Search

We study the decay t → cγ with flavor-changing neutral interactions in scalar sector of the type III Two Higgs Doublet Model (THDM-III) with mixing between neutral scalar fields as a result of considering the most general scalar potential. The branching ratio of the decay Br (t → cγ) is calculated as function of the mixing parameters and masses of the neutral scalar fields. We obtain a Br (t → cγ) of the order of 10−8 for the considered regions of the mixing parameters. Finally, one upper bound for the possible events is estimated to be n=18 by assuming an expected luminosity of the order of 300 fb−1.

We study the observability for the flavor-changing decay of a top quark $t\to ch$ at the LHC and future hadron colliders, namely, High-Luminosity LHC (HL-LHC), High-Energy LHC (HE-LHC) and Future Circular hadron-hadron Collider (FCC-hh). Two scenarios in which the Higgs boson could decay: into a quark bottom pair $(\textit{bb-channel})$ and two photons $(\textit{$\gamma\gamma$-channel})$ are analyzed. A Monte Carlo analysis of the signal and the Standard Model (SM) background is computed. Center-of-mass energies of $\sqrt{s}=14,\;27\; $\text{and}$\; 100$ TeV and integrated luminosities from $0.3$ to $30$ ab$^{-1}$ are explored. The theoretical framework adopted in this work is the Type-III Two-Higgs Doublet Model (THDM-III) for which, constraints on the parameter space from the Higgs boson coupling modifiers $\kappa_i$ are presented and used in order to evaluate the branching ratio of the $t\to ch$ decay and the ($pp\to t\bar{t},\,t\to ch$) production cross section. We find that with the integrated luminosity achieved at the LHC, the $t\to ch$ decay is out of the reach of detection. More promising results emerge for the HL-LHC, HE-LHC and FCC-hh in which potential discoveries could be claimed., Comment: Version to be published in JHEP

We study Dark Matter (DM) abundance in the framework of the extension of the Standard Model (SM) with an additional $U(1)_X$ gauge symmetry. One complex singlet is included to break the $U(1)_X$ gauge symmetry, meanwhile one of the doublets is considered inert to introduce a DM candidate. The stability of the DM candidate is analyzed with a continuous $U(1)_X$ gauge symmetry as well as discrete $Z_2$ symmetry. We find allowed regions for the free model parameters which are in agreement with the most up-to-date experimental results reported by CMS and ATLAS collaborations, the upper limit on WIMP-nucleon cross section imposed by XENON1T collaboration and the upper limit on the production cross-section of a $Z^{\prime}$ gauge boson times the branching ratio of the $Z^{\prime}$ boson decaying into $\ell^-\ell^+$. We also obtain allowed regions for the DM candidate mass from the relic density reported by the PLANCK collaboration including light, intermediate and heavy masses; depending mainly on two parameters of the scalar potential, $\lambda_{2x}$ and $\lambda_{345}=\lambda_3+\lambda_4+2\lambda_5$. We find that trough $pp\rightarrow \chi\chi \gamma$ production, it may only be possible for a future hadron-hadron Circular Collider (FCC-hh) to be able to detect a DM candidate within the range of masses 10-60 GeV., Comment: Accepted version to be published in EPJC, typos corrected, cites added

We compute the contributions to rare top decays $t\ensuremath{\rightarrow}cZ$ and $t\ensuremath{\rightarrow}c{h}_{1}$ from the scalar sector in the two Higgs doublet model type III with $CP$ violation, where ${h}_{1}$ is the Standard Model Higgs boson. The branching ratios for $\mathrm{BR}(t\ensuremath{\rightarrow}cZ)$ and $\mathrm{BR}(t\ensuremath{\rightarrow}c{h}_{1})$ are obtained as a function of the model parameters. In particular, the $\mathrm{BR}(t\ensuremath{\rightarrow}cZ)$ can increase its value up to ${10}^{\ensuremath{-}3}$ for $\mathrm{tan}\ensuremath{\beta}=1$ and masses for the additional Higgs bosons of ${m}_{{h}_{2},{h}_{3},{H}^{\ifmmode\pm\else\textpm\fi{}}}\ensuremath{\sim}0.5\text{ }\text{ }\mathrm{TeV}$. Meanwhile $\mathrm{BR}(t\ensuremath{\rightarrow}c{h}_{1})$ can reach values of the order of $\ensuremath{\sim}{10}^{\ensuremath{-}2}$. We constrain the model parameters (mixing angles of the neutral scalar fields in the $CP$ violation context and $\mathrm{tan}\ensuremath{\beta}$) using the reported values of the signal strengths ${R}_{XX}$ and $b\ensuremath{\rightarrow}s\ensuremath{\gamma}$ process.

In the framework of a left-right model containing mirror fermions (LRMM) with gauge group S U ( 3 ) C ⊗ S U ( 2 ) L ⊗ S U ( 2 ) R ⊗ U ( 1 ) Y ′ , we estimate the neutrino masses, which are found to be consistent with their experimental bounds and hierarchy. We also estimate the decay rates of heavy Majorana neutrinos in the channels N → W ± l ∓ , N → Z ν l and N → H ν l , which are roughly equal for large values of the heavy neutrino mass. Starting from the most general Majorana neutrino mass matrix, the smallness of active neutrino masses turns out from the interplay of the hierarchy of the involved scales and the double application of seesaw mechanism. An appropriate ansatz on the structure of the neutrino mass matrix imposing a symmetric mixing of electron neutrino with muon and tau neutrinos leads to tribimaximal mixing matrix for light neutrinos.

In this paper we study the Flavor-Changing mediated by Higgs boson within Two-Higgs Doublet Model-III context. We explore the parameter space and, considering recent results, find new limits for the model parameters. We also obtain the total Higgs decay width and the branching ratios for different channels taking limits for the $t\to cV$ and $b\to s\gamma$ processes. Considering different constraints, we estimate the branching ratio for the $h\to t^*_{}c$ in the model as well as the bounds for the $b \to s\gamma$, $h \to \mu\tau$ and $h\to \gamma Z.$ Considering the quark top decays to $W\bar{b},$ we obtained $Br(h \to Wc\bar{b})\sim10^{-3}$., Comment: 12 pages, 9 figures, accepted to publish in PTEP

Models beyond the standard model with extra scalars have been highly motivated by the recent discovery of the Higgs boson. The two Higgs doublet model type III considers the most general case for the scalar potential, allowing mixing between neutral $CP$-even and $CP$-odd scalar fields. This work presents the results of the study on the $t\ensuremath{\rightarrow}c\ensuremath{\gamma}$ decay at one loop level if neutral flavor changing is generated by top-charm-Higgs coupling given by the Yukawa matrix. For instance, a value for the branching ratio $\mathrm{Br}(t\ensuremath{\rightarrow}c\ensuremath{\gamma})\ensuremath{\sim}{10}^{\ensuremath{-}6}$ for $\mathrm{tan}\ensuremath{\beta}=2.5$ and general neutral Higgs mixing parameters, $1.16\ensuremath{\le}{\ensuremath{\alpha}}_{1}\ensuremath{\le}1.5$, $\ensuremath{-}0.48\ensuremath{\le}{\ensuremath{\alpha}}_{2}\ensuremath{\le}\ensuremath{-}0.1$. The number of events for the $t\ensuremath{\rightarrow}c\ensuremath{\gamma}$ decay with an integrated luminosity of $300\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ is estimated as $10\ensuremath{\lesssim}{N}_{\mathrm{Eff}}\ensuremath{\lesssim}100$ for the parameters of the model constrained by experimental data.

In this work we study the anomalous top quark-gluon couplings Chromoelectric Dipole Moment (CEDM) and Chromomagnetic Dipole Moment (CMDM) in a general THDM with CP violation. We find that this model provides an important contribution from the $Y_{tt}$ Yukawa coupling that needs to be taken into account. The CMDM and CEDM obtained are $-0.03, Comment: 9 Pages, 2 tables, 4 figures

We discuss the formalism of two Higgs doublet model type III with CP violation from CP-even CP-odd mixing in the neutral Higgs bosons. The flavor changing interactions among neutral Higgs bosons and fermions are presented at tree level in this type of model. These assumptions allow the study rare top decays mediated by neutral Higgs bosons, particularly we are interested in $t\rightarrow c l^+l^-$. For this process we estimated upper bounds of the branching ratios $\textrm{Br}(t\rightarrow c \tau^+\tau^-)$ of the order of $10^{-9}\sim 10^{-7}$ for a neutral Higgs boson mass of 125 GeV and $\tan\beta=1$, 1.5, 2, 2.5. For the case of $t\rightarrow c \tau^+\tau^-$ the number of possible events is estimated from 1 to 10 events which could be observed in future experiments at LHC with a luminosity of 300 $\textrm{fb}^{-1}$ and 14 GeV for the energy of the center of mass. Also we estimate that the number of events for the process $t\rightarrow c l^+l^-$ in different scenarios is of order of $2500$., Comment: 8 pages, 5 figures

Many extensions to the Standard Model imply the existence of new charged scalar Higgs bosons. We study the contribution of a general scalar or pseudoscalar coupling for the neutrino-electron scattering. We take a phenomenological approach in order to obtain model independent limits to the couplings that arise in this picture. We illustrate the reach of the constraints by studying the particular case of the type III two Higgs doublet model, where we have found new constraints to some elements of the Yukawa couplings mixing matrix ($|Y_{ee}| \leq 1 \times 10^{-1}$ and $|Y_{e\mu}| \leq 7\times10^{-2}$ at 90% CL)., Comment: 6 pages, 4 figures. Accepted for publication in International Journal of Modern Physics A

We consider the Inert Doublet Model (IDM) with an additional local gauge symmetry U(1) and a complex singlet scalar to break the symmetry U(1). The continuous symmetry U(1) is introduced to control the CP-conserving interaction instead of some discrete symmetries as usually. We present the mass spectrum for neutral scalar and gauge bosons and the values of the charges under U(1) for which the model could have a candidate to dark matter.

In this work we study the anomalous top quark-gluon couplings Chromoelectric Dipole Moment and Chromomagnetic Dipole Moment in a general THDM with CP violation also known as THDM Type III. We include the contribution to the color electric and magnetic couplings arising from the Y tt Yukawa coupling. We provide phenomenological restrictions to chromoelectric and chromomagnetic anomalous couplings within the model.

The models based on SU(3)C × SU(3)L × U(1)X gauge symmetry group contain an interesting source of flavor-changing neutral current at tree level. These models are known as the 331 models in the literature. The third quark family can transform differently from the first and second quark families in the 331 models. Then, flavor-changing neutral current arises from the interaction with quarks with the new neutral gauge boson, Z′. Using this coupling we estimated the partial decay width for the rare top decay t → cl+l−. We find that the corresponding branching fraction can be around 10−12−10−9 for 1 TeV ≤ MZ′ ≤ 5 TeV with mixing angle of quarks eigenstates between 0.1 and 0.5.

The rare top decay t-> c l+l-, which involves flavor violation, is studied as a possible probe of new physics. This decay is analyzed with the simplest Standard Model extensions with additional gauge symmetry formalism. The considered extension is the Left-Right Symmetric Model, including a new neutral gauge boson Z' that allows to obtain the decay at tree level through Flavor Changing Neutral Currents (FCNC) couplings. The neutral gauge boson couplings are considered diagonal but family non-universal in order to induce these FCNC. We find the $BR(t-> c l+l-)~10^{-13} for a range 1 TeV < M_{Z'} < 3 TeV.

We derive the one loop renormalization group equations for the Cabibbo-Kobayashi-Maskawa matrix for the Standard Model, its two Higgs extension and the minimal supersymmetric extension in a novel way. The derived equations depend only on a subset of the model parameters of the renormalization group equations for the quark Yukawa couplings so the CKM matrix evolution cannot fully test the renormalization group evolution of the quark Yukawa couplings. From the derived equations we obtain the invariant of the renormalization group evolution for three models which is the angle $\alpha$ of the unitarity triangle. For the special case of the Standard Model and its extensions with $v_{1}\approx v_{2}$ we demonstrate that also the shape of the unitarity triangle and the Buras-Wolfenstein parameters $\bar{\rho}=(1-{1/2}\lambda^{2})\rho$ and $\bar{\eta}=(1-{1/2}\lambda^{2})\eta$ are conserved. The invariance of the angles of the unitarity triangle means that it is not possible to find a model in which the CKM matrix might have a simple, special form at asymptotic energies., Comment: 9 pages

We solve the one loop Renormalization Group Equations (RGE) for the Yukawa couplings in the Standard Model with two Higgs doublets. In the RGE we include the contributions of the up and down quarks. In this approximation we explore universality and unification assumptions to study the mass‐hierarchy problem through the running of the vacuum expectation values.

Within the framework of the standard model (SM) of elementary particles, we obtained numerical solutions for the running Higgs mass, considering the renormalization group equations at the one and two loop approximation. Through the triviality condition (TC) and stability condition (SC) on the Higgs quartic coupling λH the bounds on the Higgs running mass have been fixed. The numerical results are presented for two special cases. One considering an unification of the three gauge couplings at the energy EU = 1013 GeV and the other using the current experimental data for the gauge couplings.

We discuss the formulation of the general two-Higgs doublet model type III, which incorporates flavor changing neutral scalar interactions (FCNSI) and CP violation from several sources. CP violation can arise either from Yukawa terms or from the Higgs potential, be it explicit or spontaneous. We discuss the limit that includes CP violation and Yukawa four textures to control FCNSI and evaluate the CP asymmetry for the decay h → bcW, which may allow to test the patterns of FCNSI and CP violation, that arises in these models.

We study the rare top decay t → cl, which involves flavor violation, as a possible probe of new physics. This decay is analyzed with the simplest Standard Model (SM) extensions with additional gauge symmetry U(l) or SU(2), known as generic Z' model or left-right symmetric model, respectively. The considered models allow to obtain this decay at tree level through Flavor Changing Neutral Currents (FCNC). We have considered diagonal non-universal couplings for up-type quark sector and found that BR(t → cl) for 1 TeV < Mz' < 3 TeV can be of order ~ 10−11 in generic Z' model or ~ 10−12 in left-right symmetric model.

Power spectra of CW phase-path sounders operating at 6.0, 4.8 and 2.4 MHz often display peak or slope changes at periods in the 5–20-min range. Plots of these periods vs. real height tend to follow mean Vaisala frequency curves calculated from Standard Atmosphere models. This suggests that statistical properties of CW phase-path sounder fluctuation can be used to monitor certain mean physical parameters of the upper atmosphere.

This paper presents a non standard analysis of systematic nonstationarity in data on ionospheric motions. The methodology is applicable to any analysis of ambient back-ground noise in communication systems which use the atmosphere as a medium. The data used in this paper were obtained from an array of radar-like devices called phase-path sounders, which measure the velocity of the vertical motion of the neutral gases in the ionosphere. The model fits between 36% and 5%, of the variation of the log spectrum for frequencies less than 3 CPH and greater than 6 CPH using a period of 24 hours (diurnal) and the first harmonic of 12 hours (semidiurnal).