mathcal{L}_d \to \mathbb{Z}_2

The group homomorphism det:LdZ2\det: \mathcal{L}_d \to \mathbb{Z}_2 from the Lorentz group Ld\mathcal{L}_d to the cyclic group of order 2. For any Lorentz transformation ΛLd\Lambda \in \mathcal{L}_d, the map sends Λ\Lambda to its determinant det(Λ){1,1}\det(\Lambda) \in \{1, -1\}, represented as an element of Z2\mathbb{Z}_2. Specifically, a determinant of 11 corresponds to the identity element of Z2\mathbb{Z}_2, and a determinant of 1-1 corresponds to the non-identity element.

theorem

The determinant representation detRep:LdZ2\text{detRep}: \mathcal{L}_d \to \mathbb{Z}_2 is continuous

Let Ld\mathcal{L}_d be the dd-dimensional Lorentz group and Z2\mathbb{Z}_2 be the cyclic group of order 2 equipped with the discrete topology. The determinant representation detRep:LdZ2\text{detRep}: \mathcal{L}_d \to \mathbb{Z}_2, which maps a Lorentz transformation Λ\Lambda to its determinant det(Λ){1,1}\det(\Lambda) \in \{1, -1\} represented in Z2\mathbb{Z}_2, is continuous.

theorem

det(Λ)=det(Λ)\det(\Lambda) = \det(\Lambda') for ΛconnectedComponent(Λ)\Lambda' \in \text{connectedComponent}(\Lambda)

For any two Lorentz transformations Λ\Lambda and Λ\Lambda' in the Lorentz group Ld\mathcal{L}_d (the group of linear transformations preserving the Lorentz metric in dd dimensions), if Λ\Lambda' belongs to the same connected component as Λ\Lambda, then their determinants are equal: det(Λ)=det(Λ)\det(\Lambda) = \det(\Lambda').

theorem

detRep(Λ)=detRep(Λ)\text{detRep}(\Lambda) = \text{detRep}(\Lambda') for Λ\Lambda' in the same connected component as Λ\Lambda

Let Ld\mathcal{L}_d be the Lorentz group in dd dimensions. For any two Lorentz transformations Λ,ΛLd\Lambda, \Lambda' \in \mathcal{L}_d, if Λ\Lambda' belongs to the same connected component as Λ\Lambda, then their images under the determinant representation detRep:LdZ2\text{detRep}: \mathcal{L}_d \to \mathbb{Z}_2 are equal, i.e., detRep(Λ)=detRep(Λ)\text{detRep}(\Lambda) = \text{detRep}(\Lambda').

theorem

det(Λ)=det(Λ)\det(\Lambda) = \det(\Lambda') for Lorentz transformations joined by a path

For any two Lorentz transformations Λ\Lambda and Λ\Lambda' in the dd-dimensional Lorentz group, if Λ\Lambda and Λ\Lambda' are joined by a path, then their determinants are equal: det(Λ)=det(Λ)\det(\Lambda) = \det(\Lambda').

definition

Proper Lorentz transformation (detΛ=1\det \Lambda = 1)

For a Lorentz transformation Λ\Lambda in the Lorentz group of dimension dd, the property IsProper(Λ)\text{IsProper}(\Lambda) holds if the determinant of the matrix representation of Λ\Lambda is equal to 11, denoted as det(Λ)=1\det(\Lambda) = 1.

instance

Decidability of the proper Lorentz transformation predicate (detΛ=1\det \Lambda = 1)

For a Lorentz transformation Λ\Lambda in the Lorentz group of dimension dd, the property IsProper(Λ)\text{IsProper}(\Lambda), which is defined by the condition that the determinant of the matrix representation of Λ\Lambda is equal to 11 (det(Λ)=1\det(\Lambda) = 1), is a decidable predicate.

theorem

Product of proper Lorentz transformations is proper

For any two Lorentz transformations Λ\Lambda and Λ\Lambda' in the Lorentz group of dimension dd, if Λ\Lambda and Λ\Lambda' are proper transformations (meaning detΛ=1\det \Lambda = 1 and detΛ=1\det \Lambda' = 1), then their product ΛΛ\Lambda \Lambda' is also a proper Lorentz transformation.

theorem

IsProper Λ    detRep Λ=1\text{IsProper } \Lambda \iff \text{detRep } \Lambda = 1

For any Lorentz transformation Λ\Lambda in the Lorentz group Ld\mathcal{L}_d of dimension dd, Λ\Lambda is a proper Lorentz transformation (IsProper Λ\text{IsProper } \Lambda) if and only if its image under the determinant representation detRep:LdZ2\text{detRep}: \mathcal{L}_d \to \mathbb{Z}_2 is the identity element 11.

theorem

The Identity Lorentz Transformation is Proper

The identity element of the Lorentz group in dd dimensions is a proper Lorentz transformation (i.e., its determinant is equal to 11).

theorem

IsProper Λ    IsProper Λ\text{IsProper } \Lambda \iff \text{IsProper } \Lambda' for Transformations in the Same Connected Component

For any two Lorentz transformations Λ\Lambda and Λ\Lambda' in the Lorentz group of dimension dd, if Λ\Lambda' belongs to the same connected component as Λ\Lambda, then Λ\Lambda is a proper Lorentz transformation if and only if Λ\Lambda' is a proper Lorentz transformation. A Lorentz transformation is called proper if its determinant is equal to 11.