arXiv subjects

E. S. Tututi

Publications and source records attributed to E. S. Tututi.

At least 19 recordsLinked to original sources

arXiv2026

Production of the top partner $T$ of the Bestest Little Higgs Model at the future muon collider

In this work, we evaluate the decay widths and branching ratios of the heavy top partner $T$, and perform a comprehensive phenomenological study of its pair and associated production at a muon collider within the framework of the Bestest Little Higgs Model (BLHM). The BLHM provides an attractive and natural mechanism for addressing the fine-tuning problem in the Standard Model (SM) of particle physics. In our study of the top partner $T$, we consider the production processes $μ^{+} μ^{-} \to (γ, Z, Z', h, H) \to T \bar{T}$ and $μ^{+} μ^{-} \to (γ, Z, Z', h, H)\to \bar{t}T+ t \bar{T}$, and we explore different center-of-mass energies of the muon collider to perform our numerical analysis of the production cross sections for the processes of interest. Our results show that pair production is the most promising channel for probing the top partner of the BLHM at a future muon collider.

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arXiv2026

Lepton-flavor violating decays induced by Lorentz violation in the Yukawa sector of the Standard Model Extension

Tree-level lepton-flavor-violating decays induced by Lorentz-violating effects within the Yukawa sector of the Standard Model Extension are studied. These new physics effects are parameterized by the $(Y_{f})_{μν}^{AB}$ tensor, with $μ$ and $ν$ denoting Lorentz indices and $A$, $B$ being indices in the flavor space. Since this tensor is antisymmetric under the interchange of Lorentz indices, in analogy with the electromagnetic tensor $F_{μν}$, $(Y_{f})_{μν}^{AB}$ can be expressed in terms of six components associated with two complex three-vectors denoted by $\mathbf{e}_l^{AB}$ and $\mathbf{b}_l^{AB}$. On the assumption that these three-vectors are pure real or pure imaginary and mutually orthogonal, constraints on their magnitudes via experimental bounds on lepton-flavor-violating processes $\mathrm{Br}(l_B\rightarrow γl_A)$ and $\mathrm{Br}(l_B\rightarrow l_A l_C \bar{l}_C)$ are estimated. Thus, the $l_B\rightarrow γl_A$ decay provides the following upper bounds: $\lvert \mathbf{e}_l^{μτ} \lvert < 1.51\times 10^{-11}$ , $\lvert \mathbf{e}_l^{eτ} \lvert < 1.34 \times 10^{-11}$, $\lvert \mathbf{e}_l^{eμ} \lvert < 3.65 \times 10^{-18}$, $\lvert \mathbf{b}_l^{μτ} \lvert < 1.95\times 10^{-11}$, $\lvert \mathbf{b}_l^{eτ} \lvert <1.73\times 10^{-11}$, $\lvert \mathbf{b}_l^{eμ} \lvert < 4.71\times 10^{-18}$. Conversely, by assuming that the Lorentz-violating parameters are purely real, for the $l_B\rightarrow l_A l_C \bar{l}_C$ process it is found that $\lvert \mathbf{e}_l^{μτ}\lvert< 3.05 \times 10^{-12}$ and $\lvert \mathbf{b}_l^{μτ}\lvert< 4.31 \times 10^{-12}$. These results offer more restrictive bounds than those previously reported in the literature.

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arXiv2025

Dipolar electroweak properties of Dirac massive neutrinos

Electroweak properties of Dirac neutrinos within the context of the Minimally Extended Standard Model are explored. In particular, the dipolar form factors that result from the radiative correction, at one-loop level, of the $ Zν\barν$ coupling are identified. The calculation is carried out in the covariant general gauge $R_ξ$. The results are shown to be independent of the gauge parameter. The outcome numerical evaluation establishes that the neutrino weak-magnetic dipole moment is of the same order of magnitude as the known prediction of the neutrino magnetic dipole moment.

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arXiv2023

The top quark chromomagnetic dipole moment in the SM from the 4-body vertex function

A new proposal to compute the anomalous chromomagnetic dipole moment of the top quark, $\hatμ_t$, in the Standard Model is presented. On the basis of the 5-dimensional effective Lagrangian operator that characterizes the quantum-loop induced chromodipolar vertices $gt\bar{t}$ and $ggt\bar{t}$, the $\hatμ_t$ anomaly is derived via radiative correction at the 1-loop level from the non-Abelian 4-body vertex function $ggt\bar{t}$. We evaluate $\hatμ_t(s)$ as a function of the energy scale $s=\pm E^2$, for $E=[10,1000]$ GeV, taking into account the running of the quark masses and alpha strong through the $\overline{\mathrm{MS}}$ scheme. In particular, we find that at the typical energy scale $E=m_Z$ for high-energy physics, similarly to $α_s(m_Z^2)$, $α(m_Z^2)$ and $s_W(m_Z^2)$, the spacelike evaluation yields $\hatμ_t(-m_Z^2)$ $=$ $-0.025$$+$$0.00384i$ and the timelike $\hatμ_t(m_Z^2)$ $=$ $-0.0318$$-$$0.0106i$. This Re$\thinspace\hatμ_t(-m_Z^2)$ $=$ $-0.025$ from $ggt\bar{t}$ is even closer to the experimental central value $\hatμ_t^\mathrm{Exp}=$ $-0.024$, than that coming from the known 3-body vertex function $gt\bar{t}$, $-0.0224$. Once again, the Im$\thinspace\hatμ_t(-m_Z^2)$ part is due to the contribution of virtual charged currents, just like in the $gt\bar{t}$ case. We can infer that the spacelike prediction is the favored one.

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arXiv2023

Decay of the Z' gauge boson with lepton flavor violation

The flavor-violating decay of a new neutral massive gauge boson $Z^\prime\toμe$ is analyzed in the context of extended models, in which this particle emerges. By means of the analysis of the $μ\to eγ$ decay, $μ-e$ conversion process in nuclei and the $μ\to e e^{+}e^{-}$ decay, the strength of the $Z^\primeμe$ coupling is estimated and used to calculate the branching ratio of the $Z^\prime\to μe$ decay. This is done for the so-called $Z_S,\,Z_{LR},\,Z_χ, Z_ψ$ and $Z_η$ bosons. We found that, through the $μ-e$ conversion process, the most restrictive bound for the coupling is provided by the $Z_{LR}$ boson. Meanwhile, by means of the $μ\to e e^{+}e^{-}$ decay, the most restrictive bound for the $Z^\primeμe$ coupling is provided by the $Z_χ$ boson. However, if we concentrate on the less restrictive prediction for the Br($Z^\prime\to μe$), this comes from the $Z_η$ boson and the resulting branching ratio is less than $10^{-4}$. On the other hand, if we consider the most restrictive bound, the branching ratio for the process is below $2\times 10^{-7}$, which results from the $Z_{RL}$ boson, and is obtained through the $μ-e$ conversion process.

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arXiv2022

Effects of Lorentz violation in the Higgs sector of the Minimal Standard Model Extension

A bound on the CPT-odd four vector coefficient $k^μ_ϕ$ that appears in Higgs sector of the Minimal Standard Model Extended (MSME) is presented. The analysis is based on the contributions arising from the sector in question to the anomalous dipole moment for leptons calculated at the one loop level, for which an analytical expression is obtained. The largest contribution of this Lorentz violating coefficient is on the lightest lepton, which results as a consequence of a strong non-decoupling effect. By using the experimental uncertainty of the electron anomalous dipole moment we predict that $|k^2_{ ϕ\,R}|<3.29\times 10^{-29}$ GeV$^2$.

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arXiv2022

Weak dipole moments of heavy fermions with flavor violation induced by $Z^\prime$ gauge bosons

A calculation of weak dipole moments of charged fermions of the Standard Model (SM) at the one-loop level, in the context of a general effective extended neutral current model with flavor changing $Z^\prime f_i \bar{f}_j$ vertices, is presented. We give numerical predictions for the anomalous weak magnetic dipole moment (AWMDM) $a^w_{fi}$, and the weak electric dipole moment (WEDM) $d^w_{f_i}$, for the $τ$ lepton and $t$ quark. For several $Z^\prime$ gauge bosons considered, we find that, for the $τ$ lepton, the best prediction for the real part of $a^w_τ$ is of the order of $10^{-9}$, while the imaginary part is four orders of magnitude below. The highest value for the WEDM, $d^w_τ$, corresponds to $10^{-26}$ $e$-cm, for its real part, and the imaginary part is three orders of magnitude below. On the other hand, we found for the top quark, that the best prediction for the real part of $a^w_t$ is of the order of $10^{-7}$ and its imaginary part is of the order of $10^{-11}$. We also found that $d^w_t$ is of the order of $10^{-26}$ $e$-cm for its real part, and its imaginary part can be as high as $10^{-31}$ $e$-cm.

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arXiv2021

Off-shell chromomagnetic dipole moments in the SM at and beyond the $Z$ gauge boson mass scale

The off-shell anomalous chromomagnetic dipole moment of the standard model quarks ($u$, $d$, $s$, $c$ and $b$), at the $Z$ gauge boson mass scale, is computed by using the $\overline{\textrm{MS}}$ scheme. The numerical results disagree with all the previous predictions reported in the literature and show a discrepancy of up to two orders of magnitude in certain situations.

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arXiv2021

Revisiting the top quark chromomagnetic dipole moment in the SM

We revisit the anomalous chromomagnetic dipole moment in the Standard Model and show that its triple gluon vertex contribution, with the on-shell gluon ($q^2=0$), generates an infrared divergent pole. Consequently, the chromomagnetic dipole should not be perturbatively evaluated at $q^2=0$. Focusing on this top quark anomaly, denoted as $\hatμ_t(q^2)$, we compute it with the off-shell gluon with a large momentum transfer, just as the $α_s(m_Z^2)$ convention scale, for both spacelike $q^2=-m_Z^2$ and timelike $q^2=m_Z^2$ cases. We found that $\hatμ_t(-m_Z^2)$ $=$ $-0.0224$ $-0.000925i$ and $\hatμ_t(m_Z^2)$ $=$ $-0.0133$ $-0.0267i$. Our $\mathrm{Re}\thinspace\hatμ_t(-m_Z^2)$ matches well with the current experimental value $\hatμ_t^\mathrm{Exp}=-0.024_{-0.009}^{+0.013}(\mathrm{stat})_{-0.011}^{+0.016}(\mathrm{syst})$, and the $\mathrm{Im}\thinspace\hatμ_t(-m_Z^2)$ part is induced by flavour changing charged currents.

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arXiv2020

Revisiting the rare $H\to q_iq_j$ decays in the Standard Model

We revisit the rare decays of the Higgs boson to two different quarks in the Standard Model, which arise at the one-loop level. We perform Taylor series expansions to the complete form factors of the decay amplitudes, according to their different mass hierarchies, this allow us to take full advantage of the GIM mechanism to eliminate spurious contributions and retain those that truly contribute. We found that Br$(H\to uc)$=$5.00\times10^{-20}$, Br$(H\to ds)$=$1.19\times10^{-11}$, Br$(H\to db)$=$5.16\times10^{-9}$ and Br$(H\to sb)$=$1.15\times10^{-7}$. Our predictions for the $H\to uc,ds$ decays disagree with previous results in the literature.

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arXiv2020

Rare decays of the top quark mediated by Z' gauge bosons and flavor violation

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 $t\to cV, uV$ induced at the one loop level, where $V =γ, g$, 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. In order to establish bound on our branching ratios, we consider the recent experimental bounds as $m_{Z^\prime}\geq$ 3.8-4.5 TeV, 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 standard model. 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 standard model.

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arXiv2020

Diphoton Higgs signal strength in universal extra dimensions

The signal strength of the $gg \to H \to γγ$ reaction in $pp$ collisions at the LHC is studied within the context of the SM with UED. The impact of an arbitrary number $n$ of UED on both the $gg\to H$ and $H\to γγ$ subprocesses is studied. The 1-loop contributions of Kaluza-Klein excitations to these subprocesses are proportional to discrete and continuous sums, which can diverge. By implementing dimensional regularization, it is shown that discrete regularized sums can naturally be expressed as multidimensional Epstein functions, and that divergences, if exist, emerge through the poles of these functions. It is found that continuous sums converge, but the discrete ones diverge, with the exception of the $n=1$ case, in which the 1-dimensional Epstein function converges. It is argued that divergences that arise from discrete sums for $n\geq 2$ are genuine UV divergences, since they correspond to short-distance effects in the compact manifold. Then, the amplitudes are renormalized in a modern sense by incorporating interactions of canonical dimension higher than four that allow us to generate the required counterterms, which are determined using a $\overline{\rm MS}$-like renormalization scheme. We find that the $gg\to H$ subprocess is quite sensitive to both the size and the dimension of the compact manifold, but the SM prediction for $H\to γγ$ subprocess is practically unchanged. In the $n=1$ case, it is found that the experimental constraint on the compactification scale $R^{-1}\geq 1.5$ TeV allow us to reproduce the experimental limit on the signal strength $1.01\leq μ^{(1)}_{γγ}\leq 1.2$. In the $n\geq 2$ cases, it is found that the experimental limit on $μ^{(n)}_{γγ}$ leads to stronger lower bounds for the compactification scale given by $R^{-1}\geq 1.55, 2.45, 3.57, 5.10, 7.25$ TeVs for $n=2, 4, 6, 8, 10$, respectively.

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arXiv2018

Flavor violation in chromo- and electromagnetic dipole moments induced by $Z^\prime$ gauge bosons and a brief revisit of the Standard Model

The electromagnetic dipole moments of the tau lepton and the chromoelectromagnetic dipole moments of the top quark are estimated via flavor-changing neutral currents, mediated by a new neutral massive gauge boson. We predict them in the context of models beyond the Standard Model with extended current sectors, in which simple analytic expressions for the dipole moments are presented. For the different $Z^\prime$ gauge boson considered, the best prediction for the magnetic dipole moment of the tau lepton, $|a_τ|$, is of the order of $10^{-8}$, while the highest value for the electric one, $|d_τ|$, corresponds to $10^{-24}$ $e\,$cm; our main result for the chromomagnetic dipole moment of the top quark, $|\hatμ_t|$, is $10^{-6}$, and the value for the chromoelectric one, $|d_t|$, can be as high as $10^{-22}$ $e\,$cm. We compare our results, revisiting the corresponding Standard Model predictions, in which the chromomagnetic dipole moment of the top quark is carefully evaluated, finding explicit imaginary contributions.

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arXiv2017

Heavy neutral pseudoscalar decays into gauge bosons in the Littlest Higgs Model

We study two-body decays of a new neutral pseudoscalar into gauge bosons within the context of the Littlest Higgs model. Concretely, the $Φ^P \to WW, VV, gg$ processes induced at the one-loop level, with $V=γ, Z$, are considered. Since the branching ratios of the $Φ^P \to VV$ decays result very suppressed, only the $Φ^P \to WW, gg$ processes are thoroughly studied. The branching ratios for the $Φ^P \to gg$ and $Φ^P \to WW$ decays are of the order of $10^{-4}$ and $10^{-6}$, respectively, for $f$ around 2 TeV, which represents the global symmetry breaking scale of the theory. The production cross section of the $Φ^P$ boson via gluon fusion at LHC is estimated.

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arXiv2017

Heavy neutral scalar decays into electroweak gauge bosons in the Littlest Higgs Model

We study the heavy neutral scalar decays into standard model electroweak gauge bosons in the context of the Littlest Higgs model. We focus our attention on the $Φ^0 \to WW, γV$ processes induced at the one-loop level, with $V=γ, Z$. Since the branching ratios of the $Φ^0 \to γV$ decays result very suppressed, only the $Φ^0 \to WW$ process is analyzed in the framework of possible experimental scenarios by using heavy scalar masses between 1.6 TeV until 3.3 TeV. The branching ratio for the $Φ^0 \to WW$ decay is of the order of $10^{-3}$ throughout the interval 2 TeV $< f <$ 4 TeV, which represent the global symmetry breaking scale of the theory. Thus, it is estimated the associated production cross section for the $pp\to Φ^0 X\to WW$, finding around ten events for $m_{Φ^0}\approx 1.6$ TeV at best.

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arXiv2015

Decays $Z\toγγ$ and $Z\to gg$ in the Standard Model Extension

The $Z\to γγ$ and $Z\to gg$ decays are studied in the context of the renormalizable version of the Standard Model Extension. The $CPT$-odd $\barψγ_5 γ^μb_μψ$ bilinear interaction, which involves the constant background field $b_α$ and which has been a subject of interest in literature, is considered. It is shown that the $Z\to γγ$ and $Z\to gg$ decays, which are strictly zero in the standard model, can be generated radiatively at the one-loop level. It is found that these decays are gauge invariant and free of ultraviolet divergences, and that the corresponding decay widths only depend on the spatial component of the background field $b$.

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arXiv2015

The $Z_H \to γH$ decay in the Littlest Higgs Model

We present the calculation of the $Z_H \to γH$ decay in the context of the Littlest Higgs model at one-loop level. Our calculations include the contributions of fermions, scalars and gauge bosons in accordance with the most recent experimental constraints on the parameters space of the model. We find branching ratios of the order of $10^{-5}$ for the energy scale $f=2,3,4$ TeV on the $0.1<c<0.9$ region. In order to provide a complementary study we calculated the production cross section of the $Z_H$ boson in $pp$ collisions at Large Hadron Collider with a center of mass energy of 14 TeV. By using the integrated luminosity projected for the Large Hadron Collider in the last stage of operation, we estimated the number of events for this process. Moreover, we analyze the SM background for the Higgs-photon associated production and found that the $pp\to Z_H X \to γH$ production is above the SM background.

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arXiv2014

One-loop nonbirefringent effects on the electromagnetic vertex in the Standard Model Extension

Lorentz violation emerged from a fundamental description of nature may impact, at low energies, the Maxwell sector, so that contributions from such new physics to the electromagnetic vertex would be induced. Particularly, nonbirefringent $CPT$-even effects from the electromagnetic sector modified by the Lorentz- and $CPT$-violating Standard Model Extension alter the structure of the free photon propagator. We calculate Lorentz-violating contributions to the electromagnetic vertex, at the one-loop level, by using a modified photon propagator carrying this sort of effects. We take the photon off shell, and find an expression that involves both isotropic and anisotropic effects of nonbirefringent violation of Lorentz invariance. Our analysis of the one-loop vertex function includes gauge invariance, transformation properties under $C$, $P$, and $T$, and tree-level contributions from Lorentz-violating nonrenormalizable interactions. These elements add to previous studies of the one-loop contributions to the electromagnetic vertex in the context of Lorentz violation in the photon sector. Finally, we restrict our analysis to the isotropic case and derive a finite contribution from isotropic Lorentz violation to the anomalous magnetic moment of fermions that coincides with the result already reported in the literature.

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