分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The effects of a scalar field, known as the "assistant field," which nonminimally couples to gravity, on single-field inflationary models are studied. The analysis provides analytical expressions for inflationary observables such as the spectral index ($n_s$), the tensor-to-scalar ratio ($r$), and the local-type nonlinearity parameter ($f_{\rm NL}^{(\rm local)}$). The presence of the assistant field leads to a lowering of $n_s$ and $r$ in most of the parameter space, compared to the original predictions. In some cases, $n_s$ may increase due to the assistant field. This revives compatibility between ruled-out single-field models and the latest observations by Planck-BICEP/Keck. The results are demonstrated using three example models: loop inflation, power-law inflation, and hybrid inflation.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2017-08-24
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 SM quarks and splits the spectrum of 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： 2017-08-24
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 (Eγ . 20 GeV). Collider signatures of colored KK particles at the LHC, especially q1q1 production, are studied in detail. Due to the large split in masses of KK quarks and other particles, hard pT jets and missing ET 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： 2017-08-24
摘要： Kaluza-Klein dark matter is an attractive weakly interacting massive particle in universal extra dimension model. In the recent extension ”split-UED”, annihilation of Kaluza-Klein dark matter with a mass range 600−1000 GeV provides excellent fits to the recently observed excesses in cosmic electron and positron fluxes of Pamela, ATIC and Fermi-LAT experiments. The cosmic gamma-ray flux in the same process can be significant around 300 GeV, thus can be observed or constrained by the forthcoming Fermi-LAT diffuse gamma-ray data. The collider signal at the LHC is the resonance in the dijets channels and the large missing energy in the missing energy plus jets.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2017-08-24
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
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2017-08-03
摘要： We propose a gauged U(1)H horizontal symmetry around TeV scale that is a subgroup of a SU(3)H horizontal gauge symmetry broken at O(1014) 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 µ−τ in the gauge eigenstate. The dangerous K − K¯ , D − D¯ mixing and Bs → µ +µ − 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 Bs and Bd mixing while keeping all the other experimental constraints within 90 % C. L. For the B meson decay, the Bs → µ ±τ ∓ is the leading leptonic decay channel which is several orders of magnitude below current experimental bound
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