### Research topics

 Quark & lepton flavor phenomenology   Quark flavor and CP violation phenomena are described in the Standard Model by a total of 4 parameters of the Cabibbo-Kobayashi-Maskawa matrix and 6 quark masses. On the other hand, realistic Standard Model extensions contain additional parameters that are subject to strong constraints from precision flavor measurements. Our studies of such new physics effects focus on processes that are either rare or can be precisely predicted in the Standard Model. They are explored both model independently and in explicit new physics scenarios, predicting correlations among quark and lepton flavor observables, including CP violation as well as baryon and lepton number violation.   Prof. dr. Svjetlana Fajfer Prof. dr. Jernej F. Kamenik Assist prof. dr. Nejc Košnik Aleks Smolkovič, M.Sc. Blaž Bortolato, M.Sc.   Back to the top

 Top and Higgs physics   The top quark and the Higgs boson are the heaviest known elementary particles. Due to their large coupling they exhibit an extreme sensitivity to dynamics at energies far above the electroweak scale of the Standard Model. As such they also serve as excellent probes of new physics. We study top quark and Higgs boson properties and processes, which are well predicted or very suppressed within the Standard Model, with the aim of disentangling possible beyond the Standard Model effects. These include collider signatures of hypothetical cosmological dark matter particles or light remnants of high scale gauge and matter unification.   Prof. dr. Jernej F. Kamenik Prof. dr. Svjetlana Fajfer Assist prof. dr. Nejc Košnik Assist prof. dr. Miha Nemevšek Aleks Smolkovič, M.Sc.   Back to the top

 Physics beyond the standard model   We are looking for signals of physics beyond the standard model, like proton decay, neutrino masses, heavy neutrinos at LHC, neutrino-less double beta decay, and flavor physics. We search for the signals of Dark Matter. The models we are studying are U(1) extensions of the SM, grand unified theories, left-right symmetric theories, with or without their supersymmetric extensions. We are interested in phenomenological and cosmological consequences of these ideas, as well as theoretical issues like spontaneous supersymmetry breaking and study of strongly interacting systems through the AdS/CFT correspondence.   Prof. dr. Jernej F. Kamenik Prof. dr. Borut Bajc Prof. dr. Svjetlana Fajfer Assist prof. dr. Nejc Košnik Back to the top

 Lattice QCD   We compute the hadron spectrum and study the interactions between hadrons from the first principles of quantum chromodynamics on the lattice. By simulating the scattering between hadrons, we determine the corresponding scattering phase shift. This lead to the first lattice determination of the mass and the width for a number of hadronic resonances in the light, strange and charm sector. Experimental candidates for the exotic hadrons often lie near thresholds, and we are performing pioneering simulations that take into account the effect of threshold on these states. The exotic charmonium-like XYZ states, which are candidates for mesonic molecules or tetraquarks, are of particular interest in light of recent experimental discoveries.   Prof. dr. Saša Prelovšek Komelj Urša Skerbiš Štok, B.Sc.   Back to the top

 Machine-learning approaches to collider physics   In the last few years, machine learning tools have opened new avenues in particle physics data analysis. In particular, advances in unsupervised or semi-supervised techniques designed to be able to separate signal and background events in mixed samples. We use such machine learning  techniques to study various collider observables and devise novel analysis and search strategies. In particular, we apply techniques from Bayesian generative statistical modeling to study jet substructure and infer the underlying structure of collider events directly from the data.   Prof. dr. Jernej F. Kamenik Aleks Smolkovič, M.Sc. Blaž Bortolato, M.Sc.   Back to the top

### Activities

Weekly seminars

The weekly "Joint FMF-JSI high energy physics seminars" of the HEP Theory Group are normally held every Thursday at 10:15 in the tea room of the JSI F1 department. Calendar with all the events can be found here. Until further notice seminars will be held remotely, via zoom.
For speakers: Please consult the current agenda. Choose a free Thursday slot and notify your host. Exceptionally, an alternative day may be used as well (usually mondays).
Subscribe to seminar notifications: Use direct e-mail subscription or write to the group administrator.

Feodor Lynen Research Fellowship applications

The particle theory group at the Jozef Stefan Institute in Ljubljana, Slovenia invites outstanding young researchers from Germany to apply for a Feodor Lyden Research Fellowship position with prof. dr. Svjetlana Fajfer, who is a member of the Humboldt Network abroad. For further information, and to apply, please see the Feodor Lynen Research Fellowship webpages and contact us at hep-th@ijs.si.

Marie Curie Fellowship applications

The group offers support for Marie Curie Fellowships applications. The group hosted succesful MC alumni in the past and has experience with writing the proposal. Slovenia is a member of the Widening countries and therefore MC applications to IJS receive additional funding under the Widening scheme. Moreover, the Slovenian national agency offers individual grants for MC applications that were above the EU threshold but not funded. More information can be found through:

Scientific meetings organized by the group

• Brda 2019: Selected topics in high energy physics, astrophysics, and cosmology, October 9 - 11 2019, Brda, Slovenia (webpage).
• Summer school on BSM particle physics and cosmology, August 26 - 31 2019, Ljubljana, Slovenia (webpage).
• Portorož 2019: Precision era in High Energy Physics, April 16 - 19 2019, Portorož, Slovenia (webpage).
• Brda 2017: Selected topics in high energy physics, October 11 - 13 2017, Brda, Slovenia (webpage).
• Portorož 2017: New physics at the junction of flavor and collider phenomenology, April 18 - 21 2017, Portorož, Slovenia (webpage).
• Brda 2016: Selected topics in flavor and collider physics, October 19 - 21 2016, Brda, Slovenia (webpage).
• Portorož 2015: Particle Phenomenology From the Early Universe to High Energy Colliders, April 7 - 10 2015, Portorož, Slovenia (webpage).
• From Strange through Charm and Beauty to the Top: Celebration of the career of Svjetlana Fajfer, April 16, 2014, Jozef Stefan Institute (webpage).
• Brda 2013: Selected Challenges in Particle Phenomenology, September 19 - 20 2013, Brda, Slovenia (webpage).
• Portorož 2013: Probing the Standard Model and New Physics at Low and High Energies, April 14 - 18 2013, Portorož, Slovenia (webpage).
• Brda 2011: Selected Challenges in Flavor Physics, September 15 - 16 2011, Brda, Slovenia (webpage).
• Portorož 2011: The Role of Heavy Fermions in Fundamental Physics, April 11 - 14 2011, Portorož, Slovenia (webpage).

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Opportunities for student projects and theses

### Selected Publications

 D. Bečirević, I. Doršner, S. Fajfer, N. Košnik, D. A. Faroughy, O. Sumensari, Scalar leptoquarks from GUT to accommodate the B-physics anomalies, Phys.Rev.D 98 (2018) 5, 055003, J. F. Kamenik, Y. Soreq & J. Zupan, Lepton flavor universality violation without new sources of quark flavor violation, Phys. Rev. D 97 (2018) no.3, 035002 D. A. Faroughy, A. Greljo, J. F. Kamenik, Confronting lepton flavor universality violation in B decays with high-pT tau lepton searches at LHC, Phys.Lett.B 764 (2017) 126-134 I. Dorsner, S. Fajfer, A. Greljo, J.F. Kamenik & N. Kosnik, Physics of leptoquarks in precision experiments and at particle colliders, Phys.Rept. 641 (2016) 1-68. L. Di Luzio, R. Gröber, J. F. Kamenik and M. Nardecchia, Accidental matter at the LHC, JHEP 07 (2015), 074 D. Mohler, C.B. Lang, L. Leskovec, S. Prelovsek, R.M. Woloshyn, $D_{s0}^*(2317)$ meson and $DK$ Scattering from Lattice QCD, Phys. Rev. Lett. 111 (2013) 222001, arXiv:1308.3175 S. Prelovsek and L. Leskovec, Evidence for X(3872) from DD* scattering on the lattice, Phys. Rev. Lett. 111 (2013) 192001, arXiv:1307.5172 D. Mohler, S. Prelovsek, R. Woloshyn, $D\pi$ scattering and $D$  meson resonances from lattice QCD, Phys.Rev. D87 (2013)  034501, arXiv:1208.4059 G. Isidori & J. F. Kamenik, Shedding light on CP violation in the charm system via D to V gamma decays, Phys.Rev.Lett. 109 (2012) 171801, arXiv:1205.3164 D. Becirevic, N. Kosnik & A. Tayduganov, B→Dτν vs. B→Dμν, Phys.Lett. B716 (2012) 208-213, arXiv:1206.4977 N. Kosnik, Model independent constraints on leptoquarks from b→sℓ+ℓ− processes, Phys.Rev. D86 (2012) 055004, arXiv:1206.2970 S. Fajfer, J. F. Kamenik, I. Nisandzic & J. Zupan, Implications of Lepton Flavor Universality Violations in B Decays, Phys.Rev.Lett. 109 (2012) 161801, arXiv:1206.1872 S. Fajfer, J. F. Kamenik & I. Nisandzic, On the B→D∗τν¯τ Sensitivity to New Physics, Phys.Rev. D85 (2012) 094025, arXiv:1203.2654 J. F. Kamenik, M. Papucci & A. Weiler, Constraining the dipole moments of the top quark, Phys. Rev. D85 (2012), 071501 A. L. Kagan, J. F. Kamenik, G. Perez & S. Stone, Top LHCb Physics, Phys. Rev. Lett. 107:082003, 2011, arXiv:1103.3747 J. F. Kamenik & J. Zupan, Discovering Dark Matter Through Flavor Violation at the LHC, Phys. Rev. D 84 (2011), 111502 J. Drobnak, S. Fajfer & J. F. Kamenik, Flavor Changing Neutral Coupling Mediated Radiative Top Quark Decays at Next-to-Leading Order in QCD, Phys.Rev.Lett.104:252001,2010, arXiv:1004.0620 R. Krivec and V.B. Mandelzweig, Quasilinearization approach to computations with singular potentials, Comp. Phys. Communications 179, 865 (2008), S. Fajfer, N. Kosnik, Leptoquarks in FCNC charm decays, Phys.Rev. D 79, 017502 (2009), arXiv:0810.4858, T. Hurth, G. Isidori, J. F. Kamenik and F. Mescia, Constraints on New Physics in MFV models: A Model-independent analysis of Delta F = 1 processes, Nucl. Phys. B808, 326-346 (2009), arXiv:0807.5039, J. F. Kamenik and F. Mescia, B --> D tau nu Branching Ratios: Opportunity for Lattice QCD and Hadron Colliders, Phys. Rev. D 78, 014003 (2008),arXiv:0802.3790, C. Bernard, C. E. DeTar, Z. Fu and S. Prelovsek, Scalar meson spectroscopy with lattice staggered fermions, Phys. Rev. D 76, 094504 (2007), arXiv:0707.2402, S. Fajfer, N. Kosnik, S. Prelovsek, Updated constraints on new physics in rare charm decays, Phys.Rev. D 76, 074010 (2007), arXiv:0706.1133, S. Prelovsek, C. Dawson, T. Izubuchi, K. Orginos, A. Soni, Scalar meson in dynamical and partially quenched two-flavor QCD: lattice results and chiral loops, Phys.Rev. D70 (2004) 094503, hep-lat/0407037 B. Bajc, A. Melfo, G. Senjanovic and F. Vissani, The minimal supersymmetric grand unified theory. I: Symmetry breaking and the particle spectrum, Phys. Rev. D 70, 035007 (2004), hep-ph/0402122, C. S. Aulakh, B. Bajc, A. Melfo, G. Senjanovic and F. Vissani, The minimal supersymmetric grand unified theory, Phys. Lett. B 588, 196 (2004), hep-ph/0306242, B. Bajc, G. Senjanovic and F. Vissani, b - tau unification and large atmospheric mixing: A case for non-canonical see-saw, Phys. Rev. Lett. 90, 051802 (2003),hep-ph/0210207, B. Bajc, P. Fileviez Perez and G. Senjanovic, Proton decay in minimal supersymmetric SU(5), Phys. Rev. D 66, 075005 (2002), hep-ph/0204311, C. S. Aulakh, B. Bajc, A. Melfo, A. Rasin and G. Senjanovic, SO(10) theory of R-parity and neutrino mass, Nucl. Phys. B 597, 89 (2001), hep-ph/0004031, B. Bajc and G. Gabadadze, Localization of matter and cosmological constant on a brane in anti de Sitter space, Phys. Lett. B 474, 282 (2000), hep-th/9912232, R. Krivec and V.B. Mandelzweig, Nonvariational calculation of the sticking probability and fusion rate for the mu-d-t molecular ion, Phys. Rev. A52, 221 (1995),

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### Selected Collaborations

 I. Doršner, University of Split, Faculty of Electrical Engineering, Croatia F. D'Eramo, University of Padova and INFN Padova, Italy J. O. Eeg, University of Oslo, Physics Department, Norway A. Falkowski, S. Descotes-Genon and D. Becirevic, IJCLab, Orsay France P. Gambino, INFN & University of Torino, Italy G. F. Giudice, CERN, Switzerland G. Isidori and O. Sumensari, University Zurich, Switzerland A. Kagan and J. Zupan, University of Cincinnati,USA J. Kopp, University Mainz, Germany S. Collins, Regensburg University, Germany C. Lang, Graz University, Austria D. Mohler and M. Padmanath, Mainz University, Germany Z. Ligeti and M. Papucci, Ernest Orlando Lawrence Berkeley National Laboratory, University of California, Berkeley, USA F. Mescia, Universitat de Barcelona, Spain Y. Nir and G. Perez, Dept. of Particle Physics, Weizmann Institute of Science, Rehovot, Israel V. Drach, University of Plymouth, UK  L. Randall, Department of Physics, Harvard University, Cambridge, USA G. Senjanovic, ICTP, Trieste, Italy A. Weiler, TU Munich, Germany

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### Alumni and former associates (subsequent affiliation)

• Prof. dr. Bojan Golli (retired)
• Dr. Luiz Vale Silva (Univ. of Valencia)
• Dr. Matej Pavšič (retired)
• Prof. Dr. Jure Zupan (Univ. of Cincinnati)
• Prof. Dr. Ilja Doršner (Univ. of Split)
• Dr. J. Julio (Indonesian Institute of Sciences)
• Dr. Jure Drobnak (Institute for Advanced Study, TU Munich)
• Dr. Admir Greljo (Univ. Zurich)
• Dr. Ivana Mustać (Cosylab)
• Dr. Ivan Nišandžić, (Univ.of  Dortmund)
• Dr. Timon Mede (Reactor Center, Josef Stefan Institute)
• Dr. Luka Leskovec (Univ. of Arizona)
• Dr. Vasja Sušič (Univ. of Basel)
• Dr. Monalisa Patra
• Dr. Darius Faroughy (Univ. Zurich)
• Dr. Barry M. Dillon (Univ. Heidelberg)

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The group is funded in part by the Slovenian Research Agency (research core funding No. P1-0035 and J1-8137).