arXiv subjects
Publications and source records attributed to J. Jesús Toscano.
Lorentz-violating Yukawa couplings lying within the renormalizable part of the SME generate Lorentz-invariant one-loop contributions to electromagnetic moments of fermions. These proceedings provide a discussion on such contributions and present bounds on SME coefficients from experimental data on electromagnetic moments. Constraints as restrictive as $\sim10^{-14}$ are found.
Yukawa couplings in the Lorentz- and $CPT$-violating Standard Model Extension (SME) induce quantum contributions to the electromagnetic moments of quarks, which are calculated in the present paper and then used to define contributions to electromagnetic moments of nucleons. High-sensitivity measurements of the proton and neutron electromagnetic moments then yield constrains on SME coefficients, reaching bounds as restrictive as $10^{-12}$. This approach notably grants access to SME effects from the second and third quark families.
The effective-Lagrangian description of Lorentz-invariance violation provided by the so-called Standard-Model Extension covers all the sectors of the Standard Model, allowing for model-independent studies of high-energy phenomena that might leave traces at relatively-low energies. In this context, the quantification of the large set of parameters characterizing Lorentz-violating effects is well motivated. In the present work, effects from the Lorentz-nonconserving Yukawa sector on the electromagnetic moments of charged leptons are calculated, estimated, and discussed. Following a perturbative approach, explicit expressions of leading contributions are derived and upper bounds on Lorentz violation are estimated from current data on electromagnetic moments. Scenarios regarding the coefficients of Lorentz violation are considered. In a scenario of two-point insertions preserving lepton flavor, the bound on the electron electric dipole moment yields limits as stringent as $10^{-28}$, whereas muon and tau-lepton electromagnetic moments determine bounds as restrictive as $10^{-14}$ and $10^{-6}$, respectively. Another scenario, defined by the assumption that Lorentz-violating Yukawa couplings are Hermitian, leads to less stringent bounds, provided by the muon anomalous magnetic moment, which turn out to be as restrictive as $10^{-14}$.
Kaluza-Klein fields characterizing, from a four-dimensional viewpoint, the presence of compact universal extra dimensions would alter low-energy observables through effects determined by some compactification scale, $R^{-1}$, since the one-loop level, thus being particularly relevant for physical phenomena forbidden at tree level by the Standard Model. The present paper explores, for the case of one universal extra dimension, such new-physics contributions to Higgs decays $h^{(0)}\to q^{(0)}_αq^{(0)}_β$, into pairs of quarks with different flavors, a sort of decay process which, in the Standard Model, strictly occurs at the loop level. Finite results, decoupling as $R^{-1}\to \infty$, are calculated. Approximate short expressions, valid for large compactification scales, are provided. We estimate that Kaluza-Klein contributions lie below predictions from the Standard Model, being about 2 to 3 orders of magnitude smaller for compactification scales within $1.4\,{\rm TeV}<R^{-1}<10\,{\rm TeV}$.
Universal extra dimensions, presumably observable at some high-energy scale, would modify low-energy observables, being particularly relevant for physical processes forbidden at tree level by the Standard Model. We address the Kaluza-Klein contributions from the 5-dimensional Standard Model to the anomalous magnetic moment and to branching ratios of electromagnetic decays of the top quark. In accordance with present bounds on the compactification scale, contributions to both quantities are found to be at least 3 orders of magnitude below Standard-Model predictions.