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.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-30
摘要: Both CDF and Dempty set report a forward-backward asymmetry in t (t) over bar production that is above the standard model prediction. We review new physics models that can give a large forward backward asymmetry in t (t) over bar production at the Tevatron and the constraints these models face from searches for dijet resonances and contact interactions, from flavor physics and the t (t) over bar cross section. Expected signals at the LHC are also reviewed.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-30
摘要: We construct a general class of pseudo-Goldstone composite Higgs models, within the minimal SO(5)/SO(4) coset structure, that are not necessarily of moose-type. We characterize the main properties these models should have in order to give rise to a Higgs mass around 125 GeV. We assume the existence of relatively light and weakly coupled spin 1 and 1/2 resonances. In absence of a symmetry principle, we introduce the Minimal Higgs Potential (MHP) hypothesis: the Higgs potential is assumed to be one-loop dominated by the SM fields and the above resonances, with a contribution that is made calculable by imposing suitable generalizations of the first and second Weinberg sum rules. We show that a 125 GeV Higgs requires light, often sub-TeV, fermion resonances. Their presence can also be important for the models to successfully pass the electroweak precision tests. Interestingly enough, the latter can also be passed by models with a heavy Higgs around 320 GeV. The composite Higgs models of the moose-type considered in the literature can be seen as particular limits of our class of models.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-28
摘要: We consider the Higgs portal through which light scalars contribute both to the Higgs production and decay and Higgs effective potential at finite temperature via quantum loops. The positive Higgs portal coupling required by a strongly first order electroweak phase transition is disfavored by the current Higgs data if we consider one such scalar. We observe that by introducing a second scalar with negative Higgs portal coupling, one can not only improve the Higgs fits, but also enhance the strength of first order EWPT. We apply this mechanism to the light stop scenario for electroweak baryogenesis in the MSSM and find a light sbottom could play the role as the second scalar, which allows the stop to be relatively heavier. Non-decoupled effects on the Higgs or sbottom self-interactions from physics beyond MSSM are found to be indispensable for this scenario to work. A clear prediction from the picture is the existence of a light sbottom (below 200 GeV) and a light stop (can be as heavy as 140 GeV), which can be directly tested in the near future.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-28
摘要: After the discovery of a standard model (SM)-like Higgs boson, naturalness strongly favors the next-to-minimal supersymmetric SM. In this letter, we point out that the natural next-to-minimal supersymmetric SM usually predicts the following CP-even Higgs H-i sector: (A) H-2 is the SM-like Higgs boson with mass pushed upward by a lighter H-1 with mass overwhelmingly within [m(H2)/2, m(H2)]; (B) m(H3) similar or equal to 2 mu/sin 2 beta greater than or similar to 300 GeV; (C) H-3 has a significant coupling to the top quark and can decay to H1H2 with a large branching ratio. Using a jet substructure we show that these three Higgs bosons can be discovered via gg -> H-3 -> H1H2 -> b (b) over barl nu jj at the 14 TeV LHC. In particular, the LEP-LHC scenario with H-1 similar or equal to 98 GeV has a very good discovery potential.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-28
摘要: We observe a generic connection between LHC Higgs data and electroweak baryogenesis: the particle that contributes to the CP-odd hgg or h gamma gamma vertex would provide the CP-violating source during a first-order phase transition. It is illustrated in the two Higgs doublet model that a common complex phase controls the lightest Higgs properties at the LHC, electric dipole moments, and the CP-violating source for electroweak baryogenesis. We perform a general parametrization of Higgs effective couplings and a global fit to the LHC Higgs data. Current LHC measurements prefer a nonzero phase for tan beta less than or similar to 1 and electric dipole moment constraints still allow an order-one phase for tan beta similar to 1, which gives sufficient room to generate the correct cosmic baryon asymmetry. We also give some prospects in the direct measurements of CP violation in the Higgs sector at the LHC.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-27
摘要: We analyze the observational potential of single t' production in both the t' -> bW and t' -> th decay channels at 8 TeV LHC using an integrated luminosity of 25 fb(-1). Our analysis is based on a simplified model with minimal coset SO(5)/SO(4) in which the t' is a singlet of the unbroken SO(4). The single t' production, as a consequence of electroweak symmetry breaking, is less kinematically suppressed, associated with a light forward jet and has boosted decay products at the 8 TeV LHC. Therefore it provides the most promising channel in searching for a heavy t'. We have exploited the above kinematical features and used the jet substructure method to reconstruct the boosted Higgs in th decay channel. It is shown that a strong constraint on the t'bW coupling (g(t'bW)/g(tbW,SM) < 0.2 similar to 0.3) at the 95% C. L. can be obtained for m(t') subset of (700, 1000) GeV.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-27
摘要: We study Higgs diphoton decays, in which both photons undergo nuclear conversion to electron-positron pairs. The kinematic distribution of the two electron-positron pairs may be used to probe the CP violating (CPV) coupling of the Higgs to photons, that may be produced by new physics. Detecting CPV in this manner requires interference between the spin-polarized helicity amplitudes for both conversions. We derive leading order, analytic forms for these amplitudes. In turn, we obtain compact, leading-order expressions for the full process rate. While performing experiments involving photon conversions may be challenging, we use the results of our analysis to construct experimental cuts on certain observables that may enhance sensitivity to CPV. We show that there exist regions of phase space on which sensitivity to CPV is of order unity. The statistical sensitivity of these cuts are verified numerically, using dedicated Monte-Carlo simulations.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-27
摘要: We perform a detailed semianalytical analysis of the electroweak phase transition (EWPT) property in the Next-to-Minimal Supersymmetric standard model, which serves as a good benchmark model in which the 126 GeV Higgs mixes with a singlet. In this case, a strongly first-order electroweak phase transition (SFOEWPT) is achieved by the tree-level effects, and the phase transition strength gamma(c) is determined by the vacua energy gap at T = 0. We make an anatomy of the energy gap at both tree level and loop level and extract out a dimensionless phase transition parameter R-kappa equivalent to 4 kappa v(s)/A(kappa), which can replace A(kappa) in the parameterization and affect the light CP-odd/even Higgs spectra. We find that SFOEWPT only occurs in R-kappa similar to -1 and positive R-kappa less than or similar to O(10), which in the non-PQ limit case would prefer either a relatively light CP-odd or CP-even Higgs boson similar to(60, 100) GeV, and therefore serves as a smoking gun signal and requires new search strategies at the LHC.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-27
摘要: With the assistance of two extra groups, i.e., an extra hidden gauge group SU(2)(D) and a global U(1) group, we propose a two component dark matter (DM) model. After the symmetry SU(2)(D) x U(1) being broken, we obtain both the vector and scalar DM candidates. The two DM candidates communicate with the standard model (SM) via three Higgs as multi-Higgs portals. The three Higgs are mixing states of the SM Higgs, the Higgs of the hidden sector and real part of a supplement complex scalar singlet. We study relic density and direct detection of DM in three scenarios. The resonance behaviors and interplay between the two component DM candidates are represented through investigating of the relic density in the parameter spaces of the two DMs masses. The electroweak precision parameters constrains the two Higgs portals couplings (lambda(m) and delta(2)). The relevant vacuum stability and naturalness problem in the parameter space of lambda(m) and delta(2) are studied as well. The model could alleviate these two problems in some parameter spaces under the constraints of electroweak precision observables and Higgs indirect search.
分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2016-06-26
摘要: A quantization scheme for an ideal loss-less mesoscopic left-handed transmission lines (LH TL) unit cell equivalent circuit is proposed and the fluctuations of the current and the voltage of the LH TL equivalent circuit in thermal Fock space are studied by thermal field dynamics (TFD) theory. In thermal Fock state the negative refractive index (NRI) of the LH TL unit cell equivalent circuit is discussed. The results indicate that the quantum fluctuations show the linear dependent of NRI at some temperature, while the frequency and the thermal photons are destructive dependent of NRI within the microwave frequency band. When the unit cell equivalent circuit operates at the rising temperature, the NRI is decreasing. The results demonstrates the ideal loss-less mesoscopic LH TL equivalent circuit operating at a lower frequency, temperature and with little thermal photons is more conducive to NRI, which coincides with the macroscopic real LH TL.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-24
摘要: The gamma-ray excess observed by the Fermi-LAT in the Galactic Center can be interpreted by the dark matter annihilation to b (b) over bar via a light pseudoscalar in the next-to-minimal supersymmetric standard model (NMSSM). It is interesting to note that the corresponding singlet scalar is useful to achieve a strongly first-order phase transition required by the electroweak baryogenesis. In this paper, we investigate the possibility that the NMSSM model can simultaneously accommodate these two issues. The phase transition strength can be characterized by the vacua energy gap at zero temperature and be sufficiently enhanced by the tree-level effect in the NMSSM. We find that the annihilation of singlino/Higgsino dark matter (DM) particles occurring close to the light pseudoscalar resonance is favored by the Galactic Center excess and the observed DM relic density, and some resulting regions in the parameter space with a small kappa/lambda. and a negative A. can simultaneously account for a successful strongly first-order electroweak phase transition.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-24
摘要: We present a class of cancellation conditions for suppressing the total contributions of Barr-Zee diagrams to the electron electric dipole moment (eEDM). Such a cancellation is of particular significance after the new eEDM upper limit was released by the ACME Collaboration, which strongly constrains the allowed magnitude of CP violation in Higgs couplings and hence the feasibility of electroweak baryogenesis (EWBG). Explicitly, if both the CP-odd Higgs-photon-photon (Z boson) and the CP-odd Higgs-electron-positron couplings are turned on, a cancellation may occur either between the contributions of a CP-mixing Higgs boson, with the other Higgs bosons being decoupled, or between the contributions of CP-even and CP-odd Higgs bosons. With a cancellation, large CP violation in the Higgs sector is still allowed, yielding successful EWBG. The reopened parameter regions would be probed by future neutron, mercury EDM measurements, and direct measurements of Higgs CP properties at the Large Hadron Collider Run II and future colliders.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-24
摘要: The W W production is the primary channel to directly probe the triple gauge couplings. We first analyze the e (+) e (-) -> W (+) W (-) process at the future lepton collider, China's proposed Circular Electron-Positron Collider (CEPC). We use the five kinematical angles in this process to constrain the anomalous triple gauge couplings and relevant dimension six operators at the CEPC up to the order of magnitude of 10(-4). The most sensible information is obtained from the distributions of the production scattering angle and the decay azimuthal angles. We also estimate constraints at the 14 TeV LHC, with both 300 fb(-1) and 3000 fb(-1) integrated luminosity from the leading lepton p (T) and azimuthal angle difference Delta I center dot (ll) distributions in the di-lepton channel. The constrain is somewhat weaker, up to the order of magnitude of 10(-3). The limits on the triple gauge couplings are complementary to those on the electroweak precision observables and Higgs couplings. Our results show that the gap between sensitivities of the electroweak and triple gauge boson precision can be significantly decreased to less than one order of magnitude at the 14 TeV LHC, and that both the two sensitivities can be further improved at the CEPC.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-24
摘要: We present a new probe of strongly coupled electroweak symmetry breaking at the 14 TeV LHC by measuring a phase shift in the event distribution of the decay azimuthal angles in massive gauge boson scattering. One generically expects a large phase shift in the longitudinal gauge boson scattering amplitude due to the presence of broad resonances. This phase shift is observable as an interference effect between the strongly interacting longitudinal modes and the transverse modes of the gauge bosons. We find that even very broad resonances of masses up to 900 GeV can be probed at 3 sigma significance with a 3000 fb(-1) run of the LHC by using this technique. We also present the estimated reach for a future 50 TeV proton-proton collider.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-06-24
摘要: We explain the recent diphoton excesses around 750 GeV by both ATLAS and CMS as a singlet scalar Phi which couples to SM gluon and neutral gauge bosons only through higher-dimensional operators. A natural explanation is that Phi is a pseudo-Nambu-Goldstone boson (pNGB) which receives parity violation through anomaly if there exists a hidden strong dynamics. The singlet and other light pNGBs will decay into two SM gauge bosons and even serves as the metastable colored states which can be probed in the future. By accurately measuring their relative decay and the total production rate in the future, we will learn the underlying strong dynamics parameter. The lightest baryon in this confining theory could serve as a viable dark matter candidate.
分类: 物理学 >> 凝聚态:结构、力学和热性能 分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间: 2016-06-23
摘要: Metal-intercalated iron selenides are a class of superconductors that have received much attention but less understood in comparison with their FeAs-based counterparts. Here, the controversial issues such as Fe vacancy, the real phase responsible for superconductivity and lattice stability have been addressed based on first-principles calculations. New insights on the distinct features in terms of carrier doping have been revealed.
分类: 图书馆学、情报学 >> 图书馆学 提交时间: 2016-06-20
摘要: [摘 要] 开展开放科技资源建设对促进科技资源的传播和利用,提升图书馆的信息服务能力有重大意义。[摘 要] 开展开放科技资源建设对促进科技资源的传播和利用,提升图书馆的信息服务能力有重大意义。当前5个著名的国外开放科技资源建设项目(OPENDOAR、BASE、PMC、eDOC及PLOS)在资源发现及获取、质量控制、利用机制、服务开发4个方面均可资借鉴。我国图书馆在开展开放科技资源建设时,除了要汲取国外经验,还要注重开放科技资源的评价和遴选、完善开放资源的利用机制、重视开放资源的长期保存。
分类: 计算机科学 >> 计算机网络 提交时间: 2016-06-19
摘要: 多媒体无线传感器网络所具有数据量大、能耗高等特性易导致网络拥塞,通过构建多路径,节点级拥塞检测与流量调度机制,实现拥塞节点调控和拥塞缓解,从而提出了带有拥塞控制机制的多路径路由协议。给出了实际的报文封装、协议时序交互,并做了TinyOS下代码实现,灌装在实际节点中,在北京市昌平区前蔺沟村现代农业示范基地实测环境下运行正常。理论仿真也验证了所提机制可提高多媒体数据传输能量高效性,延长网络生存时间。
分类: 计算机科学 >> 自然语言理解与机器翻译 提交时间: 2016-06-18
摘要: This letter presents a perceptually weighted analysis -by-synthesis vector quantization (VQ) algorithm for low bit rate MFCC codec. Different from conventional VQ of MFCCs vector, this algorithm uses an analysis-by-synthesis technique and aims to minimize the perceptually weighted spectral reconstruction distortion rather than the distortion of MFCCs vector itself. Also, to reduce the computational complexity, we propose a practical suboptimal codebook searching technique and embed it into the split and multistage vector quantization framework. Objective and subjective experimental results for Mandarin speech show that the proposed algorithm yields intelligible and natural sounding speech for speech coding at 600--2400 bit/s. Compared to current VQ in MFCC codec, the output speech quality is substantially improved in terms of frequency-weighted segmental SNR, STOI, PESQ and MOS score.