# Questions tagged [field-theory]

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### Derivatives with dummy indices not commutative after 3d derivative?

Recently I've encountered the following issue in xAct. I've defined the Manifold and tensors in the following manner Then consider the following expressions. In the case where there are 2 ...
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### How to combine symmetrized tensor expressions into single expression in xAct

Let's sayI have the following expression in xAct where covariant derivatives are commutative, $\epsilon$ and $h$ are symmetric tensors. As we can see this expression is equivalent to If we ...
0answers
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### How to speed up xTensor simplification?

I need to compute a variation of the 4th rang symmetric tensor. I've written a code that successfully computes it, but when I use the resulting tensor to compute the second variation the ...
1answer
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### How to define commutative covariant derivatives in xTensor

I'm new with working xAct package and got stuck defining covariant derivatives that commute with each other. I want to simulate flat space-time. And here is my code ...
1answer
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### Implementing the field axioms with FindEquationalProof?

I am fiddling around with FindEquationalProof, currently trying to prove some basic statements for fields. I have a set of axioms which almost constitutes the field theory axioms: ...