Building designed granular towers one drop at a time

A dense granular suspension dripping on an imbibing surface is observed to give rise to slender mechanically stable structures that we call granular towers. Successive drops of grain-liquid mixtures are shown to solidify rapidly upon contact with a liquid absorbing substrate. A balance of excess liquid flux and drainage rate is found to capture the typical growth and height of the towers. The tower width is captured by the Weber number, which gives the relative importance of inertia and capillary forces. Various symmetric, smooth, corrugated, zigzag, and chiral structures are observed by varying the impact velocity and the flux rate from droplet to jetting regime.     

From Dark Energy &; Dark Matter to Dark Metric

We present a new approach to the mathematical objects of General Relativity in terms of which a generic f(R)-gravity theory gravitation is written in a first-order (à la Palatini) formalism, and introduce the concept of Dark Metric which could bypass the emergence of disturbing concepts as Dark Energy and Dark Matter. These issues are related to the fact that General Relativity could not be the definitive theory of Gravitation due to several shortcomings that come out both from theoretical and experimental viewpoints. At large scales, the attempts to match it with the recent observational data lead to invoke Dark Energy and Dark Matter as the bulk components of the cosmic fluid. Since no final evidence, at fundamental level, exists for such ingredients, it could be useful to reconsider the gravitational sector in order to see if suitable extensions of General Relativity could solve the shortcomings present at infrared scales.     

Dark nematicons

We experimentally demonstrate and model dark spatial solitons in azo-doped liquid crystals, in the presence of saturation and nonlocality of the effective nonlinearity due to changes in molecular order. The guiding properties of dark solitons are probed with a weak input of different wavelength.     

Dark Equations

Abstract

Observing the Universe, astronomers have concluded that the motion of stars can not be accounted for unless one assumes that most of the mass in the Universe is carried on by a “dark matter”, so far impervious to all attempts at being detected. There is now a similar concept of “dark energy”. I shall discuss a different subject, “dark equations”. These have never indicated that they influence anything or even exist, but if one supposes that they do exist, one can systematically discover them and study their properties, some of which turn out to be strange and others mysterious. These equations are similar in spirit to what one gets when linearizing a given system, or studies how an external linear wave interacts with a particular solution of a given system. We define and study linear extensions of dynamical systems in general, and integrable and Hamiltonian systems in particular. Systems discussed include the KdV and mKdV equations and the associated Miura maps, the Burgers hierarchy and the associated Hopf–Cole transformations, long wave equations, the Benney hierarchy, and the KP hierarchy.     

Dark matters

Despite the new results on the estimate of cosmological parameters, the need for dark matter, both baryonic and nonbaryonic, galactic and intergalactic, is still with us. For baryonic dark matter the remaining possibilities are mostly either intergalactic hot gas or massive compact halo objects. For nonbaryonic dark matter the most likely candidates are the so-called WIMPs, the prototype of which could be the lightest supersymmetric particle. These particles are actively searched for at accelerators and, in our neighborhood, through direct detection or by their annihilation products.     

Dark Supersymmetry

We propose a model of Dark Supersymmetry, where a supersymmetric dark sector is coupled to the classically scale invariant non-supersymmetric Standard Model through the Higgs portal. The dark sector contains a mass scale that is protected against radiative corrections by supersymmetry, and the portal coupling mediates this scale to the Standard Model, resulting in a vacuum expectation value for the Higgs field and the usual electroweak symmetry breaking mechanism. The supersymmetric dark sector contains dark matter candidates, and we show that the observed dark matter abundance is generated for a natural choice of parameters, while avoiding the current experimental bounds on direct detection. Future experiments can probe this scenario if the dark sector mass scale is not too high.     

Dark Matter

I review the development of the concept of dark matter. The dark matter story passed through several stages, from a minor observational puzzle to a major challenge for theory of elementary particles. Modern data suggest that dark matter is the dominant matter component in the Universe and that it consists of some unknown non-baryonic particles. Dark matter is the dominant matter component in the Universe; therefore, properties of dark matter particles determine the structure of the cosmic web.     

暗物质与暗能量

美国《science》期刊所评2003年十大科学成就中将“证实了宇宙主要由神秘的暗物质和暗能量组成”列为首项：“宇宙是平直的；宇宙中存在4．4％重子物质，22．6％暗物质和73％暗能量．”这是科学家们分析了威尔金森微波各向异性探测器(Wilkinson Mi-     

Dark matter in Susy models

Direct detection experiments for neutralino dark matter in the Milky Way are examined within the framework of SUGRA models with R-parity invariance and grand unification at the GUT scale, M _G. Models of this type apply to a large number of phenomena, and all existing bounds on the SUSY parameter space due to current experimental constraints are included. For models with universal soft breaking at M _G (mSUGRA), the Higgs mass and b → sγ constraints imply that the gaugino mass, m _1/2, obeys m _1/2>300–400 GeV, putting most of the parameter space in the coannihilation domain, where there is a relatively narrow band in the m ₀-m _1/2 plane. For μ>0, we find that the neutralino-proton cross section is ?10^?10 pb for m _1/2<1 TeV, making almost all of this parameter space accessible to future planned detectors. For μ<0, however, there will be large regions of parameter space with cross sections <10^?12 pb and, hence, unaccessible experimentally. If, however, the muon magnetic moment anomaly is confirmed, then μ>0 and m _1/2?800 GeV. Models with nonuniversal soft breaking in the third generation and Higgs sector can allow for new effects arising from additional early Universe annihilation through the Z-channel pole. Here, cross sections that will be accessible in the near future to the next generation of detectors can arise, and can even rise to the large values implied by the DAMA data. Thus, dark matter detectors have the possibility of studying the post-GUT physics that control the patterns of soft breaking.     

Dark solitons in mode-locked lasers

Dark soliton formation in mode-locked lasers is investigated by means of a power-energy saturation model that incorporates gain and filtering saturated with energy, and loss saturated with power. It is found that general initial conditions evolve (mode-lock) into dark solitons under appropriate requirements also met in experimental observations. The resulting pulses are essentially dark solitons of the unperturbed nonlinear Schr?dinger equation. Notably, the same framework also describes bright pulses in anomalous and normally dispersive lasers.     

Dark matter in quantum gravity

We show that quantum gravity, whatever its ultra-violet completion might be, could account for dark matter. Indeed, besides the massless gravitational field recently observed in the form of gravitational waves, the spectrum of quantum gravity contains two massive fields respectively of spin 2 and spin 0. If these fields are long-lived, they could easily account for dark matter. In that case, dark matter would be very light and only gravitationally coupled to the standard model particles.     

Dark quark domains

Formation of stable domains filled with strongly correlated coherent quark matter is discussed in general terms and is exemplified further in the framework of the generalized Nambu-Jona-Lasinio model. It is argued that such domains, if exist in the Universe, appear dark to an external observer.     

暗物质的理论研究进展

文章简要综述了以下内容:(1)晴物质存在的证据,以及它为什么很可能与目前粒子物理研究紧密相关;(2)晴物质的性质,并以超对称模型和额外维模型为例,讨论了包含暗物质粒子的模型;(3)最近Pamela/Atic/Fermi实验观测对于暗物质性质的新认识;(4)讨论和展望.