Physlib.Electromagnetism.Kinematics.FieldStrength
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Field strength tensor from electromagnetic potential
#toFieldStrengthGiven an electromagnetic potential defined on a -dimensional spacetime, the function `toFieldStrength` assigns to its corresponding field strength tensor field (also known as the Faraday tensor). At each point in spacetime, the value is an element of the tensor product of two Lorentz vector spaces . The tensor is defined as the antisymmetrized derivative of the potential: \[ F^{\mu\nu} = \partial^\mu A^\nu - \partial^\nu A^\mu \] This is constructed by taking the difference between the derivative of the potential contracted with the Minkowski metric and its transpose (the same term with indices swapped).
The field strength tensor equals
#toFieldStrength_eq_addFor an electromagnetic potential in -dimensional spacetime, the value of the field strength tensor at a point is given by the difference: where is the Minkowski metric and denotes the derivative of the potential. In the formal expression, this is represented by taking the tensor and subtracting its index-permuted version .
The Tensor Representation of equals
#toTensor_toFieldStrengthFor an electromagnetic potential on a -dimensional spacetime and a point in spacetime, the representation of the field strength tensor (the Faraday tensor) in the formal tensor index notation is equal to the antisymmetrized raised-index derivative of the potential: where is the tensor constructed by contracting the Minkowski metric with the derivative of the potential at . Here, denotes the linear equivalence between the physical tensor product space and the formal index-based tensor species representation.
Component Formula for the Field Strength Tensor
#toTensor_toFieldStrength_basis_reprIn a -dimensional spacetime, let be an electromagnetic potential and be the associated field strength tensor (Faraday tensor). For any point in spacetime and any multi-index corresponding to the contravariant components of a rank-2 tensor, the component of the field strength tensor at index in the canonical basis is given by the formula: where and are the spacetime indices in corresponding to the multi-index components and , denotes the Minkowski metric, and is the partial derivative of the -th component of the potential with respect to the -th coordinate at point .
Basis Representation Equivalence for the Field Strength Tensor
#toFieldStrength_tensor_basis_eq_basisLet be the number of spatial dimensions. For an electromagnetic potential and a point in spacetime, let be the field strength tensor (Faraday tensor) at , which is an element of the tensor product space of Lorentz vectors. Let be the canonical basis for the formal -tensor space of the species `realLorentzTensor d`, and let be the basis for induced by the standard Lorentz vector basis . For any multi-index in the component index set of the formal tensor, the coordinate of in the formal tensor basis at is equal to the coordinate of in the tensor product basis at the index pair , where and are the Lorentz indices in corresponding to and via the standard index equivalence.
Component Formula for
#toFieldStrength_basis_repr_applyIn a -dimensional spacetime, let be an electromagnetic potential and be the field strength tensor (Faraday tensor) at a point . For any pair of spacetime indices , the component of the field strength tensor in the standard tensor product basis is given by: where is the Minkowski metric and denotes the partial derivative of the -th component of the potential with respect to the -th coordinate at point .
In a -dimensional spacetime, let be an electromagnetic potential and be a point in spacetime. For any pair of spacetime indices , the -th component of the field strength tensor at is given by: where is the Minkowski metric, and denotes the partial derivative of the -th component of the potential with respect to the -th coordinate evaluated at point .
Matrix representation of the field strength tensor at
#fieldStrengthMatrixGiven an electromagnetic potential defined on a -dimensional spacetime and a point in that spacetime, the function `fieldStrengthMatrix` returns the components of the field strength tensor (the Faraday tensor) at as a matrix. This matrix is obtained by taking the coordinate representation of the tensor with respect to the standard basis of the spacetime, where indices range over the temporal and spatial components .
Field Strength Matrix equals Tensor Representation
#fieldStrengthMatrix_eqFor an electromagnetic potential in a spacetime with spatial dimensions, the field strength matrix at a point is equal to the coordinate representation of the field strength tensor with respect to the basis formed by the tensor product of the standard Lorentz covector basis and the standard Lorentz vector basis.
The -th entry of the field strength matrix equals the -th component in the canonical tensor basis
#fieldStrengthMatrix_eq_tensor_basis_reprFor a -dimensional spacetime, let be an electromagnetic potential and be a point in spacetime. Let be the field strength tensor (Faraday tensor) at , and let be its matrix representation (the field strength matrix). For any indices , the -th entry of the field strength matrix is equal to the coordinate of the formal tensor representation of with respect to the canonical tensor basis at the corresponding multi-index .
For an electromagnetic potential defined on a -dimensional spacetime, the field strength tensor (the Faraday tensor) at a point can be expressed as a linear combination of the standard basis tensors . Specifically, the tensor is given by: \[ F(x) = \sum_{\mu} \sum_{\nu} F_{\mu\nu}(x) (e_\mu \otimes e_\nu) \] where are the components of the field strength matrix at , and is the standard basis for the space of Lorentz vectors .
If Electromagnetic Potential is , then its Field Strength Matrix is Differentiable
#fieldStrengthMatrix_differentiableIn a -dimensional spacetime, let be an electromagnetic potential. If is twice continuously differentiable (), then for any pair of spacetime indices and , the -th component of the field strength matrix (representing the Faraday tensor) is a differentiable function with respect to the spacetime coordinates.
If Electromagnetic Potential is , then its Field Strength Tensor is Differentiable
#toFieldStrength_differentiableIn a -dimensional spacetime, let be an electromagnetic potential. If is twice continuously differentiable (), then the associated field strength tensor field (the Faraday tensor) is differentiable with respect to the spacetime coordinates.
Spatial Differentiability of the Field Strength Matrix for Electromagnetic Potentials
#fieldStrengthMatrix_differentiable_spaceIn a -dimensional spacetime, let be an electromagnetic potential. If is twice continuously differentiable (of class ), then for any fixed time , speed of light , and indices , the -th component of the field strength matrix is differentiable with respect to the spatial coordinates . Specifically, the function , where is the spacetime point reconstructed from time and spatial position , is differentiable.
The Field Strength Matrix of a Potential is Differentiable in Time
#fieldStrengthMatrix_differentiable_timeIn a -dimensional spacetime, let be an electromagnetic potential that is twice continuously differentiable (of class ). For any fixed spatial point , speed of light , and any pair of spacetime indices and , the -th component of the field strength matrix evaluated at the spacetime point corresponding to time and position is a differentiable function with respect to time .
Continuous Differentiability of the Field Strength Matrix
#fieldStrengthMatrix_contDiffFor a -dimensional spacetime, let be an electromagnetic potential. If is times continuously differentiable (of class ), then for any spacetime indices and , the -th component of the field strength matrix of , mapping a spacetime point to , is times continuously differentiable (of class ).
smoothness of the Field Strength Matrix components
#fieldStrengthMatrix_smoothIn a -dimensional spacetime, let be an electromagnetic potential. If is infinitely differentiable (of class ), then for any spacetime indices and , the -th component of the field strength matrix, mapping a spacetime point to the value , is also infinitely differentiable (of class ).
Antisymmetry of the Field Strength Tensor
#toFieldStrength_antisymmetricIn a -dimensional spacetime, let be an electromagnetic potential and be the associated field strength tensor (Faraday tensor) defined by . For any point in spacetime and any indices and representing spacetime coordinates, the field strength tensor is antisymmetric:
Antisymmetry of the Field Strength Matrix
#fieldStrengthMatrix_antisymmIn a -dimensional spacetime, let be an electromagnetic potential and be the field strength matrix (Faraday matrix) at a point . For any spacetime indices and , the components of the field strength matrix satisfy:
Diagonal components of the field strength matrix are zero ()
#fieldStrengthMatrix_diag_eq_zeroIn a -dimensional spacetime, let be an electromagnetic potential and be its corresponding field strength matrix (Faraday matrix) at a point . For any spacetime index , the diagonal entry of the field strength matrix is zero:
Lorentz Equivariance of the Field Strength Tensor
#toFieldStrength_equivariantLet be a natural number representing spatial dimensions. Let be a differentiable electromagnetic potential field on a -dimensional spacetime. For any Lorentz transformation and any spacetime point , let be the Lorentz-transformed potential defined by . Then the field strength tensor (the Faraday tensor) satisfies the following equivariance property: \[ F[A'](x) = \Lambda \cdot F[A](\Lambda^{-1} x) \] where denotes the field strength tensor associated with potential , and the operation represents the action of the Lorentz group on a rank-2 tensor.
Lorentz transformation rule for the components of the field strength matrix
#fieldStrengthMatrix_equivariantLet be a natural number representing spatial dimensions. Let be a differentiable electromagnetic potential field on a -dimensional spacetime. For any Lorentz transformation in the Lorentz group and any spacetime point , let be the Lorentz-transformed potential defined by . Then, for any spacetime indices , the -th component of the field strength matrix associated with at point satisfies: \[ F^{\mu\nu}[A'](x) = \sum_{\kappa} \sum_{\rho} \Lambda_{\mu\kappa} \Lambda_{\nu\rho} F^{\kappa\rho}[A](\Lambda^{-1} x) \] where is the -th component of the field strength matrix associated with evaluated at the point , and denotes the -th entry of the matrix representation of the Lorentz transformation.
(Additivity of the Field Strength Tensor)
#toFieldStrength_addIn a -dimensional spacetime, let and be two differentiable electromagnetic potentials. For any point in spacetime, the field strength tensor (also known as the Faraday tensor) satisfies the additivity property: \[ F[A_1 + A_2](x) = F[A_1](x) + F[A_2](x) \] where denotes the field strength tensor derived from the potential .
for the Field Strength Matrix
#fieldStrengthMatrix_addIn a -dimensional spacetime, let and be two differentiable electromagnetic potentials. For any point in spacetime, the field strength matrix (the coordinate representation of the Faraday tensor ) of the sum is equal to the sum of the field strength matrices of and . That is: \[ [F(A_1 + A_2)](x) = [F(A_1)](x) + [F(A_2)](x) \] where denotes the matrix representation of the field strength tensor derived from the potential at point .
For any -dimensional spacetime, let be an electromagnetic potential and be a real scalar. If is differentiable, then at any point in spacetime, the field strength tensor (also known as the Faraday tensor) of the scaled potential is equal to times the field strength tensor of . That is: \[ F[c \cdot A](x) = c \cdot F[A](x) \] where denotes the field strength tensor derived from the potential via the relation .
for the Field Strength Matrix
#fieldStrengthMatrix_smulFor a -dimensional spacetime, let be an electromagnetic potential and be a real scalar. If is differentiable, then at any point in spacetime, the field strength matrix (the coordinate representation of the Faraday tensor ) of the scaled potential is equal to times the field strength matrix of . That is: \[ [F(c \cdot A)](x) = c \cdot [F(A)](x) \] where denotes the matrix representation of the field strength tensor derived from the potential at point .
Auxiliary field strength tensor for a distributional potential
#fieldStrengthAuxGiven a distributional electromagnetic potential in -dimensional spacetime and a Schwartz test function , this function defines an auxiliary rank-2 contravariant tensor (an element of ). The tensor is constructed by antisymmetrizing the distributional derivative of the potential. Specifically, let be the Minkowski metric and represent the derivative of the distribution acting on the test function . The auxiliary field strength tensor is given by the expression: This represents in distributional form. As an auxiliary definition, it provides the raw tensor value without additional linearity or continuity structures.
The Auxiliary Field Strength Tensor Equals the Difference of Permuted Derivative Tensors
#fieldStrengthAux_eq_addLet be the number of spatial dimensions. For a distributional electromagnetic potential and a Schwartz test function , the auxiliary field strength tensor (denoted by `fieldStrengthAux A ε`) is equal to the difference between the tensor and its index-permuted version . Specifically, where is the tensor resulting from the contraction of the Minkowski metric with the distributional derivative of the potential evaluated at .
The Formal Tensor of Equals the Difference of Permuted Derivative Tensors
#toTensor_fieldStrengthAuxLet be the number of spatial dimensions. For a distributional electromagnetic potential and a Schwartz test function , the formal tensor representation (given by the map `Tensorial.toTensor`) of the auxiliary field strength is equal to the difference between the tensor and its index-permuted version . Specifically, where is the tensor resulting from the contraction of the Minkowski metric with the distributional derivative of the potential evaluated at .
Basis Components of the Auxiliary Field Strength Tensor as a Sum of Potential Derivatives
#toTensor_fieldStrengthAux_basis_reprIn -dimensional spacetime, let be a distributional electromagnetic potential and be a Schwartz test function. Let be the auxiliary rank-2 contravariant field strength tensor (defined as `fieldStrengthAux A ε`). For a multi-index corresponding to spacetime indices and via the canonical isomorphism , the component of the tensor in the canonical basis is given by: where denotes the components of the Minkowski metric, and is the -th distributional derivative of the -th component of the potential evaluated at the test function .
Component Equality of Auxiliary Field Strength Tensor in Tensor and Product Bases
#fieldStrengthAux_tensor_basis_eq_basisLet be a distributional electromagnetic potential in a spacetime with spatial dimensions and be a Schwartz test function. Let be the auxiliary rank-2 contravariant field strength tensor. For any tensor multi-index consisting of two contravariant indices, the component of (viewed as a formal tensor) in the canonical tensor basis at index is equal to the component of (viewed as an element of the tensor product of Lorentz vector spaces) in the product basis at indices and , where is the canonical equivalence between tensor component indices and the spacetime index set .
Component Formula for the Auxiliary Field Strength Tensor as a Sum of Potential Derivatives
#fieldStrengthAux_basis_repr_applyIn -dimensional spacetime, let be a distributional electromagnetic potential and be a Schwartz test function. Let be the auxiliary rank-2 contravariant field strength tensor (defined as `fieldStrengthAux A ε`). For a pair of spacetime indices , the component of this tensor in the product basis of Lorentz vectors is given by: where denotes the Minkowski metric and represents the -th distributional derivative of the -th component of the potential evaluated at the test function .
Component Formula for using the Diagonal Minkowski Metric
#fieldStrengthAux_basis_repr_apply_eq_singleIn -dimensional spacetime, let be a distributional electromagnetic potential and be a Schwartz test function. The component of the auxiliary rank-2 contravariant field strength tensor (defined by `fieldStrengthAux A ε`) at the indices is given by: where denotes the Minkowski metric and represents the -th distributional derivative of the -th component of the potential evaluated at the test function . This formula simplifies the general sum over indices by leveraging the fact that the Minkowski metric is diagonal.
Basis Expansion of the Auxiliary Field Strength Tensor
#fieldStrengthAux_eq_basisIn -dimensional spacetime, let be a distributional electromagnetic potential and be a Schwartz test function. The auxiliary rank-2 contravariant field strength tensor can be expressed as a sum over the tensor products of the standard basis vectors and as follows: where are the diagonal components of the Minkowski metric and denotes the -th distributional derivative of the -th component of the potential evaluated at the test function .
Field strength tensor of a distributional potential
#fieldStrengthFor a given spatial dimension , the field strength is a linear map that associates a distributional electromagnetic potential with a rank-2 contravariant tensor distribution. Specifically, for a distributional potential , the field strength is a distribution that maps a Schwartz test function to a rank-2 tensor in . The components of this tensor are given by: where denotes the Minkowski metric and represents the distributional derivative of the -th component of the potential acting on the test function . The map is linear, and for each , the map is linear and continuous.
Equality of distributional field strength and auxiliary field strength tensor
#fieldStrength_eq_fieldStrengthAuxFor a distributional electromagnetic potential in -dimensional spacetime and a Schwartz test function , the evaluation of the field strength tensor distribution at is equal to the auxiliary field strength tensor defined by the antisymmetrized distributional derivatives of the potential.
Basis Expansion of the Distributional Field Strength Tensor
#fieldStrength_eq_basisIn -dimensional spacetime, let be a distributional electromagnetic potential and be a Schwartz test function. The field strength tensor distribution evaluated at is given by the basis expansion: where is the standard basis for the space of Lorentz vectors, are the diagonal components of the Minkowski metric, and denotes the -th distributional derivative of the -th component of the potential acting on the test function .
Component formula
#fieldStrength_basis_repr_eq_singleIn -dimensional spacetime, let be a distributional electromagnetic potential and be a Schwartz test function. The component of the rank-2 field strength tensor distribution evaluated at is given by: where denotes the diagonal Minkowski metric and represents the -th distributional derivative of the -th component of the potential acting on the test function .
Diagonal components of the field strength tensor
#fieldStrength_diag_zeroIn -dimensional spacetime, let be a distributional electromagnetic potential and be a Schwartz test function. The diagonal components of the rank-2 field strength tensor distribution evaluated at are zero. That is, for any spacetime index : where denotes the component of the tensor in the standard coordinate basis.
Diagonal Components of the Derivative of the Distributional Field Strength Tensor are Zero:
#distDeriv_fieldStrength_diag_zeroIn -dimensional spacetime, let be a distributional electromagnetic potential and be a Schwartz test function. For any spacetime indices and in the standard coordinate basis, the diagonal components of the -th distributional derivative of the field strength tensor evaluated at are zero. That is: where denotes the component of the tensor-valued distribution derivative in the standard basis.
Antisymmetry of the Distributional Field Strength Tensor:
#fieldStrength_antisymmetric_basisIn -dimensional spacetime, let be a distributional electromagnetic potential and be a Schwartz test function. Let be the rank-2 field strength tensor evaluated at . For any spacetime indices and in the standard basis, the components of the tensor satisfy the antisymmetry property:
Lorentz Equivariance of the Field Strength Tensor:
#fieldStrength_equivariantFor a given number of spatial dimensions , let be a distributional electromagnetic potential and be an element of the Lorentz group . The operation of taking the field strength tensor is equivariant under the Lorentz group action, meaning: In other words, the field strength of a Lorentz-transformed potential is equal to the Lorentz transformation of the field strength of the original potential.
