Collider signals of unparticle physics

Phenomenology of the notion of an unparticle U, recently perceived by Georgi, to describe a scale invariant sector with a nontrivial infrared fixed point at a higher energy scale is explored in details. Behaving like a collection of d(U) (the scale dimension of the unparticle operator O(U)) invisible massless particles, this unparticle can be unveiled by measurements of various energy distributions for the processes Z-->f f U and e- e+-->gammaU at e- e+ colliders, as well as monojet production at hadron colliders. We also study the propagator effects of the unparticle through the Drell-Yan tree-level process and the one-loop muon anomaly.     

Dark matter and Higgs boson collider implications of fermions in an Abelian-gauged hidden sector

We add fermions to an Abelian-gauged hidden sector. We show that the lightest can be the dark matter with the right thermal relic abundance, and discovery is within reach of upcoming dark matter detectors. We also show that these fermions change Higgs boson phenomenology at the Large Hadron Collider (LHC), and in particular could induce a large invisible width to the lightest Higgs boson state. Such an invisibly decaying Higgs boson can be discovered with good significance in the vector boson fusion channel at the LHC.     

EicC对撞光学设计

EicC是中国科学院近代物理研究所计划建造的中国电子-离子对撞机装置,该对撞机质心能位于20 GeV附近,是研究海夸克的最佳能量窗口,同时还可研究胶子和价夸克。EicC对撞粒子为高极化率质子和电子束团,质子环pRing采用八字环设计方案,可以更好地保持极化质子束团极化率,电子环eRing采用跑道形环设计方案,可以更好地利用隧道空间。该装置电子束流能量中心值为3.5 GeV,电子束RMS发射度为水平方向60 nm·rad,垂直方向60 nm·rad,对撞点b函数为水平方向0.4 m,垂直方向0.12 m;质子束流能量中心值20 GeV,质子束RMS发射度为水平方向300 nm·rad,垂直方向180 nm·rad,对撞点b函数为水平方向0.08 m,垂直方向0.04 m,设计亮度2×1033 cm–2s–1。EicC采用双对撞区非对称光学设计,通过对EicC不同色品补偿方案的研究,最终确定了弧区加短直线节共同补偿的色品补偿方案;通过研究对撞点处b函数以及对撞点间相移对动力学孔径的影响,最终得到pRing动力学孔径大于8 s(s为束团RMS尺寸)、eRing动力学孔径大于20 s,满足大于束团尺寸6 s的要求。     

Collider physics at HERA

From 1992 to 2007, HERA, the first electron-proton collider, operated at cms energies of about 320 GeV and allowed the investigation of deep-inelastic and photoproduction processes at the highest energy scales accessed thus far. This review is an introduction to, and a summary of, the main results obtained at HERA during its operation.     

Geometric fermions

We study the Kähler-Dirac equation which linearizes the laplacian on the space of antisymmetric tensor fields. In flat space-time it is equivalent to the Dirac equation with internal symmetry and on the lattice it reproduces Susskind fermions. The KD equation in curved space-time differs from the Dirac equation by coupling the gravitational field to the internal symmetry generators. This new way of treating fermionic degrees of freedom may lead to a solution of the generation puzzle but is in conflict with the equivalence principle and with Lorentz invariance on the Planck-mass scale.     

Dirac and normal fermions in graphite and graphene: implications of the quantum Hall effect

Spectral analysis of the Shubnikov-de Haas magnetoresistance oscillations and the quantum Hall effect (QHE) measured in quasi-2D highly oriented pyrolytic graphite (HOPG) [Phys. Rev. Lett. 90, 156402 (2003)] reveals two types of carriers: normal (massive) electrons with Berry phase 0 and Dirac-like (massless) holes with Berry phase pi. We demonstrate that recently reported integer- and semi-integer QHEs for bilayer and single-layer graphenes take place simultaneously in HOPG samples.     

Vortices with fermions

Vortex-like solutions of two models involving fermions are found. A method is presented for extracting the anticommuting c-number parameters in the solutions and reducing the equations to ones containing only ordinary numbers.     

中国极化电子—离子对撞机

电磁相互作用把质子与电子束缚起来,形成氢原子。人类对于电磁相互作用的深刻认识发展出智能手机和信息技术,给日常生活带来了极大的便利。相比之下,夸克和胶子如何被强相互作用束缚从而形成质子与中子,人类还缺乏充分的认识。因此,全球的中高能核物理学家提出了建设未来高精度极化电子—离子对撞机以对其进行更深入的研究。文章主要介绍中国极化电子—离子对撞机实验上的物理问题,以及量子色动力学格点计算在这些物理研究中的重要作用。     

Light composite fermions

In this paper we consider the possibility that QCD-like theories can lead to massless or near-massless composite fermions. The method of analysis relies on a conjectured equivalence between the confined and Higgs phases of certain non-abelian gauge theories. This “complementarity” principle allows us to analyze a theory as if the Higgs phenomenon occurred and then reinterpret the results in the language of composite gauge singlets. Those fermions which remain massless in the Higgs picture may then be interpreted as massless fermionic composites.The principle of complementarity, when applied to a class of extended technicolor models, implies that quarks and leptons are composites bound at a scale of order 1–100 TeV.     

Quasi nambu-goldstone fermions

We explore in detail the hypothesis that quarks and leptons are the approximately massless quasi Goldstone fermions of a supersymmetric preon theory. In particular, we discuss the possible patterns of states emerging from the spontaneous breakdown of global symmetries in supersymmetric theories and construct the low-energy effective lagrangians describing the interaction of these states. In contrast to what happens in the Goldstone sector, the interactions of the quasi Goldstone fermions contain arbitrary parameters which directly reflect the preon dynamics. Various models are explored, including both models in which the weak interactions are residual and models where these interactions are fundamental. A variety of issues are addressed, from the universality and approximate SU(2)_L nature of the weak interactions, for the former class of models, to the generation of states beyond the quarks and leptons and the nature of the dynamical breaking of SU(2)_L×U(1), for the latter class of models. Open questions and speculations connected with the origin of families and the nature of fermion mass generation, including supersymmetry breaking, are also discussed.     

On ghost fermions

The path integral for ghost fermions, which is heuristically made use of in the Batalin-Fradkin-Vilkovisky approach to quantization of constrained systems, is derived from first principles. The derivation turns out to be rather different from that of physical fermions since the definition of Dirac states for ghost fermions is subtle. With these results at hand, it is then shown that the nonminimal extension of the Becchi-Rouet-Stora-Tyutin operator must be chosen differently from the notorious choice made in the literature in order to avoid the boundary terms that have always plagued earlier treatments. Furthermore it is pointed out that the elimination of states with nonzero ghost number requires the introduction of a thermodynamic potential for ghosts; the reason is that Schwarz's Lefschetz formula for the partition function of the time-evolution operator is not capable, despite claims to the contrary, to get rid of nonzero ghost number states on its own. Finally, we comment on the problems of global topological nature that one faces in the attempt to obtain the solutions of the Dirac condition for physical states in a configuration space of nontrivial geometry; such complications give rise to anomalies that do not obey the Wess-Zumino consistency conditions. Received: 4 May 2001 / Revised version: 10 October 2001 / Published online: 8 February 2002     

Light composite fermions

't Hooft's conditions for massless composite fermions are discussed. We then study the various mechanisms through which such composite fermions can acquire a small mass. Two new mass generation mechanisms are proposed.     

Quasi goldstone fermions

We discuss a mechanism by which, in theories with an explicitly broken supersymmetry, we can obtain calculable fermion masses, provided certain softly broken R symmetries are incorporated. The corresponding fermion representations are determined by the pattern of internal symmetry breakdown. This mechanism is explicitly studied in a simple U(1) model. Prospects and limitations of this idea for constructing realistic fermion spectra are discussed.     

Two-component theory of fermions

A variation of the theory of fermions is proposed in which the fermions are described by two-component spinors obeying a relativistic equation of the second order. In order to make the probability density of the spin-1/2 particles positive definite, the rule is established that complex conjugation of functions and Hermitian conjugation of operators are accompanied by the operation of spatial reflection. A one-particle theory in Hamiltonian form, a Lagrangian formalism for a free two-component field, and the second quantization of the theory are derived. For calculations in quantum electrodynamics a Hamiltonian is proposed similar to the interaction Hamiltonian of spinless particles with the electromagnetic field but containing a spin-dependent part.Translated from Izvestiya VUZ. Fizika, No. 5, pp. 53–58, May, 1971.