1,721,032 research outputs found
Primordial nucleosynthesis constraints on Z ' properties
No full textIn models involving new TeV-scale Z(') gauge bosons, the new U(1)(') symmetry often prevents the generation of Majorana masses needed for a conventional neutrino seesaw mechanism, leading to three superweakly interacting "right-handed" neutrinos nu(R), the Dirac partners of the ordinary neutrinos. These can be produced prior to big bang nucleosynthesis by the Z(') interactions, leading to a faster expansion rate and too much He-4. We quantify the constraints on the Z(') properties from nucleosynthesis for Z(') couplings motivated by a class of E-6 models parametrized by an angle theta(E6). The rate for the annihilation of three approximately massless right-handed neutrinos into other particle pairs through the Z(') channel is calculated. The decoupling temperature, which is higher than that of ordinary left-handed neutrinos due to the large Z(') mass, is evaluated, and the equivalent number of new doublet neutrinos DeltaN(nu) is obtained numerically as a function of the Z(') mass and couplings for a variety of assumptions concerning the Z-Z(') mixing angle and the quark-hadron transition temperature T-c. Except near the values of theta(E6) for which the Z(') decouples from the right-handed neutrinos, the Z(') mass and mixing constraints from nucleosynthesis are much more stringent than the existing laboratory limits from searches for direct production or from precision electroweak data, and are comparable to the ranges that may ultimately be probed at proposed colliders. For the case T-c=150 MeV with the theoretically favored range of Z-Z(') mixings, DeltaN(nu)less than or similar to0.3 for M(Z)(')greater than or similar to4.3 TeV for any value of theta(E6). Larger mixing or larger T-c often lead to unacceptably large DeltaN(nu) except near the nu(R) decoupling limit.
Lightest neutralino in extensions of the MSSM
No full textWe study neutralino sectors in extensions of the MSSM that dynamically generate the A-term. The extra neutralino states are superpartners of the Higgs singlets and/or additional gauge bosons. The extended models may have distinct lightest neutralino properties which can have important influences on their phenomenology. We consider constraints on the lightest neutralino from LEP, Tevatron, and (g - 2)(mu) measurements and the relic density of the dark matter. The lightest neutralino can be extremely light and/or dominated by its singlino component which does not couple directly to SM particles except Higgs doublets. (c) 2005 Elsevier B.V. All rights reserved.
Solution to the B -> pi K puzzle in a flavor-changing Z ' model
No full textRecent experiments suggest that certain B --> piK branching ratios are inconsistent with the standard model expectations. We show that a flavor-changing Z' provides a solution to the problem. Electroweak penguin amplitudes are enhanced by the Z' boson for select parameters. We discuss implications for the Z' mass and its couplings to the standard model fermions. We also show that the solution is consistent with constraints from the CP asymmetries of the B --> phiK(S) decay. (C) 2004 Published by Elsevier B.V.
Muon anomalous magnetic moment in a supersymmetric U (1)' model
No full textWe study the muon anomalous magnetic moment a(mu) = (g(mu) - 2)/2 in a supersymmetric U(1)' model. The neutralino sector has extra components from the superpartners of the U(1)' gauge boson and the extra Higgs singlets that break the U(1)' symmetry. The theoretical maximum bound on the lightest neutralino mass is much smaller than that of the Minimal Supersymmetric Standard Model (MSSM) because of the mixing pattern of the extra components. In a U(1)' model where the U(1)' symmetry is broken by a secluded sector (the S-model), tan beta is required to be <= 3 to have realistic electroweak symmetry breaking. These facts suggest that the a(mu) prediction may be meaningfully different from that of the MSSM. We evaluate and compare the muon anomalous magnetic moment in this model and the MSSM and discuss the constraints on tan,8 and relevant soft breaking terms. There are regions of the parameter space that can explain the experimental deviation of au from the Standard Model calculation and yield an acceptable cold dark matter relic density without conflict with collider experimental constraints. (c) 2005 Elsevier B.V. All rights reserved.
Z′ mediated flavor changing neutral currents in B meson decays
No full textAbstractWe study the effects of an extra U(1)′ gauge boson with flavor changing couplings with fermion mass eigenstates on certain B meson decays that are sensitive to such new physics contributions. In particular, we examine to what extent the current data on Bd→φK and Bd→η′K decays may be explained in such models, concentrating on the example in which the flavor changing couplings are left-chiral. We find that within reasonable ranges of parameters, the Z′ contribution can readily account for the anomaly in SφKS but is not sufficient to explain large branching ratio of Bd→η′K with the same parameter value. SφKS and Sη′KS are seen to be the dominant observables that constrain the extra weak phase in the model
Neutralino relic density in a supersymmetric U(1)′ model
No full textAbstractWe study properties of the lightest neutralino (χ0) and calculate its cosmological relic density in a supersymmetric U(1)′ model with a secluded U(1)′ breaking sector (the S-model). The lightest neutralino mass is smaller than in the minimal supersymmetric standard model; for instance, mχ0≲100 GeV in the limit that the U(1)′ gaugino mass is large compared to the electroweak scale. We find that the Zχ0χ0 coupling can be enhanced due to the singlino components in the extended neutralino sector. Neutralino annihilation through the Z-resonance then reproduces the measured cold dark matter density over broad regions of the model parameter space
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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