Leading order CFT analysis of multi-scalar theories in d>2

We investigate multi-field multicritical scalar theories using CFT constraints on two- and three-point functions combined with the Schwinger-Dyson equation. This is done in general and without assuming any symmetry for the models, which we just define to admit a Landau-Ginzburg description that includes the most general critical interactions built from monomials of the form $\phi_{i_1} \cdots \phi_{i_m}$. For all such models we analyze to the leading order of the $\epsilon$-expansion the anomalous dimensions of the fields and those of the composite quadratic operators. For models with even $m$ we extend the analysis to an infinite tower of composite operators of arbitrary order. The results are supplemented by the computation of some families of structure constants. We also find the equations which constrain the nontrivial critical theories at leading order and show that they coincide with the ones obtained with functional perturbative RG methods. This is done for the case $m=3$ as well as for all the even models. We ultimately specialize to $S_q$ symmetric models, which are related to the $q$-state Potts universality class, and focus on three realizations appearing below the upper critical dimensions $6$, $4$ and $\frac{10}{3}$, which can thus be nontrivial CFTs in three dimensions.Comment: 58 pages; v2: minor clarifications added, to appear in EPJ

New universality class in three dimensions: The critical Blume-Capel model

We study the Blume-Capel universality class in $d=\frac{10}{3}-\epsilon$ dimensions. The RG flow is extracted by looking at poles in fractional dimension of three loop diagrams using $\overline{\rm MS}$. The theory is the only nontrivial universality class which admits an expansion to three dimensions with $\epsilon=\frac{1}{3}<1$. We compute the relevant scaling exponents and estimate some of the OPE coefficients to the leading order. Our findings agree with and complement CFT results. Finally we discuss a family of nonunitary multicritical models which includes the Lee-Yang and Blume-Capel classes as special cases.Comment: 5 pages, 1 figure, v2: new title, extended introduction, to appear in PR

Inclusive One Jet Production With Multiple Interactions in the Regge Limit of pQCD

DIS on a two nucleon system in the regge limit is considered. In this framework a review is given of a pQCD approach for the computation of the corrections to the inclusive one jet production cross section at finite number of colors and discuss the general results.Comment: 4 pages, latex, aicproc format, Contribution to the proceedings of "Diffraction 2008", 9-14 Sep. 2008, La Londe-les-Maures, Franc

Estimating Route Choice Models from Stochastically Generated Choice Sets on Large-Scale Networks Correcting for Unequal Sampling Probability:Correcting for Unequal Sampling Probability

Route choice is one of the most complex decision-making contexts to represent mathematically, and the most frequently used approach to model route choice consists of generating alternative routes and modeling the preferences of utility-maximizing travelers. The main drawback of this approach is the dependency of the parameter estimates from the choice set generation technique. Bias introduced in model estimation has been corrected only for the random walk algorithm, which has problematic applicability to large-scale networks. This study proposes a correction term for the sampling probability of routes extracted with stochastic route generation. The term is easily applicable to large-scale networks and various environments, given its dependence only on a random number generator and the Dijkstra shortest path algorithm. The implementation for revealed preferences data, which consist of actual route choices collected in Cagliari, Italy, shows the feasibility of generating routes stochastically in a high-resolution network and calculating the correction factor. The model estimation with and without correction illustrates how the correction not only improves the goodness of fit but also turns illogical signs for parameter estimates to logical signs

Analisi comportamentale della scelta del percorso attraverso l'utilizzo di nuove tecnologie di acquisizione delle informazioni

In travel demand modeling, route choice is one of the most complex decision-making contexts to understand and mathematically represent for several reasons. Firstly, a large number of available paths may exist between the same origin-destination (OD) pair. Secondly, neither the traveler nor the modeler are aware of all the available alternatives. Thirdly, individual choices are dictated by different constraints and preferences that are difficult to capture by modelers who face increasingly larger datasets where retrieving the exact path chosen by travelers is not always straightforward. Last, there is a lot of uncertainty about travelers’ perceptions of route characteristics as well as other characteristics that can influence their choices, such as age, gender, habit, weather conditions and network conditions. This highlights the difficulties encountered for interpreting individual user behavior in greater depth. The rapid advances in GPS devices, has resulted in major benefits for data collection, which now can be recorded automatically and with greater accuracy compared to the techniques used in the past (phone calls, e-mails, face-to-face interviews, laboratory experiments.). On these basis the main objective of the thesis is then to study route choice using a GPS database. The data were acquired during a survey, named "Casteddu Mobility Styles” (CMS), conducted by the University of Cagliari (Italy) in the metropolitan area of Cagliari between February 2011 and June 2012. Each participant was asked to carry a smartphone with builtin GPS in which an application called “Activity Locator” – implemented by CRiMM (Centre for Research on Mobility and Modeling) – had been installed. A total of 8831 trips were recorded by 109 individuals, of which 4791 referring to the car driver mode. Each GPS track (consisting of a sequence of referenced position points) was then treated with map-matching techniques, through which it was possible to associate each “GPS point” to a link of the network, thus creating the observed route database. The first objective of the thesis is to understand which are the characteristics of the data acquired during the CMS survey, doing firstly the same analysis that other authors did in their researches based on GPS data. In almost all the previous researches, the GPS data were collected through in-vehicle surveys that make it possible to gather objective information on trips (travel times and distances). Pre-and post-analysis interviews were conducted to gather information about the subjective characteristics of the individuals and GIS platforms were used to study the routes. In the present study, the data were collected using an integrated system able to also record the activities conducted, along with all the characteristics associated thereto. In this way a complete database was created containing all the information (objective and not) concerning the trips. For comparisons with the objectively most convenient paths, then, was used a static macrosimulation model (implemented in CUBE, Citilabs Ltd.) of the entire study area (Cagliari and its metropolitan area), which reproduces the network characteristics actually encountered by the drivers referring to the data used. From this first analysis it was observed that when more than one route is taken for repetitive trips between the same OD. In order to understand these particular behavior of users, named also intravariability, discrete choice models were estimated. It’s important to note that in the previous GPS-based researches this particular behavior was only identified, without studying it in depth. Several other studies, focused on route switching behavior, tried to understand it applying discrete choice models, but their database were based on data acquired through questionnaires or laboratory experiments, and for the majority the route switching behavior was studied in relation to the trip information provision. The objective of this analysis is then to combine the two fields of the research on route switching, trying to understand it estimating discrete choice models using a GPS based database, closing the gap of the previous researches. The final goal of the model estimations is to understand which are the main attributes of the routes and the characteristics of the users that most influence the choice of an habitual route for the same origin-destination (OD) trip. After these first analysis, the final objective of the thesis is to apply a route choice model to GPS-based data. Modeling route choice behavior is generally framed as a two-stage process: generation of the alternative routes and modeling of the choice from the generated choice set. The focus of this step of the research is on the bias that might be introduced in the model estimation by the choice set generation process. Specifically, although several explicit choice set generation techniques are found in the literature, the focus is on stochastic route generation and the correction for unequal sampling probability of routes when applying this technique that is easily applicable to large-scale networks. Indeed, stochastic route generation is a case of importance sampling where the selection of the path depends on its own properties, so route choice models based on stochastic route generation must include a sampling correction coefficient that accounts for the different selection probability. In this study is proposed a methodology for calculating and considering this correction factor into MNL-based models with choice sets generated by means of stochastic route generation. Specifically, was decided to look at the sampling correction factor proposed for the random walk algorithm and to calculate the route selection probability in order to exploit this expression. Therefore, a procedure is proposed for the computation of the selection probabilities on the basis of the stochastic generation principle, then the correction factor and last the EPS for model estimation. The modeling analysis confirms the functionality of the proposed approach that has great advantages: (i) it provides insight into the application of stochastic generation in route choice modeling, especially in large-scale networks where the only need is a standard random number generator and a Dijkstra algorithm; it proposes a simple and manageable procedure from the computational perspective for the calculation of route selection probabilities and hence the correction factor and EPS for model estimation; it proves the efficiency of the proposed methodology on revealed preference data in a dense urban network by showing an increase in goodness-of-fit of the model and a shift from illogical to logical sign in parameters estimated for key variables such as travel time

Report on LPG infrastructure impact at the WUI microscale

Preprin

The road transport of goods on behalf of a third party: tariffs and development perspectives

Il presente elaborato concerne le problematiche giuridiche connesse alla regolamentazione del settore dell’autotrasporto di cose per conto di terzi in Italia, con particolare attenzione alla disciplina dei profili tariffari ed alle dinamiche consolidatesi nella prassi in relazione alle pratiche di dumping sociale, outsourcing e delocalizzazione. Nella prima parte, dopo una premessa finalizzata a descrivere le caratteristiche strutturali dei fornitori di servizi di autotrasporto in ambito nazionale e comunitario nonchè le principali peculiarità del mercato di riferimento, viene descritta ed analizzata l’evoluzione normativa e giurisprudenziale verificatasi con riguardo ai profili tariffari dell’autotrasporto, esaminando in particolare le caratteristiche ed i profili di criticità propri delle discipline in materia di “tariffe a forcella” di cui alla L. n. 298/1974 e di “costi minimi di sicurezza” di cui all’art. 83-bis del D.L. n. 112/2008, fino a giungere all’analisi degli scenari conseguenti alla recente riforma del settore apportata dalla Legge di Stabilità 2015 (L. 23/12/2014, n. 190). Nella seconda parte, vengono esaminate alcune tematiche problematiche che interessano il settore, sia a livello nazionale che comunitario, e che risultano strettamente connesse ai sopra menzionati profili tariffari. In particolare, si fa riferimento alle fattispecie del cabotaggio stradale, del distacco transazionale di lavoratori e dell’abuso della libertà di stabilimento in ambito comunitario concretantesi nella fattispecie della esterovestizione. Tali problematiche sono state analizzate dapprima attraverso la ricostruzione del quadro normativo nazionale e comunitario di riferimento; in secondo luogo, attraverso l’esame dei profili critici emersi alla luce delle dinamiche di mercato invalse nel settore e, infine, in relazione all’analisi dello scenario futuro desumibile dalle iniziative legislative ed amministrative in atto, nonché dagli indirizzi interpretativi affermatisi in ambito giurisprudenziale.The research is focused on the analysis of the regulation of road haulage in Italy, with particular regard to issues related to tariffs and to the practices of social dumping, outsourcing and business relocation. In the first part, further to the description of the main characteristics of Italian and EU suppliers of road haulage services, it is described and analyzed the evolution of regulation and jurisprudence regarding road haulage tariffs aspects, with particular regard to the provisions set forth in Law no. 298 of 1974, Law Decree no. 112 of 2008 and Law no. 190 of 2014. The second part is focused on the analysis of some problematical issues regarding road haulage both at national and EU level, and in particular road cabotage, posting of workers and abuse of freedom of establishment within EU in the road haulage secto

A multicritical Landau-Potts field theory

We investigate a perturbatively renormalizable $S_{q}$ invariant model with $N=q-1$ scalar field components below the upper critical dimension $d_c=\frac{10}{3}$. Our results hint at the existence of multicritical generalizations of the critical models of spanning random clusters and percolations in three dimensions. We also discuss the role of our multicritical model in a conjecture that involves the separation of first and second order phases in the $(d,q)$ diagram of the Potts model.Comment: 12 pages, 5 figures; v2: improved discussion for the q=0 limit, to appear in PR