118679107
New physics effects in Top quark interactions
The Top quark stands out as the heaviest elementary particle known today and it is expected to be sensitive to the mechanism that breaks the electroweak symmetry. In particular, the study of its couplings to the electroweak gauge bosons is important as it a way to test different models beyond the SM. We review the status of Top quark couplings with the W and Z bosons, as well as FCNC couplings.
18818705
Heavy quark signals from radiative corrections to the Z-prime boson decay in 3-3-1 models
One-loop corrections to the ${Z}^{\ensuremath{'}}$ decay width are derived and analyzed in the framework of the general form of the 3-3-1 models. We identify two important sources of corrections: oblique corrections associated to the ${Z}^{\ensuremath{'}}$ propagator through vacuum polarizations induced by virtual particle-antiparticle pairs of new heavy quarks $J$, and vertex corrections to the ${Z}^{\ensuremath{'}}q\overline{q}$ vertex through virtual exchange of new ${K}^{{Q}_{1,2}}$ gauge bosons. Fixing a specific renormalization scheme, we obtain dominant oblique corrections that exhibit a quadratic dependence on the $J$ quark mass, which are absorbed into two oblique parameters: a global parameter ${\ensuremath{\rho}}_{f}^{\ensuremath{'}}$ which modify the ${Z}^{\ensuremath{'}}$ decay width, and a parameter ${\ensuremath{\kappa}}_{f}^{\ensuremath{'}}$ that define effective ${Z}^{\ensuremath{'}}$ couplings. Numerical results in an specific 3-3-1 model gives a strong contribution of the oblique corrections from about 1.3% in the $d(s)$ quark channel to 10.5% in the neutrino channel, for ${m}_{J}=2\text{ }\text{ }\mathrm{TeV}$. The vertex corrections contribute to the oblique corrections up to 1.4% for the same channel and ${m}_{J}$ value. For $pp$ collisions at the CERN LHC collider, we find that the corrections significantly modify the shape of the cross section distributions for ${e}^{+}{e}^{\ensuremath{-}}$ and $t\overline{t}$ final states, where the distributions including the radiative corrections increases up to 1.23 times the tree-level distribution for the dielectron events and to 1.07 for the top events when ${m}_{J}=3\text{ }\text{ }\mathrm{TeV}$.
15573535
NEW PHYSICS EFFECTS IN THE FLAVOR-CHANGING NEUTRAL COUPLINGS OF THE TOP QUARK
We survey the flavor-changing neutral couplings (FCNC) of the top quark predicted by some extensions of the Standard Model: THDM, SUSY, Left–Right symmetric, TC2, 331, and models with extra quarks. Since the expected sensitivity of the LHC and ILC for the tcV (V = γ, g, Z) and tcH couplings is of order of a few percent, we emphasize the importance of any new physics effect that gives a prediction for these FCNC couplings within this limit. We also review the constraints imposed on these couplings from low-energy precision measurements.
117937444
Textures of Yukawa coupling matrices in the 2HDM type III
The quark mass matrices ansatze proposed by Fritzsch, Du‐Xing and Fukuyama‐Nishiura in the framework of the general two Higgs doublet model are studied. The corresponding Cabbibo‐Kobayashi‐Maskawa matrix elements are computed in all cases and compared with their experimental values. The complex phases of the anstaze are taken into account and the CP violating phase δ is computed. Finally some phenomenology is discussed.
53625847
Top quark tensor couplings
We compute the real and imaginary parts of the one-loop electroweak contributions to the left and right tensorial anomalous couplings of the tbW vertex in the Standard Model (SM). For both tensorial couplings we find that the real part of the electroweak SM correction is close to 10% of the leading contribution given by the QCD gluon exchange. We also find that the electroweak real and imaginary parts for the anomalous right coupling are almost of the same order of magnitude. The one loop SM prediction for the real part of the left coupling is close to the 3σ discovery limit derived from b → sγ. Besides, taking into account that the predictions of new physics interactions are also at the level of a few percents when compared with the one loop QCD gluon exchange, these electroweak corrections should be taken into account in order to disentangle new physics effects from the standard ones. These anomalous tensorial couplings of the top quark will be investigated at the LHC in the near future where sensitivity to these contributions may be achieved.
124002542
Quark masses and mixing in $SU\left(3\right)_{C}\otimes SU\left(3\right)_{L}\otimes U\left(1\right)_{X}\otimes S_{3}$ models
By imposing a specific $S_{3}$ discrete symmetry for fermions and scalars, we extend the group of the model based on the gauge symmetry $SU(3)_{C}\otimes SU(3)_{L}\otimes U(1)_{X}$. We found that after the symmetry breaking of the continuous group, all the down type quarks acquire tree level masses, while in the up sector only the top quark and a new heavy T quark obtain masses at tree level. By imposing hierarchical Yukawa couplings between the ordinary down-type quarks and new heavy down-type quarks, we may explain the relation $m_{d}<<m_{s}<<m_{b}$. The massless up-type quarks get small mass terms through effective six dimensional operators according to the gauge and discrete symmetries. In particular, the smallness of the u quark can be understood by a small deviation in the universality of the dimensionless couplings associated to the effective operators. We also obtain with only four free parameters, the magnitudes of the CKM matrix elements and the Jarlskog invariant, within experimental error values.
118371403
Phenomenological aspects of the exotic T quark in 331 models
In the context of 331 models we analyze the phenomenology of exotic T quarks with electric charge 2/3. We establish bounds for the corresponding masses and mixing angles and study the decay modes T→bW, tZ and qH. It is found that the decays into scalars are strongly dependent on the model parameters and can be the dominant ones in a scenario with approximate flavor symmetry.
118990339
Upper bound of the lightest higgs boson in a supersymmetric SU(3)l x U(1)x gauge model
A supersymmetric version of the $SU(3)_L \otimes U(1)_X$ gauge model is presented. The model is embedded in a $SU(6)_L \otimes U(1)_X$ gauge group and it has been built up completely quiral anomaly free and without any exotic charges in the fermionic content. The Minimal Supersymmetric Standard Model can be seen as an effective theory of this larger symmetry. We analyze how the spectrum of the new model can shift the upper bound on the CP-even Higgs boson and we find that it can be moved up to 143 GeV.