**Next message:**Philipp: "Tarcer Recursion"**Previous message:**Maksym: "Error! DiracTrick has encountered a fatal problem and must abort the computation. The problem reads: Incorrect combination of dimensions and g^5 scheme!"**In reply to:**Maksym: "Error! DiracTrick has encountered a fatal problem and must abort the computation. The problem reads: Incorrect combination of dimensions and g^5 scheme!"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]**Mail actions:**[ respond to this message ] [ mail a new topic ]

Hi,

the reason is that your expression is a mixture of 4- and D-dimensional

quantities. So when you want to compute the trace, the given expression

is illegal in the Naive Dimensional Regularization (NDR) scheme, where

everything must be D-dimensional.

So either you ensure that your expression is purely D-dimensional

f1 = coef0 Pair[Momentum[Polarization[k2, I], D],

LorentzIndex[\[Mu], D]] SpinorUBarD[k1,

0].GAD[\[Mu]].QuarkPropagator[{k1 + k2, 0},

Explicit -> True].GAD[\[Nu]].SpinorUD[p1,

0] (-MTD[\[Nu], \[Alpha]] +

FVD[k1 + k2 - p1, \[Nu]] FVD[k1 + k2 - p1, \[Alpha]]/

mW^2) FAD[{k1 + k2 - p1, mW}] SpinorVBarD[p2,

0].GAD[\[Alpha]].(1 - GA5).SpinorUD[p3, m] // FCI

(or 4-dimensional, if it's tree level) or you switch to the

t'Hooft-Veltman scheme via

$BreitMaison=True;

where traces may contain 4- and D-dimensional objects. However, if your

input expression has any inconsistencies w.r.t the dimensions, the trace

will of course be also inconsistent.

Cheers,

Vladyslav

Am 24.07.2017 um 11:24 schrieb Maksym:

*> Hi! I'm experiencing an issue when trying to calculate the squared amplitude.
*

*>
*

*> The code is
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*>
*

*> FCClearScalarProducts[];
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*> {coef0 = u Sqrt[\[Alpha]] g/2, coef1 = 1/(32 Pi s)};
*

*> {ScalarProduct[k1, k1] = ScalarProduct[k2, k2] = 0,
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*> ScalarProduct[p1, p1] = ScalarProduct[p2, p2] = 0,
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*> ScalarProduct[p3, p3] = m^2,
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*> ScalarProduct[k1, k2] = s/2, ScalarProduct[k1, p1] = -t1/2,
*

*> ScalarProduct[k1, p2] = (s1 + t1 - t2)/2,
*

*> ScalarProduct[k1, p3] = (s - s1 + t2)/2,
*

*> ScalarProduct[k2, p1] = (s - s2 + t1)/2,
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*> ScalarProduct[k2, p2] = (s2 + t2 - t1 - m^2)/2,
*

*> ScalarProduct[k3, p3] = (m^2 - t2)/2, ScalarProduct[p1, p2] = s1/2,
*

*> ScalarProduct[p1, p3] = (s - s1 - s2)/2,
*

*> ScalarProduct[p2, p3] = (s2 - m^2)};
*

*> f1 = coef0 PolarizationVector[
*

*> k2, \[Mu]] SpinorUBar[k1,
*

*> 0].GA[\[Mu]].QuarkPropagator[{k1 + k2, 0},
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*> Explicit -> True].GA[\[Nu]].SpinorU[p1,
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*> 0] (-MetricTensor[\[Nu], \[Alpha]] +
*

*> FourVector[
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*> k1 + k2 - p1, \[Nu]] FourVector[k1 + k2 - p1, \[Alpha]]/
*

*> mW^2) PropagatorDenominator[k1 + k2 - p1,
*

*> mW] SpinorVBar[p2, 0].GA[\[Alpha]].(1 - GA5). SpinorU[p3, m] // FCI
*

*> f1star = ComplexConjugate[f1]
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*> m11 = DoPolarizationSums[f1 f1star, k2, 0]
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*> m22 = FermionSpinSum[m11] /. DiracTrace -> TR // Contract // Simplify
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*> Mfinal = m22
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*> dsigbardz = coef1 Mfinal
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*>
*

*> It displays the amplitude correctly and evaluates its complex conjugation, but faols when calculating the fermion polarization sum with the error
*

*> "Error! DiracTrick has encountered a fatal problem and must abort the computation. The problem reads: Incorrect combination of dimensions and g^5 scheme!"
*

*>
*

*> What is the reason for this?
*

*>
*

**Next message:**Philipp: "Tarcer Recursion"**Previous message:**Maksym: "Error! DiracTrick has encountered a fatal problem and must abort the computation. The problem reads: Incorrect combination of dimensions and g^5 scheme!"**In reply to:**Maksym: "Error! DiracTrick has encountered a fatal problem and must abort the computation. The problem reads: Incorrect combination of dimensions and g^5 scheme!"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]**Mail actions:**[ respond to this message ] [ mail a new topic ]

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