scholarly journals Global analysis of the top quark couplings to gauge bosons

1994 ◽  
Vol 50 (7) ◽  
pp. 4462-4477 ◽  
Author(s):  
Ehab Malkawi ◽  
C.-P. Yuan
Keyword(s):  
Top Quark ◽  
Global Analysis ◽  
Gauge Bosons

scholarly journals Neutrino oscillation constraints on U(1)′ models: from non-standard interactions to long-range forces

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Pilar Coloma ◽  
M. C. Gonzalez-Garcia ◽  
Michele Maltoni
Keyword(s):  
Contact Interaction ◽  
Equivalence Principle ◽  
Laboratory Experiments ◽  
Global Analysis ◽  
Gauge Bosons ◽  
Lepton Flavor ◽  
Long Baseline ◽  
Oscillation Analysis ◽  
Weakly Coupled ◽  
Effective Contact

Abstract We quantify the effect of gauge bosons from a weakly coupled lepton flavor dependent U(1)′ interaction on the matter background in the evolution of solar, atmospheric, reactor and long-baseline accelerator neutrinos in the global analysis of oscillation data. The analysis is performed for interaction lengths ranging from the Sun-Earth distance to effective contact neutrino interactions. We survey ∼ 10000 set of models characterized by the six relevant fermion U(1)′ charges and find that in all cases, constraints on the coupling and mass of the Z′ can be derived. We also find that about 5% of the U(1)′ model charges lead to a viable LMA-D solution but this is only possible in the contact interaction limit. We explicitly quantify the constraints for a variety of models including $$ \mathrm{U}{(1)}_{B-3{L}_e} $$ U 1 B − 3 L e , $$ \mathrm{U}{(1)}_{B-3{L}_{\mu }} $$ U 1 B − 3 L μ , $$ \mathrm{U}{(1)}_{B-3{L}_{\tau }} $$ U 1 B − 3 L τ , $$ \mathrm{U}{(1)}_{B-\frac{3}{2}\left({L}_{\mu }+{L}_{\tau}\right)} $$ U 1 B − 3 2 L μ + L τ , $$ \mathrm{U}{(1)}_{L_e-{L}_{\mu }} $$ U 1 L e − L μ , $$ \mathrm{U}{(1)}_{L_e-{L}_{\tau }} $$ U 1 L e − L τ , $$ \mathrm{U}{(1)}_{L_e-\frac{1}{2}\left({L}_{\mu }+{L}_{\tau}\right)} $$ U 1 L e − 1 2 L μ + L τ . We compare the constraints imposed by our oscillation analysis with the strongest bounds from fifth force searches, violation of equivalence principle as well as bounds from scattering experiments and white dwarf cooling. Our results show that generically, the oscillation analysis improves over the existing bounds from gravity tests for Z′ lighter than ∼ 10−8→ 10−11 eV depending on the specific couplings. In the contact interaction limit, we find that for most models listed above there are values of g′ and MZ′ for which the oscillation analysis provides constraints beyond those imposed by laboratory experiments. Finally we illustrate the range of Z′ and couplings leading to a viable LMA-D solution for two sets of models.

scholarly journals CONSTRAINTS ON THE ELECTROWEAK UNIVERSAL PARAMETERS AND THE TOP AND HIGGS MASSES FROM UPDATED LEP/SLC DATA

1995 ◽  
Vol 10 (33) ◽  
pp. 2553-2569 ◽  
Author(s):  
SEIJI MATSUMOTO
Keyword(s):  
Form Factor ◽  
Higgs Boson ◽  
Top Quark ◽  
Higgs Mass ◽  
Global Analysis ◽  
Mean Value ◽  
The Standard Model ◽  
The Mean ◽  
The Masses ◽  
Vertex Form Factor

A global analysis is performed using the recent data from LEP and SLC. Constraints on the electroweak universal parameters (S, T, U) and on the masses of the top quark and Higgs boson within the standard model (SM) are investigated. The uncertainties due to the QCD and QED effective couplings, αs(mz) and , [Formula: see text] are examined in detail. Even though the mean value of S is increased to be consistent with zero, the naive Technicolor models are still disfavored due to its reduced error. Within the SM, we find the 90% CL constraints; 133 GeV<mt<190 GeV and 10 GeV<mH< 440 GeV for αs(mz)=0.116 and [Formula: see text]. The experimental constraints on the ZbLbL vertex form factor, [Formula: see text] play an important role in disfavoring the region of large mt(mt~200GeV) and large mH(mH~1000 GeV). If mt is precisely known, the present electroweak data give a rather strict upper bound on the Higgs mass, mH<140(300) GeV at 95% CL, for mt=160(175) GeV and for the above αs(mz) and [Formula: see text].

scholarly journals Top quark polarization as a probe of models with extra gauge bosons

2011 ◽  
Vol 83 (11) ◽  
Author(s):  
Edmond L. Berger ◽  
Qing-Hong Cao ◽  
Chuan-Ren Chen ◽  
Hao Zhang
Keyword(s):  
Top Quark ◽  
Gauge Bosons

scholarly journals Non-Universal Gauge Bosons Z′ and Rare Top Decays

2003 ◽  
Vol 18 (31) ◽  
pp. 2187-2193 ◽  
Author(s):  
Chongxing Yue ◽  
Hongjie Zong ◽  
Lanjun Liu
Keyword(s):  
Parameter Space ◽  
Top Quark ◽  
Branching Ratios ◽  
New Method ◽  
Gauge Bosons ◽  
Near Future

We study a new method for detecting non-universal gauge bosons Z′ via considering their effects on rare top decays. We calculate the contributions of the non-universal gauge bosons Z′ predicted by topcolor-assisted technicolor (TC2) models and flavor-universal TC2 models on the rare top decays t → cV (V = g,γ,Z) and t → clilj (li,lj = τ,μ, or e). We show that the branching ratios of these processes can be significantly enhanced. Over a sizeable region of the parameter space, we have Br (t → cg) ~ 10-5 and Br (t → cττ) ~ 10-7, which may approach the observable threshold of near future experiments. Non-universal gauge bosons Z′ may be detected via the rare top decay processes at the top-quark factories such as the CERN LHC.

PREDICTION OF THE TOP QUARK MASS IN A FINITE ELECTROWEAK THEORY

1991 ◽  
Vol 06 (29) ◽  
pp. 2697-2703
Author(s):  
M. CLAYTON ◽  
J. W. MOFFAT
Keyword(s):  
Top Quark ◽  
Quark Mass ◽  
Vacuum Polarization ◽  
Local Scale ◽  
Higgs Mechanism ◽  
Electroweak Theory ◽  
Particle Spectrum ◽  
Top Quark Mass ◽  
Gauge Bosons ◽  
Non Local

A parameter-free prediction of the top quark mass is obtained from the calculation of [Formula: see text] in a finite non-local electroweak theory, in which the W and Z gauge bosons acquire their masses through the lowest order vacuum polarization graphs containing fermion loops. The SU (2)× U (1) gauge symmetry is broken to U (1) em by a symmetry breaking measure factor in the path integral without resorting to a Higgs mechanism. Using the ratio of the W and Z masses obtained from the average of the UAI, UA2 and the CDF experiments, we predict mt=86±33 GeV and the gauge boson non-local scale Λw=523±4 GeV . Using the CDF measured W mass, we find mt=125±40 GeV and Λw=529±6 GeV . The particle spectrum in the model contains the W, Z and photon gauge bosons and the standard three generations of leptons and quarks, including the anticipated top quark.

scholarly journals Rare decays of the top quark mediated by Z′ gauge bosons and flavor violation

2020 ◽  
Vol 35 (18) ◽  
pp. 2050153
Author(s):  
J. I. Aranda ◽  
D. Espinosa-Gómez ◽  
J. Montaño ◽  
F. Ramírez-Zavaleta ◽  
E. S. Tututi
Keyword(s):  
Gauge Boson ◽  
Top Quark ◽  
Branching Ratios ◽  
Gauge Bosons ◽  
Flavor Violation ◽  
Gauge Symmetries ◽  
Quark Decays ◽  
The Standard Model ◽  
Order Of Magnitude ◽  
The One

The rare top quark decays mediated by a new neutral massive gauge boson that is predicted in models with extended gauge symmetries are studied. We focus on the processes [Formula: see text] induced at the one loop level, where [Formula: see text], by considering different extended models. It is found that, within a broad range of mass of the new neutral gauge boson, the models predict branching ratios for the decays in study that are competitive with respect to the corresponding branching ratios in the Standard Model (SM). In order to establish bound on our branching ratios, we consider the recent experimental bounds as [Formula: see text], depending on the model, which also impose restrictions on our calculation. Even in this case, the resulting branching ratios are of the same order of magnitude as that predicted by the SM. It should be noted that for the case of two models studied here, since no experimental bound exists to compare with, the results could be important, as they are, in the best of cases, two orders of magnitude larger than the predicted by the SM.

scholarly journals A Monte Carlo global analysis of the Standard Model Effective Field Theory: the top quark sector

2019 ◽  
Vol 2019 (4) ◽  
Author(s):  
Nathan P. Hartland ◽  
Fabio Maltoni ◽  
Emanuele R. Nocera ◽  
Juan Rojo ◽  
Emma Slade ◽  
...  
Keyword(s):  
Field Theory ◽  
Monte Carlo ◽  
Standard Model ◽  
Effective Field Theory ◽  
Top Quark ◽  
Global Analysis ◽  
Effective Field ◽  
Quark Sector ◽  
The Standard Model

UPPER LIMITS ON THE TOP QUARK MASS IN MODELS WITH NEW GAUGE BOSONS

1990 ◽  
Vol 05 (02) ◽  
pp. 115-123 ◽  
Author(s):  
THOMAS G. RIZZO
Keyword(s):  
Top Quark ◽  
Quark Mass ◽  
Top Quark Mass ◽  
Gauge Bosons ◽  
Gauge Sector ◽  
Upper Limit ◽  
Upper Limits ◽  
The Standard Model ◽  
Lower Limits ◽  
Rule Out

The experimental value of the ρ parameter is used to obtain an upper limit on the top-quark mass (mt) in models with extended gauge sectors. This limit is found to be generally stronger than that obtained from similar considerations in the Standard Model (SM). This bound, however, is shown to depend strongly on the particular extension of the usual SM gauge sector under consideration. Improved experimental lower limits on mt can also be used to rule out large regions of the parameter space of extended electroweak models.

scholarly journals NEW GAUGE BOSONS FROM STRING MODELS

1996 ◽  
Vol 11 (15) ◽  
pp. 1247-1262 ◽  
Author(s):  
MIRJAM CVETIČ ◽  
PAUL LANGACKER
Keyword(s):  
Standard Model ◽  
Supersymmetry Breaking ◽  
Large Class ◽  
Top Quark ◽  
Fine Tuning ◽  
Electroweak Symmetry ◽  
Gauge Bosons ◽  
Exotic Particles ◽  
Yukawa Couplings ◽  
String Models

We address the mass ranges of new neutral gauge bosons and constraints on the accompanying exotic particles as predicted by a class of superstring models. Under certain assumptions about the supersymmetry breaking parameters we show that breaking of an additional U(1)′ symmetry is radiative when the appropriate Yukawa couplings of exotic particles are of order one, analogous to the radiative breaking of the electroweak symmetry in the supersymmetric standard model due to the large top-quark Yukawa coupling. Such large Yukawa couplings occur for a large class of string models. The Z′ and exotic masses are either of [Formula: see text], or of a scale intermediate between the string and electroweak scales. In the former case, [Formula: see text] may be achieved without excessive fine-tuning, and is within future experimental reach.

Sign in / Sign up

Export Citation Format

Share Document