Massless spin-2 propagator

I do not know how to write propagator and matrix density for massless
particle spin-2.

Best

    Alexander Pukhov

On 7/3/21 3:01 PM, Jiaming Zheng wrote:
> New question #697827 on CalcHEP:
> https://answers.launchpad.net/calchep/+question/697827
>
> I want to study the decay rate and cross section of some processes mediated by a massless spin-2 particle(graviton). The gravitons are virtual and do not appear in the external states. According to the manual, only massive spin-2 particle and its propagator are implemented in CalcHEP. There is a discontinuity between the massive and massless spin-2 theory so setting a small mass to a massive spin-2 particle does not seem to be a safe workaround for my purpose.
>
> I can get the analytical expression of matrix elements with other packages. However, I hope I can use CalcHEP to integrate numerically the multiple particle phase space.
>
> Is there any way to implement a massless spin-2 propagator in CalcHEP? I guess it might be done by changing the hard-coded massive spin-2 propagator in the source code. If this is the case, which part of the code should I look at?
>

One can implement the model discussed here
https://core.ac.uk/download/pdf/85124739.pdf

On 04/07/2021 12:15, Alexander Pukhov wrote:
> Question #697827 on CalcHEP changed:
> https://answers.launchpad.net/calchep/+question/697827
>
> Status: Open => Answered
>
> Alexander Pukhov proposed the following answer:
> I do not know how to write propagator and matrix density for massless
> particle spin-2.
>
> Best
>
>    Alexander Pukhov
>
>
> On 7/3/21 3:01 PM, Jiaming Zheng wrote:
>> New question #697827 on CalcHEP:
>> https://answers.launchpad.net/calchep/+question/697827
>>
>> I want to study the decay rate and cross section of some processes mediated by a massless spin-2 particle(graviton). The gravitons are virtual and do not appear in the external states. According to the manual, only massive spin-2 particle and its propagator are implemented in CalcHEP. There is a discontinuity between the massive and massless spin-2 theory so setting a small mass to a massive spin-2 particle does not seem to be a safe workaround for my purpose.
>>
>> I can get the analytical expression of matrix elements with other packages. However, I hope I can use CalcHEP to integrate numerically the multiple particle phase space.
>>
>> Is there any way to implement a massless spin-2 propagator in CalcHEP? I guess it might be done by changing the hard-coded massive spin-2 propagator in the source code. If this is the case, which part of the code should I look at?
>>

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Thanks a lot for the messages!

The massless spin-2 propagator I want to have has the form of, for example, Eq.(47) in https://arxiv.org/abs/gr-qc/0607045

Is there a way to define my own propagator in CalcHEP?

Best,
Jiaming Zheng

Thanks Alexander Pukhov, that solved my question.