4,176 research outputs found

    Invisible Z decay width bounds on active-sterile neutrino mixing in the (3+1) and (3+2) models

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    In this work we consider the standard model extended with singlet sterile neutrinos with mass in the eV range and mixed with the active neutrinos. The active-sterile neutrino mixing renders new contributions to the invisible Z decay width which, in the case of light sterile neutrinos, depends on the active-sterile mixing matrix elements only. We then use the current experimental value of the invisible Z decay width to obtain bounds on these mixing matrix elements for both (3+1) and (3+2) models.Comment: 10 pages, 5 figure

    Five-Dimensional QED, Muon Pair Production and Correction to the Coulomb Potential

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    We consider QED in five dimensions in a configuration where matter is localized on a 3-brane while foton propagates in the bulk. The idea is to investigate the effects of the Kaluza-Klein modes of the photon in the relativistic regime, but in low energy, and in the nonrelativistic regime. In the relativistic regime, we calculate the cross section for the reaction e++e−→μ++μ−e^+ + e^- \to \mu^+ + \mu^-. We compare our theoretical result with a precise measurement of this cross section at s=57.77\sqrt{s}=57.77 GeV. As result, we extract a lower bound on the size of the extra dimension. In the nonrelativistic regime, we derive the contribution for the Coulomb potential due to the whole tower of the Kaluza-Klein excited modes of the photon. We use the modified potential to calculate the Rutherford scattering differential cross section.Comment: minor changes, three new refs. added, to appear in IJMP

    Estudo da herança da resistência a brusone em duas cultivares de arroz (Oryza sativa).

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    O objetivo do presente trabalho foi de identificar o número de alelos envolvidos na expressão da resistência qualitativa à brusone nas folhas nas cultivares Cica-8 e Metica-1.Conpeex 2010

    Combining type I and type II seesaw mechanisms in the minimal 3-3-1 model

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    The minimal 3-3-1 model is perturbative until energies around 4-5TeV, posing a challenge to generate neutrino masses at eV scale, mainly if one aims to take advantage of the seesaw mechanism. As a means to circumvent this problem we propose a modification of the model such that it accommodates the type I and type II seesaw mechanisms altogether. We show that the conjunction of both mechanisms yield a neutrino mass expression suppressed by a high power of the cutoff scale, M5M^5, in its denominator. With such a suppression term we naturally obtain neutrino masses at eV scale when MM is around few TeV. We also investigate the size of lepton flavor violation through the process μ→eγ\mu \rightarrow e\gamma.Comment: about 15 pages, no figure
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