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Final Report Summary - LEAGUE (Low-Energy Aspects of Gauge Unifications and their Experimental Implications)

In spite of its enormous success, there are nowadays several hints that the Standard Model of elementary particle interactions, a beautiful quantum field theory capable of describing physics phenomena on energy scales stretching up to the TeV scale, is not necessarily a complete theory of nature. Barring its incapability to supply a consistent quantum description of the gravitational interaction, it must also be extended in order to account for an accurate picture of the enigmatic world of neutrinos, feebly interacting particles (produced in stars, nuclear reactors, in the Earth’s atmosphere and even in the first moments of the very existence of the Universe) passing through our bodies in billions every second. In doing so, formerly unquestionable principles of particle physics such as the conservation of the baryon and lepton numbers in particle reactions could be at stake. As a matter of fact, there is no deep reason why, at the next level of physics reality corresponding to yet higher energies, these observables should be invariant.

Perhaps the most conservative approach to modelling how their violation can come about has to do with the so called Grand unification of the electromagnetic, weak and strong nuclear forces, a class of Standard Model extensions dating back to mid 1970’s. Remarkably enough, as old as these ideas are, only a limited progress has been achieved in transforming them into firm predictions that may be testable in laboratories. One of the main reasons behind is the remoteness of the energy scales at which this kind of new dynamics should exhibit itself which, at the laboratory level, translates to an extreme rarity of the corresponding low-energy processes such as the instability of the proton, one of the fundamental constituents of all atoms.

The LEAGUE project was aiming mainly at the conundrum of the calculability of the proton lifetime in the simplest grand unified models and related phenomena expected in their low-energy regime. It was focusing on a thorough quantitative scrutiny of some of the most popular scenarios of that kind, making use of some of their unique features like, e.g., their robustness with respect to the effects of quantum gravity.

Among the main results of the project there is a big progress in the calculation techniques necessary for dealing with the most promising (yet usually rather technically demanding) unified scenarios such as the minimal SO(10) grand unified model. A number of potentially realistic realisations of the same was identified with very interesting features like accidentally light extra scalar particles likely to be within reach of the Large Hadron Collider. Another nice and important results was an identification of an interesting class of scenarios based on the so-called flipped SU(5) gauge symmetry in which a beautiful idea of radiative generation of neutrino masses (due to E. Witten in 1980’s) could have eventually been implemented in a potentially realistic and testable setting. Third, the studies performed during the project execution elucidated some of the long-standing issues in the theory of two-loop renormalization in the so called “multi-Abelian” gauge theories, hence addressing a big historical gap in the existing literature.

These achievements have been described in detail in 8 scientific articles published in high ranking peer-reviewed international journals (+2 currently in the review process), 2 monographs, 5 other papers in conference proceedings and 2 semi-popular contributions in the local journals. The fellow has delivered a number of invited presentations including those given at the prominent international conferences such as the “Baryon and lepton number violation” (BLV) meeting and the “International Conference in High Energy Physics” (ICHEP) and a number of seminars stretching from the purely scientific presentations at many research centres in Europe to the popular lectures to the general public in his home country.

The high level of the fellow’s expertise in BSM physics can be further demonstrated by the number of regular graduate-level courses delivered either at the premises of the Charles University in Prague or during invited sessions at international summer schools. Besides this, the fellow (co-)organized several successful meetings such as the 2014 Advanced Computing and Analysis Techniques in physics research (ACAT) meeting; recently, he became a member of the local organisation committees of the 2017 FPCP (Flavour Physics and CP violation) and the 2020 ICHEP conferences to be held in Prague.

At the national level, the fellow’s work has been widely recognised recently by being rewarded by the highly prestigious “2014 Neuron grant in physics” awarded by the Foundation for support of science and research Neuron and the “2016 Learned Society Under 40 Scientist Award” granted by The Learned Society of the Czech Republic.

The benefit of the fellow from the current Marie-Curie CIG project execution was enormous. Not only that it facilitated his return to the home country and his establishing there as an expert in a very lively and exciting research field that has historically happened to be out of the local mainstream but it has also helped him in securing a stable academic position with a clear long-term perspective. A new research group devoted to the theory and phenomenology of physics beyond the Standard Model of particle interactions has been founded at the host institution (Institute of Particle and Nuclear Physics of the Charles University in Prague) and funds are being successfully raised in order to sustain it with the goal to become a stable part of the institute’s research portfolio in the long-term perspective.

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