Dynamical Phase Transitions for Fluxes of Mass on Finite Graphs

We study the time-averaged flux in a model of particles that randomly hop on a finite directed graph. In the limit as the number of particles and the time window go to infinity but the graph remains finite, the large-deviation rate functional of the average flux is given by a variational formulation involving paths of the density and flux. We give sufficient conditions under which the large deviations of a given time averaged flux is determined by paths that are constant in time. We then consider a class of models on a discrete ring for which it is possible to show that a better strategy is obtained producing a time-dependent path. This phenomenon, called a dynamical phase transition, is known to occur for some particle systems in the hydrodynamic scaling limit, which is thus extended to the setting of a finite graph

On the dynamical breaking of chiral symmetry: a new mechanism

We consider a U(1) gauge theory, minimally coupled to a massless Dirac field, where a higher-derivative term is added to the pure gauge sector, as in the Lee-Wick models. We find that this term can trigger chiral symmetry breaking at low energy in the weak coupling regime. Then, the fermion field acquires a mass that turns out to be a function of both the energy scale associated to the higher-derivative term and the gauge coupling. The dependence of the fermion mass on the gauge coupling is non-perturbative. Extensions to SU(N) gauge theories and fermion-scalar interactions are also analyzed, as well as to theories with massive gauge fields. A few implications of these results in the framework of quark-mass generation are discussed.Comment: 15 pages 2 figures, a few comments and 4 references added. To appear in Physical Review

Level 2.5 large deviations for continuous time Markov chains with time periodic rates

We consider an irreducible continuous time Markov chain on a finite state space and with time periodic jump rates and prove the joint large deviation principle for the empirical measure and flow and the joint large deviation principle for the empirical measure and current. By contraction we get the large deviation principle of three types of entropy production flow. We derive some Gallavotti-Cohen duality relations and discuss some applications.Comment: 37 pages. corrected versio

A perturbative approach to the Bak-Sneppen Model

We study the Bak-Sneppen model in the probabilistic framework of the Run Time Statistics (RTS). This model has attracted a large interest for its simplicity being a prototype for the whole class of models showing Self-Organized Criticality. The dynamics is characterized by a self-organization of almost all the species fitnesses above a non-trivial threshold value, and by a lack of spatial and temporal characteristic scales. This results in {\em avalanches} of activity power law distributed. In this letter we use the RTS approach to compute the value of $x_c$, the value of the avalanche exponent $\tau$ and the asymptotic distribution of minimal fitnesses.Comment: 4 pages, 3 figures, to be published on Physical Review Letter

Theory of Boundary Effects in Invasion Percolation

We study the boundary effects in invasion percolation with and without trapping. We find that the presence of boundaries introduces a new set of surface critical exponents, as in the case of standard percolation. Numerical simulations show a fractal dimension, for the region of the percolating cluster near the boundary, remarkably different from the bulk one. We find a logarithmic cross-over from surface to bulk fractal properties, as one would expect from the finite-size theory of critical systems. The distribution of the quenched variables on the growing interface near the boundary self-organises into an asymptotic shape characterized by a discontinuity at a value $x_c=0.5$, which coincides with the bulk critical threshold. The exponent $\tau^{sur}$ of the boundary avalanche distribution for IP without trapping is $\tau^{sur}=1.56\pm0.05$; this value is very near to the bulk one. Then we conclude that only the geometrical properties (fractal dimension) of the model are affected by the presence of a boundary, while other statistical and dynamical properties are unchanged. Furthermore, we are able to present a theoretical computation of the relevant critical exponents near the boundary. This analysis combines two recently introduced theoretical tools, the Fixed Scale Transformation (FST) and the Run Time Statistics (RTS), which are particularly suited for the study of irreversible self-organised growth models with quenched disorder. Our theoretical results are in rather good agreement with numerical data.Comment: 11 pages, 13 figures, revte

Invasion Percolation with Temperature and the Nature of SOC in Real Systems

We show that the introduction of thermal noise in Invasion Percolation (IP) brings the system outside the critical point. This result suggests a possible definition of SOC systems as ordinary critical systems where the critical point correspond to set to 0 one of the parameters. We recover both IP and EDEN model, for $T \to 0$, and $T \to \infty$ respectively. For small $T$ we find a dynamical second order transition with correlation length diverging when $T \to 0$.Comment: 4 pages, 2 figure

Laser scanning e photo scanning. Tecniche di rilevamento per la documentazione 3D di beni architettonici ed archeologici

Laser scanner and digital photogrammetric systems (photo scanning) must be considered at present two of the main techniques used for archaeological and architectural surveying. The integration of both 3D scanning systems allowed us to improve the scientific knowledge, the management, the use and the safeguarding of Cultural Heritage. The aim of this article is to identify analogies and differences between the two surveying techniques applied to different archaeological contexts. Starting from a general introduction to the concept of measurement and the management of the data acquired from different techniques of surveying, the article focuses on the laser scanner applications with particular attention on the intrinsic properties of the instrument, the problems of measurement and the methodology used during the survey. The second part is focused on the digital photogrammetry applied on a particular archaeological context. Digital photogrammetry was developed and experimented in order to acquire territorial data quickly. The optimization of the working speed, while maintaining accuracy of data, means cost savings and an optimal use of funds. Our workgroup decided to transfer that methodology to the archaeological excavations of Rome Metro Line C in collaboration with some public institutions and private companies. The final results have produced 2D and 3D graphic documentations of all the archaeological area up to highly-accurate ortho-recti ??ed images. Point clouds allowed us to simultaneously view a general 3D model of all open archaeological areas, providing an opportunity for observation and an analysis not possible by other means. Each area can be studied together with the others in a global view of the excavation. Every stratigraphic unit can be displayed in the same area and switched on in the same way as a layer

Living arrangements of adult children of immigrants in selected European countries

The living arrangements of adult children of immigrants are shaped across Europe by both the dominant norms of mainstream society and the intergenerational transmission of values and practices. The paper describes the heterogeneous scenario across Europe in three specific living arrangements (living with parents, in a partnership, and, among those living with a partner, being in nonmarital cohabitation) by developing a multiple-origin/multipledestination analysis based on migratory generation and by questioning adaptation and socialization hypotheses. The 2014 ad hoc module of the EU Labour Force Survey provides significant insights on young adults aged 20 to 34 in eight EU countries. The propensity to experience the three specific behaviors is estimated through logit models aiming at comparing southern and northwestern Europe. Adult children of immigrants mostly tend to resemble the majority groups in the different destination contexts. Nevertheless, contextual factors cannot explain the whole intra-European heterogeneity. Results are not fully consistent with the expected gradual adaptation across migratory generations, and some differences based on the area of origin persist in all destination areas, especially for the decision to experience a nonmarital cohabitation. Young adults originating from South and East Asia and sub- Saharan Africa show stronger influence of their cultural inheritance than the other groups

Statistical properties of fractures in damaged materials

We introduce a model for the dynamics of mud cracking in the limit of of extremely thin layers. In this model the growth of fracture proceeds by selecting the part of the material with the smallest (quenched) breaking threshold. In addition, weakening affects the area of the sample neighbour to the crack. Due to the simplicity of the model, it is possible to derive some analytical results. In particular, we find that the total time to break down the sample grows with the dimension L of the lattice as L^2 even though the percolating cluster has a non trivial fractal dimension. Furthermore, we obtain a formula for the mean weakening with time of the whole sample.Comment: 5 pages, 4 figures, to be published in Europhysics Letter