Tilman Plehn

Greetings from Heidelberg, the most beautiful theoretical physics institute in Germany. Come and visit us at the villas to judge for yourself.

If I am not playing my trombone in the Mannheim University Bigband I am interested in Higgs physics, QCD, and new physics at the LHC, and I am still completely convinced we will find something exciting once the LHC reaches its design energy. You can find all my publications on all those topics here, including all the great ideas which turned out not to be realized in nature. Please also feel free to browse through my linked talks.

For a long time I used to calculate higher order cross sections in supersymmetry, working on a Fortran package called Prospino2. It also includes some private results on charged Higgs bosons. In the good old days I also worked on proper simulations of physics beyond the Standard Model with a Monte Carlo generator called Madgraph. But that is a long time ago, and by now we have become users of this tools like many other groups. However, with our LHC group we still take some pride in simulating LHC events properly, even if it takes us and our computers some extra time. QCD is just too much fun to use short cuts.

During the years of early LHC running the Higgs boson has transitioned from the most exciting discovery to a new, precision handle to search for physics beyond the Standard Model. One way to search for such effects is through the extension of the Standard Model to an effective field theory, either a Higgs effective field theory (HEFT) or a Standard Model effective field theory (SMEFT). In addition to some field theory work we established a global Higgs and gauge boson fit through our SFitter tool - run by a French-German coalition of the difficult. With this tool we are having great fun learning frequentist and Bayesian statistics and applying it right to LHC data. And we are always just a little bit ahead of the official combinations, which fills us with pride and gives ATLAS and CMS a reason to never officially cite us.

I am convinced that the Higgs boson will not be the last discovery in the LHC era. For example the Fermi-LAT experiment might well have observed a dark matter particle, without being able to establish it beyond all scientific doubt. This is another case for the SFitter team, because indirect detection through gamma rays is not the only way to search for dark matter. And it turned out that the interpretation of the Fermi-LAT data combined with everything else we know about dark matter does change the picture, inspiring for example LHC searches for invisible Higgs decays. The nice aspects of such links is that they only appear once we really understand the statistics and uncertainties, turning a general interest in statistics into a useful physics application.

Talking about statistics, together with a group from NYU we just developed a way to compute and understand where information on signal processes at the LHC actually come from; which regions of phase space we should study, and what we can expect from different production and decay channels. This application of information geometry is a great example how we can apply advanced mathematics to LHC physics without following of the usual path of formal physics. So if you are interested in such links between maths and LHC physics, just drop me an mail.

Finally, we are just diving into applications of machine learning in LHC physics. And this is not the usual multivariate analyses, but proper and really cool neural networks. It all started with the question how we can identify boosted top quarks using QCD jet algorithms, where our HEPTopTagger really made a difference. By now, we have upgraded it to DeepTop, based on convolutional networks, and a completely new DeepTopLoLa setup. And that is just the start, because from what we have seen in that community machine learning will revolutionize not the way we think about the fundamental physics, but the way we extract information about it. Trust me!

So, if you are interested in any of these things: call me, come by, catch me if you can. We do have bachelor, master, and PhD thesis projects in all research directions of our group. Our group has a lot of fun thinking about LHC theory, so please come and join us for a coffee or a thesis. The only thing we require is a nice set of lectures heard, indicating that your studies are driven more by the excitement for physics than a career perspective as a management consultant. This definitely includes having heard Quantum Field Theory I and II, Standard Model physics, and some of the advanced lectures and seminars we offer in particle phenomenology. If you started off as an experimentalist and you would like to switch to theory we will try hard to make this possible. In general, Heidelberg offers a huge number of advanced lectures, so please make use of them to then get a rapid start into a research project.

Finally, if you are interested how I ended up here, have a look at my short CV. Even though in our group we have seen some really nice careers unfold, please do yourself the favor and have a good plan B before trying your luck the same way...