Calculating traces with FeynCalc

In summary, the person is seeking help with FeynCalc and is trying to evaluate a trace from a Feynman diagram. They want to impose a condition on the momentum of particles that are all massless. They have tried various methods found online but have not been successful. They have attached their code for reference.
  • #1
Aleolomorfo
73
4
TL;DR Summary
Evaluating a trace coming from a Feynman diagrams with the assumptions that all particles are massless
Hello everybody!

I need a little help with FeynCalc. I think the problem is really simple but I can't find how to fix it.
I want to evaluate a trace coming from a Feynman diagram. Since the particles are all massless, I want to impose the condition on the momentum ##p^2=k^2=p'^2=0##.
I've attached the code in txt file.
I've tried everything I've found on the net(Simplify, Assumption, Refine, DotSimplify, DotSimplifyRelation, /. , ecc.)
Thank you in advance!
 

Attachments

  • Trace.txt
    936 bytes · Views: 343
Physics news on Phys.org
  • #2
<code>&lt;&lt; FeynCalc`Pair[Momentum[p], Momentum[p]] = 0;Pair[Momentum[k], Momentum[k]] = 0;Pair[Momentum[pp], Momentum[pp]] = 0;expr = (DiracTrace[DiracSlash[p] . DiracMatrix[5] . DiracSlash[k] . DiracMatrix[5] . DiracSlash[pp]]);FCPrint[Simplify[expr]]</code>
 

FAQ: Calculating traces with FeynCalc

What is FeynCalc and how does it help with calculating traces?

FeynCalc is a Mathematica package designed to assist with calculations in quantum field theory, particularly in the context of Feynman diagrams. It contains tools for simplifying expressions, performing tensor algebra, and calculating traces of matrices.

How do I install and use FeynCalc?

To install FeynCalc, you will need to have Mathematica installed on your computer. Once you have Mathematica, you can download the FeynCalc package and follow the installation instructions provided. To use FeynCalc, you will need to load the package in your Mathematica notebook by typing <

What is a trace and why is it important in quantum field theory?

A trace is a mathematical operation that involves summing the diagonal elements of a matrix. In quantum field theory, traces are important because they can be used to calculate physical quantities such as scattering amplitudes and decay rates. They also allow us to simplify complicated expressions involving matrices and tensors.

How can I calculate traces using FeynCalc?

To calculate traces using FeynCalc, you can use the Tr or TrSimplify functions. These functions take in a matrix or expression and return the trace of that matrix or expression. You can also use the TrExpand function to expand traces of products of matrices into sums of traces of individual matrices.

Can FeynCalc handle traces of higher order tensors?

Yes, FeynCalc has tools for handling traces of higher order tensors, including vector and tensor fields. You can use the Tr and TrSimplify functions with these higher order tensors, as well as the TrContract function which allows you to contract indices of tensors within a trace.

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