scholarly journals Effective Lagrangian Approach to Top Decay via Flavor Changing Neutral Current

2019 ◽  
Author(s):  
Kazumasa Ohkuma ◽  
Zenro Hioki ◽  
Akira Uejima
Keyword(s):  
Neutral Current ◽  
Lagrangian Approach ◽  
Flavor Changing ◽  
Effective Lagrangian ◽  
Flavor Changing Neutral Current

scholarly journals Studying flavor-changing neutral tqZ couplings: Current constraints and future prospects

2019 ◽  
Vol 34 (34) ◽  
pp. 1950278 ◽  
Author(s):  
Zenrō Hioki ◽  
Kazumasa Ohkuma ◽  
Akira Uejima
Keyword(s):  
Top Quark ◽  
Neutral Current ◽  
Branching Fractions ◽  
Hadron Collider ◽  
Coupling Constants ◽  
Flavor Changing ◽  
Lagrangian Framework ◽  
Effective Lagrangian ◽  
Flavor Changing Neutral Current ◽  
Invariant Dimension

Possible nonstandard tuZ and tcZ interactions, which induce flavor-changing neutral-current decays of the top quark, are studied in the effective-Lagrangian framework. The corresponding Lagrangian consists of four kinds of nonstandard couplings coming from [Formula: see text] invariant dimension-6 effective operators. The four coupling constants in each interaction are treated as complex numbers independent of each other and constraints on them are derived by using the present experimental limits of the branching fractions for [Formula: see text] and [Formula: see text] processes. Future improvements of those constraints are also discussed as well as possibilities of measurements of these couplings at the High-Luminosity Large Hadron Collider.

scholarly journals Lepton flavor violating decays of B and K mesons in models with extended gauge group

2018 ◽  
Vol 33 (14n15) ◽  
pp. 1850087 ◽  
Author(s):  
Fayyazuddin ◽  
Muhammad Jamil Aslam ◽  
Cai-Dian Lu
Keyword(s):  
Gauge Group ◽  
Particle Physics ◽  
Neutral Current ◽  
Representation Formula ◽  
Decay Modes ◽  
Lepton Flavor ◽  
Flavor Changing ◽  
Effective Lagrangian ◽  
Flavor Changing Neutral Current ◽  
Promising Area

Lepton flavor violating (LFV) decays are forbidden in the Standard Model (SM) and to explore them one has to go beyond it. The flavor changing neutral current induced lepton flavor conserving and LFV decays of [Formula: see text] and [Formula: see text] mesons is discussed in the gauge group [Formula: see text]. The lepto-quark [Formula: see text] corresponding to gauge group [Formula: see text] allows the quark–lepton transitions and hence giving a framework to construct the effective Lagrangian for the LFV decays. The mass of lepto-quark [Formula: see text] provides a scale at which the gauge group [Formula: see text] is broken to the SM gauge group. Using the most stringent experimental limit [Formula: see text], the upper bound on the effective coupling constant [Formula: see text] is obtained for certain pairing of lepton and quark generations in the representation [Formula: see text] of the group [Formula: see text]. Later, the effective Lagrangian for the LFV meson decays for the gauge group [Formula: see text] is constructed. Using [Formula: see text], the bound on the ratio of effective couplings is obtained to be [Formula: see text]. A number of decay modes are discussed which provide a promising area to test this model in the current and future particle physics experiments.

scholarly journals Probing the anomalous tqγ couplings through single top production at the future lepton–hadron colliders

2019 ◽  
Vol 34 (36) ◽  
pp. 1950298 ◽  
Author(s):  
E. Alici ◽  
M. Köksal
Keyword(s):  
Cross Sections ◽  
Top Quark ◽  
Neutral Current ◽  
New Physics ◽  
Main Reaction ◽  
Flavor Changing ◽  
Effective Lagrangian ◽  
Quark Flavor ◽  
The Future ◽  
Flavor Changing Neutral Current

The measurements of the top quark flavor changing neutral current interactions are one of the most important goals of the top quark physics program in the present and the future collider experiments. These measurements provide direct information on nonstandard interactions of the top quark. Within the framework of new physics beyond the Standard Model, these interactions can be defined by an effective Lagrangian. In this study, we have investigated the potential of the future [Formula: see text] colliders on the top quark flavor changing neutral current interactions through the subprocesses [Formula: see text], where [Formula: see text]. These subprocesses have been produced through the main reaction [Formula: see text] at the LHC-[Formula: see text], the FCC-[Formula: see text] and the SPPC-[Formula: see text]. For the main reaction, the total cross-sections have been calculated as a function of the anomalous [Formula: see text] couplings. In addition, sensitivities on [Formula: see text] at 95% Confidence Level have been calculated. We obtain that the best constraints on [Formula: see text] are at the order of [Formula: see text] which is four orders of magnitude better than the LHC’s experimental results.

scholarly journals Structure of flavor changing Goldstone boson interactions

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Jin Sun ◽  
Yu Cheng ◽  
Xiao-Gang He
Keyword(s):  
Symmetry Breaking ◽  
Model Building ◽  
Neutral Current ◽  
Goldstone Boson ◽  
New Physics ◽  
Majorana Neutrino ◽  
Neutrino Masses ◽  
Type I ◽  
Flavor Changing ◽  
Flavor Changing Neutral Current

Abstract General flavor changing Goldstone boson (GB) interactions with fermions from a spontaneous global U(1)G symmetry breaking are discussed. This GB may be the Axion, solving the strong QCD CP problem, if there is a QCD anomaly for the assignments of quarks U(1)G charge. Or it may be the Majoron, producing seesaw Majorana neutrino masses by lepton number violation, if the symmetry breaking scale is much higher than the electroweak scale. It may also, in principle, play the roles of Axion and Majoron simultaneously as far as providing solution for the strong CP problem and generating a small Majorana neutrino masses are concerned. Great attentions have been focused on flavor conserving GB interactions. Recently flavor changing Axion and Majoron models have been studied in the hope to find new physics from rare decays in the intensity frontier. In this work, we will provide a systematic model building aspect study for flavor changing neutral current (FCNC) GB interactions in the fermion sectors, or separately in the quark, charged lepton and neutrino sectors and will identify in detail the sources of FCNC interactions in a class of beyond standard model with a spontaneous global U(1)G symmetry breaking. We also provide a general proof of the equivalence of using physical GB components and GB broken generators for calculating GB couplings to two gluons and two photons, and discuss some issues related to spontaneous CP violation models. Besides, we will also provide some details for obtaining FCNC GB interactions in several popular models, such as the Type-I, -II, -III seesaw and Left-Right symmetric models, and point out some special features in these models.

scholarly journals Search for the flavor-changing neutral current decay D0→μ+μ− with the HERA-B detector

2004 ◽  
Vol 596 (3-4) ◽  
pp. 173-183 ◽  
Author(s):  
I. Abt ◽  
M. Adams ◽  
H. Albrecht ◽  
A. Aleksandrov ◽  
V. Amaral ◽  
...  
Keyword(s):  
Neutral Current ◽  
Current Decay ◽  
Flavor Changing ◽  
Flavor Changing Neutral Current ◽  
Neutral Current Decay

scholarly journals SCALAR DARK MATTER EFFECTS IN HIGGS AND TOP QUARK DECAYS

2007 ◽  
Vol 22 (25n28) ◽  
pp. 2121-2129 ◽  
Author(s):  
XIAO-GANG HE ◽  
HO-CHIN TSAI ◽  
TONG LI ◽  
XUE-QIAN LI
Keyword(s):  
Dark Matter ◽  
Top Quark ◽  
Neutral Current ◽  
Higgs Doublet ◽  
Tree Level ◽  
Flavor Changing ◽  
Higgs Decay ◽  
Dark Matter Relic Density ◽  
Flavor Changing Neutral Current ◽  
Two Higgs Doublet Model

We study possible observational effects of scalar dark matter, the darkon D, in Higgs h and top quark t decay processes, h → DD and t → cDD in the minimal Standard Model (SM) and its two Higgs doublet model (THDM) extension supplemented with a SM singlet darkon scalar field D. We find that the darkon D can have a mass in the range of sub-GeV to several tens of GeV, interesting for LHC and ILC colliders, to produce the required dark matter relic density. In the SM with a darkon, t → cDD only occurs at loop level giving a very small rate, while the rate for Higgs decay h → DD can be large. In THDM III with a darkon, where tree level flavor changing neutral current (FCNC) interaction exists, a sizable rate for t → cDD is also possible.

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