We consider a spin-0 unparticle and calculate its contribution to the weak properties of a fermion, which in the proper limit reduce to previously reported results for the electromagnetic properties. We then obtain an estimate for the electromagnetic and weak properties of the τ lepton. For the unparticle parameters, we consider the most recent bounds from the lepton flavor violating decay τ → 3µ, the muon anomalous magnetic moment, and the data for monojet production plus missing transverse energy at the LHC. In the most promising promising scenario, it is found that the unparticle contributions to the τ electromagnetic properties can be larger than the contributions predicted by the standard model (SM) and some of its extensions, such as the SeeSaw model and extensions of the minimal supersymmetric standard model (MSSM) with a mirror fourth generation and vectorlike multiplets. As for the contributions to the weak properties, they are larger than the SM contributions but are much smaller than the current experimental limits. We also discuss the case of the electromagnetic and weak properties of the bottom and top quarks. PACS numbers: 13.40.Em, 12.60.-i I. INTRODUCCIÓN where the EDM is expressed in units of 10 −16 e cm. These results are well beyond the theoretical predictions of the SM: a SM τ = 1177.21(5) × 10 −6 [5] and d SM τ < 10 −34 e cm [6]. On the other hand, the weak properties of the τ lepton *

Low-energy Lorentz-invariant quantities could receive contributions from a fundamental theory producing small Lorentz-violating effects. Within the Lorentz-violating extension of quantum electrodynamics, we investigate, perturbatively, the contributions to the one-loop f f γ vertex from the CP T -violating axial coupling of a vector background field to fermions. We find that the resulting vertex function has a larger set of Lorentz structures than the one characterizing the usual, Lorentz invariant, parametrization of the f f γ vertex. We prove gauge invariance of the resulting one-loop expression through a set of gauge invariant nonrenormalizable operators introducing new-physics effects at the first and second orders in Lorentz violation, and which generate tree-level contributions to the f f γ vertex. Whereas loop contributions involving parameters that violate Lorentz invariance at the first order are CP T -odd, those arising at the second order are CP T -even, so that contributions to low-energy physics are restricted to emerge for the first time at the second order. In this context, we derive a contribution to anomalous magnetic moment of fermions, which we use to set a bound on Lorentz violation.

The one-loop contributions to the trilinear neutral gauge boson couplings $$ZZV^*$$ Z Z V ∗ ($$V=\gamma ,Z,Z'$$ V = γ , Z , Z ′ ), parametrized in terms of one CP-conserving $$f_5^{V}$$ f 5 V and one CP-violating $$f_4^{V}$$ f 4 V form factors, are calculated in models with CP-violating flavor changing neutral current couplings mediated by the Z gauge boson and an extra neutral gauge boson $$Z'$$ Z ′ . Analytical results are presented in terms of Passarino-Veltman scalar functions. Constraints on the vector and axial couplings of the Z gauge boson $$\left| g_{{VZ}}^{tu}\right| < 0.0096$$ g VZ tu < 0.0096 and $$\left| g_{{VZ}}^{tc}\right| <0.011$$ g VZ tc < 0.011 are obtained from the current experimental data on the $$t\rightarrow Z q$$ t → Z q decays. It is found that in the case of the $$ZZ\gamma ^*$$ Z Z γ ∗ vertex the only non-vanishing form factor is $$f_5^{\gamma }$$ f 5 γ , which can be of the order of $$10^{-3}$$ 10 - 3 , whereas for the $$ZZZ^*$$ Z Z Z ∗ vertex both form factors $$f_5^{Z}$$ f 5 Z and $$f_4^{Z}$$ f 4 Z are non-vanishing and can be of the order of $$10^{-6}$$ 10 - 6 and $$10^{-5}$$ 10 - 5 , respectively. Our estimates for $$f_5^{\gamma }$$ f 5 γ and $$f_5^{Z}$$ f 5 Z are smaller than those predicted by the standard model, where $$f_4^{Z}$$ f 4 Z is absent up to the one loop level. We also estimate the $$ZZ{Z'}^{*}$$ Z Z Z ′ ∗ form factors arising from both diagonal and non-diagonal $$Z'$$ Z ′ couplings within a few extension models. It is found that in the diagonal case $$f_{5}^{Z'}$$ f 5 Z ′ is the only non-vanishing form factor and its real and imaginary parts can be of the order of $$10^{-1}$$ 10 - 1 –$$10^{-2}$$ 10 - 2 and $$ 10^{-2}$$ 10 - 2 –$$10^{-3}$$ 10 - 3 , respectively, with the dominant contributions arising from the light quarks and leptons. In the non-diagonal case $$f_{5}^{Z^\prime }$$ f 5 Z ′ can be of the order of $$10^{-4}$$ 10 - 4 , whereas $$f_4^{Z'}$$ f 4 Z ′ can reach values as large as $$10^{-7}$$ 10 - 7 –$$10^{-8}$$ 10 - 8 , with the largest contributions arising from the $$Z'tq$$ Z ′ t q couplings.

The chromomagnetic dipole moment (CMDM) and chromoelectric dipole moment (CEDM) of the top quark are calculated at the one-loop level in the framework of the two-Higgs doublet model with four fermion generations (4GTHDM), which is still consistent with experimental data and apart from new scalar bosons (H 0 , A 0 , and H ± ) and quarks (b and t ) predicts new sources of CP violation via the extended 4 × 4 CKM matrix. Analytical expressions for the CMDM and CEDM of a quark are presented both in terms of Feynman parameter integrals, which are explicitly integrated, and Passarino-Veltman scalar functions, with the main contributions arising from loops carrying the scalar bosons accompanied by the third-and fourth-generation quarks. The current bounds on the parameter space of the 4GTHDM are discussed and a region still consistent with the LHC data on the 125 GeV Higgs boson and the oblique parameters is identified. It is found that the top quark CMDM, which is induced by all the scalar bosons, can reach values of the order of 10 −2 -10 −1 . As for the top quark CEDM, it only receives contributions from the charged scalar boson and can reach values of the order of 10 −20 -10 −19 ecm for relatively light m H ± and heavy m b , with the dominant contribution arising from the b quark. The CEDM would be the most interesting prediction of this model as it can be larger than the value predicted by the usual THDMs by one order of magnitude.

A new estimate of the one loop contributions of the standard model to the chromomagnetic dipole moment (CMDM) μq of quarks is presented with the aim to address a few disagreements arising in previous calculations. We consider the most general case with non-zero gluon transfer momentum q 2 and obtain analytical results in terms of Feynman parameter integrals and Passarino-Veltman scalar functions, which are then expressed in terms of closed form functions when possible. It is found that the QCD contribution from a three-gluon Feynman diagram diverges at q 2 = 0, which agrees with a previous evaluation and stems from the fact that the static CMDM [μ(0)] has no sense in perturbative QCD. For the numerical analysis we consider the region 30 GeV< q < 1000 GeV and analyze the behavior of μq (q 2 ) for all the SM quarks. It is found that the CMDM of light quarks is considerably smaller than that of the top quark as it is directly proportional to the quark mass. In the considered energy interval, both the real and imaginary parts of μt (q 2 ) are of the order of 10 −2 − 10 −3 , with the largest contribution arising from the QCD induced diagrams, though around the threshold q 2 = 4m 2 t there are also important contributions from diagrams with Z gauge boson and Higgs boson exchange.