Projects / Programmes source: ARIS

New physics implications of scalar resonances at the LHC

Research activity

Code Science Field Subfield
1.02.02  Natural sciences and mathematics  Physics  Theoretical physics 

Code Science Field
P210  Natural sciences and mathematics  Elementary particle physics, quantum field theory 

Code Science Field
1.03  Natural Sciences  Physical sciences 
Physics beyond standard model, Large hadron collider, Higgs boson, Flavour physics, Neutrino mass, Grand unified theories, Field theory on the lattice
Evaluation (rules)
source: COBISS
Researchers (7)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  37468  PhD Darius A. Faroughy Carias  Physics  Researcher  2017 - 2020  21 
2.  24264  PhD Jernej Fesel Kamenik  Physics  Head  2017 - 2020  277 
3.  39135  PhD Victor F. Guada Escalona  Physics  Junior researcher  2017 - 2020 
4.  26459  PhD Nejc Košnik  Physics  Researcher  2017 - 2020  79 
5.  25656  PhD Miha Nemevšek  Physics  Researcher  2017 - 2020  158 
6.  15643  PhD Saša Prelovšek Komelj  Physics  Researcher  2017 - 2020  221 
7.  38192  PhD Urša Skerbiš Štok  Physics  Junior researcher  2017 - 2020 
Organisations (2)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0106  Jožef Stefan Institute  Ljubljana  5051606000  90,976 
2.  1554  University of Ljubljana, Faculty of Mathematics and Physics  Ljubljana  1627007  34,275 
In many extensions of the standard model (SM), the light fermion (quark and lepton) masses are not directly determined by their coupling to the Higgs boson (HB). Consequently, the HB decay widths to light fermions can significantly deviate from SM predictions. Because of their smallness, they are very difficult to test experimentally at the LHC. In the proposed project we will investigate new approaches to testing HB interactions with light fermions. In particular, we will derive novel methods for probing HB decays to charm and strange quarks at the LHC. In the scope of this task, we will implement a new Higgs jet tagging algorithm as well as investigate novel possibilities to tag quarkonia in HB decays. These new approaches will then be applied to searches for new scalar resonances beyond SM, decaying to light quarks, which could elucidate the light fermion mass origin. A special role is played by neutrino masses. In the SM, lepton number (L) is to a good approximation a preserved global symmetry. However, it typically gets broken in SM extensions explaining small neutrino masses. If L is broken spontaneously, new HBs are present around the scale of breaking and observable processes are expected in experiments at low and high energies. We will study the production and exotic decay channels of such scalars that break lepton number and/or flavor. The possible presence of light scalars is especially interesting and motivated within theories of matter unification. We intend to study the impact of scalar representations within grand unified theories on the neutrino mass generation and flavor physics. We will identify leptoquarks (LQs) that are suitable to endow neutrinos with Majorana mass at one-loop and in particular focus on the LQ states that can be light while maintaining consistency with existing flavour constraints. Finally we will study the effects of such light LQs on the physics of HB decays as well as their direct production and decay patterns at the LHC. A peculiar feature of scalar fields is that they can form interactions which are not related to symmetries. This makes them ideal candidates to mediate interactions between otherwise sequestered physics sectors, the cosmological particle DM being a specific example. We propose to examine the generic LHC phenomenology of such models within an effective field theory framework. We will focus on the role of SM gauge invariance to correlate different possible production mechanisms and decay signatures of such states. This in turn allows to scrutinize perturbative unitarity constraints, which bound the validity of such an approach to describe new physics at the LHC. The theoretical background for studying light scalar particles also requires an understanding of stability of scalar potentials that determine the masses, mixings and couplings of extra scalars with the SM HB. We will investigate the positivity and stability of potentials for some minimal SM extensions, and relate the results with the phenomenology described above. Finally, light scalar resonances are predicted also within strongly-coupled theories based on the SU(NTC) gauge symmetry, containing elementary particles with mass m and leading to confinement below the scale ΛTC. These non-perturbative models will be considered using quantum field theory on the lattice. In the m≪ΛTC limit we intend to consider theories with new fermions that have spontaneously broken approximate chiral symmetry. Some of the lowest lying scalar states represent the Goldstone bosons which can be related to electroweak symmetry breaking, while the theory also supports the description of a composite HB. In the opposite parametric region m)ΛTC the bound states are analogues of cc/bb quarkonia and are stable against the decay via the strong interactions. The probability for their decays to SM states depends on their binding energy and wave function at the origin. We intend to determine these two quantities for interesting choices of SU(NTC)
Significance for science
The new results from the LHC run II, the Belle II flavor factory and some smaller precision experiments in particle physics will most probably fundamentally deepen our understanding of the basic laws of physics in the coming decade. Therefore, the proposed project, combining in a novel way the physics capabilities of all these facilities, has a high potential impact. The proposed research on the search for the origin of mass and fermionic flavors at the LHC is expected to open new opportunities in the field as they propose alternative ways to look for departures from standard theory predictions. This is useful for theorists since it sets constraints on any model with for example spontaneous origin of neutrino mass as well as for experimentalists since the searches address kinematic regions that were not looked into previously. Also, the visible Universe is composed of fermions - quarks and leptons. For the development of further research directions it is very important to explore whether also the Higgs boson and/or dark matter could be composed of new, yet-undiscovered fermions. Ab-initio simulations can establish whether this could be realized within strongly-coupled gauge theories. In general, such theoretical studies are crucial to maximize the impact of the upcoming experiments and use the collected data to full potential. Theoretical analyses can provide useful benchmarks and motivate new experimental searches. They also broaden the physics scope of the LHC and extend its coverage of new physics scenarios.
Significance for the country
The discovery of the Higgs boson had a direct impact on the society. It generated public interest in fundamental physics we are addressing as particle physicists and highlighted the questions that were answered and those that remain open. Mass and flavor origin remain crucial such issues and Higgs processes as well as searches for possible additional new scalar resonances are a promising venue to look for answers. Results of the proposed project will already during its execution be of high relevance for the experimental high energy physics groups at the F 9 department of the Jozef Stefan Institute, which are involved in the ATLAS experiment at the LHC as well as the Belle II experiment at the super B factory. Through the direct cooperation and idea exchange they could namely obtain an important competitive advantage compared to similar experimental groups abroad in the execution of the new suggested measurements, which could be key in the unfolding of new physics affecting the electroweak symmetry breaking or mass and flavor generation. Proposed project team members would transfer the newly gained insights and findings in the scope of the project into the University education practices through their involvement in the education processes at the Faculty of mathematics and physics of the University of Ljubljana; both through work with individual students on their seminar assignments, as well as through improvements in the curriculum, supplementing it with the latest research results. In this way we would improve the standard of higher education in Slovenia. The results of our studies would also be disseminated and conveyed to the general public through public lectures and writings (such practices relating to our previous research have been well received by the public). Last but not least, the proposed research will motivate new experiments, which would search for new predicted phenomena. The construction and execution of such experiments has generally a positive influence on economy through involvement of small and medium size enterprises, resulting in boosts in research and development and increased employment of highly educated population. This aspect will be especially relevant with the upcoming associate CERN membership of Slovenia.
Most important scientific results Interim report, final report
Most important socioeconomically and culturally relevant results Interim report, final report
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