1,721,113 research outputs found
WMAP and inflation
No full textAbstractWe assay how inflationary models whose properties are dominated by the dynamics of a single scalar field are constrained by cosmic microwave background (CMB) data from the Wilkinson Microwave Anisotropy Probe (WMAP). We classify inflationary models in a plane defined by the horizon-flow parameters. Our approach differs from that of the WMAP Collaboration in that we analyze only WMAP data and take the spectral shapes from slow-roll inflation rather than power-law parameterizations of the spectra. The only other information we use is the measurement of h from the Hubble Space Telescope (HST) Key Project. We find that the spectral index of primordial density perturbations lies in the 1σ range 0.94⩽ns⩽1.04 with no evidence of running. The ratio of the amplitudes of tensor and scalar perturbations is smaller than 0.61 and the inflationary scale is below 2.8×1016 GeV, both at the 2σ C.L. No class of inflation or ekpyrotic/cyclic model is excluded. The λφ4 potential is excluded at 3σ only if the number of e-folds is assumed to be less than 45
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.
Report of the SUGRA Working Group for run II of the Tevatron
No full textWe present an analysis of the discovery reach for supersymmetric particles at the upgraded Tevatron collider, assuming that SUSY breaking results in universal soft breaking parameters at the grand unification scale, and that the lightest supersymmetric particle is stable and neutral. We first present a review of the literature, including the issues of unification, renormalization group evolution of the supersymmetry breaking parameters and the effect of radiative corrections on the effective low energy couplings and masses of the theory. We consider the experimental bounds coming from direct searches and those arising indirectly from precision data, cosmology and the requirement of vacuum stability. The issues of flavor and CP-violation are also addressed. The main subject of this study is to update sparticle production cross sections, make improved estimates of backgrounds, delineate the discovery reach in the supergravity framework, and examine how this might vary when assumptions about universality of soft breaking parameters are relaxed. With 30 fb −1 luminosity and one detector, charginos and neutralinos, as well as third generation squarks, can be seen if their masses are not larger than 200-250 GeV, while first and second generation squarks and gluinos can be discovered if their masses do not significantly exceed 400 GeV. We conclude that there are important and exciting physics opportunities at the Tevatron collider, which will be significantly enhanced by continued Tevatron operation beyond the first phase of Run II
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.
Effective number of neutrinos and baryon asymmetry from BBN and WMAP
No full textAbstractWe place constraints on the number of relativistic degrees of freedom and on the baryon asymmetry at the epoch of Big Bang Nucleosynthesis (BBN) and at recombination, using cosmic background radiation (CBR) data from the Wilkinson Microwave Anisotropy Probe (WMAP), complemented by the Hubble Space Telescope (HST) Key Project measurement of the Hubble constant, along with the latest compilation of deuterium abundances and Hii region measurements of the primordial helium abundance. The agreement between the derived values of these key cosmological and particle physics parameters at these widely separated (in time or redshift) epochs is remarkable. From the combination of CBR and BBN data, we find the 2σ ranges for the effective number of neutrinos Nν and for the baryon asymmetry (baryon to photon number ratio η) to be 1.7–3.0 and 5.53–6.76×10−10, respectively
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
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
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