**Short name: **DTHEP

**Phone: **+7 495 939 31 73

**Email: **savrin@theory.sinp.msu.ru

**Site: **http://theory.sinp.msu.ru/

**Department of theoretical high energy physics**

The Department of theoretical high energy physics (DTHEP) is organized in 1990. From the very beginning and till present it is headed by Professor, DSc. Viktor Savrin.

The Department was organized in order to join the efforts of the scientists for the solution of the present-day physical problems and to conduct the research within the frames of the state scientific and technical program "High energy physics".

Directions of the Department's research are represented by the titles of its Laboratories: Laboratory of field theory, Laboratory of analytical calculations in the field of high energy physics, Laboratory of fundamental interactions theory.

Within the frames of scientific directions of the Department its scientists carry out theoretical studies on the fundamental problems of physics of elementary praticles and high energy physics. The objective of these studies is to obtain new knowledge about the fundamental characteristics of the matter at distances about 10^{-16}-10^{-17} cm and less.

The basic directions of scientific reseacrh are the following:

• development of new theories and models of elementary particles interactions at the energy over 1 TeV (for instance, supersymmetry theories, superstring theories and theories with additional space-time measurements);

• development of new effective analytical, numerical and computer methods for calculation of the processes with the involvement of many particles in final states at tree and arc levels;

• calculation of the processes of elementary particles collisions in different calibration theories (standard model and its generalization) and development of recommendations for the experimental set up at the operated and developed colliders basing on it;

• development of new methods in quantum theories out of the frames of perturbation approach and calculation of spectra and other characteristics of localized states and dissipative systems basing on it;

• development of distributed calculations and intensive operations with data (GRID) for physical research.

From the very beginning the scientists of the Department were involved into development othe programs of physical experiments at almost all operated and planned colliders, including LEP, Tevatron, HERA, LHC, ILC, NIСA.

Over a number of years the scientists carry out joint projects with the leading scientific centers in the field of high energy physics: DESY and Max-Planck Institute (Germany), CERN (Switzerland), KEK (Japan), FermiLab (USA), LAPP (France). They actively cooperate with a number of leading uniersities, such as London, Helsinki, Tokio, Hamburg, Lisboa, Leipzig, Dublin, Seoul, Chicago Unversities. Among the Russian colleagues the most productive contacts are with scientific groups from Institute of High Energy Physics (Protvino), Joint Insitute of Nuclear Research (Dubna), Insitute of Nuclear Research RAS, Novosibirsk, S.-Petersburg and Samara Universities.

Incomplete list of basic results obtained by the scientists of the Laboratory is presented below:

• a new method for account of radiation corrections at the level of the evnets simulation was proposed and developed, generator of the events SingleTop was discovered, a new method for selection of the effective kinematic variables which allows to select signal from the backgrounds effectively was developed. These methods provided a basis for the discovery of single top-quark production during D0 experiment at Tevatron collider, detection of single top-quark production during CMS experiment at LHC collider;

• possible departures from the predictions of the Standard model for single top-quark production were calculated, simulated and analyzed. The scientists of the Laboratory contributed decisively into determination of new limits for the masses of possible unconditional vector and scalar bosons, for the value of abnormal constants of top-quark interaction with W-boson and b-quark (Wtb), for neutral currents of top-quark with change of flavor (FCNC) during the D0 experiment;

• cross-sections of single top-quark production at future lepton collider were determined for all discussed collision modes e+e-, e-e-, γ -e и γ - γ under the Standard model and a number of its extensions. It was shown that at sufficiently high energy the process of single top-quark production during γ -e, related to so-called “gold plated” processes will allow to study the structure of Wtb peak with record accuracy unaccessible at other colliders;

• a new method for separation of full sets of Feynman diagrams to calibrating-invariant sub-sets was developed. It will significantly decrease the volume of calculations. Full sets of tree Feynamn diagrams with production of four, five and six fermions in final states were calculated taking into account signal and background inputs and their interferation for the processes of hadron and lepton collisions with participation of top-quark, Higgs boson and a number of particles out of the frames of the Standard model;

• mode of intensive interaction within the minimum super-symmetric model (MSSM) was discovered and analyzed for the first time. At this mode tree Higgs bosons have similar masses an abnormally strong interact with fermions of the third generation. Basing on the calculations of characteristics of the basic processes of Higgs bosons production it was shown to what extent these ststes can be separated at LHC and linear colliders;

• scenario of "splitted super-symmetry" was studied for Higgs bosons under the minimum super-symmetric model (MSSM). An effective MSSM potential for this scenario is determined. One-arc corrections induced by interactions between gaugino and higgsino and Higgs boson were calculated. It was shown that input of gaugino and higgsion are comparable to the input of scalar super-partners of the third generation of fermions;

• one-arc temperature corrections like intristic energy for the two-doublet Higgs MSSM potential induced by super-partners of the third generation quarks were calculated. Ananlytic expressions for the corrections like intristic energy are obtained for the extremes of high and low temperatures. It allows to describe the surfaces of crytical points and Higgs bosons states in mass basis;

• cross-sections of pair vector leptoquarks production was calculated for the first time taking into account the inputs of abnormal electric dipole and magnetic quadropole moments. Basing on the calculated cross-sections record limits for masses and interaction constants for vector leptoquarks were obtained during the experiment at Tevatron collider;

• characteristics of the excited electrons, muons and quarks production in different types of collisions were calculated. It allowed to define the limits for the masses of the corresponding particles more accurately;

• Possibility for the search for so-called para-photon was analyzed. It is a new mass-free vector meson, very weakly interacting with the particles under the Standard model and the interaction constant is proportional to the mass of the particle. It was shown that it will be impractical to find para-photon at LHC even in the mode of high radiancy. At the linear collider para-photon can be found in the selected field of the model parameters during the process of associative production of para-photon and a pair of top and anti-top quarks;

• The role and possibility for the measurements of polarization of tau-leptons and top-quarks produced during the decay of stau (super-partner of tau-lepton) and stop, sbottom (super-partners of top- and bottom-quarks) for the changes of the parameters of Minimum super-symmetric extension of the Standard model (MSSM) were analyzed in details;

• the possibility for the search for excited modes of graviton and calibrating bosons was calculated and analyzed within the frames of the sstabilized model of Randell-Sundroom with additional spatial measurements with exponentially changing curvature for the scenario wiith possibility for calibrating bosons to spread in the multi-dimensional bulk for the cases when accessible energy of collision at LHC is higher or lower than the threhold of the first excited mode production. For the first time it was shown that in order to separate the signal correctly it is necessary to take into account the input of interferation of the first excited mode with the remaining tower of excitements;

• a famous and used by many international experimental groups program CompHEP was developed within the frames of CompHEP collaboration. This program is intended for automated calculations of the characteristics of the processes of elementary particles collisions and decay and allows to carry out the full cycle of theoretical simulation beginning from assignment of Lagrange function up to the final flow of the events; QCD Green functions which satisfy simulataneously dynamical equations of Schwinger-Dyson and claibrating identical equations of Ward-Slavnov-Taylor are obtained. Basing on the obtained asytotic solutions the values of gluon and quark condensates and a number of other vacuum correlators (for instance, chromomagnetic sensibility) were estimated. They are in good correspondense with the values of these quantities obtained by other methods. Mass of glueball was evaluated by analysing of Bete-Solpiter equation;

• a number of new unique methods for calculation of Feynman loopback integral in quantum field theory was developed;

• a procedure for recocnstruction for the model of modified gravity with scalar fields, which interact with gravity in non-minimum manner, is developed. This procedure allowed to develop the models with de-sitter solutions and solutions with power law relations for which Hubble parameter is inversly related to time;

• an experimental sample of software complex of RESTful-web-services for access to super-computer resources and data-storage resources which provide simplified integration of the resources for scientific purposes is developed. This complex will give Russian organizations an option of essential increasing of the volume of necessary data and information, decreasing time and improving quality of data processing. It will help to increase the level and competitive advantages of the resulats of scientific activity;

• matrix elements out of mass surface were calculated for a number of parton sub-processes taking into consideration non-zero transverse momentum of primary quarks and gluons. Basin on these equations full and differenial cross-sections of the processes of associated generation of direct photons and heavy (c and b) quarks and double generation of direct photons at the energies of Tevatron and LHC colliders were calculated. Theoretical calculations and experimental data obtained by D0, CDF, CMS and ATLAS collaborations are in a good quantitative agreement. The calculation results were used by D0 and CDF collaborations for analysis of the last experimental results;

• a new quantum model of a system with dissipation appearing at the systems with long-term memory of power-type was offered. It was shown that open quantum system interacting with environment get property of long-term memory which can be described by integro-differentiation of noninteger order;

• An explicit form of tensor operator of magnetic momentum of non-dirak particle with spin of rest equal to 1/2 and its essential deffernece fromspin operator are estimated. Possible influence of this factor on the description of spin rotation in magnetic field and on the values of magnetic momenta of a number of nuclei is marked;

• a problem of cooling of Universe due to emission of gravitons generated during the particles reactions in a four-dimensional space into additional dimension was studied within the frames of cosmological model with one big additional dimension. It was shown that basic emission process is annihilation of the particles of hot Universe not to one, but to two gravitons. Due to small value of gravitation constant cooling caused by this process is small comparing to cooling caused by expansion of Universe.

In average Scientists of the Department each year take part in approximately 20 conferences in different points of physics of elementary particles and theoretical physics of high energy and publish about 70 new articles. Each year scientists of the Department work as supervisors of 5 student diploma projects and 3 post-graduate students of MSU Physics faculty.