MadGraph5_aMC@NLO

complex mass scheme

Asked by HuanyuBi

Hi

If I use
mg5> set complex_mass True
then
Q1:the introduction of the width of W and Z is: A.complex mass scheme; B.fixed width scheme.
Q2:the introduction of the width of top is: A.complex mass scheme; B.fixed width scheme

if I don't use
mg5> set complex_mass True
then
Q3:the introduction of the width of W and Z is: A.complex mass scheme; B.fixed width scheme.
Q4:the introduction of the width of top is: A.complex mass scheme; B.fixed width scheme.

I think the answer for Q1 is A and the answer for Q3 is B. but i am not sure the answer for Q2 Q4.

Q5: if i want fixed width scheme for WZ and complex mass scheme for top. what should i do.

Best regards
Huanyu

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Solved by:
Olivier Mattelaer
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Best Olivier Mattelaer (olivier-mattelaer) said : 		#1

If you use the complex mass-scheme.

This applies to ALL masses.
So answer to
Q1 is A
Q2 is A
Q3 is B
Q4 is B

For Q5, we do not support such mix mode.
One solution is to create your own UFO model where all propagator (and the rest) are within that scheme.

Cheers,

Olivier

> On 16 Oct 2020, at 21:20, HuanyuBi <email address hidden> wrote:
>
> New question #693492 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/693492
>
> Hi
>
> If I use
> mg5> set complex_mass True
> then
> Q1:the introduction of the width of W and Z is: A.complex mass scheme; B.fixed width scheme.
> Q2:the introduction of the width of top is: A.complex mass scheme; B.fixed width scheme
>
> if I don't use
> mg5> set complex_mass True
> then
> Q3:the introduction of the width of W and Z is: A.complex mass scheme; B.fixed width scheme.
> Q4:the introduction of the width of top is: A.complex mass scheme; B.fixed width scheme.
>
> I think the answer for Q1 is A and the answer for Q3 is B. but i am not sure the answer for Q2 Q4.
>
> Q5: if i want fixed width scheme for WZ and complex mass scheme for top. what should i do.
>
> Best regards
> Huanyu
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
HuanyuBi (bihuanyu) said : 		#2

Hi Olivier,

Thank you for your answer. This solved my problem.

Best regards
Huanyu

Revision history for this message
Emily Lees (eemilylees09) said : 		#3

Perturbative calculations with unstable particles require the inclusion of their finite decay widths. A convenient, universal scheme for this purpose is the complex-mass scheme. It fully respects gauge-invariance, is straightforward to apply, and has been successfully used for the calculation of various tree-level processes and of the electroweak radiative corrections to e+ e- -> 4f and H -> 4f.
https://maritimemedicinals.ca/