It is becoming increasingly clear that the concept of a diquark (a two-quark system) is important for understanding hadron structure and high-energy particle reactions. According to our present knowledge of quantum chromodynamics (QCD), diquark correlations arise in part from spin-dependent interactions between two quarks, from quark radial or orbital excitations, and from quark mass differences. Diquark substructures affect the static properties of baryons and the mechanisms of baryon decay. Diquarks also play a role in hadron production in hadron-initiated reactions, deep-inelastic lepton scattering by hadrons, and in e + e~ reactions. Diquarks are important in the formation and properties of baryonium and mesonlike semistable states. Many spin effects observed in high-energy exclusive reactions pose severe problems for the pure quark picture of baryons and might be explained by the introduction of diquarks as hadronic constituents. There is considerable controversy, not about the existence of diquarks in hadrons, but about their properties and their effects. In this work a broad selection of the main ideas about diquarks is reviewed.

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Some H ii regions surrounding young stellar clusters contain tiny dusty clouds, which on photos look like dark spots or teardrops against a background of nebular emission. From our collection of H images of 10 H ii regions gathered at the Nordic Optical Telescope, we found 173 such clouds, which we call ''globulettes,'' since they are much smaller than normal globules and form a distinct class of objects. Many globulettes are quite isolated and located far from the molecular shells and elephant trunks associated with the regions. Others are attached to the trunks (or shells), suggesting that globulettes may form as a consequence of erosion of these larger structures. None of our objects appear to contain stellar objects. The globulettes were measured for position, dimension, and orientation, and we find that most objects are smaller than 10 kAU. The Rosette Nebula and IC 1805 are particularly rich in globulettes, for which the size distributions peak at mean radii of $2.5 kAU, similar to what was found by Reipurth and coworkers and De Marco and coworkers for similar objects in other regions. We estimate total mass and density distributions for each object from extinction measures and conclude that a majority contain <13 M J , corresponding to planetary-mass objects. We then estimate the internal thermal and potential energies and find, when also including the effects from the outer pressure, that a large fraction of the globulettes could be unstable and would contract on short timescales, <10 6 yr. In addition, the radiation pressure and ram pressure exerted on the side facing the clusters would stimulate contraction. Since the globulettes are not screened from stellar light by dust clouds farther in, one would expect photoevaporation to dissolve the objects. However, surprisingly few objects show bright rims or teardrop forms. We calculate the expected lifetimes against photoevaporation. These lifetimes scatter around 4 ; 10 6 yr, much longer than estimated in previous studies and also much longer than the free-fall time. We conclude that a large number of our globulettes have time to form central low-mass objects long before the ionization front, driven by the impinging Lyman photons, has penetrated far into the globulette. Hence, the globulettes may be one source in the formation of brown dwarfs and free-floating planetary-mass objects in the galaxy.

PACS. 12.15.Ff -Quark and lepton masses and mixing. PACS. 12.60.Rc -Composite models. PACS. 14.60.St -Non-standard-model neutrinos, right-handed neutrinos, etc..Abstract. -Quarks, leptons and heavy vector bosons are suggested to be composed of stable spin-1/2 preons, existing in three flavours, combined according to simple rules. Straightforward consequences of an SU (3) preon-flavour symmetry are the conservation of three lepton numbers, oscillations and decays between some neutrinos, and the mixing of the d and s quarks, as well as of the vector fields W 0 and B 0 . We find a relation between the Cabibbo and Weinberg mixing angles, and predict new (heavy) leptons, quarks and vector bosons, some of which might be observable at the Fermilab Tevatron and the future CERN LHC. A heavy neutrino might even be visible in existing data from the CERN LEP facility.Introduction. -The phenomenological success of the standard model of quarks and leptons, and their observed patterns, indicate that there exist a more fundamental basis. Here we present a simple preon model where leptons, quarks and heavy vector bosons are composite, and where many of the ad hoc ingredients of the standard model are clear-cut consequences of this inner structure. We limit the present discussion to straightforward, qualitative consequences of the model, and leave a more quantitative analysis, requiring extra assumptions, to future publications.Although there is currently no direct experimental evidence for (or against) preons, there are quite a few phenomenological, and logical, circumstances that point at compositeness, some of which have been known for long [1]:• There are "too many" leptons and quarks, but still a pattern among them. Historically, such patterns have led to ideas about compositeness, with the quark model as a modern example, and the periodic system as an older one.• The least elegant (mathematical) features of the standard model are due to the weak gauge bosons being massive (and unstable and of different charges). They might be preon-antipreon states, in analogy to the nuclear force being "leaked" by quark-antiquark states. If so, there is no fundamental weak force, nor a Higgs mechanism. The photon-Z 0 mixing is equivalent to the photon-ρ 0 mixing in the vector-dominance model.

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