120951273
Parameters S, T, and U of radiative corrections and masses of scalar leptoquarks in the minimal model featuring four-color symmetry
The contributions to the parameters S, T, and U of radiative corrections are discussed within the minimal model featuring four-color symmetry of the Pati-Salam type. A numerical analysis of these contributions is given for the Higgs mechanism of mass generation for scalar leptoquarks and the simplest version of scalar-leptoquark mixing. It is shown that up-to-date experimental data on S, T, and U are compatible with the existence of relatively light scalar leptoquarks (of masses about 1 TeV or below), still lighter scalar leptoquarks (of masses below 1 TeV) improving the agreement of theoretical results with experimental data on S, T, and U.
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.
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.
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.
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
118447115
COLORED SCALAR PARTICLES PRODUCTION IN pp-COLLISIONS AND POSSIBLE MASS LIMITS FOR SCALAR GLUONS FROM FUTURE LHC DATA
Cross sections of the colored scalar particle production in pp-collisions are calculated and differential and total cross sections of the corresponding parton subprocesses are obtained. The total cross section of scalar gluon production in pp-collisions at the LHC is estimated and the dominant decays of scalar gluons are discussed. The production cross section of scalar gluons F with masses mF ≲ 1300 GeV is shown to be sufficient for the effective production of these particles at the LHC.
119273437
Neutrino Masses and a Fourth Generation of Fermions
Abstract We study neutrino mass generation in models with four chiral families of leptons and quarks and four right handed neutrinos. Generically, in these models there are three different contributions to the light neutrino masses: the usual see-saw contribution, the tree-level contribution due to mixing of light neutrinos with neutrino of the fourth generation, and the two loop contribution due to the Majorana mass term of the fourth neutrino. We study properties of these contributions and their experimental bounds. The regions of the parameters (mixings of the fourth neutrino, masses of RH neutrino components, etc.) have been identified where various contributions dominate. New possibilities of a realisation of the flavour symmetries in the four family context are explored. In particular, we consider applications of the smallest groups, e.g. SG ( 20 , 3 ) , with irreducible representation 4 .
7456908
Light Singlet Fermions and Neutrino Physics
The existence of a light singlet fermion mixed with the electron neutrino is hinted by the simultaneous explanation of various neutrino anomalies. We show that supersymmetry can provide a natural framework for the existence and the desired properties of such a fermion. Quasi Goldstone fermions (QGF) of spontaneously broken global symmetries like the Peccei-Quinn symmetry or lepton number can mix properly with the neutrinos provided the presence of the R-parity breaking term $\e LH_2$. The lightness of QGF can be a consequence of non-minimal K\"ahler potentials like that of no-scale supergravity. In order to keep R-parity, such a sterile component has to be placed in a new singlet superfield with no vacuum expectation value. In the context of the standard seesaw mechanism the lightness of such a singlet can be understood by imposing a $R$-symmetry.
122988289
Solar neutrinos in four dimensions and beyond
Abstract Recent data give some indications in favor of the Large Mixing Angle (LMA) MSW-solution of the solar neutrino problem. Signatures of this solution are considered in details and confronted with experimental results. Recent theoretical developments - theories with low fundamental scale of quantum gravity and large extra dimensions - give new “bulk-brane” mechanism of generation of neutrino mass. In this framework new solution of the solar neutrino problem is possible via resonance conversion of the electron neutrino in the bulk states. The solution implies that one of extra dimensions has the size about 0.1 mm.
7188792
Neutrinos and structure of the intermediate mass scale
Abstract Neutrino data lead via the see-saw mechanism to masses of the right handed neutrinos at the intermediate mass scale. A simple formalism is suggested which incorporates the quark-lepton symmetry and allows one to find properties of the intermediate scale (masses and mixing) from neutrino data. The averaged mass scale and the mass hierarchy parameter are introduced and fixed by the data. They determine natural ranges of masses and mixing at the intermediate scale. In particular, a scenario which includes the MSW solution of the solar neutrino problem and tau neutrino as the hot component of the dark matter in the Universe leads to M2 = (2–4) × 1010 GeV and M3 = (4–8) × 1012 GeV in agreement with the linear mass hierarchy. Strong deviations from these natural ranges imply fine tuning of parameters or/and certain symmetry of the Majorana mass matrix of the right handed neutrinos.
118473269
Adiabaticity and spectral splits in collective neutrino transformations
Neutrinos streaming off a supernova core transform collectively by neutrino-neutrino interactions, leading to 'spectral splits' where an energy E{sub split} divides the transformed spectrum sharply into parts of almost pure but different flavors. We present a detailed description of the spectral-split phenomenon which is conceptually and quantitatively understood in an adiabatic treatment of neutrino-neutrino effects. Central to this theory is a self-consistency condition in the form of two sum rules (integrals over the neutrino spectra that must equal certain conserved quantities). We provide explicit analytic and numerical solutions for various neutrino spectra. We introduce the concept of the adiabatic reference frame and elaborate on the relative adiabatic evolution. Violating adiabaticity leads to the spectral split being 'washed out'. The sharpness of the split appears to be represented by a surprisingly universal function.