The general contact address for the PYTHIA collaboration is, from which we will sort out who should answer your inquiry. Guidelines for bug reports and physics questions must be followed.

Questions written to, will be answered on our service desk hosted on gitlab, with an answer sent back to you automatically. We publish historic answers in the same place, so please take a look to check if your question has already been answered.

If you write an email, please put a line in your email saying that we are allowed to publish the answer publicly on our service desk. Public answers help the community, and help yourself, by freeing up more of our time to implement physics.

Mailing list for news and new version alerts

If you want to be alerted whenever a new public version is released, you can subscribe on our announcement mailing list. See Subscribe to News.

Bug reports and physics questions

No code is perfect, and we rely on PYTHIA users to report suspect behaviour to us. To help us in the subsequent debugging efforts, however, it is most helpful if you can present your case in as clear terms as possible. A convenient path is the following.

For general bug reports and physics questions, always use the address Never contact several persons independently on the same topic, thereby potentially leading to doublework. Abuse will have consequences.

Do note that the major experimental collaborations, such as ATLAS and CMS, have their own Monte Carlo support groups, with a lot of experience in solving typical issues, many of which are related to the setups and interfaces created inside the collaborations. If you are a member of a major collaboration you should always turn to these groups in the first place, and only turn to us when it has been confirmed as a true problem going beyond the local installation.

You may also direct PYTHIA-related questions to us, following the same pattern as above, but note that manpower is limited, so focus on topics that do require our expertise. We cannot act as teachers of particle physics in a broader sense, however. If you are a PhD student it is the task of your supervisor to see to it that you are offered the particle physics courses you need, and to answer all general questions you may have. Summer schools can offer a most useful complement to the basic courses at you local university. In particular we would like to mention the MCnet annual Monte Carlo school for general information on the physics and usage of event generators, and the CTEQ annual summer school on QCD analysis and phenomenology.

Author specialities

In almost all cases, your best option is to use the general address, but it might be neccesary for some to contact the PYTHIA person(s) most directly involved in your issue. Here is a brief list of specialities:

Name Email Topics
Javira Altmann Junction colour reconnection
Christian Bierlich     rope hadronization and string shoving;
heavy-ion collisions; ALICE matters
Naomi Cooke NRQCD charmonium
Nishita Desai SUSY; SLHA; BSM
Leif Gellersen scale uncertainties; matching and merging
Ilkka Helenius photoproduction; gamma-gamma; diffraction
Philip Ilten taus, onia; configure and Makefile;
core structure; LHCb matters
Leif Lönnblad heavy-ion collisions (pA and AA)
Stephen Mrenna SUSY, BSM, matching and merging;
CMS matters
Christian T Preuss VINCIA; matching and merging; external MEs
Torbjörn Sjöstrand SM processes, parton showers, MPIs,
colour reconnection, hadronization,
core structure and utilities
Peter Skands SLHA, parton showers, MPIs, tuning,
colour reconnection, hadronization, VINCIA
Marius Utheim hadronic rescattering
Rob Verheyen Weak showers, VINCIA

Code contributions and feature requests

In addition to bug reports, we welcome contributions of code that can be made a part of the public PYTHIA distribution. This could be the implementation of a new process or of some other physics mechanism. There are numerous such examples of external code that have been incorporated.

To be successful, a contribution must not only introduce useful new functionality but also be written in a form that fits nicely into the existing PYTHIA framework. To ensure this, code contributions to PYTHIA 8 should follow the style guide which is defined by the CODINGSTYLE file in the PYTHIA distribution. Please ensure that your code conforms reasonably well with this style before sending it on to us. We do not have manpower on our side to do it, and cannot compromise on maintaining a clean and uniform style throughout PYTHIA 8.

See also our Guidelines for PYTHIA Authors and Contributors.

Also feel free to propose new features you believe would improve PYTHIA, but be aware that manpower is a limiting factor.
Ultimately we will have to set our own priorities.

Feel free to consult beforehand whether a specific contribution would be welcome, so you don't waste time on something that e.g. may already be under way, or that may not fit so well. This in particular is the case if linking to external libraries are involved, since fitting a new library into the PYTHIA build procedure can be a rather delicate process, not always worth the bother.

These pages

These pages are maintained by Christian Bierlich who can be reached on