arXiv subjects

José Filipe Bastos

Publications and source records attributed to José Filipe Bastos.

6 recordsLinked to original sources

arXiv2026

Feasible Deviations from Unitarity with Vector-Like Quark Singlets

We deduce pertinent relations between the elements of the CKM matrix, and find that not all of these are totally compatible with experiment and/or the assumption of the SM $3 \times 3$ unitarity. We identify relations between moduli and complex phases of the CKM-elements which may signal deviations from unitary (DUs). Recent analyses of $|V_{cs}|$ appear to be in tension with the SM assumption of CKM unitarity in the second row, similar to previous hints of DUs in the first row from previous $|V_{ud,s}|$ results. Here, we explore DUs induced in VLQ iso-singlet models, in particular the possibility of having significant DUs of the first and second rows of the CKM matrix. We perform a extensive analysis of $n\leq 5$ VLQ iso-singlet models and identify a useful set of parametrizations with the intention of coherently exploring parameter space. We assess the feasibility of each model and confront it with constraints from key flavor observables, with particular attention to the neutral kaon and $D^0$-meson sectors, especially $ε_K$ and $x_D$. We find that smaller $n\leq 2$ VLQ-models cannot accommodate the new $|V_{cs}|$ results in the DUs of the second CKM-row. In contrast, larger models extending both up- and down-type sectors, can indeed produce significant second-row DUs, e.g. in a model with 3 up- and 2 down-type VLQs, even reaching the order of the Cabibbo angle. To our knowledge, the phenomenology of extensions combining both up- and down-type VLQs has yet to be thoroughly studied. Finally, we find that VLQ-singlet models may induce very large enhancements in the rephasing invariant phase $β_K$, entering in the Cabibbo sector.

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arXiv2024

Reducing Complex Phases and other Subtleties of CP Violation

When extending the SM, e.g. with vector-like quarks (VLQ), one inevitably encounters more than one CP violating complex phases. In this work, we develop a method useful in reducing the number of complex phases in scenarios with one and two VLQs. We show that these VLQ-models can be described with just one or two physical complex phases respectively and present an explicit alternative parametrization for the quark mixing matrix. Making use of this Reduction of Complex Phases in the case of the Bento-Branco-Parada (BBP) model, i.e. the simplest implementation of the Nelson-Barr solution to the strong CP problem, one also recovers the single phase formulation of BBP model. We comment on how this specific scenario can be distinguished from the general VLQ case with weak-basis invariants

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arXiv2023

CP-odd and CP-even Weak-Basis Invariants in the Presence of Vector-Like Quarks

We propose a minimal set of weak-basis invariants in an extension of the SM where one up-type isosinglet vector-like quark is introduced, which allows us to obtain all the physical content of the CKM matrix. We present CP-odd invariants of lower order in mass than the one in the SM, which may have important consequences for Baryogenesis. We study the extreme chiral limit, where the two lightest generations have vanishing mass, showing that in this extension, contrary to the SM, CP violation can be observed in collisions much above the electroweak scale.

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arXiv2023

Does Quark Mixing play a role in the Lepton Sector?

We suggest a simple relation between the quark and the lepton mixing within the framework of type-I seesaw mechanism. We show that within our ansatz the empirical King-Mohapatra-Smirnov relation, which suggests a connection between the CKM and PMNS mixing where $|V^\text{PMNS}_{13}|\approx \frac{1}{\sqrt{2}}\sin(θ_C) $, can be derived. This is possible within a restricted region of the Dirac and Majorana mass parameters.

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arXiv2023

Do the Small Numbers in the Quark Mixing arise from New Physics?

We put forward the conjecture that the small numbers in the $V_\text{CKM}$ matrix, are generated by physics beyond the Standard Model. We identify as small numbers $V_{ub}$ and the strength of CP violation, measured by $|\text{Im}Q|$, where $Q$ stands for a rephasing invariant quartet of $V_\text{CKM}$. We illustrate how the conjecture can be realised in the context of an extension of the Standard Model where an up-type vector-like quark is introduced leading to a realistic spectrum of quark masses and an effective $V_\text{CKM}$ in agreement with experiment.

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arXiv2022

Decays of the Heavy Top and New Insights on $ε_K$ in a one-VLQ Minimal Solution to the CKM Unitarity Problem

We propose a minimal extension of the Standard Model where an up-type vector-like quark, denoted $T$, is introduced and provides a simple solution to the CKM unitarity problem. We adopt the Botella-Chau parametrization in order to extract the $4\times 3$ quark mixing matrix which contains the three angles of the $3\times 3$ CKM matrix plus three new angles denoted $θ_{14}$, $θ_{24}$, $θ_{34}$. It is assumed that the mixing of $T$ with standard quarks is dominated by $θ_{14}$. Imposing a recently derived, and much more restrictive, upper-bound on the New Physics contributions to $ε_{K}$, we find, in the limit of exact $θ_{14}$ dominance where the other extra angles vanish, that $ε_{K}^{\text{NP}}$ is too large. However, if one relaxes the exact $θ_{14}$ dominance limit, there exists a parameter region, where one may obtain $ε_{K}^{\text{NP}}$ in agreement with experiment while maintaining the novel pattern of $T$ decays with the heavy quark decaying predominantly to the light quarks $d$ and $u$. We also find a reduction in the decay rate of $K_L\rightarrow π^o ν\barν$.

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