Physics[Tetrads][gamma_] - represent and compute the Ricci rotation coefficients
Physics[Tetrads][lambda_] - represent a linear combination of the Ricci rotation coefficients - see reference
Calling Sequence
gamma_[a, b, c]
gamma_[a, b, c, matrix]
gamma_[keyword]
lambda_[a, b, c]
lambda_[a, b, c, matrix]
lambda_[keyword]
Parameters
_mu, nu_
-
the spacetime indices related to a global system of references, these are names representing integer numbers between 0 and the spacetime dimension, they can also be the numbers themselves
_a, b, c_
the tetrad indices related to a local system of references, as names representing integer numbers the same way as the spacetime indices
keyword
optional, it can be definition, matrix, nonzero
Description
The components of the gamma_[a, b, c] tensor are the Ricci rotation coefficients and the components of the lambda_[a, b, c] tensor are linear combinations of them, according to the definitions in the Landau, L.D., and Lifshitz, E.M. The Classical Theory of Fields, Course of Theoretical Physics Volume 2 (definitions (98.9) and (98.10)). Thus,
γa,b,c=𝔢b⁢μ⁢𝔢c⁢ν⁢▿ν𝔢a,μ
where ▿ν𝔢a,μ, represented in Maple by D_[nu](e_[a,mu]), is the covariant derivative of the tetrad, and
λa,b,c=𝔢b⁢μ⁢𝔢c⁢ν⁢▿ν⁡𝔢a,μ−▿μ⁡𝔢a,ν
From these definitions it follows that gammaa,b,c is antisymmetric in its first pair of indices, and the covariant derivatives entering the definition of lambdaa,b,c can be replaced by non-covariant ones using the d_ operator. You can retrieve these definitions directly in the worksheet entering gamma_[definition] and lambda_[definition].
Both gamma_ and lambda_ accept the keywords accepted by the other tensors of the Physics package, these are definition, matrix and nonzero, that can be given with or without indices. If given with indices, the corresponding output takes their character (covariant or contravariant) into account.
Examples
with⁡Physics:with⁡Tetrads
⁢_______________________________________________________
Setting lowercaselatin_ah letters to represent tetrad indices
Defined as tetrad tensors see ?Physics,tetrads, 𝔢a,μ , ηa,b , γa,b,c , λa,b,c
Defined as spacetime tensors representing the NP null vectors of the tetrad formalism see ?Physics,tetrads, lμ , nμ , mμ , m&conjugate0;μ
IsTetrad,NullTetrad,OrthonormalTetrad,PetrovType,SegreType,TransformTetrad,WeylScalars,e_,eta_,gamma_,l_,lambda_,m_,mb_,n_
Setup⁡mathematicalnotation=true
mathematicalnotation=true
Set the spacetime to be curved, for instance set the Schwarzschild metric in spherical coordinates (see g_):
g_sc
⁢Systems of spacetime coordinates are:⁢X=r,θ,φ,t
⁢Default differentiation variables for d_, D_ and dAlembertian are:⁢X=r,θ,φ,t
Setting lowercaselatin_is letters to represent space indices
⁢The Schwarzschild metric in coordinates ⁢r,θ,φ,t
Parameters: m
Signature: - - - +
gμ,ν=
The definition of the Ricci rotation coefficients and related λa,b,c
gamma_definition
γa,b,c=▿ν⁡𝔢a,μ⁢𝔢bμbμ⁢𝔢cνcν
lambda_definition
λa,b,c=▿ν⁡𝔢a,μ−▿μ⁡𝔢a,ν⁢𝔢bμbμ⁢𝔢cνcν
Isolating the covariant derivative that appears on the right-hand side, of the definitions of γa,b,c, we have
e_b,α⁢e_c,β⁢
γa,b,c⁢𝔢⁢bα⁢bα⁢𝔢⁢cβ⁢cβ=▿ν⁡𝔢a,μ⁢𝔢b,α⁢𝔢c,β⁢𝔢⁢b,μ⁢b,μ⁢𝔢⁢c,ν⁢c,ν
Simplify⁡rhs⁡=lhs⁡
▿β⁡𝔢a,α=γa,b,c⁢𝔢⁢bα⁢bα⁢𝔢⁢cβ⁢cβ
The γa,b,c and λa,b,c tensors are related by formulas (98.10) and (98.11) of Landau's book referenced at the end, this relationship can be obtained as follows
SubstituteTensor⁡,
λa,b,c=−γa,d,e⁢𝔢⁢dν⁢dν⁢𝔢⁢eμ⁢eμ+𝔢⁢fμ⁢fμ⁢𝔢⁢gν⁢gν⁢γa,f,g⁢𝔢bμbμ⁢𝔢cνcν
Simplifying the repeated indices,
Simplify⁡
λa,b,c=−γa,c,b+γa,b,c
Substituting the free indices in this expression and adding as follows, then isolating gammaa,b,c, we obtain the inverse of this relationship
+subs⁡a=b,b=c,c=a,−subs⁡a=c,b=a,c=b,
λa,b,c−λb,a,c−λc,a,b=2⁢γa,b,c
isolate⁡,gamma_a,b,c
γa,b,c=λa,b,c2−λb,a,c2−λc,a,b2
The nonzero Ricci coefficients and related λa,b,c components for the Schwarzschild metric
gamma_nonzero
γa,b,c=1,2,2=I⁢2⁢m−rr32,1,3,3=I⁢2⁢m−rr32,1,4,4=I⁢mr32⁢2⁢m−r,2,1,2=−I⁢2⁢m−rr32,2,3,3=cot⁡θr,3,1,3=−I⁢2⁢m−rr32,3,2,3=−cot⁡θr,4,1,4=−I⁢mr32⁢2⁢m−r
lambda_nonzero
λa,b,c=2,1,2=−I⁢2⁢m−rr32,2,2,1=I⁢2⁢m−rr32,3,1,3=−I⁢2⁢m−rr32,3,2,3=−cot⁡θr,3,3,1=I⁢2⁢m−rr32,3,3,2=cot⁡θr,4,1,4=−I⁢mr32⁢2⁢m−r,4,4,1=I⁢mr32⁢2⁢m−r
The value of γ⁢⁢1,11
gamma_~1,1,1
0
The components of γ⁢⁢a,b1
gamma_~1,a,b,matrix
γ⁢1a,b⁢1a,b=
The Riemann tensor in the tetrad system of coordinates can be expressed in terms of the Ricci rotation coefficients γa,b,c using formula (98.13) of Landau's book
Riemanna,b,c,d=d_d⁡gamma_a,b,c−d_c⁡gamma_a,b,d+gamma_a,b,f⁢gamma_f,c,d−gamma_f,d,c+gamma_a,f,c⁢gamma_f,b,d−gamma_a,f,d⁢gamma_f,b,c
Ra,b,c,d=∂d⁡γa,b,c−∂c⁡γa,b,d+−γc,f,d+γd,f,c⁢γa,bfa,bf−γa,f,c⁢γbfdbfd+γa,f,d⁢γbfcbfc
You can verify identities like this one by taking left-hand side minus right-hand side and computing an Array of components of this tensorial expression using TensorArray, then get its elements (components) using ArrayElems; recalling, ArrayElems returns a set with the elements of an Array, omitting all those elements equal to zero, so we expect an empty set here:
ArrayElems⁡TensorArray⁡lhs−rhs⁡,simplifier=simplify
∅
Let's verify in the same way the expression of the covariant derivative in terms of the Ricci rotation coefficients
See Also
Array, ArrayElems, d_, D_, e_, eta_, g_, IsTetrad, l_, m_, mb_, n_, NullTetrad, OrthonormalTetrad, Physics, Physics conventions, Physics examples, Physics Updates, Tensors - a complete guide, Mini-Course Computer Algebra for Physicists, TensorArray, Tetrads, TransformTetrad
References
Landau, L.D., and Lifshitz, E.M. The Classical Theory of Fields, Course of Theoretical Physics Volume 2, fourth revised English edition. Elsevier, 1975.
Compatibility
The Physics[Tetrads][gamma_] and Physics[Tetrads][lambda_] commands were introduced in Maple 2015.
For more information on Maple 2015 changes, see Updates in Maple 2015.
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