分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-07-08
摘要: Motivated by the recent observation of the high energy electron and positron excesses in cosmic ray by PAMELA and ATIC/PPB-BETS, we suggest an anomaly-free scenario for the universal extra dimension that localizes the standard model quarks and splits the spectrum of Kaluza-Klein (KK) quarks from KK leptons. When the SM quarks are "well localized" at the boundaries, the most stringent bound of the model (1/R > 510 GeV) comes from the resonance search for the Tevatron dijet channels. Even at the early stage of LHC, one can discover the second KK gluon for masses up to 4 TeV.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-07-08
摘要: We discuss general on-shell couplings of a scalar with two Z bosons using an operator analysis. In addition to the operator that originated from the Higgs mechanism, two dimension-five operators, one CP even and one CP odd, are generated only at the loop level. Simple formulas are derived for the differential decay distributions when the Z pair subsequently decays into four leptons by computing the helicity amplitudes, from which it is shown the CP-odd operator merely induces a phase shift in the azimuthal angular distribution between the two decay planes of the Z bosons. We also investigate new physics scenarios giving rise to loop-induced decays of a scalar into the ZZ pair, and argue that the total decay width of such a scalar would be an order-of-magnitude smaller than that of a Higgs boson, should such decays be observed in the early running of the LHC. Therefore, the total decay width alone is a strong indicator of the Higgs nature, or the lack thereof, of a scalar resonance in ZZ final states. In addition, we study the possibility of using the azimuthal angular distribution to disentangle effects among all three operators.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-07-08
摘要: A flavor-nonuniversal chiral color model is introduced. It is used for comparison to the recent data on (p) over barp -> (t) over bart. We concluded that the data are consistent with interpretation as an axigluon exchange within 1 sigma and a unique rise and fall behavior is predicated with regard to the asymmetry A(FB)(t) as a function of t (t) over bar invariant mass, which can distinguish our model from others before one discovers the axigluon resonance. Further aspects of the model are discussed. (C) 2009 Elsevier B.V. All rights reserved.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-07-08
摘要: We consider the recent measurement of the top quark forward-backward asymmetry at the Fermilab Tevatron, which shows a discrepancy of slightly more than 2 sigma compared to the standard model prediction. We find that t-channel exchange of a color sextet or triplet scalar particle can explain the measurement, while leaving the cross section for t (t) over bar production within measured uncertainties. Such particles have good discovery prospects by study of the kinematic structure of t (t) over bar + jets at the LHC.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-07-05
摘要: We discuss the neutrino constraints from solar and terrestrial dark matter (DM) annihilations in the inelastic dark matter (iDM) scenario after the recent CDMS II results. To reconcile the DAMA/LIBRA data with constraints from all other direct experiments, the iDM needs to be light (m(chi) , and tau(+)tau(-). For soft channels such as b (b) over bar and c (c) over bar, the limits are loose, but could be tested or further constrained by future IceCube plus DeepCore. For neutrino constraints from the DM annihilation in the Earth, due to the weaker gravitational effect of the Earth and inelastic capture condition, the constraint exists only for small mass splitting delta < 40 keV and m(chi) similar to (10, 50) GeV even in the tau(+)tau(-) channel.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-07-05
摘要: We propose a gauged Ud(1)(H) horizontal symmetry around a TeV scale that is a subgroup of a SU(3)(H) horizontal gauge symmetry broken at O(10(14)) GeV. The breaking generates right-handed Majorana neutrino masses through a SU(3)(H) sextet scalar. A particular Majorana right-handed neutrino mass matrix explicitly determines the remnant U(1)(H) at low energy which only couples to b - s and mu - tau in the gauge eigenstate. The dangerous K - (K) over bar, D - (D) over bar mixing and B-s -> mu(+) mu(-) are kept to be safe because the relevant couplings are suppressed through high powers of small mixing angles in the fermion rotation matrix. Our analysis which applies to the general case shows that the Tevatron di-muon anomaly can be explained through the B-s and B-d mixing while keeping all the other experimental constraints within 90% C.L. For the B meson decay, the B-s -> mu(+/-) tau(-/+) is the leading leptonic decay channel which is several orders of magnitude below current experimental bounds.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-07-05
摘要: 5D UED is not automatically minimally flavor violating. This is due to flavor asymmetric counter-terms required on the branes. Additionally, there are likely to be higher dimensional operators which directly contribute to flavor observables. We document a mostly unsuccessful attempt at utilizing localization in a flat extra dimension to resolve these flavor constraints while maintaining KK-parity as a good quantum number. It is unsuccessful insofar as we seem to be forced to add brane operators in such a way as to precisely mimic the effects of a double throat warped extra dimension. In the course of our efforts, we encounter and present solutions to a problem common to many extra dimensional models in which fields are "doubly localized:" ultra-light modes. Under scrutiny, this issue seems tied to an intrinsic tension between maintaining Kaluza-Klein parity and resolving mass hierarchies via localization.