arXiv subjects

J. Montaño

Publications and source records attributed to J. Montaño.

12 recordsLinked to original sources

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

Radiative neutrino masses and exotic right-handed neutrinos

We consider an extension of the standard electroweak model with three Higgs doublets and global $B-L$ and $\mathbb{Z}_2$ symmetries. Two of the scalar doublets are inert due to the $\mathbb{Z}_2$ symmetry. We calculated all the mass spectra in the scalar and lepton sectors and accommodate the leptonic mixing matrix as well. We also include an analysis of the scalar sector, showing that the potential is limited from below, and we obtain the masses of the scalar sector. Furthermore we consider the effects of the model on the anaomalous magnetic dipole of charged leptons and the $μ\to eγ$ decay. We also present the SUSY version of the model with global $B-L$.

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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

Charged scalar production at the Compact Linear Collider for the $S_3 \otimes \mathbb{Z}_2$ model

We present a model with $S_3 \otimes \mathbb{Z}_2$ model plus a sterile neutrino and its phenomenological expectations for the production of charged scalars at the Compact Linear Collider. At tree level, our model predicts a total cross section in between 0.1 and $10^{-5}$ pb for the $e^- e^+ \to H^+ H^-$ process, considering all possible mass values for the charged scalar in the CLIC experiment. We also show that this prediction holds regardless of the masses of the other exotic particles and their couplings.

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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

One-loop structure of the photon propagator in the Standard Model Extension

We study radiative corrections on the photon propagator from the electroweak sector of the minimal Lorentz- and $CPT$-violating Standard Model Extension. We derive the most general Lorentz-violating ghost sector from BRST symmetry and renormalization theory. We introduce a Lorentz-violating nonlinear gauge that simplifies both the Higgs and gauge-sector extensions, which can be helpful in radiative corrections. At one loop, these sectors contribute to the $CPT$-even part of the photon propagator, characterized by the Riemann-type tensor $(k_F)_{αβμν}$. We give exact results for the contributions to the SO(1,3) irreducible parts of $(k_F)_{αβμν}$, namely, the Weyl-type tensor $(\hat{k}_F)_{αβμν}$, the Ricci-type tensor $(k_F)_{αβ}$, and the curvature-type scalar $k_F$. In the Yukawa sector, one-loop contributions are ultraviolet finite, but most of them are unobservable due to finite renormalization. The only observable effect is a contribution proportional to $(k_F)_{αβ}$ that emerges via a dimension-6 term that is observer and gauge invariant. In the Higgs and gauge sectors, all the irreducible parts of the corresponding Riemann-type tensors receive divergent contributions, so they are observable. The only finite contribution corresponds to the dimension-6 term. We think of these contributions as radiative corrections to the renormalized tensors and assume that both effects are of the same order of magnitude to find bounds from vacuum birefringence and compare with the literature. Bounds on $(k_F)_{αβ}$ contributions, innocuous to birefringence, are also derived using limits on the renormalized tensor from Laser-Interferometer-Gravitational-Wave-Observatory data. We compare these bounds with the literature. Beta functions associated with $(\hat{k}_F)_{αβμν}$ and $(k_F)_{αβ}$ are derived.

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arXiv2017

Analytical solution for the Zee mechanism

We found an analytical solution for the neutrino mass matrix in the most general case of the Zee model. Using the recent data on the neutrino parameters besides generating neutrino masses at 1-loop level we fit also the masses of the charged leptons and the leptonic mixing matrix. We also show in what conditions the model is not compatible with neutrino data.

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arXiv2017

Lepton masses and mixing in a scotogenic model

We consider an extension of the standard model with three Higgs doublet model and $S_3\times \mathbb{Z}_2$ discrete symmetries. Two of the scalar doublets are inert due to the $\mathbb{Z}_2$ symmetry. We have calculated all the mass spectra in the scalar and lepton sectors and accommodated the leptonic mixing matrix as well. We also show that the model has scalar and pseudoscalar candidates to dark matter. Constraints on the parameters of the model coming from the decay $μ\to eγ$ were considered and we found signals between the current and the upcoming experimental limits, and from that decay we can predict the one-loop $μ\to ee\bar{e}$ channel.

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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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arXiv2016

Lepton flavor violating processes in the minimal 3-3-1 model with singlet sterile neutrinos

We consider the minimal 3-3-1 model with three sterile neutrinos transforming as singlet under the $SU(3)_L\otimes U(1)_X$ symmetry. This model, with or without sterile neutrinos, predicts flavor violating interactions in both quark and lepton sectors, since all the charged fermions mass matrices can not be assumed diagonal in any case. Here we accommodate the lepton masses and the Pontecorvo-Maki-Nakawaga-Sakata matrix at the same time, and as consequence the Yukawa couplings and the unitary matrices which diagonalize the mass matrices are not free parameters anymore. We study some phenomenological consequences, i.e., $l_i\to l_jl_k \bar{l}_k$ and $l_i\to l_jγ$ which are induced by neutral and doubly charged particles present in the model. In particular we find that if the decay $μ\to ee\bar{e}$ is observed in the future, the only particle in the model that could explain this decay is the doubly charged vector bilepton.

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arXiv2015

Prediction of $h\toγZ$ from $h\toγγ$ at LHC for the IMDS$_3$ Model

We consider the decays $h\toγγ,γZ$ in the context of an extension of the standard model with two inert doublets and an additional $S_3$ symmetry. This model has contributions for these processes through new charged scalar-loops. Comparing our $h\toγγ$ with the more precise available experimental data we can predict the behaviour of $h\toγZ$ due that they depend on the same parameters, our estimation for this channel is 1.05 times the standard model value, but can be up to 1.16 if consider the $+1σ$ uncertainty from the $h\toγγ$ data, and down to 0.96 if consider $-1σ$.

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arXiv2014

Scalar Dark Matter Candidates in Two Inert Higgs Doublet Model

We study a two scalar inert doublet model (IDMS$_3$) which is stabilized by a $S_3$ symmetry. We consider two scenarios: i) two of the scalars in each charged sector are mass degenerated due to a residual $Z_2$ symmetry, ii) there is no mass degeneracy because of the introduction of soft terms that break the $Z_2$ symmetry. We show that both scenarios provide good dark matter candidates for some range of parameters.

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