H→ℓℓ′ in the Simplest Little Higgs Model
(Submitted on 31 Mar 2016)
Little Higgs Models are promising constructs to solve the hierarchy problem affecting the Higgs boson mass for generic new physics. However, their preservation of lepton universality forbids them to account for the H→τμ CMS hint and at the same time respect (as they do) the severe limits on H→μe inherited from the non-observation of μ→eγ. We compute the predictions of the Simplest Little Higgs Model for the H→ℓℓ′ decays and conclude that the measurement of any of these decays at LHC (even with a much smaller rate than currently hinted) will rule out this model. This result is consistent with our earlier observation of very suppressed lepton flavor violating semileptonic tau decays within this model.
Flavor-changing decays of the top quark in 5D warped models
(Submitted on 29 Mar 2016)
We study flavor changing neutral current decays of the top quark in the context of general warped extra dimensions, where the five dimensional metric is slightly modified from 5D anti-de-Sitter (AdS5). These models address the Planck-electroweak hierarchies of the Standard Model and can obey all the low energy flavor bounds and electroweak precision tests, while allowing the scale of new physics to be at the TeV level, and thus within the reach of the LHC at Run II. We perform the calculation of these exotic top decay rates for the case of a bulk Higgs, and thus include in particular the effect of the additional Kaluza-Klein (KK) Higgs modes running in the loops, along with the usual KK fermions and KK gluons.
The distinctive ultraviolet structure of extra-dimensional Yang-Mills theories by integration of heavy Kaluza-Klein modes
(Submitted on 12 Mar 2016)
One-loop Standard Model observables produced by virtual heavy Kaluza-Klein fields play a prominent role in the minimal model of universal extra dimensions. Motivated by this aspect, we integrate out all the Kaluza-Klein heavy modes coming from the Yang-Mills theory set on a spacetime with an arbitrary number, n, of compact extra dimensions. After fixing the gauge with respect to the Kaluza-Klein heavy gauge modes in a covariant manner, we calculate a gauge independent effective Lagrangian expansion containing multiple Kaluza-Klein sums that entail a bad divergent behavior. We use the Epstein-zeta function to regularize and characterize discrete divergences within such multiple sums, and then we discuss the interplay between the number of extra dimensions and the degree of accuracy of effective Lagrangians to generate or not divergent terms of discrete origin. We find that nonrenormalizable terms with mass dimension k are finite as long as k>4+n. Multiple Kaluza-Klein sums of nondecoupling logarithmic terms, not treatable by Epstein-zeta regularization, are produced by four-dimensional momentum integration. On the grounds of standard renormalization, we argue that such effects are unobservable.
Leptonic CP phases near the μ−τ symmetric limit
(Submitted on 7 Mar 2016)
Neutrino masses and mixings, as indicated by current neutrino oscillation experiments, suggest that neutrino mass matrix posses an approximated μ−τexchange symmetry. We explore neutrino parameter space and find that a slight μ−τ symmetry breaking can only occur for quasidegenerate neutrino mass hierarchy with unequal (non zero) Majorana CP violation phases, which are found to be strongly correlated to the Dirac CP violating phase. Within this framework, robust predictions for the values of Majorana phases are thus obtained.
See-Saw scale discrete dark matter and two-zero texture Majorana neutrino mass matrices
(Submitted on 7 Mar 2016)
In this paper we present a scenario where the stability of dark matter and the phenomenology of neutrinos are related by the spontaneous breaking of a non-Abelian flavor symmetry. In this scenario the breaking is done at the seesaw scale, in such a way that what remains of the flavor symmetry is a Z2 symmetry, which stabilizes the dark matter. We have proposed two models based on this idea, for which we have calculated their neutrino mass matrices achieving two-zero texture in both cases. Accordingly, we have updated this two-zero texture phenomenology finding an interesting correlation between the reactor mixing angle and the sum of the light neutrino masses. We also have a correlation between the lightest neutrino mass and the neutrinoless double beta decay effective mass, obtaining a lower bound for the effective mass within the region of the nearly future experimental sensitivities.
Constructing Scalar-Photon Three Point Vertex in Massless Quenched Scalar QED
(Submitted on 3 Mar 2016)
Non perturbative studies of Schwinger-Dyson equations (SDEs) require their infnite, coupled tower to be truncated in order to reduce them to a practically solvable set. In this connection, a physically acceptable ansatz for the three point vertex is the most favorite choice. Scalar quantum electrodynamics (sQED) provides a simple and neat platform to address this problem. The most general form of the three point scalar-photon vertex can be expressed in terms of only two independent form factors, a longitudinal and a transverse one. Ball and Chiu have demonstrated that the longitudinal vertex is fixed by requiring the Ward-Fradkin-Green-Takahashi identity (WFGTI), while the transverse vertex remains undetermined. In massless quenched sQED, we construct the transverse part of the non perturbative scalar-photon vertex. This construction (i) ensures multiplicative renormalizability (MR) of the scalar propagator in keeping with the Landau-Khalatnikov-Fradkin transformations (LKFTs), (ii) has the same transformation properties as the bare vertex under charge conjugation, parity and time reversal, (iii) has no kinematic singularities and (iv) reproduces one loop asymptotic result in the weak coupling regime of the theory.
Amplitude analysis of K¯N scattering
(Submitted on 2 Mar 2016)
We present the results of a coupled-channel model for K¯N scattering in the resonance region. The model fulfills unitarity, has the correct analytical properties for the amplitudes and the partial waves have the right threshold behavior. The parameters of the model have been established by fitting single-energy partial waves up to J=7/2 and up to 2.15 GeV of center-of-mass energy. The Λ∗ and Σ∗ spectra has been obtained, providing a comprehensive picture of the S=−1 hyperon spectrum. We use the structure of the hyperon spectrum and Regge phenomenology to gain insight on the nature of the Λ(1405) resonances.