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First initialize an 8-dimensional Lie algebra. We shall create various deformations of this Lie algebra. Here are the structure equations.
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| (2.1) |
Use the commands LieAlgebraData and DGsetup to initialize this Lie algebra.
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| (2.2) |
We also need a vector space on which we can define the adjoint representation (See Adjoint and Representation).
alg >
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alg >
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alg >
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| (2.5) |
The linear deformations are given in terms of the Lie algebra cohomology of with coefficients in the adjoint representation. This cohomology is computed to be:
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| (2.6) |
We note that the 2-forms in are all closed.
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Example 1.
We consider the Lie algebra deformation defined by the first cohomology class, represented by .
| (2.8) |
algW >
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| (2.9) |
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We use the Query command to check that this deformation defines a Lie algebra.
Example 2.
Here we look at the Lie algebra deformation defined by the third cohomology class, represented by
| (2.12) |
algW >
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| (2.13) |
| (2.14) |
This time the linear deformation defined by does not satisfied the Jacobi identity.
To continue, we calculate the quadratic deformation. For this, we need the Massey product of with itself.
algW >
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| (2.16) |
Next we use the command CohomologyDecomposition to determine if the Massey product is exact.
algW >
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| (2.17) |
The 3-form is exact. The second order deformation term is given by
algW >
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| (2.18) |
We find the second order deformation to the original Lie algebra.
Alg1 >
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| (2.19) |
| (2.20) |
The second order deformation also fails to satisfy the Jacobi identity so we repeat the previous steps to find the third order deformation.
algD22 >
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| (2.22) |
algD22 >
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| (2.23) |
The next Massey products are zero. This means that the third order deformation is a Lie algebra.
algW >
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| (2.24) |
algW >
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| (2.25) |
Alg1 >
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| (2.26) |
| (2.27) |
Example 3.
Here we using the calling sequence with the keyword argument parameters to find the most general linear deformation that can be constructed from the first 4 cohomology classes in .
algD23 >
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| (2.29) |
algD24 >
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| (2.30) |
We therefore have two possibilities.The first is
| (2.31) |
algD24 >
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and the second is
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algD24 >
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