We present a recursive procedure to calculate the parameters of the recently introduced multicanonical ensemble and explore the approach for spin glasses. Temperature dependence of the energy, the entropy and other physical quantities are easily calculable and we report results for the zero temperature limit. Our data provide evidence that the large L increase of the ergodicity time is greatly improved. The multicanonical ensemble seems to open new horizons for simulations of spin glasses and other systems which have to cope with conflicting constraints.

Using percolation theory to determine transition points, we show that strongly interacting bulk systems exhibit hadronic matter behaviour for densities 0.48 n o ~< n ~< 14.0 n o and quark matter behavior for n > 3.84 no, where n o = 0.17 fm -3 is nuclear density. For 3.84 n o ~< n ~< 14.0 no, we find a coexistence region of the two phases.Possible phase transitions of strongly interacting matter from a hadron to a quark state have in the past years received considerable attention [1 ]. Recently Baym [2] suggested that this problem might be treated by percolation theory [3] and obtained some first estimates for "percolative" transition points. The aim of this note is to extend his considerations, showing that a percolation approach can provide both an appealing qualitative picture of the transitions in strongly interacting matter and rather reasonable quantitative values tbr the transition densities.Hadrons are on one hand extended objects, on the other built-up of strongly confined quark constituents. The interaction between quarks must provide the scale for both the size of hadrons and for the range of hadronic forces as seen e.g. in typical ("soft" or "small" PT") scattering and production experiments [4]. Let us use this to determine some hadronic size parameters. For simplicity, we assume quarks inside a hadron (e.g., the q-q pair in a pion) as confined in an infinite squarewell potential of radius RQ. If the same range also holds for the "soft" interaction force between to hadrons, then the radius of a hadron as seen in a scattering experiment is 2RQ; at a separation distance r <~ 2RQ, the quarks in each of the collision partners can be close enough to interact; for r > 2RQ, this is impossible (see fig. 1). Hence the volume of a hadron is given by V H = 8 VQ, if VQ = 4nR ~/3 is the size of the confinement sphere or hadronic "core".We can now easily distinguish different density regions. For a many hadron system of density n =-N/V r < 2RQ Fig. 1. Hadronic collision.1 / VH, we have a hadron gas with interactions only during collisions -so we expect at equilibrium a free gas ofhadrons. However, when the density becomes high enough to have arbitrarily large subsystems of clusters of hadrons in simultaneous interaction, then we shall speak of hadronic matter. Although hadronic matter thus provides a connected multihadron system, the quarks involved are in general still associated to a given hadron, as illustrated in fig. 2: all but one of the quarks shown are at distances r > 2RQ from the antiquarl~ x. We are therefore not yet in a density regime corresponding to "delocalized" [2] quarks; this is reached only when the hadronic cores VQ themselves form an interconnected cluster, since with overlapping

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We study the finite temperature deconfinement transition in SU(3) Yang-Mills theory, using a high statistics Monte Carlo evaluation on a 83 X 3 lattice. It is shown to be of first order: at th e critical temperature, there is a clear two-state signal; above and below, we have hysteresis behaviour.At sufficiently high physical temperatures, the SU(N) Yang-Mills system consists of deconfined gluons [ I ] ; at sufficiently low temperatures, we have confinement, and the system consists of gluonium states. The deconfinement transition was first predicted by strong coupling lattice considerations [2] ; for the SU(2) and SU(3) systems, it has in the past two years been studied extensively by Monte Carlo methods [3--7].The transition is related to a global symmetry under the center Z N of the SU(N) gauge group; this symmetry is realized in the "disordered" confinement phase, but broken in the "ordered" deconfinement phase [6]. Thus Z N should characterize tile universality class of the theory, and the critical behaviour of the SU(N) gauge system should parallel that of the corresponding Z N gauge system, it is moreoever conjecture [8] that the universal finite temperature aspects of a (d + l)-dimensional euclidean gauge theory are the same as those of an effective d-dimensional spin theory with only nearest neighbour interactions; this equivalence was shown to hold in the strong coupling limit [2] and is supported by recent Monte Carlo studies of the Z 2 and Z 3 systems [9]. For the SU(2) YangMills system in three space dimensions we thus expect the critical behaviour of the three-dimensional lsing model, while the SU(3) system should correspond to the three-dimensional Z 3 or three-state Potts model i Alexander van llumboldt fellow, on leave from Hacettepe University, Ankara, Turkey.[10]. In particular, this implies that the finite temperature deconfinement transition should be of second order for SU(2), but of first order for SU(3) gauge theory. Previous Monte Carlo results on the SU(2) [3,5,7] and SU(3) [4,7] Yang-Mills systems are qualitatively in accord with this prediction: both order parameter and energy density drop at T c much more rapidly for SU(3) than tbr SU(2), and low statistics SU(3) calculations gave some indications of hysteresis-like behaviour [4]. However, a rapid change of behvaiour can also be due to a sharp second order transition, and preequilibrium behaviour can simulate metastable states. The main aim of the present paper is therefore to establish the order of the deconfinement transition in SU(3)-Yang-Mills theory by a high statistics Monte Carlo analysis, comparing the development of the system when starting from completely ordered and completely disordered initial states at the same coupling value [11].In addition, we shall see that such an evaluation provides a determination of the transition point, which is independent of spatial lattice size; this is to be contrasted to previous determinations using either the average order parameter or the specific heat; both do show such a dependence...

We simulated the Edwards-Anderson Ising spin glass model in three dimensions via the recently proposed multicanonical ensemble. Physical quantities such as energy density, specific heat and entropy are evaluated at all temperatures. We studied their finite size scaling, as well as the zero temperature limit to explore the ground state properties.