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M. A. Perez

Publications and source records attributed to M. A. Perez.

At least 19 recordsLinked to original sources
arXiv2016

Sensitivity of the decay $h\to ZZ^*\to Zl+l-$ to the Higgs self coupling through radiative corrections

We study the radiative corrections induced by the triple Higgs boson coupling $hhh$ in the three body decay $h\to ZZ^*\to Zl\bar l$. We show that these corrections are potentially sensitive to the specific value of this coupling in the Standard Model and the Two Higgs Doublet Model (2HDM). These effects may induce corrections to the integrated decay width of the three-body decay of order few percent in the 2HDM and thus open a new window to test the Higgs boson self interaction in physics beyond the standard model.

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arXiv2014

One-loop decays ${A^0} \to ZZ, Zγ, γγ$ within the 2HDM and its search at the LHC

The general two-higgs doublet model (2HDM) contains a rich spectrum of neutral and charged Higgs bosons, whose detection would be a clear signal of new physics. When the Higgs potential is CP-conserving, the spectrum includes a pseudoscalar mass eigenstate $A^{0}$, which does not couple to vector bosons at tree-level. However, fermionic loops (top and bottom mainly) induce the coupling $AVV'$ (with $V,V'=γ, Z$) at higher orders. We evaluate the amplitude for the decays ${A^0} \to ZZ, Zγ, γγ$, including a generic fermionic loop contribution, and present results on the branching ratios for 2HDM-I,II and III. Current LHC searches on heavy Higgs bosons are used as an estimate to constrain the allowed mass range for $A^0$.

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arXiv2014

Impact of a four-zero Yukawa texture on $h\to γγ$ and $γZ$ in the framework of the Two Higgs Doublet Model Type III

We study the substantial enhancement, with respect to the corresponding Standard Model rates, that can be obtained for the branching ratios of the decay channels $h \to γγ$ and $h\to γZ$ within the framework of the Two Higgs Doublet Model Type III, assuming a four-zero Yukawa texture and a general Higgs potential. We show that these processes are very sensitive to the flavor pattern entering the Yukawa texture and to the triple coupling structure of the Higgs potential, both of which impact onto the aforementioned decays. We can accommodate the parameters of the model in such a way to obtain the $h \to γγ$ rates reported by the Large Hadron Collider and at the same time we get a $h\to γZ$ fraction much larger than in the Standard Model, indeed within experimental reach. We present some scenarios where this phenomenology is realized for spectrum configurations that are consistent with current constraints. We also discuss the possibility of obtaining a light charged Higgs boson compatible with all such measurements, thereby serving the purpose of providing a hallmark signal of the scenario considered.

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arXiv2012

Decays Z' -> γγγ and Z -> γγγ in the minimal 331 model

The possibility of a significant effect of exotic particles on the Z'->γγγ and Z->γγγ decays is investigated in the context of the minimal 331 model. This model, which is based in the SU_C(3)xSU_L(3)xU_X(1) gauge group, predicts the existence of many exotic charged particles that can significantly enhance the decay widths. It is found that the standard model prediction for the Z->γγγ decay remains essentially unchanged, as the new physics effects quickly decouples. On the other hand, it is found that the contributions of the new exotic quarks and gauge bosons predicted by this model lead to a branching fraction for the Z'->γγγ decay of about 10^(-6), which is about three orders of magnitude larger than that of the Z->γγγ decay.

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arXiv2011

New Physics effects on hadronic decay asymmetries of the Top quark

We study some New Physics effects on the hadronic decays of the Top quark, like t-> b bbar c, and on a forward-backward-like CP even asymmetry A_t constructed in such a way that it is zero in the SM. We find that an anomalous right-handed contribution of the effective tbW vertex may induce an asymmetry A_t of the order of 20 %. A light W' boson with pure right handed couplings tdW' may induce an asymmetry A_t of the same order of magnitude.

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arXiv2009

Higgs FCNC h -> t* c decay at the muon collider

We study the discovery potential of the flavor-changing neutral coupling (FCNC) htc of the Higgs boson and the top quark through the rare tree-body decay h -> Wbc at Muon colliders for a light Higgs boson with mass 114 < m_h < 145 GeV. This decay mode may compete with the SM background induced by the hWW coupling in some models with a tree-level htc coupling and with models that predict this coupling at the one-loop level in the range 10^{-2} - 10^{-1}. A future muon collider could test the scalar FCNC decay t -> hc via Higgs decay h -> t* c -> b W+ c down to values of the coupling g_{tc}=0.5 (that are equivalent to BR(t -> hc) = 5 x 10^{-3}). The LHC could probe values of g_{tc} one order of magnitude smaller, unless other processes beyond the SM appear that through intense multi jet activity may clutter the t -> hc signal.

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arXiv2008

Probing the ZZgamma and Zgammagamma Couplings Through the Process e+e- --> nu anti-nu gamma

We study the sensitivity for testing the anomalous triple gauge couplings $ZZγ$ and $Zγγ$ via the process $e^+e^-\to ν\barνγ$ at high energy linear colliders. For integrated luminosities of 500 $fb^{-1}$ and center of mass energies between 0.5 and 1.5 $TeV$, we find that this process can provide tests of the triple neutral gauge boson couplings of order $10^{-4}$, one order of magnitude lower than the standard model prediction.

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arXiv2008

Constraints on Left-Right Symmetric and $E_6$ Superstring Models from the Number of Light Neutrino Species

Using the experimental value for the rate $R^{LEP} _{exp}=Γ_{inv}/Γ_{l\bar l}=5.942\pm 0.016$, we derive constraints on the number of light neutrino species with the invisible width method in the framework of a left-right symmetric model (LRSM) and a $E_6$ superstring model as a function of their respective mixing angles for the neutral vector gauge bosons. Using the above LEP result we get the constraints $-1.6\times 10^{-3}\leqϕ\leq 1.1\times 10^{-3}$ and $-1.3\times 10^{-2}\leqϕ_{E_6} \leq 0.4\times 10^{-2}$, which are stronger than those obtained in previous studies of these models.

hep-ph↗
arXiv2007

Limits on the Electromagnetic and Weak Dipole Moments of the Tau-Lepton in E_6 Superstring Models

We obtain limits on the electromagnetic and weak dipole moments of the tau-lepton in the framework of a Left-Right symmetric model (LRSM) and a class of $E_6$ inspired models with an additional neutral vector boson $Z_θ$. Using as an input the data obtained by the L3 and OPAL Collaborations for the reaction $e^+e^-\to τ^+τ^-γ$, we get a stringent limit on the LRSM mixing angle $ϕ$, $-1.66\times 10^{-3}< ϕ<1.22\times 10^{-3}$, which in turn induces bounds on the tau weak dipole moments which are consistent with the bounds obtained recently by the DELPHI and ALEPH Collaborations from the reaction $e^+e^-\to τ^+τ^-$. We also get similar bounds for the weak dipole moments of the tau lepton in the framework of $E_6$ superstring models.

hep-ph↗
arXiv2007

Bounding the Number of Light Neutrinos Species in a Left-Right Symmetric Model

Using the experimental values for the rates $R^{LEP} _{exp}=Γ_{inv}/Γ_{l\bar l}=5.942\pm 0.016$, $R^{Giga-Z_1}=Γ_{inv}/Γ_{l\bar l}=5.942\pm 0.012$ (most conservative) and $R^{Giga-Z_1}=Γ_{inv}/Γ_{l\bar l}=5.942\pm 0.006$ (most optimistic) we derive constraints on the number of neutrinos light species $(N_ν)_{LRSM}$ with the invisible width method in the framework of a left-right symmetric model (LRSM) as a function of the LR mixing angle $ϕ$. Using the LEP result for $N_ν$ we may place a bound on this angle, $-1.6\times 10^{-3}\leqϕ\leq 1.1\times 10^{-3}$, which is stronger than those obtained in previous studies of the LRSM.

hep-ph↗
arXiv2006

Bounding the magnetic and electric dipole moments of tau nu from the process e+e- --> nu bar nu gamma in E6 Superstring Models

We obtain bounds on the anomalous magnetic and electric dipole moments of the tau-neutrino through the reaction $e^{+}e^{-}\to ν\bar νγ$ at the $Z_1$-pole in the framework of a Left-Right symmetric model and a class of $E_6$ inspired models with an additional neutral vector boson $Z_θ$. We use the data collected by the L3 Collaboration at LEP. For the parameters of the $E_6$ model we consider the mixing angle $θ_{E_6}=37.8^o$ and $M_{Z_θ}=7M_{Z_1}$. We find that our bounds are of the same order of magnitude as those obtained in other extensions of the Standard Model.

hep-ph↗
arXiv2006

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, L-R 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.

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arXiv2005

Constraints on top quark FCNC from electroweak precision measurements

We study the one-loop contributions of the effective flavor changing neutral couplings (FCNC) tcZ and tcH on the electroweak precision observables Gamma_Z, R_c, R_b, R_l, A_c and A^FB_c. Using the known experimental limits on these observables, we may place 95% CL bounds on these FCNC couplings which in turn translate into the following limits for the branching ratios: BR(t -> cZ) < 6.7 10^-2 and BR(t -> cH) < (0.09 - 2.9) 10^-3 for 114 < m_H < 170 GeV.

hep-ph↗
arXiv2005

CP violating effects in the decay Z -> mu^+mu^-gamma induced by ZZgamma and Zgammagamma couplings

We analyze possible CP-violating effects induced in the $Z$ decay with hard photon radiation by $γZZ$ and $γγZ$ anomalous vertices. We estimate the sensibility of future linear collider experiments on these couplings coming from CP-odd asymmetries associated to angular correlations of the three particle final state in $e^+e^- \to Z \to μ^+μ^-γ$. We find that a linear collider with an integrated luminosity of 500 $fb^{-1}$ and $\sqrt{s} = 0.05$ TeV can place the bound $|h_1^{γ,Z}| < 0.92$ at the 90% confidence level for these couplings.

hep-ph↗
arXiv2004

Top-pions and single top production at HERA and THERA

We study single top quark production at the HERA and THERA colliders as coming from the FCNC vertices tcgamma and tcZ that appear at one loop level in Topcolor-assisted technicolor models (TC2). In contrast with previous expectations, we find that the production cross section is of order 10^-6 pb for HERA and 10^-4 pb for THERA (even lower that the SM prediction). Therefore, none of the two colliders are capable to probe the pseudoscalar top-pion or the scalar top-higgs predicted in TC2 models via single top production.

hep-ph↗
arXiv2004

Effective Lagrangian approach to Higgs-mediated FCNC top quark decays

The flavor changing neutral current (FCNC) transitions t --> q'H and t --> q'V_i (V_i=γ, g, Z) are studied in the context of the effective Lagrangian approach. We focus on the scenario in which these decays are predominantly induced by new physics effects arising from the Yukawa sector extended with dimension-six SU_L(2) X U_Y(1)-invariant operators, which generate the most general CP-even and CP-odd tq'H vertex at the tree level. For the unknown coefficients, we assume a slightly modified version of the Cheng-Sher ansatz. We found that the branching ratio for the Higgs-mediated FCNC t--> q'V_i decays are enhanced by two or three orders of magnitude with respect to the results expected in models with extended Higgs sectors, such as the general two-Higgs doublet model. We discuss the possibilities of detecting this class of decays at the LHC.

hep-ph↗
arXiv2004

Decay H^+ -> W^+ gamma in a nonlinear R_xi-gauge

A new evaluation of the charged Higgs boson decay $H^+ -> W^+γ$ is presented in the context of the general two-Higgs doublet model. A nonlinear $R_ξ$-gauge which considerably simplifies the calculation is introduced and simple expressions are obtained for the fermionic and bosonic contributions. The $H^+ -> W^+γ$ branching ratio is analyzed for several values of the parameters of the model. Although this decay can have a branching fraction as large as $10^{-4}$ in a certain region of the parameter space, it is found that such a region is disfavored by the most recent constraints on $b -> sγ$, $g-2$ of the muon, $Z -> b \bar b$, and the $ρ$ parameter, along with the exclusions from direct searches at the CERN $e^-e^+$ LEP collider. The possibility of detecting this decay at future colliders is discussed.

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