Showing papers on "Gauge boson published in 1995"

Cosmology with a TeV mass Higgs field breaking the grand-unified-theory gauge symmetry.

Abstract: The most natural way to break the grand-unified-theory gauge symmetry is with a Higgs field whose vacuum expectation value is of order 1${0}^{16}$ GeV but whose mass is of order 1${0}^{2}$ to 1${0}^{3}$ GeV. This can lead to a cosmological history radically different from what is usually assumed to have occurred between the standard inflationary and nucleosynthesis epochs, which may solve the gravitino and Polonyi-moduli problems in a natural way.

Search for New Gauge Bosons Decaying into Dileptons in p̄p Collisions at s} = 1.8 TeV

Abstract: We have searched for heavy neutral gauge bosons (2’) in jjp collisions at Js = 1.8 TeV. The data were obtained using the CDF detector during 19921993 run corresponding to an integrated luminosity of 19.7f0.7 pb-‘. We present a 95% confidence level upper limit on the production cross section times branching ratio of 2’ decaying into dielectrons as a function of 2’ mass. Assuming Standard Model coupling strengths, we exclude a 2’ with mass less than 505 GeV/c 2. We also present lower mass limits for 2’ bosons from & models and the Alternative Left-Right Model. PACS numbers: 13.85.Rm, 12.15.Cc, 14.80.Er Neutral gauge bosons in addition to the 2’ are expected in many extensions of the Standard Model [l]. These models typically specify the strengths of the couplings of such bosons to quarks and leptons but make no mass predictions [2]. In up collisions, 2’ bosons may be observed directly via their decay to lepton pairs. Observation of a 2’ boson would provide dramatic evidence for physics beyond the Standard Model. To date there is no experimental evidence for the existence of any 2’ [3]. The current experimental 2’ mass limit Mzt > 412 GeV/c2 (95% C.L.) was established by the CDF collaboration [4] with the assumption that the coupling strengths of the 2’ to quarks and leptons were the same as those for the Standard Model (SM) 2’. This result was based upon data collected during the 1988-89 run with an integrated luminosity of 4 pb-’ and used both the dielectron [5] and dimuon decay modes. We report an extension of this search using 19.7 pb* of integrated luminosity from the 1992-93 run. Results reported here are obtained using only the dielectron decay mode. We present a 95% confidence level upper limit on the production cross section times branching ratio of 2’ decaying into dielectrons (g(Z) . B(Z’ + ee)). Mass limits are 5 again derived assuming SM coupling strengths. In addition, we present 2’ mass limits using several different theoretical models based on the Es symmetry group [6][‘7] and one limit based upon an Alternative Left-Right Model [8]. The CDF detector has been described in detail elsewhere [9]. We give a brief description of the components relevant to this analysis. Momenta of charged particles are measured in the Central Tracking Chamber (CTC), which is immersed in a 1.4 T axial magnetic field. Outside the CTC, electromagnetic and hadronic calorimeters are arranged in a projective tower geometry. There are three separate pseudorapidity (7) regions of calorimeters, central, end-plug, and forward, where 7 = ln(tan $) and 0 is the polar angle with respect to the direction of the proton beam. Each region has an electromagnetic calorimeter and behind it a hadronic calorimeter. For this analysis we use electrons detected in the central (CEM) or end-plug (PEM) regions. The CEM covers ]q] 9 GeV or an energy cluster in the PEM with ET > 20 GeV. If the cluster was in the CEM the trigger also required a coincidence with a track of transverse momentum PT > 9.2 GeV/c. In addition, the trigger required that the ratio of hadronic to electromagnetic energy (HAD/EM) in the trigger cluster be less than 12.5%. For electrons with 25 150 GeV), the energy deposited

Higgs phenomenology of the supersymmetric model with a gauge singlet

Abstract: We discuss the Higgs sector of the supersymmetric standard model extended by a gauge singlet for the range of parameters, which is compatible with universal soft supersymmetry breaking terms at the GUT scale. We present results for the masses, couplings and decay properties of the lightest Higgs bosons, in particular with regard to Higgs boson searches at LEP. The prospects differ significantly from the ones within the MSSM.

Discovery and Identification of Extra Gauge Bosons

Abstract: The discovery potential and diagnostic abilities of proposed future colliders for new heavy neutral ($Z'$) and charged ($W'$) gauge bosons are summarized. Typical bounds achievable on $M_{Z',W'}$ at the TEVATRON, DI-TEVATRON, LHC, 500 GeV NLC, and 1 TeV NLC are $\sim$1~TeV, $\sim$2~TeV, $\sim$4~TeV, 1--3~TeV, and 2--6~TeV, respectively. For $M_{Z'} \sim$1 TeV the LHC will have the capability to determine the magnitude of normalized $Z'$ quark and lepton couplings to around $10-20\%$, while the NLC would allow for determination of the couplings (including their signs) with a factor of 2 larger error-bars, provided heavy flavor tagging and longitudinal polarization of the electron beam is available.

Lorentz symmetry breaking in Abelian vector-field models with Wess-Zumino interaction.

Abstract: We consider Abelian vector-field models in the presence of the Wess-Zumino interaction with pseudoscalar matter. The occurrence of the dynamic breaking of Lorentz symmetry at classical and one-loop levels is described for massless and massive vector fields. This phenomenon appears to be the nonperturbative counterpart of the perturbative renormalizability and/or unitarity breaking in chiral gauge theories.

Neutrinos from particle decay in the Sun and Earth.

Abstract: Weakly interacting massive particles (WIMP's) may be indirectly detected by observation of upward muons induced by energetic neutrinos from annihilation of WIMP's that have accumulated in the Sun and/or Earth. Energetic muon neutrinos come from the decays of \ensuremath{\tau} leptons, c, b, and t quarks, gauge bosons, and Higgs bosons produced by WIMP annihilation. We provide analytic expressions, suitable for computing the flux of upward muons, for the neutrino energy spectra from decays of all these particles in the center of the Sun and Earth. These analytic expressions should obviate the need for Monte Carlo calculations of the upward-muon flux. We investigate the effects of polarization of the gauge bosons on the neutrino spectra, and find that they are small. We also present simple expressions for the second moments of the neutrino distributions which can be used to estimate the rates for observation of neutrino-induced muons from WIMP annihilation.

Predictions of SUSY masses in the minimal supersymmetric grand unified theory

Abstract: The Minimal Supersymmetric Standard Model (MSSM) distinguishes itself from other GUT's by a successful prediction of many unrelated phenomena with a minimum number of parameters. Among them: a) Unification of the gauge couplings constants; b) Unification of the b-quark and τ-lepton masses; c) Proton stability; d) Electroweak symmetry breaking at a scale far below the unification scale and the corresponding relation between the gauge boson masses and the top quark mass. A combined fit of the free parameters in the MSSM to these low energy constraints shows that the MSSM model can satisfy these constraints simultaneously. From the fitted parameters the masses of the as yet unobserved superpartners of the SM particles are predicted, the top mass is constrained to a range between 140 and 200 GeV, and the second order QCD coupling constant is required to be between 0.108 and 0.132. The complete second order renormalization group equations for the gauge and Yukawa couplings are used and analytical solutions for the neutral gauge boson, the Higgs masses and the sparticle masses are derived, taking into account the one-loop corrections to the Higgs potential.

Left-Right Symmetry Breaking in NJL Approach

Abstract: We study left-right symmetric models which contain only fermion and gauge boson fields and no elementary scalars. The Higgs bosons are generated dynamically through a set of gauge- and parity-invariant 4-fermion operators. It is shown that in a model with a composite bi-doublet and two triplet scalars there is no parity breaking at low energies, whereas in the model with two doublets instead of two triplets parity is broken automatically regardless of the choice of the parameters of the model. For phenomenologically allowed values of the right-handed scale a tumbling symmetry breaking mechanism is realized in which parity breaking at a high scale $\mu_R$ propagates down and eventually causes the \EW symmetry breaking at the scale $\mu_{EW}\sim 100~GeV$. The model exhibits a number of low and intermediate mass Higgs bosons with certain relations between their masses. In particular, the components of the $SU(2)_L$ Higgs doublet $\chi_L$ are pseudo--\GBs of an accidental (approximate) $SU(4)$ symmetry of the Higgs potential and therefore are expected to be relatively light.

The Universal Renormalization Factors Z_1/Z_3 and Color Confinement Condition in Non-Abelian Gauge Theory

Abstract: The ratio Z_1/Z_3 of vertex and wave-function renormalization factors, which is universal (i.e., matter-independent), is shown to equal 1+u which gives the residue of the scalar pole $\propto p_\mu p_ u /p^2$ of 2-point function . This relation is interesting since 1+u=0 has been known to give a sufficient condition for color confinement. We also give an argument that, when 1+u=0 holds, it will be realized by the disappearance of the massless gauge boson pole and is related with the restoration of a certain ``local gauge symmetry" as was discussed by Hata. (Talk given at International Symposium on BRS Symmetry, Sept.~18 -- 22, 1995, Kyoto.)

Physical Parameters and Renormalization of U(1)_a x U(1)_b Models

Abstract: We analize the structure of models with unbroken and spontaneously broken U(1)_a x U(1)_b gauge symmetry. We show that the quantum corrections to the 2N gauge charges, with N = #fermions + #scalars, can be absorbed in the redefinition of three independent gauge couplings (g_a,g_b and g_ab). We establish the (one-loop) conditions on the matter cotent for g_ab= = 0 (a value usually assumed in the literature) and we show that in the minimal extensions of the Standard Model with an extra U(1) symmetry the choice g_ab = 0 is not stable under radiative corrections induced by the standard Higgs fields. Moreover, g_ab = 0 to all orders seems to require an exact symmetry. The spontaneous breaking of the gauge symmetry induces further mixing between the two gauge bosons and introduces a fourth independent physical parameter. A consequence of our analysis is that the usual tree-level description with only three physical parameters (i.e., two gauge couplings and one gauge boson mixing angle) is not in general a justified zero order limit of the treatment including radiative corrections.

Dynamical electroweak symmetry breaking

Abstract: We review the status of and recent developments in dynamical electroweak symmetry breaking, concentrating on the ideas of technicolour and top quark condensates. The emphasis is on the essential physical ideas and experimental implications rather than on detailed mathematical formalism. After a general overview of the subject, we give a first introduction to technicolour, and extended technicolour, illustrating the ideas with a simple (unrealistic) model. Then we review the progress that has been made with enhancing the technicolour condensate, using the Schwinger-Dyson gap equation. The discussion includes the so-called walking technicolour and strong extended technicolour approaches. We then turn to the experimental prospects of technicolour models, including longitudinal gauge boson scattering experiments at the LHC, the detection of pseudo-Goldstone bosons and the hints about electroweak symmetry breaking which comes from precision measurements at LEP. We also discuss a low-scale technicolour model, which has experimental signatures at LEP and the Tevatron. Finally we turn to the idea of the top quark condensate. After reviewing the basic ideas of this approach, we turn to some extensions of these ideas involving fourth-family condensates and the role of irrelevant operators.

Gauge dependence of the high-temperature two-loop effective potential for the Higgs field

Abstract: The high-temperature limit of the two-loop effective potential for the Higgs field is calculated from an effective three-dimensional theory, in a general covariant gauge. It is shown explicitly that a gauge-independent result can be extracted for the equation of state from the gauge-dependent effective potential. The convergence of perturbation theory is estimated in the broken phase, utilizing the gauge dependence of the effective potential.

Dual superconductivity in the SU(2) pure gauge vacuum: A lattice study

Abstract: We investigate the dual superconductivity hypothesis in pure SU(2) lattice gauge theory. We focus on the dual Meissner effect by analyzing the distribution of the color fields due to a static quark-antiquark pair. We find evidence of the dual Meissner effect both in the maximally Abelian gauge and without gauge fixing. We measure the London penetration length. Our results suggest that the London penetration length is a physical gauge-invariant quantity. We put out a simple relation between the penetration length and the square root of the string tension. We find that our estimation is quite close to the extrapolated continuum limit available in the literature. A remarkable consequence of our study is that an effective Abelian theory can account for the long range properties of the SU(2) confining vacuum.

Chiral symmetry breaking in Abelian-projected SU(2) lattice gauge theory.

Abstract: Chiral-symmetry-breaking parameters are calculated in quenched SU(2) lattice gauge theory and with Abelian gauge fields projected in the maximal Abelian gauge and in the field-strength gauge. Maximal Abelian gauge-projected fields lead to chiral condensate values which are quite similar to those of the full non-Abelian theory. Pseudoscalar and vector meson correlators are calculated and found to be reproduced by the use of maximal Abelian gauge fields for small quark masses. In the field-strength gauge, Abelian-projected fields give a chiral condensate which closely resembles the results of strongly coupled ({beta}{lt}1) gauge theory: the chiral condensate is insensitive to {beta} and the quark mass and hence violates scaling badly.

The Universal Renormalization Factors Z_1/Z_3 and Color Confinement Condition in Non-Abelian Gauge Theory

Abstract: The ratio Z_1/Z_3 of vertex and wave-function renormalization factors, which is universal (i.e., matter-independent), is shown to equal 1+u which gives the residue of the scalar pole $\propto p_\mu p_ u /p^2$ of 2-point function . This relation is interesting since 1+u=0 has been known to give a sufficient condition for color confinement. We also give an argument that, when 1+u=0 holds, it will be realized by the disappearance of the massless gauge boson pole and is related with the restoration of a certain ``local gauge symmetry" as was discussed by Hata. (Talk given at International Symposium on BRS Symmetry, Sept.~18 -- 22, 1995, Kyoto.)