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Tensor[RicciSpinor] - compute the spinor form of the trace-free Ricci tensor

Calling Sequences

     RicciSpinor(σ, R)

Parameters

   σ   - a solder form

   R   - (optional) the Ricci tensor for the metric determined by the solder form σ

 

Description

Examples

See Also

Description

• 

Let g be a metric tensor. The trace-free Ricci tensor for g is defined by Tij=Rij14gijS , where Rij is the Ricci tensor and S=gijRij the Ricci scalar of g.

• 

The command RicciSpinor(sσ ) first computes the metric tensor g defined by the solder form s. The trace-free Ricci tensor T for g is then computed and converted, using the solder form σ to a rank 4 covariant spinor with index type TABA'B' . (See convert/DGspinor.) Finally, a scalar factor of 12 is introduced according to standard conventions. See Stewart, page 85.

• 

If the Ricci tensor R for the metric g has been previously computed, then the Ricci spinor will be computed more quickly using the second calling sequence RicciSpinor(σ, R).

• 

This command is part of the DifferentialGeometry:-Tensor package, and so can be used in the form RicciSpinor(..) only after executing the commands with(DifferentialGeometry); with(Tensor); in that order. It can always be used in the long form DifferentialGeometry:-Tensor:-RicciSpinor.

Examples

withDifferentialGeometry:withTensor:

 

Example 1.

First create a vector bundle M with base coordinatest,x,y,z and fiber coordinates z1,z2,w1,w2.

M > 

DGsetupt,x,y,z,z1,z2,w1,w2,M

frame name: M

(2.1)

 

Define a metric g on the base. For this example we use the Godel metric. (See (12.26) in Exact Solutions to Einstein's Field Equations.) Note that we have adjusted the metric to conform to the signature conventions 1,1,1,1 used by the spinor formalism in the DifferentialGeometry package. See SpacetimeConventions.

M > 

gevalDGdt &t dt+ⅇxdt &s dzdx &t dxdy &t dy+1ⅇ2xdz &t dz2

g:=_DGtensor,M,cov_bas,cov_bas,,1,1,1,1,4,ⅇx2,2,2,−1,3,3,−1,4,1,ⅇx2,4,4,ⅇ2x2,_DGtensor,M,cov_bas,cov_bas,,1,1,1,1,4,ⅇx2,2,2,−1,3,3,−1,4,1,ⅇx2,4,4,ⅇ2x2,_DGtensor,M,cov_bas,cov_bas,,1,1,1,1,4,ⅇx2,2,2,−1,3,3,−1,4,1,ⅇx2,4,4,ⅇ2x2,_DGtensor,M,cov_bas,cov_bas,,1,1,1,1,4,ⅇx2,2,2,−1,3,3,−1,4,1,ⅇx2,4,4,ⅇ2x2

(2.2)

 

Use DGGramSchmidt to calculate an orthonormal frame F for the metric g.

M > 

FDGGramSchmidtD_t,D_x,D_y,D_z,g,signature=1,1,1,1assumingx::real

F:=_DGvector,M,,1,1,_DGvector,M,,1,1,_DGvector,M,,1,1,_DGvector,M,,1,1,_DGvector,M,,2,1,_DGvector,M,,2,1,_DGvector,M,,2,1,_DGvector,M,,2,1,_DGvector,M,,3,1,_DGvector,M,,3,1,_DGvector,M,,3,1,_DGvector,M,,3,1,_DGvector,M,,1,I,4,2Iⅇx,_DGvector,M,,1,I,4,2Iⅇx,_DGvector,M,,1,I,4,2Iⅇx,_DGvector,M,,1,I,4,2Iⅇx

(2.3)

 

Use SolderForm to compute the solder form σ from the frame F.

M > 

σSolderFormF

σ:=_DGtensor,M,cov_bas,con_vrt,con_vrt,,1,5,7,22,1,6,8,22,2,5,8,22,2,6,7,22,3,5,8,I22,3,6,7,I22,4,5,7,Iⅇx24+ⅇx24,4,6,8,Iⅇx24+ⅇx24,_DGtensor,M,cov_bas,con_vrt,con_vrt,,1,5,7,22,1,6,8,22,2,5,8,22,2,6,7,22,3,5,8,I22,3,6,7,I22,4,5,7,Iⅇx24+ⅇx24,4,6,8,Iⅇx24+ⅇx24,_DGtensor,M,cov_bas,con_vrt,con_vrt,,1,5,7,22,1,6,8,22,2,5,8,22,2,6,7,22,3,5,8,I22,3,6,7,I22,4,5,7,Iⅇx24+ⅇx24,4,6,8,Iⅇx24+ⅇx24,_DGtensor,M,cov_bas,con_vrt,con_vrt,,1,5,7,22,1,6,8,22,2,5,8,22,2,6,7,22,3,5,8,I22,3,6,7,I22,4,5,7,Iⅇx24+ⅇx24,4,6,8,Iⅇx24+ⅇx24

(2.4)

 

Calculate the Ricci spinor from the solder form σ.

M > 

Φ1RicciSpinorσ

Φ1:=_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,5,7,7,12,5,5,8,8,38,5,6,7,8,116,5,6,8,7,116,6,5,7,8,116,6,5,8,7,116,6,6,7,7,38,6,6,8,8,12,_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,5,7,7,12,5,5,8,8,38,5,6,7,8,116,5,6,8,7,116,6,5,7,8,116,6,5,8,7,116,6,6,7,7,38,6,6,8,8,12,_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,5,7,7,12,5,5,8,8,38,5,6,7,8,116,5,6,8,7,116,6,5,7,8,116,6,5,8,7,116,6,6,7,7,38,6,6,8,8,12,_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,5,7,7,12,5,5,8,8,38,5,6,7,8,116,5,6,8,7,116,6,5,7,8,116,6,5,8,7,116,6,6,7,7,38,6,6,8,8,12

(2.5)

 

Example 2.

In this example we first calculate the Ricci tensor of the metric g and then use the second calling sequence for RicciSpinor.

M > 

R2RicciTensorg

R2:=_DGtensor,M,cov_bas,cov_bas,,1,1,12,1,4,ⅇx4,2,2,32,4,1,ⅇx4,4,4,ⅇ2x4,_DGtensor,M,cov_bas,cov_bas,,1,1,12,1,4,ⅇx4,2,2,32,4,1,ⅇx4,4,4,ⅇ2x4,_DGtensor,M,cov_bas,cov_bas,,1,1,12,1,4,ⅇx4,2,2,32,4,1,ⅇx4,4,4,ⅇ2x4,_DGtensor,M,cov_bas,cov_bas,,1,1,12,1,4,ⅇx4,2,2,32,4,1,ⅇx4,4,4,ⅇ2x4

(2.6)
M > 

Φ2RicciSpinorσ,R2

Φ2:=_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,5,7,7,12,5,5,8,8,38,5,6,7,8,116,5,6,8,7,116,6,5,7,8,116,6,5,8,7,116,6,6,7,7,38,6,6,8,8,12,_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,5,7,7,12,5,5,8,8,38,5,6,7,8,116,5,6,8,7,116,6,5,7,8,116,6,5,8,7,116,6,6,7,7,38,6,6,8,8,12,_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,5,7,7,12,5,5,8,8,38,5,6,7,8,116,5,6,8,7,116,6,5,7,8,116,6,5,8,7,116,6,6,7,7,38,6,6,8,8,12,_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,5,7,7,12,5,5,8,8,38,5,6,7,8,116,5,6,8,7,116,6,5,7,8,116,6,5,8,7,116,6,6,7,7,38,6,6,8,8,12

(2.7)

 

Example 3.

We can check the result of Example 1 by direct computation, starting from the solder form σ. First use the command SpinorInnerProduct to calculate the metric g3 from σ. (Note that g3 coincides with the original metric g.)

M > 

g3SpinorInnerProductσ,σ

g3:=_DGtensor,M,cov_bas,cov_bas,,1,1,1,1,4,ⅇx2,2,2,−1,3,3,−1,4,1,ⅇx2,4,4,ⅇ2x2,_DGtensor,M,cov_bas,cov_bas,,1,1,1,1,4,ⅇx2,2,2,−1,3,3,−1,4,1,ⅇx2,4,4,ⅇ2x2,_DGtensor,M,cov_bas,cov_bas,,1,1,1,1,4,ⅇx2,2,2,−1,3,3,−1,4,1,ⅇx2,4,4,ⅇ2x2,_DGtensor,M,cov_bas,cov_bas,,1,1,1,1,4,ⅇx2,2,2,−1,3,3,−1,4,1,ⅇx2,4,4,ⅇ2x2

(2.8)

 

Second, calculate the curvature tensor C, the Ricci tensor R, and the Ricci scalar S.

M > 

CCurvatureTensorg

C:=_DGtensor,M,con_bas,cov_bas,cov_bas,cov_bas,,1,1,1,4,ⅇx8,1,1,4,1,ⅇx8,1,2,1,2,14,1,2,2,1,14,1,2,2,4,ⅇx,1,2,4,2,ⅇx,1,4,1,4,ⅇ2x8,1,4,4,1,ⅇ2x8,2,1,1,2,14,2,1,2,1,14,2,1,2,4,ⅇx8,2,1,4,2,ⅇx8,2,4,1,2,ⅇx8,2,4,2,1,ⅇx8,2,4,2,4,3ⅇ2x8,2,4,4,2,3ⅇ2x8,4,1,1,4,14,4,1,4,1,14,4,2,2,4,74,4,2,4,2,74,4,4,1,4,ⅇx8,4,4,4,1,ⅇx8,_DGtensor,M,con_bas,cov_bas,cov_bas,cov_bas,,1,1,1,4,ⅇx8,1,1,4,1,ⅇx8,1,2,1,2,14,1,2,2,1,14,1,2,2,4,ⅇx,1,2,4,2,ⅇx,1,4,1,4,ⅇ2x8,1,4,4,1,ⅇ2x8,2,1,1,2,14,2,1,2,1,14,2,1,2,4,ⅇx8,2,1,4,2,ⅇx8,2,4,1,2,ⅇx8,2,4,2,1,ⅇx8,2,4,2,4,3ⅇ2x8,2,4,4,2,3ⅇ2x8,4,1,1,4,14,4,1,4,1,14,4,2,2,4,74,4,2,4,2,74,4,4,1,4,ⅇx8,4,4,4,1,ⅇx8,_DGtensor,M,con_bas,cov_bas,cov_bas,cov_bas,,1,1,1,4,ⅇx8,1,1,4,1,ⅇx8,1,2,1,2,14,1,2,2,1,14,1,2,2,4,ⅇx,1,2,4,2,ⅇx,1,4,1,4,ⅇ2x8,1,4,4,1,ⅇ2x8,2,1,1,2,14,2,1,2,1,14,2,1,2,4,ⅇx8,2,1,4,2,ⅇx8,2,4,1,2,ⅇx8,2,4,2,1,ⅇx8,2,4,2,4,3ⅇ2x8,2,4,4,2,3ⅇ2x8,4,1,1,4,14,4,1,4,1,14,4,2,2,4,74,4,2,4,2,74,4,4,1,4,ⅇx8,4,4,4,1,ⅇx8,_DGtensor,M,con_bas,cov_bas,cov_bas,cov_bas,,1,1,1,4,ⅇx8,1,1,4,1,ⅇx8,1,2,1,2,14,1,2,2,1,14,1,2,2,4,ⅇx,1,2,4,2,ⅇx,1,4,1,4,ⅇ2x8,1,4,4,1,ⅇ2x8,2,1,1,2,14,2,1,2,1,14,2,1,2,4,ⅇx8,2,1,4,2,ⅇx8,2,4,1,2,ⅇx8,2,4,2,1,ⅇx8,2,4,2,4,3ⅇ2x8,2,4,4,2,3ⅇ2x8,4,1,1,4,14,4,1,4,1,14,4,2,2,4,74,4,2,4,2,74,4,4,1,4,ⅇx8,4,4,4,1,ⅇx8

(2.9)
M > 

RRicciTensorC

R:=_DGtensor,M,cov_bas,cov_bas,,1,1,12,1,4,ⅇx4,2,2,32,4,1,ⅇx4,4,4,ⅇ2x4,_DGtensor,M,cov_bas,cov_bas,,1,1,12,1,4,ⅇx4,2,2,32,4,1,ⅇx4,4,4,ⅇ2x4,_DGtensor,M,cov_bas,cov_bas,,1,1,12,1,4,ⅇx4,2,2,32,4,1,ⅇx4,4,4,ⅇ2x4,_DGtensor,M,cov_bas,cov_bas,,1,1,12,1,4,ⅇx4,2,2,32,4,1,ⅇx4,4,4,ⅇ2x4

(2.10)
M > 

SRicciScalarg,C

S:=52

(2.11)

 

Calculate the trace-free Ricci tensor T.

M > 

TevalDGR1gS4

T:=_DGtensor,M,cov_bas,cov_bas,,1,1,98,1,4,9ⅇx16,2,2,78,3,3,58,4,1,9ⅇx16,4,4,ⅇ2x16,_DGtensor,M,cov_bas,cov_bas,,1,1,98,1,4,9ⅇx16,2,2,78,3,3,58,4,1,9ⅇx16,4,4,ⅇ2x16,_DGtensor,M,cov_bas,cov_bas,,1,1,98,1,4,9ⅇx16,2,2,78,3,3,58,4,1,9ⅇx16,4,4,ⅇ2x16,_DGtensor,M,cov_bas,cov_bas,,1,1,98,1,4,9ⅇx16,2,2,78,3,3,58,4,1,9ⅇx16,4,4,ⅇ2x16

(2.12)

 

Convert T to a spinor U.

M > 

UconvertT,DGspinor,σ,1,2

U:=_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,7,5,7,−1,5,7,6,8,18,5,8,5,8,34,5,8,6,7,18,6,7,5,8,18,6,7,6,7,34,6,8,5,7,18,6,8,6,8,−1,_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,7,5,7,−1,5,7,6,8,18,5,8,5,8,34,5,8,6,7,18,6,7,5,8,18,6,7,6,7,34,6,8,5,7,18,6,8,6,8,−1,_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,7,5,7,−1,5,7,6,8,18,5,8,5,8,34,5,8,6,7,18,6,7,5,8,18,6,7,6,7,34,6,8,5,7,18,6,8,6,8,−1,_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,7,5,7,−1,5,7,6,8,18,5,8,5,8,34,5,8,6,7,18,6,7,5,8,18,6,7,6,7,34,6,8,5,7,18,6,8,6,8,−1

(2.13)

 

Rearrange the indices of U and scale by 12 to arrive at the Ricci spinor Φ1 (or Φ2).

M > 

Φ1 &minus RearrangeIndices12U,2,3

_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,5,5,5,0,_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,5,5,5,0,_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,5,5,5,0,_DGtensor,M,cov_vrt,cov_vrt,cov_vrt,cov_vrt,,5,5,5,5,0

(2.14)

See Also

DifferentialGeometry, Tensor, Convert, CurvatureTensor, Physics[Riemann],  RicciTensor, Physics[Ricci],  SolderForm, SpinorInnerProduct, WeylSpinor, Physics[Weyl]