Bag model predictions for polarized structure functions and theirQ 2-evolutions

It is shown that modified versions of the MIT bag model can fairly describe non-singlet pieces of experimentally known structure functions if theQ ²-evolution equations are trusted down to the model scale. Further on we utilize these models to study the presently unmeasured transversely polarized structure functionsg ₂ andh ₁. Using recently developed approximate evolution equations we focus on the relevance of the twist-3 contribution tog ₂. Finally, a simple first guess-model for the transversity distributionh ₁ is presented.     

Two methods for discretizing a delta function supported on a level set

This paper presents two new methods for discretizing a Dirac delta function which is concentrated on the zero level set of a smooth function u: Rⁿ  R. The function u is only known at the discrete set of points belonging to a regular mesh covering Rⁿ. These two methods are used to approximate integrals over the manifold defined by the level set. Both methods are conceptually simple and easy to implement. We present the results of numerical experiments indicating that as the mesh size h goes to zero, the rate of convergence is at least O(h) for the first method, and O(h²) for the second method. We perform a limited analysis of the proposed algorithms, including a proof of convergence for both methods.     

Calculation of the indirect nuclear spin-spin coupling constant of the hydrogen molecule by the truncated matrix sum method

The hydrogen molecule coupling constant has been calculated from the second-order perturbation theory summation expression of Ramsey, truncated after the first few terms. The most accurate available wave functions, those of the James-Coolidge type, give a value for the coupling constant of circa 163 hz compared with the experimental value of 278 hz. Values of the largest discrete term (the first term) calculated from various approximate wave functions vary widely. In particular, the calculation analogous to the usual molecular orbital calculation gives a value of 726 hz for the first term (compared with 199 hz calculated from James-Coolidge type wave functions).     

Gauge gravitation theory

The particularity of the gauge gravitation theory is that Dirac fermion fields possess only Lorentz exact symmetries. It follows that different tetrad gravitational fieldsh define nonisomorphic representations _h of cotangent vectors to a space-time manifoldX ⁴ by Dirac's-matrices on fermion fields. One needs these representations in order to construct the Dirac operator defined in terms of jet spaces. As a consequence, gravitational fieldsh fail to form an affine space modeled after any vector space of deviationsh'–h of some background fieldh. They therefore fail to be quantized in accordance with the familiar quantum field theory. At the same time, deformations of representation _h describe deviations ofh such thath + is not a gravitational field. These deviations form a vector space, i.e., satisfy the superposition principle. Their Lagrangian, however, differs from familiar Lagrangians of gravitation theory. For instance, it contains masslike terms.     

On equivalence of Floer's and quantum cohomology

We show that the Floer cohomology and quantum cohomology rings of the almost Kähler manifoldM, both defined over the Novikov ring of the loop space M, are isomorphic. We do it using a BRST trivial deformation of the topological A-model. The relevant aspect of noncompactness of the moduli of pseudoholomorphic instantons is discussed. It is shown nonperturbatively that any BRST trivial deformation of A model which does not change the dimensions of BRST cohomology does not change the topological correlation functions either.     

The dependence of susceptibility on the high-frequency field at ferromagnetic resonance

The dependence of the uniform precession amplitude and susceptibility at ferromagnetic resonance on the high-frequency fieldh is discussed on the basis of an equation for the energy balance and classical equations for the spin wave amplitudes. The dependence (h) is first determined in the lowest non-linear approximation. According to these calculations, the initial decline of the susceptibility differs from Schlömann's quadratic law. The influence of other nonlinear interactions between spin wavesk0 is then discussed on a certain special assumption of the type of two-magnon scattering. It is shown that such interactions can lead to the appearance of a maximum in the h.f. field dependence of the uniform precession amplitude.     

On the layering transition of an SOS surface interacting with a wall. I. Equilibrium results

We consider the model of a 2D surface above a fixed wall and attracted toward it by means of a positive magnetic fieldh in the solid-on-solid (SOS) approximation when the inverse temperature is very large and the external fieldh is exponentially small in . We improve considerably previous results by Dinaburg and Mazel on the competition between the external field and the entropic repulsion with the wall, leading, in this case, to the phenomenon of layering phase transitions. In particular, we show, using the Pirogov-Sinai scheme as given by Zahradník, that there exists a unique critical valueh _k ^* () in the interval (1/4e ^–4k , 4e ^–4k ) such that, for allh(h _k+1 ^* ,h _k ^* ) and large enough, there exists a unique infinite-volume Gibbs state. The typical configurations are small perturbation of the ground state represented by a surface at heightk+1 above the wall. Moreover, for the same choice of the thermodynamic parameters, the influence of the boundary conditions of the Gibbs measure in a finite cube decays exponentially fast with the distance from the boundary. Whenh=h _k ^* () we prove instead the convergence of the cluster expansion for bothk andk+1 boundary conditions. This fact signals the presence of a phase transition. In the second paper of this series we will consider a Glauber dynamics for the above model and we will study the rate of approach to equilibrium in a large finite cube with arbitrary boundary conditions as a function of the external fieldh. Using the results proven in this paper, we will show that there is a dramatic slowing down in the approach to equilibrium when the magnetic field takes one of the critical values and the boundary conditions are free (absent).     

Slow droplet-driven relaxation of stochastic Ising models in the vicinity of the phase coexistence region

We consider the stochastic Ising models (Glauber dynamics) corresponding to the infinite volume basic Ising model in arbitrary dimensiond2 with nearest neighbor interaction and under a positive external magnetic fieldh. Under minimal assumptions on the rates of flip (so that all the common choices are included), we obtain results which state that when the system is at low temperatureT, the relaxation time when the evolution is started with all the spins down blows up, whenh0, as exp((T)/h ^d–1) (the precise results are lower and upper bounds of this form). Moreover, after a time which does not scale withh and before a time which also grows as an exponential of a multiple of 1/h ^d–1 ash0, the law of the state of the process stays, whenh is small, close to the minus-phase of the same Ising model without an external field. These results may be considered as a partial vindication of a conjecture raised by Aizenman and Lebowitz in connection to the metastable behavior of these stochastic Ising models.Partially supported by NSF, under grant DMS 91-00725     

Probabilistic bond percolation in random arrays

We consider the problem of percolation in a system having sites distributed at random, but in which only a fractionh of the physical overlaps form viable links. We convert this to a site problem on the covering lattice, and then show that in two dimensionsh - 1/S ⁴ forh - 1, andh - 4)S² forh 1, whereS is proportional to the critical percolation radius in the original array. This result reproduces the T^–1/3 behavior for log(conductivity) expected of variable-range hopping and found by numerical methods. It also accounts for the region of transition tor-percolation asT . We make a prediction that in three dimensions,h = 1/8S³ + const/S⁶, but numerical confirmation is lacking for this case. While the argument is not exact, we have demonstrated a novel approach to random systems.Supported by the National Research Council of Canada.     

The semiclassical limit for gauge theory onS 2

It is shown that the Yang-Mills measureZ _h ^–1 e^–S()/h[D], whereh>0, describing gauge fields on the two-sphere converges to a probability measure on the moduli space of Yang-Mills connections onS ², ash0.This work was partially supported by NSF Grants DMS-8922941, and PHY-8912067     

h-Deformation of GL(1∣1)

An h-deformation of a (graded) Hopf algebra of functions on supergroup GL(11) is introduced via a contraction of GL _q (11). The deformation parameter h is odd (Grassmann). A related differential calculus on h-superplane is presented.     

Isotropic singularities and isotropization in a class of Bianchi type-VI h cosmologies

The evolution of a class of exact spatially homogeneous cosmological models of Bianchi type VI _h is discussed. It is known that solutions of type VI _h cannot approach isotropy asymptotically at large times. Indeed the present class of solutions become asymptotic to an anisotropic vacuum plane wave solution. Nevertheless, for these solutions the initial anisotropy can decay, leading to a stage of finite duration in which the model is close to isotropy. Depending on the choice of parameters in the solution, this quasi-isotropic stage can commence at the initial singularity, in which case the singularity is of the type known as isotropic or Friedmann-like. The existence of this quasi-isotropic stage implies that these models can be compatible in principle with the observed universe.     

Finite-Volume Glauber Dynamics in a Small Magnetic Field

We consider Glauber dynamics on a finite cube in d-dimensional lattice (d2), which is associated with basic Ising model at temperature T=1/1 under a magnetic field h > 0. We prove that if the effective magnetic field is positive, then the relaxation of the Glauber dynamics in the uniform norm is exponentially fast, uniformly over the size of underlying cube. The result covers the case of the free-boundary condition with arbitrarily small positive magnetic field. This paper is a continuation of an attempt initiated earlier by Schonmann and Yoshida to shed more light on the relaxation of the finite-volume Glauber dynamics when the thermodynamic parameter (, h) is so near the phase transition line, (, h); _c < &h = 0, that the Dobrushin–Shlosman mixing condition is no longer available.     

Bethe-Ansatz solution of the ground-state of theSU (2j+1) Kondo (Coqblin-Schrieffer) model: Magnetization,magnetoresistance and universality

The magnetization, the magnetoresistance and the populations of the spin components of the Coqblin-Schrieffer model forj5/2 are calculated from the Kondo limit of a mixed-valence model discussed previously. The results forj=1/2 andj=1 agree with those given in the literature. Forj3/2 only an approximate solution of the integral equations is given, which interpolates between the exact low and high-field results. The universality is discussed and the exact Wilson-numbers are obtained. The Kondo limit of the mixed-valent model is shown to be equivalent to the Coqblin-Schrieffer model by using the Bethe-ansatz equations.     

Percolation in strongly correlated systems: The massless Gaussian field

We derive a number of new results for correlated nearest neighbor site percolation onZ ^d. We show in particular that in three dimensions the strongly correlated massless harmonic crystal, i.e., the Gaussian random field with mean zero and covariance –, has a nontrivial percolation behavior: sites on whichS _x h percolate if and only ifh _c . with0 _c < . This provides the first rigorous example of a percolation transition in a system with infinite susceptibility.     

Observer-Dependence of Chaos Under Lorentz and Rindler Transformations

The behavior of Lyapunov exponents and dynamical entropies h, whose positivity characterizes chaotic motion, under Lorentz and Rindler transformations is studied. Under Lorentz transformations, and h are changed, but their positivity is preserved for chaotic systems. Under Rindler transformations, and h are changed in such a way that systems, which are chaotic for an accelerated Rindler observer, can be nonchaotic for an inertial Minkowski observer. Therefore, the concept of chaos is observer-dependent.     

Bosons in Disc-Shaped Traps: From 3D to 2D

We present a mathematically rigorous analysis of the ground state of a dilute, interacting Bose gas in a three-dimensional trap that is strongly confining in one direction so that the system becomes effectively two-dimensional. The parameters involved are the particle number, , the two-dimensional extension, , of the gas cloud in the trap, the thickness, of the trap, and the scattering length a of the interaction potential. Our analysis starts from the full many-body Hamiltonian with an interaction potential that is assumed to be repulsive, radially symmetric and of short range, but otherwise arbitrary. In particular, hard cores are allowed. Under the premises that the confining energy, ~ 1/h ², is much larger than the internal energy per particle, and a/h→ 0, we prove that the system can be treated as a gas of two-dimensional bosons with scattering length a _2D = hexp(−(const.)h/a). In the parameter region where , with the mean density, the system is described by a two-dimensional Gross-Pitaevskii density functional with coupling parameter ~ Na/h. If the coupling parameter is and thus independent of a. In both cases Bose-Einstein condensation in the ground state holds, provided the coupling parameter stays bounded.     

Entropy Preservation Under Markov Coding

Using the notion of topological entropy for non-compact sets we prove that for a C ¹⁺ -map with a finite Markov partition the corresponding coding map preserves topological entropy of subsets. We also provide an example of a piecewise linear conformal repeller with a Markov coding decreasing topological entropy. These results are generalized to the notions of u-dimensions.     

Some remarks on pathologies of renormalization-group transformations for the Ising model

The results recently obtained by van Enter, Fernandez, and Sokal on non-Gibbsianness of the measurev =T _{b ,h} arising from the application of a single decimation transformationT _b , with spacingb, to the Gibbs measure _,h , of the Ising model, for suitably chosen large inverse temperature and nonzero external fieldh, are critically analyzed. In particular, we show that if, keeping fixed the same values of, h, andb, one iterates a sufficiently large number of timesn the transformationT _b , one obtains a new measurev = (T _b )_n,h which is Gibbsian and moreover very weakly coupled.     

High-spin states and band structures in the doubly odd <Superscript>136</Superscript>La nucleus

High-spin states of ¹³⁶La have been investigated with the reaction ¹³⁰Te( ¹¹B, 5n) at a beam energy of 60 MeV. The level scheme with three collective bands has been updated with spin up to 20 . The observed h_11/2 h_11/2 band shows -instability with increasing spin according to the TRS calculations. The band crossing and the signature splitting and inversion have been discussed. Other two collective bands based on 12^-and 16⁺ levels were proposed as oblate deformation with -60^°. They most probably originate from four- and six-quasiparticle configurations, that is, h_11/2 g_7/2h_11/2² and g_7/2 g_7/2²d_5/2h_11/2² respectively.