arXiv subjects

Jorge C. Romao

Publications and source records attributed to Jorge C. Romao.

17 recordsLinked to original sources

arXiv2026

Scrutinizing the Mass Matrices in Three-Higgs-Doublet Models with Generalized CP Symmetries

We investigate three-Higgs-doublet models with a softly broken generalized CP (GCP) symmetry, focusing on the Yukawa sector and its compatibility with quark flavor data. We first show that the 40 GCP-symmetric models previously identified are not all physically distinct, by constructing the basis transformations relating equivalent realizations and identifying spurious parameters. We then perform numerical fits to the six quark masses and the four independent parameters of the Cabibbo--Kobayashi--Maskawa matrix, further reducing the set of viable models. In contrast to the GCP-symmetric two-Higgs-doublet case, we find that GCP-symmetric three-Higgs-doublet models can successfully reproduce all quark masses and mixings. In total, 22 inequivalent models are compatible with current experimental data, and representative benchmark points are presented. Our results establish softly broken GCP-symmetric three-Higgs-doublet models as phenomenologically viable extensions of the Standard Model and provide a framework for further studies of their flavor phenomenology.

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arXiv2024

New physics interpretations for nonstandard values of $h\to Zγ$

Current measurement of the $h\to Zγ$ signal strength invite us to speculate about possible new physics interactions that exclusively affect $μ_{Zγ}$ without altering the other signal strengths. Additional consideration of tree-unitarity enables us to correlate the nonstandard values of $μ_{Zγ}$ with an upper limit on the scale of new physics. We find that even when $μ_{Zγ}$ deviates from the SM value by only $20\%$, the scale of new physics should be well within the reach of the LHC.

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arXiv2023

Fingerprinting the Type-Z three Higgs doublet models

There has been great interest in a model with three Higgs doublets in which fermions with a particular charge couple to a single and distinct Higgs field. We study the phenomenological differences between the two common incarnations of this so-called Type-Z 3HDM. We point out that the differences between the two models arise from the scalar potential only. Thus we focus on observables that involve the scalar self-couplings. We find it difficult to uncover features that can uniquely set apart the $Z_3$ variant of the model. However, by studying the dependence of the trilinear Higgs couplings on the nonstandard masses, we have been able to isolate some of the exclusive indicators for the $Z_2\times Z_2$ version of the Type-Z 3HDM. This highlights the importance of precision measurements of the trilinear Higgs couplings.

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arXiv2023

A viable $A_4$ 3HDM theory of quark mass matrices

It is known that a three Higgs doublet model (3HDM)symmetric under an exact $A_4$ symmetry is not compatible with nonzero quark masses and/or non-block-diagonal CKM matrix. We show that a 3HDM with softly broken $A_4$ terms in the scalar potential does allow for a fit of quark mass matrices. Moreover, the result is consistent with $m_h=125\textrm{GeV}$ and the $h \rightarrow WW, ZZ$ signal. We also checked numerically that, for each point that passes all the constraints, the minimum is a global minimum of the potential.

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arXiv2022

Conditions for global minimum in the A4 symmetric 3HDM

There has been a great interest in three Higgs doublet models (3HDM) symmetric under an exact A4 symmetry. We provide the complete analytic necessary and sufficient conditions for a point to be the global minimum along the neutral directions in such models, discussing many of the subtleties involved. We also present a number of numerical examples, to highlight those issues. We then turn to the directions which break electric charge, presenting a safe analytical sufficient condition for bounded from below (BFB) potentials. Based on extensive numerical simulations, we discuss one conjecture on BFB along charge breaking directions.

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arXiv2020

One-loop corrections to the $Zb\bar{b}$ vertex in models with scalar doublets and singlets

We study the one-loop corrections to the $Zb\bar{b}$ vertex in extensions of the Standard Model with arbitrary numbers of scalar doublets, neutral scalar singlets, and charged scalar singlets. Starting with a general parameterization of theories with neutral and singly-charged scalar particles, we derive the conditions that, in a renormalizable model, must be obeyed by the couplings in order for the divergent contributions to cancel. Then, we show that those conditions are indeed obeyed by the models that we are interested in, and we write down the full finite expression for the vertex in those models. We apply our results to some particular cases, highlighting the importance of the diagrams with neutral scalars.

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arXiv2020

Nondecoupling in Multi-Higgs doublet models

We consider models with any number of Higgs doublets and study the conditions for decoupling. We show that, under very general circumstances, all the quadratic coefficients of the scalar potential must be present, except in special cases, which include terms related to directions of vanishing vacuum expectation values. We give a few examples. Moreover, we show that the decoupling of all charged scalars implies the decoupling of all extra neutral scalars and vanishing $\mathcal{CP}$ violation in scalar-pseudoscalar mixing.

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arXiv2020

Basis-independent treatment of the complex 2HDM

The complex 2HDM (C2HDM) is the most general CP-violating two Higgs doublet model that possesses a softly-broken $\mathbb{Z}_2$ symmetry. However, the physical consequences of the model cannot depend on the basis of scalar fields used to define it. Thus, to get a better sense of the significance of the C2HDM parameters, we have analyzed this model by employing a basis-independent formalism. This formalism involves transforming to the Higgs basis (which is defined up to an arbitrary complex phase) and identifying quantities that are invariant with respect to this phase degree of freedom. Using this method, we have obtained the constraints that enforce the softly-broken $\mathbb{Z}_2$ symmetry. One can then relate the C2HDM parameters to basis-independent quantities up to a two-fold ambiguity. We then show how this remaining ambiguity is resolved. We also examine the possibility of spontaneous CP violation when the scalar potential of the C2HDM is explicitly CP-conserving. Basis-independent constraints are presented that govern the presence of spontaneous CP violation.

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arXiv2019

Electroweak Breaking and Higgs Boson Profile in the Simplest Linear Seesaw Model

We examine the simplest realization of the linear seesaw mechanism within the Standard Model gauge structure. Besides the standard scalar doublet, there are two lepton-number-carrying scalars, a nearly inert SU2 doublet and a singlet. Neutrino masses result from the spontaneous violation of lepton number, implying the existence of a Nambu-Goldstone boson. Such "majoron" would be copiously produced in stars, leading to stringent astrophysical constraints. We study the profile of the Higgs bosons in this model, including their effective couplings to the vector bosons and their invisible decay branching ratios. A consistent electroweak symmetry breaking pattern emerges with a compressed spectrum of scalars in which the "Standard Model" Higgs boson can have a sizeable invisible decay into the invisible majorons.

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arXiv2012

A resource for signs and Feynman diagrams of the Standard Model

When performing a full calculation within the Standard Model or its extensions, it is crucial that one utilizes a consistent set of signs for the gauge couplings and gauge fields. Unfortunately, the literature is plagued with differing signs and notations. We present all Standard Model Feynman rules, including ghosts, in a convention-independent notation, and we table the conventions in close to 40 books and reviews.

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arXiv2011

LHC and Lepton Flavour Violation Phenomenology in Seesaw Models

We review Lepton Flavour Violation (LFV) in the supersymmetric version of the seesaw mechanism (type I, II, III) and in Left-Right models. The LFV needed to explain neutrino masses and mixings is the only source of LFV and has experimental implications both in low-energy experiments where we search for the radiative decays of leptons, and at the LHC where we look at its imprint on the LFV decays of the sparticles and on slepton mass splittings. We discuss how this confrontation between high- and low-energy LFV observables may provide information about the underlying mechanism of LFV.

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arXiv2007

Supersymmetric Models for Neutrino Mass

We review models for neutrino mass, with special emphasis in supersymmetric models where R-parity is broken either explicitly or spontaneously. The simplest unified extension of the MSSM with explicit bilinear R-parity violation provides a predictive scheme for neutrino masses and mixings which can account for the observed atmospheric and solar neutrino anomalies. Despite the smallness of neutrino masses R-parity violation is observable at present and future high-energy colliders, providing an unambiguous cross-check of the model. This model can be shown to be an effective model for the, more theoretically satisfying, spontaneous broken theory. The main difference in this last case is the appearance of a massless particle, the majoron, that can modify the decay modes of the Higgs boson, making it decay invisibly most of the time.

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arXiv2003

Spontaneous CP Violation in Non-Minimal Supersymmetric Models

We study the possibilities of spontaneous CP violation in the Next-to-Minimal Supersymmetric Standard Model with an extra singlet tadpole term in the scalar potential. We calculate the Higgs boson masses and couplings with radiative corrections including dominant two loop terms. We show that it is possible to satisfy the LEP constraints on the Higgs boson spectrum with non-trivial spontaneous CP violating phases. We also show that these phases could account for the observed value of epsilonK.

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arXiv2002

Testing Neutrino Parameters at Future Accelerators

The simplest unified extension of the Minimal Supersymmetric Standard Model with bilinear R--Parity violation provides a predictive scheme for neutrino masses which can account for the observed atmospheric and solar neutrino anomalies.Despite the smallness of neutrino masses R-parity violation is observable at present and future high-energy colliders, providing an unambiguous cross-check of the model.

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arXiv1998

Supersymmetric Theories with R-Parity Violation

In these Lectures we review the Minimal Supersymmetric Standard Model as well as some of its extensions that include R-Parity violation. The cases of spontaneous breaking of R-Parity as well as that of explicit violation through bilinear terms in the superpotential are studied in detail. The signals at LEP and the prospects for LHC are discussed.

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arXiv1998

Gauge and Yukawa Unification with Broken R-Parity

We study gauge and Yukawa coupling unification in the simplest extension of the Minimal Supersymmetric Standard Model (MSSM) which incorporates R-Parity violation through a bilinear superpotential term. Contrary to what happens in the MSSM, we show that bottom-tau unification at the scale M_GUT where the gauge couplings unify can be achieved for any value of tan(beta) by choosing appropriately the sneutrino vacuum expectation value. In addition, we show that bottom-tau-top unification occurs in a slightly wider tan(beta) range than in the MSSM.

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arXiv1997

Minimal Supergravity with R-Parity Breaking

We show that the minimal R-parity breaking model characterized by an effective bilinear violation of R-parity in the superpotential is consistent with minimal N=1 supergravity unification with radiative breaking of the electroweak symmetry and universal scalar and gaugino masses. This one-parameter extension of the MSSM-SUGRA model provides therefore the simplest reference model for the breaking of R-parity and constitutes a consistent truncation of the complete dynamical models with spontaneous R-parity breaking proposed previously. We comment on the lowest-lying CP-even Higgs boson mass and discuss its minimal N=1 supergravity limit, determine the ranges of $\tanβ$ and bottom quark Yukawa couplings allowed in the model, as well as the relation between the tau neutrino mass and the bilinear R-parity violating parameter.

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