Anomalous magnetic and weak magnetic dipole moments of the τ\tau lepton in the simplest little Higgs model

We obtain analytical expressions, both in terms of parametric integrals and Passarino-Veltman scalar functions, for the one-loop contributions to the anomalous weak magnetic dipole moment (AWMDM) of a charged lepton in the framework of the simplest little Higgs model (SLHM). Our results are general and can be useful to compute the weak properties of a charged lepton in other extensions of the standard model (SM). As a by-product we obtain generic contributions to the anomalous magnetic dipole moment (AMDM), which agree with previous results. We then study numerically the potential contributions from this model to the $\tau$ lepton AMDM and AWMDM for values of the parameter space consistent with current experimental data. It is found that they depend mainly on the energy scale $f$ at which the global symmetry is broken and the $t_\beta$ parameter, whereas there is little sensitivity to a mild change in the values of other parameters of the model. While the $\tau$ AMDM is of the order of $10^{-9}$, the real (imaginary) part of its AWMDM is of the order of $10^{-9}$ ($10^{-10}$). These values seem to be out of the reach of the expected experimental sensitivity of future experiments.Comment: 23 pages, 11 figures, new analysis and References adde

Has a Higgs-flavon with a 750750 GeV mass been detected at the LHC13?

Higgs-flavon fields appear as a part of the Froggatt-Nielsen (FN) mechanism, which attempts to explain the hierarchy of Yukawa couplings. We explore the possibility that the 750 GeV diphoton resonance recently reported at the LHC13, could be identified with a low-scale Higgs-flavon field $H_F$ and find the region of the parameter space consistent with CMS and ATLAS data. It is found that the extra vector-like fermions of the ultraviolet completion of the FN mechanism are necessary in order to reproduce the observed signal. We consider a standard model (SM) extension that contains two Higgs doublets (a standard one and an inert one) and one complex FN singlet. The inert doublet includes a stable neutral boson, which provides a viable dark matter candidate, while the mixing of the standard doublet and the FN singlet induces flavor violation in the Higgs sector at the tree-level. Constraints on the parameters of the model are derived from the LHC Higgs data, which include the search for the lepton flavor violating decay of the SM Higgs boson $h\to \bar{\mu}\tau$. It is also found that in some region of the parameter space the model may give rise to a large branching ratio for the $H_F \to hh$ decay, of the order of 0.1, which could be searched for at the LHC.Comment: 18 pages, 7 Figures, includes updated files to match published versio

cLFV processes and suppression of non-unitary mixing effects in low scale seesaw models

We examine the parameter space region of the inverse seesaw model that is consistent with neutrino oscillation data. We focus on the correlation between the current limits from the search of the $\mu\to e\gamma$ lepton flavour violating decay and the non-standard effects associated with the presence of new heavy neutrino states. Unlike what we would expect from an inverse seesaw model, we have found a parametrization for the mass matrices in which the rates of charged lepton flavour-violating processes are negligible. Additionally, we provide a model where the inverse seesaw is obtained naturally, and the mass matrices get this structure with negligible violation of the lepton flavour.Comment: 20 pages, 3 figures and 3 table

ρ parameter and H 0 → ℓ i ℓ j in models with TeV sterile neutrinos

The presence of massive sterile neutrinos N mixed with the active ones induces flavor violating processes in the charged lepton sector at the loop level. In particular, the amplitude of H 0 → ¯ ℓ i ℓ j is expected to be proportional to the product of heavy-light Yukawa couplings y i y j = 2 s ν i s ν j m 2 N / v 2 , where s ν i , j express the heavy-light neutrino mixings. Here, we revisit these Higgs decays in the most generic extension of the neutrino sector, focusing on large values of y i . We show that decoupling effects and a cancellation between the two dominant contributions to these processes makes the amplitude about 100 times smaller than anticipated. We find that perturbative values of y i giving an acceptable contribution to the ρ parameter imply B ( H 0 → ¯ ℓ i ℓ j ) < 10 − 8 for any lepton flavors, a rate that is not accessible at current colliders.Spanish Ministry of Science, Innovation and Universities FPA2016-78220-C3 PID2019-107844GB-C21/AEI/10.13039/501100011033Junta de Andalucia FQM 101 SOMM17/6104/UGR P18-FR-1962 P18-FR-5057Consejo Nacional de Ciencia y Tecnologia (CONACyT

Neutrino events within muon bundles at neutrino telescopes

This work was partially supported by the Spanish Ministry of Sci-ence, Innovation and Universities (PID2019-107844GB-C21/AEI/10.13039/501100011033) and by the Junta de Andalucia, Spain (FQM 101, SOMM17/6104/UGR, P18-FR-1962, P18-FR-5057) . MGG acknowledges a grant from Programa Operativo de Empleo Juvenil (Junta de Andalucia) . The work of GHT has been funded by the program Es-tancias Postdoctorales en el Extranjero 2019-2020 of CONACYT, Mexico. GHT also acknowledges Prof. Pablo Roig for partial support through Catedra Marcos Moshinsky (Fundacion Marcos Moshinsky) . Funding for open access charge: Universidad de Granada/CBUA.The atmospheric neutrino flux includes a component from the prompt decay of charmed hadrons that becomes significant only at E >= 10 TeV. At these energies, however, the diffuse flux of cosmic neutrinos discovered by IceCube seems to be larger than the atmospheric one. Here we study the possibility to detect a neutrino interaction in down-going atmospheric events at km3 telescopes. The neutrino signal will always appear together with a muon bundle that reveals its atmospheric origin and, generically, it implies an increase in the detector activity with the slant depth. We propose a simple algorithm that could separate these events from regular muon bundles.Spanish Ministry of Science, Innovation and Universities PID2019-107844GB-C21/AEI/10.13039/501100011033Junta de Andalucia European Commission FQM 101- SOMM17/6104/UGR- P18-FR-1962- P18-FR-5057Junta de AndaluciaProgram Es-tancias Postdoctorales en el Extranjero 2019-2020 of CONACYT, MexicoUniversidad de Granada/CBUACatedra Marcos Moshinsky (Fundacion Marcos Moshinsky

Effects of heavy Majorana neutrinos on lepton flavor violating processes

The observation of lepton flavor violating processes at colliders could be a clear signal of a non-minimal neutrino sector. We define a 5-parameter model with a pair of TeV fermion singlets and arbitrary mixings with the three active neutrino flavors. Then we analyze several flavor violating transitions (ℓ→ℓ′γ,ℓ′ℓ′′ℓ¯′′′ or μ−e conversions in nuclei) and Z→ℓ¯ℓ′ decays induced by the presence of heavy neutrinos. In particular, we calculate all the one-loop contributions to these processes and present their analytic expressions. We focus on the genuine effects of the heavy Majorana masses, comparing the results in that case with the ones obtained when the two heavy neutrinos define a Dirac field. Finally, we use our results to update the bounds on the heavy-light mixings in the neutrino sector.This work was supported in part by the Spanish Ministry of Science, Innovation and Universities, under Grant No. FPA2016-78220-C3-1,2,3- P (fondos FEDER), and Junta de Andalucía, Grants No. FQM 101 and No. SOMM17/6104/UGR. G. H. T. wants to acknowledge financial support from Conacyt through the program “Estancia Postdoctoral en el Extranjero.” The work of P. R. has been partially funded by Conacyt through the Project No. 250628 (Ciencia Básica) and Fondo SEP-Cinvestav 2018 (Project No. 142)

Flavor violating leptonic decays of τ and μ leptons in the Standard Model with massive neutrinos

We have revisited the computations of the flavor violating leptonic decays of the τ and μ leptons into three lighter charged leptons in the Standard Model with massive neutrinos. We were driven by a claimed unnaturally large branching ratio predicted for the τ − → μ − l + l − (l = μ, e) decays (Pham, Eur Phys J C 8:513 1999), which was at odds with the corresponding predictions for the μ − → e−e−e+ processes (Petcov, Sov J Nucl Phys 25:340 1977). In contrast with the prediction in [17], our results are strongly suppressed and in good agreement with the approximationmade in Ref. [15], where masses and momenta of the external particles were neglected in order to deal with the loop integrals. However -as a result of keeping external momenta and masses in the computation of the dominant penguin and box diagrams- we even find slightly smaller branching fractions. Therefore, we confirm that any future observation of such processes would be an unambiguous manifestation of new physics beyond the Standard Model.Finally, we also acknowledge support from Conacyt through projects FOINS-296-2016 (Fronteras de la Ciencia), and 236394 and 250628 (Ciencia Básica)