Theoretical Particle Physics

   The Standard Model of particle physics seems presently to be at the height of its success. No signals of new physics were so far found neither in electroweak precision tests nor in flavor physics studies. However, in spite of remarkable success, there are profound experimental and theoretical reasons to think that the Standard Model is incomplete. They include the gauge hierarchy problem, family regularities in the observed spectrum of quarks and leptons which are slightly smeared by their weak (CP-violating in general) mixing, tiny (but non-vanishing) neutrino masses and others, as well as the very fact that the Standard Model does not yet incorporate the gravity which seems to be a basic drive for a present development in particle physics and cosmology.
    A possible intermediate solution to these problems is commonly related to supersymmetry, supergravity and grand unified theories, enlarged enough to include also some family symmetries treating quark-lepton generations. At present they receive some indirect experimental support from the apparent lightness of the Higgs boson, the values of the electroweak and strong interaction gauge couplings given by precision measurements, the heavy top quark mass, and an experimental evidence for non-zero neutrino masses which could explain (via their oscillations) the persistent atmospheric and solar neutrino deficit.
    As to the final solution, it is widely believed that the known four fundamental forces which govern all physical phenomena observed have a common origin in terms of the ultimate superstring theory in which gravitation appears unified with the strong and electroweak forces through extra space-time dimensions involved. While usually this unification is proposed to be in the range of ~10¹⁶ to ~10¹⁸GeV, the possibility of unification at much lower energies is also existed if extra dimensions properly appear at larger distances. However, any persuasive link between present string theory and the SM physics with all particular features observed at low energies is rather difficult to be established. Any particular superstring theory set-up usually appears too restrictive to cover the existing realistic models in a valuable phenomenological way.
    In this respect, the “bottom-up” approach starting with an effective quantum field theory framework for elementary quarks and leptons, both standard and supersymmetric, which we follow in a systematic way, looks more promising since it might provide guiding rules for search for new physical phenomena, as well as could shed light on the underlying string dynamics towards the final theory of matter. One of the most interesting examples of this type could be an origin of internal symmetry patterns in particle physics owing to spacetime instabilities (spontaneous Lorentz violation) at very small distances leading to realistic schemes for unified theories of quarks and leptons.
    Present research interests of the Center are focused to physics beyond the Standard Model: grand unified theories and supersymmetry, spontaneous Lorentz violation and origin of symmetries, emergent QED and Gravity theories, extra spacetime dimensions in particle physics and cosmology. Special line in the research program is related to supersymmetric grand unification and proton decay, the problems of quark-lepton flavor mixing and CP violation, model building for neutrino oscillations and others. One of the main concerns of the group members is in sharpening of their ideas for their phenomenological applications at facilities, such as the large hadron collider (LHC) and underground detectors.

Cosmology and Gravity Theory

    Among all the fundamental forces playing a crucial role in making the Universe, as it looks to date, gravitation seems to be most important force for understanding of the large scale structure and evolution of the Universe. As is well known, the structure formation, galaxy rotation curves and gravitational lensing, and, first of all, the accelerating expansion of the Universe can not be explained by general relativity coupled to the known matter. These effects are conventionally attributed to dark matter and dark energy that together comprise about 95% of energy budget of the Universe. Presently, the two major problems of modern cosmology dark matter and dark energy are extensively addressed both from the perspectives of particle physics and gravity. Thus far gravity remains the most enigmatic of all the fundamental interactions in nature. Experimentally, gravity has been probed at distance scales ranging from ~10^-1mm (in short-range force experiments) to at least ~10¹⁴cm (the size of the solar system). So, we know that general relativity provides correct description of gravity within this range of distances. However, the situation is far less clear on cosmological distance and time scales. Alternatively, the effects requiring the introduction of dark matter and dark energy may be thought of as a result of the modified gravity. There are also some interesting phenomenological scenarios relating dark energy to quantum gravity. Generally, the quantum gravity is expected to have an essential impact on our understanding of space-time and the meaning of reality at distances set by the quantum gravity scale. Even if this scale is given by the Planck mass, the theory could make it clear what happens in circumstances when the gravity becomes comparable to other interaction - such as in the very early universe. It is expected this theory may provide a likely contender for initial conditions of the universe (inflation) and also affect significantly the cosmological perturbations to lead to a successful explanation of dark energy problem and many others. So, the research along all these lines seems to be very promising for revealing the basic structure of Nature. 
    Present research interests of the Center concern the gauge theory of gravity and its phenomenology, particle physics models for inflation, new sources of CP violation and leptogenesis, theory and phenomenology of (quantum) field theory on noncommutative space-time (mainly in context of cosmology and black hole physics), phenomenological implications of minimum- length deformed quantum mechanics, dark energy models arising due to microstructure of space-time, theory and phenomenology of quantum gravitational running of space-time dimension and coupling of general relativity with effective quantum field theory.