Order parameters forn-vector spin glasses ind dimensions

We report Monte Carlo simulations of the time-dependent behavior of Edwards-Anderson spin glasses with Gaussian nearest-neighbor exchange, for both spin dimensionalityn and space dimensionalityd from 2 up to 6. A (nearly) logarithmic decay of the Edwards-Anderson order parameter with time is observed for alln and alld, similar to earlier studies forn=1. But the Monte Carlo data forn>1 suggest stronger than those forn=1 that all order parameters considered vanish in thermal equilibrium for nonzero temperature, because the decay forn>1 is faster at the temperatures of interest. For Heisenberg spins (n=3) no significant dependence of the Edwards-Anderson order parameterq on the size of the lattice was observed ford=2,3 and 4, whereas ford=5 and 6,q was smaller for smaller systems (in contrast to thed=5 Ising case). These results are the first Monte Carlo indication of a change in the bulk behavior of Heisenberg spin glasses at dimensionalityd=4. Quenching the system to zero temperature and then applying a field we find that the order parameter , measuring the alignment with respect to the state at zero field, is destroyed by a sufficiently strong magnetic field, for all observedn andd.Sonderforschungsbereich 125 Aachen-Jülich-Köln, FRG     

Annealedn-vectorp-spin model

A disorderedn-vector model withp spin interactions is introduced and studied in mean field theory for the annealed case. We present complete solutions for the casesn=2 andn=3, and have obtained explicit order parameter equations for all the stable solutions for arbitraryn. For alln andp we find one stable high-temperature phase and one stable low-temperature phase. The phase transition is of first order. Forn=2, it is continuous in the order parameters for p4 and has a jump discontinuity in the order parameters ifp>4. Forn=3, it has a jump discontinuity in the order parameters for allp.     

The principal series ofSp(n, ℝ)

The principal series of unitary representations of the noncompact symplectic groupSp(n, ) is constructed for alln. The Lie algebra ofSp(n, ) is isomorphic to the algebra of bilinear products of boson operators inn dimensions. The spectrum of the number operator for the principal series representations is shown to be unbounded, both from above and from below.     

Currents,stress tensor and generalized unitarity in conformal invariant quantum field theory

Matrix elements of internal symmetry currents and energy momentum density tensor are constructed in Migdal Polyakov conformal invariant bootstrap field theory. Their 3-point functions satisfy Bethe Salpeter equations which determine any free coefficients that may still occur in the conformal invariant Ansatz. Ward identities are verified for alln-point functions. They imply correct equal time current commutation relations. A proof of generalized unitarity is also given. Various equivalent forms of the propagator bootstrap are discussed. Our algebraic techniques also yield an eigenvalue equation for first order correction to the exactly conformal invariant theory, assuming the latter is Gell-Mann Low large momentum asymptote of a renormalizable finite mass theory.     

Generalization of the proof on the existence of hidden measurements to experiments with an infinite set of outcomes

We generalize Aerts' proof concerning the existence of hidden measurements for experiments withn outcomes to general experiments with an infinite set of outcomes. More specific we prove that, if is a set of experiments on an entityS with a set of pure states , and alle are such that the outcomes can be represented as a measurable subset of a finite dimensional real space, on which for every initial state of the entity there exists a probability measure, then there exists a hidden measurement representation for this set of experiments.Research Assistant of the National Fund for Scientific Research.Supported by Flanders' Federale Diensten voor Wetenschappelijke, Technische en Culturele Aangelegenheden in the framework of IUAP-III No 9.     

A heuristic theory of phase transitions

LetZ be a suitable Banach space of interactions for a lattice spin system. Ifn+1 thermodynamic phases coexist for ₀ Z, it is shown that a manifold of codimensionn of coexistence of (at least)n+1 phases passes through ₀. There are alson+1 manifolds of codimensionn–1 of coexistence of (at least)n phases; these have a common boundary along the manifold of coexistence ofn+1 phases. And so on for coexistence of fewer phases. This theorem is proved under a technical condition (R) which says that the pressure is a differentiable function of the interaction at ₀ when restricted to some codimensionn affine subspace ofZ. The condition (R) has not been checked in any specific instance, and it is possible that our theorem is useless or vacuous. We believe however that the method of proof is physically correct and constitutes at least a heuristic proof of the Gibbs phase rule.     

Classification of lattices withZ m symmetry

We consider then-dimensional Euclidean lattices withZ _m symmetries. It is shown that such lattices can be considered as ideals of some cyclotomic fields. Therefore we can translate problems about the above lattices into those about number theory. For alln (n22), we have obtained the classification of such lattices.     

A note on differentiability of the cluster density for independent percolation in high dimensions

The cluster density function of independent percolation in ad-dimensional lattice is considered. For eachn, it is shown that(p) has finitenth leftderivative at critical probabilityp _c ifd is sufficiently large. This result agrees with the Bethe lattice approximation, where thenth one-sided derivative of(p) is bounded atp _c for alln.     

Space-time as a micromorphic continuum

We review generally-covariant Lagrangians for the field of linear coframes in ann-dimensional manifold. Discussed are Lagrangians invariant under the internal groupGL(n, ) and under its pseudo-Euclidean subgroups. It is shown that group spaces of semisimple Lie groups and certain of their modifications are natural vacuumlike solutions for allGL(n, )-invariant models. In some sense the signature of space-time may be interpreted as a consequence of differential equations; the velocity of light is an integration constant.     

Quenchedn-vectorp-spin model

A disorderedn-vector model withp spin interactions previously introduced is studied for the quenched case by means of the replica method and a generalized Parisi theory. We present formal solutions for generaln andp and then study the casep . The high-temperature solution is stable at all temperatures and there is only one phase transition at a temperatureT _g. Only longitudinal lowtemperature solutions are possible. There is one spin-glass solution, and it is stable for allT _g. The phase transition atT _g is of first order and displays a jump discontinuity in the order parametersq _j ^(L) andd. The spin-glass free energy is temperature dependent forn > 1 while it is constant whenn = 1.     

Necessity and sufficiency of f being a divergence for vanishing of variational derivatives of f: General case

Concise proofs are presented for the necessity and sufficiency of f being a divergence for the variational derivatives of f to vanish identically, where f is a function of N functions of n variables, their partial derivatives to arbitrary order, and the n variables. The approach is conventional.     

Simplex equations and their solutions

We investigate ann-simplex generalization of the classical and quantum Yang-Baxter equation. For the case ofsl(2) we find the most general solution of the classicaln-simplex equation for alln. These classical solutions can be quantized (in the sense of quantum group theory) forn=2,3 and we exhibit a quantum solution to the tetrahedron equations (n=3). The classical nondegenerate solutions cannot be quantized forn=4.     

q-Sigma-algebra generated by balls

The q--algebra, i.e., the system of sets closed under complementation, countable disjoint unions, and containing the empty set, generated by the system of open balls coincides with the -field of Borel sets inR sun forn=1,2, and 3. A first step to extend the proof forn=4, 5, 6, and 7 is indicated.     

Bell’s Theorem Without Inequalities and Only Two Distant Observers

A proof of Bell's theorem without inequalities and involving only two observers is given by suitably extending a proof of the Bell-Kochen-Specker theorem due to Mermin. This proof is generalized to obtain an inequality-free proof of Bell's theorem for a set of n Bell states (with n odd) shared between two distant observers. A generalized CHSH inequality is formulated for n Bell states shared symmetrically between two observers and it is shown that quantum mechanics violates this inequality by an amount that grows exponentially with increasing n.     

Multiphoton transitions for the harmonic oscillator

2- and 3-photon electric dipole transitions for the harmonic oscillator are shown to have zero intensity. This is extended to the general cases of Δv?=?n and Δv?=?n???2 for n-photon transitions. Although not proved in general, it seems likely that all multiphoton transition moments vanish. This suggests that electric dipole multiphoton transition intensity is due to anharmonicity.     

Intersections of random walks in four dimensions. II

Letf(n) be the probability that the paths of two simple random walks of lengthn starting at the origin in ⁴ have no intersection. It has previously been shown thatf(n)c(logn)^–1/2. Here it is proved that for allr>1/2, .Research Supported by NSF grant MCS-8301037     

Off-diagonal long-range order and superconducting particle density

Relations between the existence of ODLRO in the reduced density matrix _n (for alln1) and that of superconducting currents in a hollow cylinder are discussed. Some concrete behaviours of _n , including the power law decaying behaviour, in the coordinate space representation are considered and the corresponding effective superconducting particle densities are given. Some restraint conditions caused by the existence of the ODLRO (including quasi-ODLRO) have been found and discussions on the minimum unit of flux quantization are also included.     

Critical dynamics and stability of elastically coupled systems at marginal dimensionalities

Static and dynamic behavior of an-component classical model atd=4 has been investigated assuming a coupling to a fluctuating lattice displacement field. Solutions of renormalization-group (RG) equations are given for elastically isotropic and anisotropic systems, and the temperature dependences of elastic constants and of the corresponding damping coefficients are calculated. For isotropic and weakly anisotropic systems it is found that forn<4 the critical regime can be split into a rigid regimet>t _s , and a compressible regimet<t _s , wheret=(T–T _c )/T _c andt _s is a crossover temperature. In the rigid regime, the logarithmic correction factors characterizing deviations from Landau theory have the same form as in systems without elastic coupling; in the compressible regime the exponents are renormalized by the coupling. Forn4 rigid behavior prevails at all temperatures; similarly only rigid behavior is found for strongly anisotropic systems for alln. The thermodynamic stability of the system is investigated by evaluating the contribution of ring diagrams for the casen=1. It is thus shown that under constant hydrostatic pressure a first-order transition occurs in both isotropic and anisotropic systems, and the corresponding equations for the transition temperature and the value of the order parameter atT _c are derived.     

Comment on a paper by G. H. Weiss,S. Havlin,and A. Bunde

A simple proof is pointed out for the asymptotic exponential decay of then-step survival probability of a random walk on a finite lattice with traps in the limit asn . Some bounds are mentioned, which are valid for finiten and for symmetric random walks.     

Classical lattice gas model with a unique nondegenerate but unstable periodic ground state configuration

We construct a classical lattice gas model with a unique periodic ground state configuration such that the Peierls' condition is not satisfied. The ground state configuration is nondegenerate, which means that for any fixed energyE and any integern, the diameter of the support of alln-connected local excitations, with energy less thanE, is bounded. Nevertheless the configuration is not stable: it does not give rise to a low temperature phase. Any translation invariant Gibbs state of our model corresponds to quasiperiodic ground state configurations. This requires the modification of a recent hypothesis of Dobrushin and Shlosman.