Questions tagged [field-theory]

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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 ...
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23 views

How to define tensors similar to Riemann tensor in xAct xTensor xTras

I'm working on a project where we deal with objects very similar to Riemann tensor. In fact they are Christoffel symbols for higher spins. I'm using xTras for modeling problems in wolfram mathematica. ...
1
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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 ...
0
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23 views

Help with a custom coordinate transformation

I'm just starting to use Mathematica and can't wrap my head around the task I have at hand. It comes from field-theory. (Sorry I had to insert formulas as images instead of proper LaTex as it would ...
0
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18 views

Problem replacing an ansatz in a field equation with spin-isospin matrices

I've been lately trying to replicate a calculation but it is not working. The main problem is simple. I just have to replace an ansatz in a equation, that is (sorry for putting an image of that ) ...
0
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33 views

How to define custom operator for working with tensors with multiple indices?

I've symmetric tensor $h(z)$ with rank $s$. Instead of writing symmetric tensor with its components I use the following notation $h^{(s)}(z;a) = \sum_{\mu_i}(\prod_{i=1}^{s}a^{\mu_i})h^{(s)}_{\mu_1\...