分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-07-26
摘要: Kibble mechanism drastically underestimates the production of point-like topological defects, as confirmed recently in atomic and condensed matter systems If non-thermally produced, they can be cosmological dark matter of mass 1-10 PeV or heavier If thermalized, skyrimon of mass 1-10 TeV is also a viable dark matter candidate, whose decay may explain e(+/-) spectra in cosmic rays recently measured by PAMELA, FERMI, and HESS Collaborations Models that produce magnetic monopoles below the inflation scale, such as Pati-Salam unification, are ruled out unless new annihilation mechanism for monopoles is introduced (C) 2010 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 explicitly show that split-universal extra dimension (split-UED), a recently suggested extension of universal extra dimension (UED) model, can nicely explain recent anomalies in cosmic-ray positrons and electrons observed by PAMELA and ATIC/PPB-BETS. Kaluza-Klein (KK)dark matters mainly annihilate into leptons because the hadronic branching fraction is highly suppressed by large KK quark masses and the antiproton flux agrees very well with the observation where no excess is found. The flux of cosmic gamma-rays from pion decay is also highly suppressed and hardly detected in low energy region (E-gamma less than or similar to 20GeV). Collider signatures of colored KK particles at the LHC, especially q(1)q(1) production, are studied in detail. Due to the large split in masses of KK quarks and other particles, hard p(T) jets and missing E-T are generated, which make it possible to suppress the standard model background and discover the signals.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-07-05
摘要: Recent studies of precision electroweak observables have led to the conclusion that a fourth generation is highly constrained. However, we point out that a long-lived fourth generation can reopen a large portion of the parameter space. In addition, it preserves baryon and lepton asymmetries against sphaleron erasure even if B - L = 0. It opens up the possibility of exact B - L symmetry and hence Dirac neutrinos. The fourth generation can be observed at the LHC with unique signatures of long-lived particles in the near future. (C) 2011 Elsevier B.V. All rights reserved.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-30
摘要: We address the possibility that CP violation in B-s-(B) over bar (s) mixing may help explain the origin of the cosmic baryon asymmetry. We propose a new baryogenesis mechanism-"electroweak beautygenesis"-explicitly showing that these two CP-violating phenomena can be sourced by a common CP phase. As an illustration, we work in the two-Higgs-doublet model. Because the relevant CP phase is flavor off diagonal, this mechanism is less severely constrained by null results of electric dipole moment searches than other scenarios. We show how measurements of flavor observables by the D0, CDF, and LHCb collaborations test this scenario.