123279554
Chiral color quark symmetry and possible constraints on the G′-boson mass from tevatron and LHC data
A gauge model featuring a chiral color symmetry of quarks was considered, and possible manifestations of this symmetry in proton-antiproton and proton-proton collisions at the Tevatron and LHC energies were studied. The cross section $$\sigma _{t\bar t}$$ for the production of $$t\bar t$$ quark pairs at the Tevatron and the forward-backward asymmetry $$A_{FB}^{p\bar p}$$ in this process were calculated and analyzed with allowance for the contributions of the G′-boson predicted by the chiral color symmetry of quarks, the G′-boson massmG′ and the mixing angle θG being treated as free parameters of the model. Limits on mG′ versus θG were studied on the basis of data from the Tevatron on $$\sigma _{t\bar t}$$ and $$A_{FB}^{p\bar p}$$, and the region compatible with these data within one standard deviation was found in the mG′-θG plane. The region ofmG′-mass values that is appropriate for observing the G′-boson at LHC is discussed.
118758893
Minimal four-color model with quark-lepton symmetry and constraints on the Z{prime}-boson mass
A minimal model with quark-lepton symmetry is considered. This model, which describes unified electroweak and strong interactions, is a minimal extension of the standard model that involves four-color symmetry of quarks and leptons. Predicted relations between the masses of leptoquarks and W{sup +-}, Z, and Z{prime} bosons are studied, and the contributions of an additional Z{prime} boson to the cross sections for e{sup +}e{sup -} annihilation and the asymmetry A{sub FB} at TRISTAN and LEP200 energies are analyzed. Experimental data are shown to be consistent with the existence of a relatively light Z{prime} boson associated with four-color quark-lepton symmetry. 12 refs., 3 figs., 1 tab.
122714200
Limits on the scalar-leptoquark and scalar-gluon masses from the parameters S, T, and U in the minimal model based on four-color symmetry
The contributions to the parameters S, T, and U of radiative corrections from the doublets of scalar leptoquarks and scalar gluons are analyzed within the minimal model based on four-color symmetry of the Pati-Salam type. It is shown that current experimental data on the parameters S, T, and U admit the existence of relatively light scalar leptoquarks and scalar gluons (of mass lower than 1 TeV), the best fit to experimental data being attained at mass values not greater than 400 GeV. In particular, the existence of scalar leptoquarks of mass below 300 GeV is found to be compatible with data on the parameters S, T, and U at χ2 < 3.1 (3.2) for mH = 115 (300) GeV as against χSM2 = 3.5 (5.0) in the Standard Model. The mass of the lightest scalar gluon is then predicted to be less than 850 (720) GeV. It is emphasized that the aforementioned doublets of scalar leptoquarks and scalar gluons can play a significant role in processes involving a t quark at LHC.
120359559
Z′-boson decays as a test of the four-color symmetry of quarks and leptons
The quark and leptonic widths of the Z′ boson that arises from four-color quark-lepton symmetry are calculated and compared with the predictions of the E6 and the left-right (LR) model. It is shown that this four-color symmetry leads to a specific relation of the type v′q+a′q between the vector and axial coupling constants for Z′-boson interaction with quarks and leptons. Calculations with allowance for the four-color symmetry in question yield leptonic widths of the Z′ boson that are considerably greater than those predicted within the E6 and the LR model and result in a relativelys mall hadronic-to-leptonic width ratio. Since these features are associated with the four-color symmetry, their observation would suggest its manifestation in Z′-boson decays.
17592505
Bounds on Scalar Leptoquark Masses from S T U in the Minimal Model With the Four Color Symmetry
The contributions into radiative correction S T U parameters from the scalar leptoquarks are considered in frame of the minimal model with the four color gauge symmetry Taking the current exper imental data on S T U into account the bounds on the scalar lep toquark masses are obtained and discussed In particular it is shown that the current experimental data on S T U allow the existence of relatively light scalar leptoquark with electric charge The search for a new physics beyond the Standard Model SM is now one of the aims of the high energy physics It is interesting to know what kind of the new physics can manifest itself as the energy of the colliding particles increase What are the possible manifestations of such new physics at attainable energies One of the possible variants of the new physics beyond the SM can turn out to be the variant induced by the possible four color symmetry between quarks and leptons The main feature of the four color gauge symmetry is the prediction of the vector leptoquarks with the masses of about the mass scale Mc of the four color symmetry breaking In the models induced by the grand uni cation ideas the four color symmetry can manifest itself as an intermediate E mail asmirnov univ uniyar ac ru symmetry with mass scaleMc expected to be usually very high For instance in SO model it is of about Mc GeV but it can be essentially lowered up to Mc GeV by appropriate scheme of the symmetry breaking In the models regarding the four color symmetry as a primary symmetry the lower limit on the mass scale Mc is determined mainly by the low energy experimental data and it can be essentially lower for example of about TeV or about TeV or slightly less or even of about TeV The four color symmetry can manifest itself not only by the vector lep toquark physics but also due to the scalar leptoquarks Some of the scalar leptoquarks should have SU doublet structure and hence can mani fest themselves in the oblique radiative corrections in particular a ecting the S T U parameters of Peskin and Takeuchi Taking into account the rather stringent current experimental limits on S T U it is interesting to know what bounds on the scalar leptoquark masses can be extracted from the current experimental data on S T U For this purpose it is interesting to know the e ect of the scalar leptoquarks on S T U in some simple gauge model predicting these particles In this talk I would like to consider the contributions into S T U pa rameters from the scalar leptoquarks in frame of a minimal model with the four color symmetry in comparison with the current experimental data on S T U and to discuss the bounds on scalar leptoquark masses which can be extracted in this model from these data The minimal quark lepton symmetry model MQLS model to be used here as a minimal extension of the SM containing the four color gauge symmetry is based on the gage group SUV SUL UR The fermion sector of the model contains only the known fermions quarks and leptons whereas the gauge sector predicts the new gauge particles vector leptoquarks V with electric charge and an extra neutral Z boson The scalar sector of the model contains in general the four multiplets a a a transforming according to the representations of the SUV SUL UR group and having the VEV s respectively the content of the multiplets and notations can be found in more detail in Refs As regards the S T U parameters the most intersting of these multiplets is the muliplet which has been introduced to split the masses of quarks and leptons This multiplet contains fteen doublets which can be arranged into two scalar leptoquark doublets S a and S a with the SM hy percharge Y SM and respectively eight scalar gluon doublets Fja j with Y SM and the doublet a which in admixture with a gives the SM doublet SM with SM VEV p p GF GeV and an additional scalar doublet In addition to the scalar leptoquark doublets S a of the multiplet the multiplets and contain the singlet scalar leotoquarks S and S with electric charge which give in admixture with S S the Goldstone mode S and three mass eigenstate leptoqurk elds S S S As a result in the unitary gauge we obtain in general ve scalar leptoquarks S S with electric charge and respectively and Sk k with electric charge The resulting contributions into S T U from leptoquarks can be pre sented in the form S LQ nc X X k jC k j Y SM ln m m k X
15376747
ON A POSSIBLE MANIFESTATION OF THE FOUR-COLOR SYMMETRY Z' BOSON IN μ+μ- EVENTS AT THE LHC
The cross section of the μ+μ- pair production in pp-collisions at the LHC is calculated with account of the Z' boson induced by the minimal four-color quark–lepton symmetry (MQLS). The μ+μ- invariant mass spectrum with account of the MQLS Z' boson is analyzed in dependence on the Z' mass. The mass region for the MQLS Z' boson observable at the LHC is found in dependence on the significance and on the integrated luminosity.
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.
17273669
Rescuing grand unification scenario for neutrino mass
Abstract The see-saw mechanism for neutrino masses based on the Grand Unification leads to the mass of the heaviest neutrino (≈ ν τ ) in the range (2−3)·10 −3 eV and hence to a solution of the solar neutrino problem through the ν e → ν τ conversion. We suggest the existence of a light singlet fermion S which mixes predominantly with muon neutrino through the mixing mass m μs ∼ O (1) eV. The introduction of such a singlet allows one (i) to solve the atmospheric neutrino problem via the ν μ ↔ S oscillations, (ii) to explain the LSND result and (iii) to get two component hot dark matter in the Universe. The phenomenology of this scenario is considered and the origin of the singlet as well as of the scale m μs is discussed.
16212033
The solar neutrino problem: Neither astrophysics nor oscillations?
There is no consistent solar model which can describe all experimental data on the solar neutrinos. The problem can be formulated essentially in a model independent way. The key points are the comparison of the Homestake and the Kamiokande data as well as the comparison of the GALLEX and SAGE results with minimal signal estimated from the solar luminosity. It is argued that in such a compaxison one should use the Homestake-II data (only after 1986) with caution. The results of the model independent analysis show strong suppression of the beryllium neutrino flux. The data can be well described by the resonant flavor conversion. For the ``low flux model`` which can accommodate the Kamiokande signal, a consistent solution can be found for the neutrino mass squared difference {Delta}m{sup 2} = (0.3 - 1.0) {center_dot} {sup {minus}5} 10 eV{sup 2} and values of mixing angle sin {sup 2} 2{theta} > 5 {center_dot} 10{sup {minus}5} eV{sup 2} and values of mixing angle sin {sup 2} 2{theta} (``very small mixing solution``).
125260667
SLIDING SINGLET AND STABILITY OF THE MASS HIERARCHY. (IN RUSSIAN)
17377891
Right-handed neutrinos at CERN LHC and the mechanism of neutrino mass generation
We consider the possibility to detect right-handed neutrinos, which are mostly singlets of the standard model gauge group, at future accelerators. Substantial mixing of these neutrinos with the active neutrinos requires a cancellation of different contributions to the light neutrino mass matrix at the level of 10{sup -8}. We discuss possible symmetries behind this cancellation and argue that for three right-handed neutrinos they always lead to conservation of total lepton number. Light neutrino masses can be generated by small perturbations violating these symmetries. In the most general case, LHC physics and the mechanism of neutrino mass generation are essentially decoupled; with additional assumptions, correlations can appear between collider observables and features of the neutrino mass matrix.