Mixed symmetry tensors in the worldline formalism

We consider the first quantised approach to quantum field theory coupled to a non-Abelian gauge field. Representing the colour degrees of freedom with a single family of auxiliary variables the matter field transforms in a reducible representation of the gauge group which - by adding a suitable Chern-Simons term to the particle action - can be projected onto a chosen fully (anti-)symmetric representation. By considering F families of auxiliary variables, we describe how to extend the model to arbitrary tensor products of F reducible representations, which realises a U(F) "flavour" symmetry on the worldline particle model. Gauging this symmetry allows the introduction of constraints on the Hilbert space of the colour fields which can be used to project onto an arbitrary irreducible representation, specified by a certain Young Tableau. In particular the occupation numbers of the wavefunction - i.e. the lengths of the columns (rows) of the Young Tableau - are fixed through the introduction of Chern-Simons terms. We verify this projection by calculating the number of colour degrees of freedom associated to the matter field. We suggest that, using the worldline approach to quantum field theory, this mechanism will allow the calculation of one-loop scattering amplitudes with the virtual particle in an arbitrary representation of the gauge group.Comment: 1+32 page

A route to explain water anomalies from results on an aqueous solution of salt

In this paper we investigate the possibility to detect the hypothesized liquid-liquid critical point of water in supercooled aqueous solutions of salts. Molecular dynamics computer simulations are conducted on bulk TIP4P water and on an aqueous solution of sodium chloride in TIP4P water, with concentration c = 0.67 mol/kg. The liquid-liquid critical point is found both in the bulk and in the solution. Its position in the thermodynamic plane shifts to higher temperature and lower pressure for the solution. Comparison with available experimental data allowed us to produce the phase diagrams of both bulk water and the aqueous solution as measurable in experiments. Given the position of the liquid-liquid critical point in the solution as obtained from our simulations, the experimental determination of the hypothesized liquid-liquid critical point of water in aqueous solutions of salts appears possible.Comment: 5 pages, 6 figures. Accepted for publication on the Journal of Chemical Physics (2010)

Structural Properties of High and Low Density Water in a Supercooled Aqueous Solution of Salt

We consider and compare the structural properties of bulk TIP4P water and of a sodium chloride aqueous solution in TIP4P water with concentration c = 0.67 mol/kg, in the metastable supercooled region. In a previous paper [D. Corradini, M. Rovere and P. Gallo, J. Chem. Phys. 132, 134508 (2010)] we found in both systems the presence of a liquid-liquid critical point (LLCP). The LLCP is believed to be the end point of the coexistence line between a high density liquid (HDL) and a low density liquid (LDL) phase of water. In the present paper we study the different features of water-water structure in HDL and LDL both in bulk water and in the solution. We find that the ions are able to modify the bulk LDL structure, rendering water-water structure more similar to the bulk HDL case. By the study of the hydration structure in HDL and LDL, a possible mechanism for the modification of the bulk LDL structure in the solution is identified in the substitution of the oxygen by the chloride ion in oxygen coordination shells.Comment: 10 pages, 10 figures, 2 tables. Accepted for publication on J. Phys. Chem

Simulating Stochastic Dynamics Using Large Time Steps

We present a novel approach to investigate the long-time stochastic dynamics of multi-dimensional classical systems, in contact with a heat-bath. When the potential energy landscape is rugged, the kinetics displays a decoupling of short and long time scales and both Molecular Dynamics (MD) or Monte Carlo (MC) simulations are generally inefficient. Using a field theoretic approach, we perform analytically the average over the short-time stochastic fluctuations. This way, we obtain an effective theory, which generates the same long-time dynamics of the original theory, but has a lower time resolution power. Such an approach is used to develop an improved version of the MC algorithm, which is particularly suitable to investigate the dynamics of rare conformational transitions. In the specific case of molecular systems at room temperature, we show that elementary integration time steps used to simulate the effective theory can be chosen a factor ~100 larger than those used in the original theory. Our results are illustrated and tested on a simple system, characterized by a rugged energy landscape.Comment: 17 pager, 7 figure

Fragile to strong crossover coupled to liquid-liquid transition in hydrophobic solutions

Using discrete molecular dynamics simulations we study the relation between the thermodynamic and diffusive behaviors of a primitive model of aqueous solutions of hydrophobic solutes consisting of hard spheres in the Jagla particles solvent, close to the liquid-liquid critical point of the solvent. We find that the fragile-to-strong dynamic transition in the diffusive behavior is always coupled to the low-density/high-density liquid transition. Above the liquid-liquid critical pressure, the diffusivity crossover occurs at the Widom line, the line along which the thermodynamic response functions show maxima. Below the liquid-liquid critical pressure, the diffusivity crossover occurs when the limit of mechanical stability lines are crossed, as indicated by the hysteresis observed when going from high to low temperature and vice versa. These findings show that the strong connection between dynamics and thermodynamics found in bulk water persists in hydrophobic solutions for concentrations from low to moderate, indicating that experiments measuring the relaxation time in aqueous solutions represent a viable route for solving the open questions in the field of supercooled water.Comment: 6 pages, 4 figures. Accepted for publication on Physical Review

Cognitive and personality components underlying spoken idiom comprehension in context. An exploratory study.

In this exploratory study, we investigated whether and to what extent individual differences in cognitive and personality variables are associated with spoken idiom comprehension in context. Language unimpaired participants were enrolled in a cross-modal lexical decision study in which semantically ambiguous Italian idioms (i.e., strings with both a literal and an idiomatic interpretation as, for instance, break the ice), predictable or unpredictable before the string offset, were embedded in idiom-biasing contexts. To explore the contributions of different cognitive and personality components, participants also completed a series of tests respectively assessing general speed, inhibitory control, short-term and working memory, cognitive flexibility, crystallized and fluid intelligence, and personality. Stepwise regression analyses revealed that online idiom comprehension was associated with the participants\u2019 working memory, inhibitory control and crystallized verbal intelligence, an association modulated by idiom type. Also personality-related variables (State Anxiety and Openness to Experience) were associated with idiom comprehension, although in marginally significant ways. These results contribute to the renewed interest on how individual variability modulates language comprehension, and for the first time document contributions of individual variability on lexicalized, high frequency multi-word expressions as idioms adding new knowledge to the existing evidence on metaphor and sarcasm

Thermodynamic behaviour and structural properties of an aqueous sodium chloride solution upon supercooling

We present the results of a molecular dynamics simulation study of thermodynamic and structural properties upon supercooling of a low concentration sodium chloride solution in TIP4P water and the comparison with the corresponding bulk quantities. We study the isotherms and the isochores for both the aqueous solution and bulk water. The comparison of the phase diagrams shows that thermodynamic properties of the solution are not merely shifted with respect to the bulk. Moreover, from the analysis of the thermodynamic curves, both the spinodal line and the temperatures of maximum density curve can be calculated. The spinodal line appears not to be influenced by the presence of ions at the chosen concentration, while the temperatures of maximum density curve displays both a mild shift in temperature and a shape modification with respect to bulk. Signatures of the presence of a liquid-liquid critical point are found in the aqueous solution. By analysing the water-ion radial distribution functions of the aqueous solution we observe that upon changing density, structural modifications appear close to the spinodal. For low temperatures additional modifications appear also for densities close to that corresponding to a low density configurational energy minimum.Comment: 10 pages, 13 figures, 2 tables. To be published in J. Chem. Phy