arXiv subjects

O. A. Sampayo

Publications and source records attributed to O. A. Sampayo.

At least 19 recordsLinked to original sources

arXiv2020

Angular and polarization observables for Majorana-mediated B decays with effective interactions

We probe the effective field theory extending the Standard Model with a sterile neutrino in B meson decays at B factories and lepton colliders, using angular and polarization observables. We put bounds on different effective operators characterized by their distinct Dirac-Lorentz structure, and probe the $N$-mediated B decays sensitivity to these interactions. We define a Forward-Backward asymmetry $A_{FB}^{\ell γ}$ between the muon and photon directions for the $B \to μνγ$ decay, which allows us to separate the SM contribution from the effective lepton number conserving and violating processes, mediated by a near on-shell $N$. Using the most stringent constraints on the effective parameter space from Belle and BaBar we find that a measurement of the final polarization $P_τ$ in the rare $B^-\rightarrow \ell^-_{1}\ell^-_{2} π^+$ decays can help us infer the scalar or vector interaction content in the $N$ production or decay vertices. We find that the B meson decays are more sensitive to scalar operators.

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arXiv2015

Majorana neutrino decay in an Effective Approach

The search strategy or the finding of new effects for heavy neutrinos often relies on their different decay channels to detectable particles. In particular in this work we study the decay of a Majorana neutrino with interactions obtained from an effective general theory modeling new physics at the scale $Λ$. The results obtained are general because they are based in an effective theory and not in specific models. We are interested in relatively light heavy Majorana neutrinos, with masses lower than the $W$ mass ($m_N<m_W$). This mass range simplifies the study by reducing the possible decay modes. Moreover, we found that for $Λ\sim 1$ T$e$V, the neutrino plus photon channel could give explanation to different observations: we analyze the potentiality of the studied interactions to explain some neutrino-related problems like the MiniBooNE and SHALON anomalies. We show in different figures the dominant branching ratios and the decay length of the Majorana neutrino in this approach. This kind of heavy neutral leptons could be searched for in the LHC with the use of displaced vertices techniques. \

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arXiv2011

Higgs Boson Self-Coupling at High Energy $γγ$ Collider

We analyzed the double production and the triple self-coupling of the standard model Higgs boson at future $γγ$ collider energies, with the reactions $γγ\rightarrow f \bar f HH$ $(f=b, t)$. We evaluated the total cross section for $f\bar fHH$ and calculated the total number of events considering the complete set of Feynman diagrams at tree-level and for different values of the triple coupling $κλ_{HHH}$. We have also analyzed the sensitivity for the considered reaction and we show the results as 95% C.L. regions in the $κ-M_H$ plane for different values of the center of mass energy and different levels of background. The numerical computation was done for the energies which are expected to be available at a possible Future Linear $γγ$ Collider with a center-of-mass energy 500-3000 $GeV$ and luminosities of 1 and $5 ab^{-1}$. We found that the number of events for the process $γγ\rightarrow t \bar t HH$, taking into account the decay products of both $t$ and $H$, is small but enough to obtain information on the triple Higgs boson self-coupling in a independent way, complementing other studies on the triple vertex.

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arXiv2009

Leptoquarks signals in KM$^3$ neutrino telescopes

Leptoquarks are predicted in several extensions of the Standard Model (SM) of particle physics attempting the unification of the quark and lepton sectors. Such particles could be produced in the interaction of high energy neutrinos with matter of the Earth. We investigate the effects of this particles on the neutrino flux to be detected in a kilometer cubic neutrino telescope such as IceCube. We calculate the contribution of leptoquarks to the neutrino-nucleon interaction and, then, to the angular observable $α(E)$ recently proposed in order to evaluate detectable effects in IceCube. Our results are presented as an exclusion plot in the relevant parameters of the leptoquarks physics.

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arXiv2009

Neutral Higgs Boson Pair-Production and Trilinear Self-Couplings in the MSSM at ILC and CLIC Energies

We study pair-production as well as the triple self-couplings of the neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) at the Future International Linear $e^{+}e^{-}$ Collider (ILC) and Compact Linear Collider (CLIC). The analysis is based on the reactions $e^{+}e^{-}\to b \bar b h_ih_i, t \bar t h_ih_i$ with $h_i=h, H, A$. We evaluate the total cross-section for both $b\bar bh_ih_i$, $t\bar th_ih_i$ and calculate the total number of events considering the complete set of Feynman diagrams at tree-level. We vary the triple couplings $κλ_{hhh}$, $κλ_{Hhh}$, $κλ_{hAA}$, $κλ_{HAA}$, $κλ_{hHH}$ and $κλ_{HHH}$ within the range $κ=-1$ and +2. The numerical computation is done for the energies expected at the ILC with a center-of-mass energy 500, 1000, 1600 $GeV$ and a luminosity 1000 $fb^{-1}$. The channels $e^{+}e^{-}\to b \bar b h_ih_i$ and $e^{+}e^{-}\to t \bar t h_ih_i$ are also discussed to a center-of-mass energy of 3 $TeV$ and luminosities of 1000 $fb^{-1}$ and 5000 $fb^{-1}$.

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arXiv2008

The Triple Higgs Boson Self-Coupling at Future Linear e+e- Colliders Energies: ILC and CLIC

We analyzed the triple Higgs boson self-coupling at future $e^{+}e^{-}$ colliders energies, with the reactions $e^{+}e^{-}\to b \bar b HH, t \bar t HH$. We evaluate the total cross-sections for both $b\bar bHH$ and $t\bar tHH$, and calculate the total number of events considering the complete set of Feynman diagrams at tree-level. We vary the triple coupling $κλ_{3H}$ within the range $κ=-1$ and +2. The numerical computation is done for the energies expected to be available at a possible Future Linear $e^{+}e^{-}$ Collider with a center-of-mass energy $800, 1000, 1500$ $GeV$ and a luminosity 1000 $fb^{-1}$. Our analysis is also extended to a center-of-mass energy 3 $TeV$ and luminosities of 1000 $fb^{-1}$ and 5000 $fb^{-1}$. We found that for the process $e^{+}e^{-}\to b \bar b HH$, the complete calculation differs only by 3% from the approximate calculation $e^{+}e^{-}\to ZHH(Z\to b\bar b)$, while for the process $e^{+}e^{-}\to t \bar tHH$, the expected number of events, considering the decay products of both $t$ and $H$, is not enough to obtain an accurate determination of the triple Higgs boson self-coupling.

hep-ph↗

arXiv2008

Constraints on unparticle physics from the $gt\bar t$ anomalous coupling

We study the impact of unparticle physics to the chromomagnetic dipole moment (CMDM) of the top quark. We compute the effect induced by unparticle operators of scalar and vector nature coupled to fermions on the CMDM. We find that this dipole moment is sensitive to the scale dimensions $d_u$ of the unparticle and the new couplings of the respective effective operators. Using the bounds imposed on the CMDM by low-energy precision and Tevatron measurements we derive indirect limits on the unparticle parameter space. In particular, we find that the scalar-unparticle operator contribution fulfills both constraints for most of the unparticle parameter space, while the low-energy precision bound on the CMDM excludes a vector-unparticle contribution for low values of respective scale dimension $d_u$.

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arXiv2006

Studying the Triple Higgs Self-Coupling Via e+e- --> b bar b HH, t bar t HH at Future Linear e+e- Colliders

We study the triple Higgs self-coupling at future $e^{+}e^{-}$ colliders energies, with the reactions $e^{+}e^{-}\to b \bar b HH$ and $e^{+}e^{-}\to t \bar t HH$. We evaluate the total cross section of $b\bar bHH$, $t\bar tHH$ and calculate the total number of events considering the complete set of Feynman diagrams at tree-level. The sensitivity of the triple Higgs coupling is considered in the Higgs mass range 110-190 $GeV$, for the energy which is expected to be available at a possible Next Linear $e^{+}e^{-}$ Collider with a center-of-mass energy $800, 1000, 1500$ $GeV$ and luminosity 1000 $fb^{-1}$.

hep-ph↗

arXiv2005

Pairs-Production of Higgs in Association with Bottom Quarks Pairs at $e^+e^-$ Colliders

In a previous paper, we studied the Higgs pair production in the standard model with the reaction $e^{+}e^{-}\to t \bar t HH$. Based on this, we study the Higgs pair production via $e^{+}e^{-}\to b \bar b HH$. We evaluate the total cross section of $b\bar bHH$ and calculate the number total of events considering the complete set of Feynman diagrams at tree-level, and compare this process with the process $e^{+}e^{-}\to t \bar t HH$. The numerical computation is done for the energy which is expected to be available at a possible Next Linear $e^{+}e^{-}$ Collider with a center-of-mass energy $800, 1000, 1600$ $GeV$ and luminosity 1000 $fb^{-1}$.

hep-ph↗

arXiv2003

$τ$ Anomalous Couplings and Radiation Zeros in the $e^+e^- \to τ\barτγ$ process

The process $e^+e^- \to τ\barτγ$ contains configurations of the four-momenta for which the scattering amplitude vanishes (Radiation Zeros or Null Zone). These Radiation Zeros only occur for couplings given by a gauge theory, in particular the standard model. Therefore they are sensitive to physics beyond the standard model as the anomalous magnetic and weak moment of the $τ$ lepton. In this article we compute the effect of these anomalous interactions on the Radiation Zeros in the above mentioned process.

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arXiv2003

Higgs Pair-Production in the Standard Model at Next Generation Linear $e^+e^-$ Colliders

We study the Higgs pair-production in the Standard Model of the strong and electroweak interactions at future $e^{+}e^{-}$ collider energies, with the reaction $e^{+}e^{-}\to t \bar t HH$. We evaluated the total cross section of $t\bar tHH$ and calculate the number total of events considering the complete set of Feynman diagrams at tree-level. The numerical computation is done for the energy which is expected to be available at a possible Next Linear $e^{+}e^{-}$ Collider: with center-of-mass energy $800, 1600$ $GeV$ and luminosity 1000 $fb^{-1}$.

hep-ph↗

arXiv2003

Excited tau lepton contribution to $W->tau nu(tau)$ decay at the one-loop level

We evaluate the compositeness effects of tau lepton on the vertex W-tau-nu(tau) in the context of an effective Lagrangian approach. We consider that only the third family is composed and we get the corrections to the non universal lepton coupling g_(tau)/g_(e). As the experimental bounds on non universal lepton couplings in W decays are weak, we find that the excited particles contributions do not give realistic limits on the excited mass, since they lead to Lambda<m*.

hep-ph↗

arXiv2002

Signals for Majorana neutrinos in a $γγ$ collider

We study the possibilities to detect Majorana neutrinos in $γγ$ colliders for different center of mass energies. We study the $W^\pm W^\pm l_j^{\mp} l_k^{\mp}$ ($l_j\equiv e ,μ,τ$) final states which are, due to leptonic number violation, a clear signature for intermediate Majorana neutrino contribution. Such a signal (final dileptons of the same sign) is not possible if the heavy neutrinos are Dirac particles. We present our results for the total cross-section as a function of the neutrino mass and the center of mass energies.

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arXiv2001

$τ$ magnetic moment in a $γγ$ collider

We analyze different observables to study the magnetic dipole moment of the tau pairs produced by photon linear colliders. We use the circular polarized photon beam and study distributions of polarized $τ$ final pairs to define sensibly asymmetries to magnetic dipole moment.

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arXiv2001

Production of the MSSM Higgs Bosons at Next Generation Linear $e^+e^-$ Colliders

% insert abstract here We study the production of the Higgs bosons predicted in the Minimal Supersymmetric extension of the Standard Model $(h^0, H^0, A^0, H^\pm)$, with the reactions $e^{+}e^{-}\to b\bar b h^0 (H^0, A^0)$, and $e^+e^-\to τ^-\bar ν_τH^+, τ^+ν_τH^-$, using the helicity formalism. We evaluate cross section of $h^0, H^0, A^0$ and $H^\pm$ in the limit when $\tanβ$ is large. The numerical computation is done considering two stages of a possible Next Linear $e^{+}e^{-}$ Collider: the first with $\sqrt{s}=500$ $GeV$ and design luminosity 50 $fb^{-1}$, and the second with $\sqrt{s}=1$ $TeV$ and luminosity 100-200 $fb^{-1}$.

hep-ph↗

arXiv2001

Signatures for Majorana neutrinos in $e^- γ$ collider

We study the possibilities to detect Majorana neutrinos in $e^- γ$ colliders for different center of mass energies. We study the $W^- W^- l_j^{+}(l_j^+\equiv e^+ ,μ^+ ,τ^+)$ final state which are, due to leptonic number violation, a clear signature for intermediate Majorana neutrino contribution. Such a signal (final lepton have the opposite charge of the initial lepton) is not possible if the heavy neutrinos are Dirac particles. In our calculation we use the helicity formalism to obtain analytic expressions for the amplitude and we have considered that the intermediate neutrinos can be either on shell or off shell. Finally we present our results for the total cross-section and for the angular distribution of the final lepton. We also include a discussion on the expected events number as a function of the input parameters.

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arXiv2000

Detecting the MSSM Higgs Bosons at Future $e^+e^-$ Colliders

We investigate the possibility of detecting the Higgs bosons predicted in the Minimal Supersymmetric extension of the Standard Model $(h^0, H^0, A^0, H^\pm)$, with the reactions $e^{+}e^{-}\to b\bar b h^0 (H^0, A^0)$, and $e^+e^-\to τ^-\bar ν_τH^+, τ^+ν_τH^-$, using the helicity formalism. We analyze the region of parameter space $(m_{A^0}-\tanβ)$ where $h^0, H^0, A^0$ and $H^\pm$ could be detected in the limit when $\tanβ$ is large. The numerical computation is done considering two stages of a possible Next Linear $e^{+}e^{-}$ Collider: the first with $\sqrt{s}=500$ $GeV$ and design luminosity 50 $fb^{-1}$, and the second with $\sqrt{s}=1$ $TeV$ and luminosity 100-200 $fb^{-1}$.

hep-ph↗

arXiv2000

Limits on excited tau leptons masses from leptonic tau decays

We study the effects induced by excited leptons on the leptonic tau decay at one loop level. Using a general effective lagrangian approach to describe the couplings of the excited leptons, we compute their contributions to the leptonic decays and use the current experimental values of the branching ratios to put limits on the mass of excited states and the substructure scale.

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