# how to define Mandelstam variables in UFO format

Hello,

I want to write a UFO model where I need to use Mandelstam variables s, t and u. From Table 6 of this reference http://

I see that the momentum of the particle is defined as P(1,N) (momentum of the Nth particle).

If I have a two-particle collision, how do I define the variable s inside the UFO model? Should it be:

s = ( (P(1,1)

?

Thank you,

Arka

## Question information

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- Last query:
- 2017-11-01

- Last reply:
- 2017-11-01

Hi,

Variable in UFO are local to the vertex, therefore I do not see how you can define in the UFO format such type of variable (but eventually for 4-point vertices and still it will break some UFO convention)

You can obviously ask the opinion of other UFO author and/or FeynRules author if they see a way for that.

Cheers,

Olivier

> On Nov 1, 2017, at 18:23, Arka Santra <email address hidden> wrote:

>

> New question #660235 on MadGraph5_aMC@NLO:

> https:/

>

> Hello,

> I want to write a UFO model where I need to use Mandelstam variables s, t and u. From Table 6 of this reference http://

> I see that the momentum of the particle is defined as P(1,N) (momentum of the Nth particle).

>

> If I have a two-particle collision, how do I define the variable s inside the UFO model? Should it be:

>

> s = ( (P(1,1)

> ?

>

> Thank you,

> Arka

>

> --

> You received this question notification because you are an answer

> contact for MadGraph5_aMC@NLO.

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