[seminar] [DANAS] Bruno Klajn, 23.05. (ponedjeljak) 11 sati c.t., dvorana krila Ivana Supeka

[Kornelija Passek-Kumericki]

                       SEMINAR  TEORIJSKE  FIZIKE


   (Zajednički seminari Fizičkog odsjeka PMF-a te Zavoda za teorijsku
    fiziku i Zavoda za eksperimentalnu fiziku IRB-a)

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Direct numerical approach to one-loop amplitudes


Bruno Klajn
Zavod za teorijsku fiziku, IRB


   Datum:  ponedjeljak, 23. svibnja 2016.
   Vrijeme: 11 sati c.t.
   Mjesto: IRB, dvorana krila Ivana Supeka


Sazetak:

The conventional way of calculating one-loop Feynman amplitudes follows a
familiar scheme: first the amplitude is written in terms of contributing
Feynman diagrams, then each diagram is reduced to a linear combination of
known master scalar integrals, and, finally, all the diagrams are combined
to give an expression for the amplitude. This, diagram-by-diagram approach,
implemented either as an analytical or a numerical calculation, has several
shortcomings. For large number of external particles, the number of
contributing diagrams grows rapidly, making the calculations very demanding
and repetitive. Also, it is known that the expression for the amplitude is,
more often than not, much simpler than the bare sum of the diagrams
themselves. This means there are large cancellations between contributions
of different diagrams, implying that a lot of laborious calculation is
probably avoidable. Furthermore, the analytical expressions obtained in such
a way are usually used only to numerically evaluate integrals over different
phase spaces, questioning the need for the complete analytical evaluation.
On the other hand, if a numerical implementation of above diagram-by-diagram
approach is used, one confronts inevitable numerical instabilities and loss
of precision due to the aforementioned cancellations.
In the seminar, I will present a completely numerical approach for
evaluation of the one-loop Feynman amplitudes. The approach is complementary
to the conventional diagram-by-diagram method in that it calculates the
complete amplitude at once and considerably softens the above shortcomings.
As an example, N-scalar and N-photon amplitudes are calculated and compared
to the exact results.




Voditeljica seminara: Kornelija Passek-Kumericki (passek at irb dot hr)
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