The physics of fine powders: plugging and surface instabilities

The behavior of granular matter depends greatly on the size of its elementary components. Besides the well studied field of granulates made up of large sized particles which ignore the interaction of the particles with the fluid or gas environment, the physics of a collection of tiny particles such as fine or superfine powders concerns a majority of industrial applications. This paper briefly outlines several basic behavior of powders showing that new features come into play when the particle interaction with the surrounding gas is taken into account. It starts from two key mechanisms: the first arises when the typical particle velocity is in the order of the free fall velocity of that particle, which simply means that fluid drag comes into play. The second consists in considering the powder cakes as a porous material. Combining these two basic mechanisms with well-known granulate properties such as avalanching or heaping, leads to previously ignored sets of plugging effects or surface instabilities resulting from what we call the ‘volcano effect’. Furthermore, we show that, up to a certain extent, the physics of fine powders interacting with gas, may mimic the physics of wetting liquids. To cite this article: J. Duran, C. R. Physique 3 (2002) 217–227.     

Cold dark matter in the doublet-triplet model

We analyze in detail a particle physics model which gives rise to light neutrinos as the cold dark matter of the universe. Contrary to the Gelmini-Roncadelli model, our model requires an explicit breaking of the B−L quantum number in the lagrangian.     

Color models of hadrons

The evidence for a three-valued “color” degree of freedom in hadron physics is reviewed. The structure of color model is discussed. Consequences of color models for elementary particle physics are discussed, including saturation properties of hadronic states, π^o → 2ψ and related decays, leptoproduction, and lepton pair annihilation. Signatures are given which distinguish theories with isolated colored particles from those in which color is permanently bound.     

Spontaneous CP violation in the left-right model and the kaon system

A left-right model with spontaneous CP breakdown, consistent with the particle physics phenomenology, is presented. Constraints on free parameters of the model: mass of the new righthanded gauge boson M₂ and ratio r of the two vacuum expectation valuesof the bidoublet, are found from the measurement of ϵ in the kaon system. For most of the parameter space, M₂ is restricted to be below 10 TeV Higher masses can be achieved only by fine tuning of Kobayashi-Maskawa matrix elements, quark masses, r and the phase α which is the unique source of CP violation in the model. Large number of combinations of signs of quark masses, which are observables of the model, are found to be not allowed since they contradict with data. The range of ϵ'/ϵ the model predicts is around 10⁻⁴ in magnitude.     

Models for new particle production in nuclear collisions

Following up our earlier work and also stimulated by recent experimental results on positron production in heavy ion collisions we investigate various mechanisms for the production of a light, previously unknown particle in such collisions. As more conventional mechanisms seem to be inadequate we concentrate on processes directly or indirectly connected with the strong electric or magnetic fields and quark degrees of freedom in nuclei. We also consider modifications of the color confinement scheme. Our analysis is confined to schemes staying within the framework of the standardSU(3)_c ×SU(2)×U(1) model. Since most of the possibilities discussed can be rejected, severe modifications of basic concepts of particle physics seem to be required if the production of a new particle is confirmed.     

Hadron Pt spectra from 0.03 to 6 GeV/c from PHOBOS

We review some of the latest results on identified and non-identified particle spectra for d+Au and Au+Au collisions at √s _NN =200 GeV from the PHOBOS Experiment at RHIC. No enhancement of hadron yields at very low PT is observed. Analysis of the high-PT spectra in d+Au and Au+Au collisions reveal the strong final state effects for central Au+Au collisions. The first measurements of identified particle spectra and particle ratios from the PHOBOS Time of Flight (ToF) detector are presented for d+Au collisions. Detailed results on centrality and pseudorapidity dependence of transverse momentum spectra, which may have important physics implications. are also shown.     

Probing physics at extreme energies with cosmic ultra-high energy radiation

The highest energy cosmic rays observed possess macroscopic energies and their origin is likely to be associated with the most energetic processes in the universe. Their existence triggered a flurry of theoretical explanations ranging from conventional shock acceleration to particle physics beyond the standard model (SM) and processes taking place at the earliest moments of our universe. Furthermore, many new experimental activities promise a strong increase of statistics at the highest energies and a combination with γ-ray and neutrino astrophysics will put strong constraints on these theoretical models. We give an overview over this quickly evolving research field with focus on testing new particle physics.     

New spectra in the HEIDI Higgs models

We study the so-called HEIDI models, which are renormalizable extensions of the standard model with a higher-dimensional scalar singlet field. As an additional parameter we consider a higher-dimensional mixing mass parameter. This leads to enriched possibilities compared to a previous study. We find effective spectral densities of the Higgs propagator, consisting of one, two or no particle peaks, together with a continuum. We compare with the LEP-2 data and determine for which range of the model parameters the data can be described. Assuming two peaks to be present we find for the new mass scale ν≈56±12 GeV, largely independent of the dimension. In the limiting case of d→6 and two peaks we find a higher-dimensional coupling constant α₆=0.70±0.18, indicative of strong interactions among the higher-dimensional fields. This Higgs might escape discovery at the LHC. That would provide a strong physics case for building a new lepton collider.     

More supersymmetric technicolor

We propose a supersymmetric model of particle physics in which supersymmetry is broken by strong gauge forces. Unlike previous realistic supersymmetric technicolor theories, the model contains only one extra strong gauge group, and it lends itself readily to grand unification. The model also has no light axions which can burn out stars. A variety of new particles, many weighing less than 100 GeV, are predicted. A no-go theorem due to Witten is discussed.     

M theory and singularities of exceptional holonomy manifolds

M theory compactifications on G₂ holonomy manifolds, whilst supersymmetric, require singularities in order to obtain non-Abelian gauge groups, chiral fermions and other properties necessary for a realistic model of particle physics. We review recent progress in understanding the physics of such singularities. Our main aim is to describe the techniques which have been used to develop our understanding of M theory physics near these singularities. In parallel, we also describe similar sorts of singularities in Spin(7) holonomy manifolds which correspond to the properties of three dimensional field theories. As an application, we review how various aspects of strongly coupled gauge theories, such as confinement, mass gap and non-perturbative phase transitions may be given a simple explanation in M theory.     

Propagation of Chaos for a Thermostated Kinetic Model

We consider a system of N point particles moving on a d-dimensional torus $\mathbb{T}^{d}$ . Each particle is subject to a uniform field E and random speed conserving collisions $\mathbf{v}_{i}\to\mathbf{v}_{i}'$ with $|\mathbf{v}_{i}|=|\mathbf{v}_{i}'|$ . This model is a variant of the Drude-Lorentz model of electrical conduction (Ashcroft and Mermin in Solid state physics. Brooks Cole, Pacific Grove, 1983). In order to avoid heating by the external field, the particles also interact with a Gaussian thermostat which keeps the total kinetic energy of the system constant. The thermostat induces a mean-field type of interaction between the particles. Here we prove that, starting from a product measure, in the limit N→∞, the one particle velocity distribution f(q,v,t) satisfies a self consistent Vlasov-Boltzmann equation, for all finite time t. This is a consequence of “propagation of chaos”, which we also prove for this model.     

物质结构在夸克-轻子层次上的动力学规律和研究发展趋势

文章综述了粒子物理中标准模型理论的历史发展、面临挑战以及未来的发展趋势.目前阶段物质结构最小组成单元是夸克和轻子,量子色动力学是描述夸克-胶子之间强相互作用的基本理论,它具有渐近自由和夸克禁闭的特点.量子色动力学和电弱统一理论一起构成粒子物理中标准模型理论.标准模型理论成功同时也面临两大挑战:对称性破缺的本质和夸克禁闭难题,这意味着标准模型理论需要发展和突破.人们期望粒子物理学、天文学和宇宙学交叉发展联手解决物质结构和早期宇宙研究中面临的难题,最终揭示超出标准模型的新物理规律.     

A scalar boson as a messenger of new physics

Quantum corrections generate a quadratically divergent mass term for the Higgs boson in the standard model. Thus, if the Higgs boson has a mass of order 100 GeV, it implies the presence of a cut-off of the theory around TeV scale, and some particles associated with the new physics may appear around the cut-off scale Λ. However, if Λ is several TeV, it may be difficult to find such particles at the LHC. In this Letter, we consider a situation in which the new physics provides relatively light particles compared with the scale Λ. In such a situation, we show that diphoton event and four lepton event by the decay of the Higgs and/or a new particle have naturally large cross section, and LHC may test the new physics in a considerably broad parameter region even if Λ is several TeV.     

The large-N limit in statistical physics and the one-particle Schrödinger equation

Nonlinear d-dimensional vector σ models, such as O(N), SU(N), and CP ^N, are considered in the limit of an infinite number of components N. It is shown that the equation for the two-point correlation function in these models is similar to the Schrödinger equation for a quantum particle moving in a δ-function potential well (?T)δ(x), where T is the temperature. This equation adequately describes the systems under study both above and below the Curie point. Within this approach, the critical behavior of the SU(N)-invariant Ginzburg-Landau model in an external uniform magnetic field is determined in the vicinity of the upper critical magnetic field. The critical indices in this case are the same as in the spherical model in a random magnetic field. An exact equation describing the H _c2(T) curve of continuous phase transitions is derived, which allows one to determine the asymptotes of this curve in strong and weak fields. The relation between the one-particle Schrödinger equation and critical phenomena is analyzed, and applications of this method to various models in solid state physics and statistical mechanics are discussed.     

“Red shift” of the surface plasmon resonance absorption by fine metal particles

The plasma resonance absorption of fine metal particles was found by Smithard et al. to shift to longer wavelengths with decreasing particle size.We propose here a hydrodynamic model that allows us to explain this phenomenon in terms of the diffuseness of the metal particle surface. Some new data are also presented, that agree with the findings of Smithard et al.     

Localization of quasiparticles in a disordered vortex

We study the diffusive motion of low-energy normal quasiparticles along the core of a single vortex in a dirty, type-II, s-wave superconductor. The physics of this system is argued to be described by a one-dimensional supersymmetric non-linear σ model, which differs from the σ models known for disordered metallic wires. For an isolated vortex and quasiparticle energies less than the Thouless energy E_Th, we recover the spectral correlations that are predicted by random matrix theory for the universality class C. We then consider the transport problem of transmission of quasiparticles through a vortex connected to particle reservoirs at both ends. The transmittance at zero energy exhibits a weak localization correction reminiscent of quasi-one-dimensional metallic systems with symmetry index β = 1. Weak localization disappears with increasing energy over a scale set by E_Th This crossover should be observable in measurements of the longitudinal heat conductivity of an ensemble of vortices under mesoscopic conditions. In the regime of strong localization, the localization length is shown to decrease by a factor of 8 as the quasiparticle energy goes to zero.     

Photonic dark matter portal and quantum physics

We study a model of dark matter in which the hidden sector interacts with standard model particles via a hidden photonic portal.We investigate the effects of this new interaction on the hydrogen atom,including the Stark,Zeeman and hyperfine effects.Using the accuracy of the measurement of energy,we obtain an upper bound for the coupling constant of the model as f≤10~(-12).We also calculate the contribution from the hidden photonic portal to the anomalous magnetic moment of the muon as α_μ≤ 2.2 × 10~(-23)(for the dark particle mass scale 100MeV),which provides an important probe of physics beyond the standard model.