The O(2) model in polar coordinates at nonzero temperature

We study the restoration of spontaneously broken symmetry at nonzero temperature in the framework of the O(2) model using polar coordinates. We apply the CJT formalism to calculate the masses and the condensate in the double-bubble approximation, both with and without a term that explicitly breaks the O(2) symmetry. We find that, in the case with explicitly broken symmetry, the mass of the angular degree of freedom becomes tachyonic above a temperature of about 300 MeV. Taking the term that explicitly breaks the symmetry to be infinitesimally small, we find that the Goldstone theorem is respected below the critical temperature. However, this limit cannot be performed for temperatures above the phase transition. We find that, no matter whether we break the symmetry explicitly or not, there is no region of temperature in which the radial and the angular degree of freedom become degenerate in mass. These results hold also when the mass of the radial mode is sent to infinity.Comment: 23 pages, 10 figure

Observation of the 5p Rydberg states of sulfur difluoride radical by resonance-enhanced multiphoton ionization spectroscopy

Sulfur difluoride radicals in their ground state have been produced by a "laser-free" pulsed dc discharge of the SF$_{6}$/Ar gas mixtures in a supersonic molecular beam and detected by mass-selective resonance-enhanced multilphoton ionization (REMPI) spectroscopy in the wavelength range of 408 - 420 nm. Analyses of the (3 + 1) REMPI excitation spectrum have enabled identification of three hitherto unknown Rydberg states of this radical. Following the Rydberg state labeling in our previous work [see J. Phys. Chem. A 102, 7233 (1998)], these we label the K(5p$_{1}$) [$nu_{0-0}$ = 71 837 cm$^{-1}$, $omega_{1}^{'}$(a$_{1}$ sym str) = 915 cm$^{-1}$], L(5p$_{2}$) [$nu_{0-0}$ = 72 134 cm$^{-1}$, $omega_{1}^{'}$(a$_{1}$ sym str) = 912 cm$^{-1}$], and M(5p$_{3}$) [$nu_{0-0}$ = 72 336 cm$^{-1}$, $omega_{1}^{'}$(a$_{1}$ sym str) = 926 cm$^{-1}$] Rydberg states, respectively. [Origins, relative to the lowest vibrational level of the X$^{1}$A$_{1}$ ground state, and vibrational frequencies of the symmetric S-F stretching mode are suggested by the numbers in brackets.] Photofragmentation process of SF$_{2}$$^{+}$--SF$^{+}$ + F that relates to the REMPI spectrum was discussed.Comment: 17 pages, 1 table, 2 figure

Finite temperature density matrix and two-point correlations in the antiferromagnetic XXZ chain

We derive finite temperature versions of integral formulae for the two-point correlation functions in the antiferromagnetic XXZ chain. The derivation is based on the summation of density matrix elements characterizing a finite chain segment of length $m$. On this occasion we also supply a proof of the basic integral formula for the density matrix presented in an earlier publication.Comment: 35 page

Form factor expansion for thermal correlators

We consider finite temperature correlation functions in massive integrable Quantum Field Theory. Using a regularization by putting the system in finite volume, we develop a novel approach (based on multi-dimensional residues) to the form factor expansion for thermal correlators. The first few terms are obtained explicitly in theories with diagonal scattering. We also discuss the validity of the LeClair-Mussardo proposal.Comment: 41 pages; v2: minor corrections, v3: minor correction

Weak Interactions in Dimethyl Sulfoxide (DMSO)-Tertiary Amide Solutions: The Versatility of DMSO as a Solvent

The structures of equimolar mixtures of the commonly used polar aprotic solvents dimethylformamide (DMF) and dimethylacetamide (DMAc) in dimethyl sulfoxide (DMSO) have been investigated via neutron diffraction augmented by extensive hydrogen/deuterium isotopic substitution. Detailed 3-dimensional structural models of these solutions have been derived from the neutron data via Empirical Potential Structure Refinement (EPSR). The intermolecular center-of-mass (CoM) distributions show that the first coordination shell of the amides comprises ∼13-14 neighbors, of which approximately half are DMSO. In spite of this near ideal coordination shell mixing, the changes to the amide-amide structure are found to be relatively subtle when compared to the pure liquids. Analysis of specific intermolecular atom-atom correlations allows quantitative interpretation of the competition between weak interactions in the solution. We find a hierarchy of formic and methyl C-H···O hydrogen bonds forms the dominant local motifs, with peak positions in the range of 2.5-3.0 Å. We also observe a rich variety of steric and dispersion interactions, including those involving the O═C-N amide π-backbones. This detailed insight into the structural landscape of these important liquids demonstrates the versatility of DMSO as a solvent and the remarkable sensitivity of neutron diffraction, which is critical for understanding weak intermolecular interactions at the nanoscale and thereby tailoring solvent properties to specific applications

Algebraic Bethe ansatz for the gl(1∣|2) generalized model II: the three gradings

The algebraic Bethe ansatz can be performed rather abstractly for whole classes of models sharing the same $R$-matrix, the only prerequisite being the existence of an appropriate pseudo vacuum state. Here we perform the algebraic Bethe ansatz for all models with $9 \times 9$, rational, gl(1$|$2)-invariant $R$-matrix and all three possibilities of choosing the grading. Our Bethe ansatz solution applies, for instance, to the supersymmetric t-J model, the supersymmetric $U$ model and a number of interesting impurity models. It may be extended to obtain the quantum transfer matrix spectrum for this class of models. The properties of a specific model enter the Bethe ansatz solution (i.e. the expression for the transfer matrix eigenvalue and the Bethe ansatz equations) through the three pseudo vacuum eigenvalues of the diagonal elements of the monodromy matrix which in this context are called the parameters of the model.Comment: paragraph added in section 3, reference added, version to appear in J.Phys.

Strong structuring arising from weak cooperative O-H···π and C-H···O hydrogen bonding in benzene-methanol solution

Weak hydrogen bonds, such as O-H···π and C-H···O, are thought to direct biochemical assembly, molecular recognition, and chemical selectivity but are seldom observed in solution. We have used neutron diffraction combined with H/D isotopic substitution to obtain a detailed spatial and orientational picture of the structure of benzene-methanol mixtures. Our analysis reveals that methanol fully solvates and surrounds each benzene molecule. The expected O-H···π interaction is highly localised and directional, with the methanol hydroxyl bond aligned normal to the aromatic plane and the hydrogen at a distance of 2.30 Å from the ring centroid. Simultaneously, the tendency of methanol to form chain and cyclic motifs in the bulk liquid is manifest in a highly templated solvation structure in the plane of the ring. The methanol molecules surround the benzene so that the O-H bonds are coplanar with the aromatic ring while the oxygens interact with C-H groups through simultaneous bifurcated hydrogen bonds. This demonstrates that weak hydrogen bonding can modulate existing stronger interactions to give rise to highly ordered cooperative structural motifs that persist in the liquid phase

Modeling metallic island coalescence stress via adhesive contact between surfaces

Tensile stress generation associated with island coalescence is almost universally observed in thin films that grow via the Volmer-Weber mode. The commonly accepted mechanism for the origin of this tensile stress is a process driven by the reduction in surface energy at the expense of the strain energy associated with the deformation of coalescing islands during grain boundary formation. In the present work, we have performed molecular statics calculations using an embedded atom interatomic potential to obtain a functional form of the interfacial energy vs distance between two closely spaced free surfaces. The sum of interfacial energy plus strain energy provides a measure of the total system energy as a function of island separation. Depending on the initial separation between islands, we find that in cases where coalescence is thermodynamically favored, gap closure can occur either spontaneously or be kinetically limited due to an energetic barrier. Atomistic simulations of island coalescence using conjugate gradient energy minimization calculations agree well with the predicted stress as a function of island size from our model of spontaneous coalescence. Molecular dynamics simulations of island coalescence demonstrate that only modest barriers to coalescence can be overcome at room temperature. A comparison with thermally activated coalescence results at room temperature reveals that existing coalescence models significantly overestimate the magnitude of the stress resulting from island coalescence.Comment: 20 pages, 8 figures, 2 tables, submitted to PR