Next-to-next-to leading order calculations; Lepton-flavour violation; Regularization schemes; Search for physics beyond the Standard Model
Engel T., Signer A., Ulrich Y. (2022), Universal structure of radiative QED amplitudes at one loop, in Journal of High Energy Physics
, 2022(4), 97-97.
Banerjee Pulak, Engel Tim, Schalch Nicolas, Signer Adrian, Ulrich Yannick (2022), Møller scattering at NNLO, in Physical Review D
, 105(3), L031904-L031904.
Banerjee Pulak, Engel Tim, Schalch Nicolas, Signer Adrian, Ulrich Yannick (2021), Bhabha scattering at NNLO with next-to-soft stabilisation, in Physics Letters B
, 820, 136547-136547.
Torres Bobadilla W. J., Sborlini G. F. R., Banerjee P., Catani S., Cherchiglia A. L., Cieri L., Dhani P. K., Driencourt-Mangin F., Engel T., Ferrera G., Gnendiger C., Hernández-Pinto R. J., Hiller B., Pelliccioli G., Pires J., Pittau R., Rocco M., Rodrigo G., Sampaio M., Signer A., Signorile-Signorile C., Stöckinger D., Tramontano F., Ulrich Y. (2021), May the four be with you: novel IR-subtraction methods to tackle NNLO calculations, in The European Physical Journal C
, 81(3), 250-250.
Banerjee Pulak, Engel Tim, Signer Adrian, Ulrich Yannick (2020), QED at NNLO with McMule, in SciPost Physics
, 9(2), 027-027.
Coutinho Antonio M., Crivellin Andreas, Manzari Claudio Andrea (2020), Global Fit to Modified Neutrino Couplings and the Cabibbo-Angle Anomaly, in Physical Review Letters
, 125(7), 071802-071802.
Naterop L., Signer A., Ulrich Y. (2020), handyG—Rapid numerical evaluation of generalised polylogarithms in Fortran, in Computer Physics Communications
, 253, 107165-107165.
Banerjee P., Carloni Calame C. M., Chiesa M., Di Vita S., Engel T., Fael M., Laporta S., Mastrolia P., Montagna G., Nicrosini O., Ossola G., Passera M., Piccinini F., Primo A., Ronca J., Signer A., Torres Bobadilla W. J., Trentadue L., Ulrich Y., Venanzoni G. (2020), Theory for muon-electron scattering @ 10 ppmA report of the MUonE theory initiative, in The European Physical Journal C
, 80(6), 591-591.
Engel T., Signer A., Ulrich Y. (2020), A subtraction scheme for massive QED, in Journal of High Energy Physics
, 2020(1), 85-85.
Signer Adrian (2019), Charged lepton flavour violating processes, in SciPost Physics Proceedings
, (1), 014-014, SciPost Foundation, Amsterdam(1), 014-014.
Engel T., Gnendiger C., Signer A., Ulrich Y. (2019), Small-mass effects in heavy-to-light form factors, in Journal of High Energy Physics
, 2019(2), 118-118.
With the completion of the Standard Model (SM) through the discoveryof the Higgs boson, particle physics has reached a very peculiarpoint. On the one hand we have an extremely successful theory that isable to explain all (?) data from collider and low-energy precisionexperiments. On the other hand, we know that the theory cannot becomplete, as it fails to explain e.g. the abundance of matter overantimatter, neutrino masses, dark matter and dark energy.Hence, the main thrust of particle physics in the coming years is tosearch for deviations from the SM that can be produced in laboratoryexperiments, using high-energy colliders and low-energy precisionmeasurements. In fact, some rather intriguing hints for possibledeviations from the SM have been reported already (hence the questionmark above). There are some indications of possible lepton-flavouruniversality (LFU) violations from $B$~decays and there is a longstanding discrepancy between theory and experiment for the anomalousmagnetic moment of the muon, $a_\mu$. This project contributes to thescrutiny of these hints, focussing on leptonic processes. It followstwo lines.First, computational techniques are developed and adapted to calculateprocesses at next-to-next-to leading order (NNLO) in quantumelectrodynamics (QED). In particular a completely differentialcalculation of the muon decay at NNLO will be performed for a masslessand a massive electron. The corresponding phase-space integration willbe analysed in different regularization schemes and the relationbetween the massive and massless results as well as resummation oflarge logarithms will be studied. The project also contributessubstantially to the international effort of computing muon-electronscattering at NNLO. The main motivation for this is to extract theleading hadronic contribution to $a_\mu$.Second, the project is concerned with searches for physics beyond theSM related to processes with charged lepton-flavour violation(LFV). The connection to LFU makes this more topical than ever. Themain focus will be on a systematic analysis of LFV in taudecays. Apart from a detailed phenomenological investigation thisinvolves the calculation of some selected two-loop anomalous dimensionswithin an effective field theory approach that parametrizes newphysics in a model independent way. The possibility to find some lightnew particles like dark photons using very precisely measured andcalculated observables with muons will also be investigated.