119111785
Applications of FIESTA
Sector decomposition in its practical aspect is a constructive method used to evaluate Feynman integrals numerically. We present a new program performing the sector decomposition and integrating the expression afterwards. The program can be also used in order to expand Feynman integrals automatically in limits of momenta and masses with the use of sector decompositions and Mellin--Barnes representations. The program is parallelizable on modern multicore computers and even on multiple computers. Also we demonstrate some new numerical results for four-loop massless propagator master integrals.
2122861
Decoupling of heavy quarks in HQET
Decoupling of c-quark loops in b-quark HQET is considered. The decoupling coefficients for the HQET heavy-quark field and the heavy–light quark current are calculated with the three-loop accuracy. The last result can be used to improve the accuracy of extracting fB from HQET lattice simulations (without c-quark loops). The decoupling coefficient for the flavour-nonsinglet QCD current with n antisymmetrized γ-matrices is also obtained at three loops; the result for the tensor current (n = 2) is new.
1669343
Applying Gröbner bases to solve reduction problems for Feynman integrals
We describe how Grobner bases can be used to solve the reduction problem for Feynman integrals, i.e. to construct an algorithm that provides the possibility to express a Feynman integral of a given family as a linear combination of some master integrals. Our approach is based on a generalized Buchberger algorithm for constructing Grobner-type bases associated with polynomials of shift operators. We illustrate it through various examples of reduction problems for families of one- and two-loop Feynman integrals. We also solve the reduction problem for a family of integrals contributing to the three-loop static quark potential.
55043207
DESIGN OF THE NUCLOTRON BOOSTER IN THE NICA PROJECT
NICA is the new complex being constructed on the JINR aimed to provide collider experiments with ions up to uranium at energy of 3.5x3.5 GeV/u. The NICA layout includes Electron String Ion Source, 6.2 Mev/u linac, 600 MeV/u booster synchrotron, upgraded Nuclotron and ion collider with average luminosity of 10 27 cm -2 s -1 . The main goals of the Booster are the following: accumulation of 4·10 9 Au 32+ ions; acceleration of the heavy ions up to energy required for effective stripping; forming of the required beam emittance with electron cooling system. The present layout makes it possible to place the Booster having 211 m circumference and four fold symmetry lattice inside the yoke of the Synchrophasotron (shut down in 2002). The features of this booster, the requirement to the main synchrotron systems and their parameters are presented in this paper.
18145511
On the reduction of Feynman integrals to master integrals
The reduction of Feynman integrals to master integrals is an algebraic problem that requires algorithmic approaches at the modern level of calculations. Straightforward applications of the classical Buchberger algorithm to construct Grobner bases seem to be inefficient. An essential modification designed especially for this problem has been w orked out. It has been already applied in two- and three-loop calculations. We are also suggesting to combine our method with the Laporta’s algorithm.
15948639
S-bases as a tool to solve reduction problems for Feynman integrals
We suggest a mathematical definition of the notion of master integrals and present a brief review of algorithmic methods to solve reduction problems for Feynman integrals based on integration by parts relations. In particular, we discuss a recently suggested reduction algorithm which uses Grobner bases. New results obtained with its help for a family of three-loop Feynman integrals are outlined.
11320046
Bounds on scalar leptoquark and scalar gluon masses from current data on S, T, U
The contributions into radiative correction parameters S, T, U from scalar leptoquark and scalar gluon doublets are investigated in the minimal four color symmetry model. It is shown that the existence of the relatively light scalar leptoquarks and scalar gluons (with masses of order of 1 TeV or less) is consistent with the current experimental data on S, T, U and the more light particles (with masses below 400 GeV) improve the fit. In particular, the lightest scalar leptoquarks with masses below 300 GeV are consistent with the current data on S, T, U at $\chi^2 < 3.1(3.2)$ for $m_H=115(300) GeV$ in comparison with $\chi^2 = 3.5(5.0)$ in the Standard Model. The lightest scalar gluon in this case is expected to lie below $ 850(720) GeV.$ The possible significance of such particles in the t-quark physics at LHC is emphasized and their effect on the gauge coupling constant unification is briefly discussed.
122307796
3ν oscillations in matter and solar neutrino data
Abstract A method of searching for 3ν solutions of the solar neutrino problem in terms of 2ν solutions is proposed. It gives “iso-SNU strips” on the plot of Δm 2 versus sin 2 2θ. A combined analusis of ClAr experiment data and results of the 8 B neutrino flux measurement by νe scattering (Kamiokande II) is presented.
18167542
Fermionic Decays of Scalar Leptoquarks and Scalar Gluons in the Minimal Four-Color Symmetry Model
Fermionic and weak decays of the scalar leptoquarks S = S1(+), S1(−), and Sm and the scalar gluons F = F1 and F2 predicted by the minimal model involving four-color symmetry and the Higgs mechanism of quark-and lepton-mass splitting are considered. The widths and the branching ratios are calculated for these decays, and the results are analyzed versus the couplings and masses of decaying particles. It is shown that, at relatively small mass splittings Δm within scalar doublets (Δm mW, the weak decays S → S′W and F → F’W compete with the above fermionic decays. In the case of mS < mt, the processes S1(+) → clj+, S1(−) → vi\(\tilde b\), Sm → blj+, and Sm → c\(\tilde \nu \)j, whose total branching ratios are Br(S1(+) → cl+) ≈ Br(S1(−) → v\(\tilde b\)) ≈ 1, Br(Sm → bl+) ≈ 0.9, and Br(Sm → c\(\tilde \nu \)) ≈ 0.1, appear to be dominant decays of scalar leptoquarks. Searches for these decays at LHC and the Tevatron are of interest.
53330684
Neutrino Mass and New Physics
Reconstruction of the neutrino mass and flavor spectrum is described. Essentially two processes are relevant for interpretation of the neutrino results which were used in determination of neutrino parameters: oscillations (averaged and non-averaged) in vacuum and matter and the adiabatic flavor conversion in matter (the MSW-effect). Detailed physics picture of these processes is elaborated and their realizations in solar and atmospheric neutrinos as well as in K2K, KamLAND and MINOS experiments are described. Important bounds have been obtained from neutrinoless double beta decay and cosmology. Implications of the obtained results to fundamental physics are discussed. Among various mechanisms for small neutrino masses we consider the seesaw (which has the highest priority) and overlap suppression in extra dimensions. The observed pattern on neutrino mixing may testify for existence of new symmetries of nature. One of the key issues on the way to underlying physics is comparison of the quarks and lepton masses and mixing. In this connections concepts of quark-lepton symmetry and unification, quark-lepton universality and quark-lepton complementarity are described.
118706146
Discrete symmetries and models of flavor mixing
Evidences of a discrete symmetry behind the pattern of lepton mixing are analyzed. The program of symmetry building is outlined. Generic features and problems of realization of this program in consistent gauge models are formulated. The key issues include the flavor symmetry breaking, connection of mixing and masses, ad hoc prescription of flavor charges, missing representations, existence of new particles, possible accidental character of the TBM mixing. Various ways are considered to extend the leptonic symmetries to the quark sector and to reconcile them with Grand Unification. In this connection the quark-lepton complementarity could be a viable alternative to TBM. Observational consequences of the symmetries and future experimental tests of their existence are discussed.