Asymptotically free Gauged-Yukawa systems

In this thesis we take a fresh look at asymptotic freedom for gauged-Yukawa models from a perspective that supersedes conventional studies within standard perturbation theory. In fact, our findings can be viewed as a generalization of previous investigations for non-Abelian Higgs models to systems which include a fermionic matter sector. We start with a minimalistic toy-model containing only a Yukawa and a QCD-like gauge sector. We then extend the analysis to a larger class of models which include the whole non-Abelian sector of the Standard Model. In both models we discover the existence of novel asymptotically free trajectories beyond standard perturbation theory. We construct such trajectories as quasi-fixed points for the Higgs scalar potential, whose couplings approach the noninteracting Gaußian fixed point with specific scalings with respect to the asymptotically free gauge couplings. We corroborate our findings in an effective-field-theory approach, and subsequently we obtain a comprehensive picture using the functional renormalization group. The latter method allows us to study the stability of the scalar potential for large field amplitudes. In contrast to standard perturbation theory, these new solutions become visible beyond the deep-Euclidean-regime, because of the important role of mass-threshold effects. Since one-loop universality is no longer guaranteed once threshold corrections are included, we investigate whether the existence of these ultraviolet complete trajectories is universal, i.e., a scheme-independent feature. We consider a wide class of regularization schemes that account for threshold behavior persisting in the infinite-energy limit, firstly focusing on the conventional minimal subtraction scheme and subsequently on mass-dependent schemes based on general momentum-space infrared regularizations. We argue that the existence of these asymptotically free solutions is a scheme-independent phenomenon

‘We are rolling and vaulting tonight’: sport programmes, urban regeneration and the politics of parkour in Turin, Italy.

The following paper aims to contribute to an interdisciplinary field of enquiry addressing the ways in which lifestyle and informal sports can inform policy debate and development at various levels. It will do so by considering the ambivalent position that parkour is taking within policies of urban and community re-branding enacted in Turin, Italy. Parkour in Turin is an increasingly structured discipline often endorsed by events celebrating the city’s vibrancy, and by local projects that target youth, and promote social participation. However, this discipline implies also a spontaneous and irreverent engagement with urban spaces that often creates frictions and conflicts between traceurs (parkour practitioners) and other actors in relation to what constitutes the public, how it should be used and by whom. Drawing on 14 months of ethnographic research with a group of 20 traceurs predominantly of migrant origins, this study focuses on the participants’ ambivalent engagement with one project promoting social participation through sports in Turin’s urban spaces. Building on the ethnographic material, this paper addresses the emerging relationship between social projects, informal urban practices and emerging forms of creative urbanism. The discussion focuses on the ambiguities and fault lines of urban agendas incorporating lifestyle and informal sports in their (neoliberal) vocabulary of community and place regeneration. However, this paper calls also for the necessity to engage with spontaneous, informal physical practices as a way to acknowledge, and support existing, contested negotiations of citizenship and belonging in urban spaces

‘If I climb a wall of ten meters’: capoeira, parkour and the politics of public space among (post)migrant youth in Turin, Italy

Rather than being seen as citizens, the children of immigrants are portrayed as a population to be controlled and contained across Europe. In Italy today, debates about cultural ‘authenticity’ and renewed nationalism accompany waves of moral panic that depict a country under siege by illegal and unwanted immigrants. Specifically in cities, immigrants and their children are imagined and portrayed as alien and out of place. Drawing on fourteen months of ethnographic research in Turin, Italy, with children of immigrants aged between 16 and 21, De Martini Ugolotti and Moyer illustrate how these youth make use of their bodies through capoeira and parkour practices to contest and reappropriate public spaces, thereby challenging dominant visions about what constitutes the public, how it should be used and by whom. They analyse the ‘body in place’ to understand how the children of immigrants navigate unequal spatial relations and challenge dominant regimes of representation, while also attempting to improve their life conditions and reach their personal goals

What can we learn from multi-objective meta-optimization of Evolutionary Algorithms in continuous domains?

Properly configuring Evolutionary Algorithms (EAs) is a challenging task made difficult by many different details that affect EAs' performance, such as the properties of the fitness function, time and computational constraints, and many others. EAs' meta-optimization methods, in which a metaheuristic is used to tune the parameters of another (lower-level) metaheuristic which optimizes a given target function, most often rely on the optimization of a single property of the lower-level method. In this paper, we show that by using a multi-objective genetic algorithm to tune an EA, it is possible not only to find good parameter sets considering more objectives at the same time but also to derive generalizable results which can provide guidelines for designing EA-based applications. In particular, we present a general framework for multi-objective meta-optimization, to show that "going multi-objective" allows one to generate configurations that, besides optimally fitting an EA to a given problem, also perform well on previously unseen ones

Coverage-dependent electronic and optical properties of H- or F-passivated Si/Ag(111) from first principles

Chemical functionalization of silicene can be devised to tune the intrinsic properties for optoelectronic applications of this material, as well as for optimizing the interface formed by ultrathin Si and a substrate. This work is focused on the (2 1a3 72 1a3)R30 18 phase of silicene grown on Ag(111), and the adsorption of H or F atoms, at half and full coverage, is simulated within density functional theory. The optical response is constructed through the independent particle\u2013random-phase approximation and analyzed thoroughly. The connection between the electronic structure and the features in the optical absorption and reflection is therefore investigated in order to highlight either the role of the adatoms or the effect of the metallic surface. As the coverage is increased, the silicene phases are effectively decoupled from Ag by H or F adatoms and the freestanding properties of the corresponding systems are recovered, for which a coverage-dependent band gap is opened in the states of the overlayer. However, despite being effectively decoupled from the substrate, the properties of functionalized silicene do not show the peculiar characteristics expected from the ideal freestanding Si layer

Meta-optimization of Bio-inspired Techniques for Object Recognition

Il riconoscimento di oggetti consiste nel trovare automaticamente un oggetto all'interno di un'immagine o in una sequenza video. Questo compito è molto importante in molti campi quali diagnosi mediche, assistenza di guida avanzata, visione artificiale, sorveglianza, realtà aumentata. Tuttavia, questo compito può essere molto impegnativo a causa di artefatti (dovuti al sistema di acquisizione, all'ambiente o ad altri effetti ottici quali prospettiva, variazioni di illuminazione, etc.) che possono influenzare l'aspetto anche di oggetti facili da identificare e ben definiti . Una possibile tecnica per il riconoscimento di oggetti consiste nell'utilizzare approcci basati su modello: in questo scenario viene creato un modello che rappresenta le proprietà dell'oggetto da individuare; poi, vengono generate possibili ipotesi sul posizionamento dell'oggetto, e il modello viene trasformato di conseguenza, fino a trovare la migliore corrispondenza con l'aspetto reale dell'oggetto. Per generare queste ipotesi in maniera intelligente, è necessario un buon algoritmo di ottimizzazione. Gli algoritmi di tipo bio-ispirati sono metodi di ottimizzazione che si basano su proprietà osservate in natura (quali cooperazione, evoluzione, socialità). La loro efficacia è stata dimostrata in molte attività di ottimizzazione, soprattutto in problemi di difficile soluzione, multi-modali e multi-dimensionali quali, per l'appunto, il riconoscimento di oggetti. Anche se queste euristiche sono generalmente efficaci, esse dipendono da molti parametri che influenzano profondamente le loro prestazioni; pertanto, è spesso richiesto uno sforzo significativo per capire come farle esprimere al massimo delle loro potenzialità. Questa tesi descrive un metodo per (i) individuare automaticamente buoni parametri per tecniche bio-ispirate, sia per un problema specifico che più di uno alla volta, e (ii) acquisire maggior conoscenza sul ruolo di un parametro in questi algoritmi. Inoltre, viene mostrato come le tecniche bio-ispirate possono essere applicate con successo in diversi ambiti nel riconoscimento di oggetti, e come è possibile migliorare ulteriormente le loro prestazioni mediante il tuning automatico dei loro parametri.Object recognition is the task of automatically finding a given object in an image or in a video sequence. This task is very important in many fields such as medical diagnosis, advanced driving assistance, image understanding, surveillance, virtual reality. Nevertheless, this task can be very challenging because of artefacts (related with the acquisition system, the environment or other optical effects like perspective, illumination changes, etc.) which may affect the aspect even of easy-to-identify and well-defined objects. A possible way to achieve object recognition is using model-based approaches: in this scenario a model (also called template) representing the properties of the target object is created; then, hypotheses on the position of the object are generated, and the model is transformed accordingly, until the best match with the actual appearance of the object is found. To generate these hypotheses intelligently, a good optimization algorithm is required. Bio-inspired techniques are optimization methods whose foundations rely on properties observed in nature (such as cooperation, evolution, emergence). Their effectiveness has been proved in many optimization tasks, especially in multi-modal, multi-dimensional hard problems like object recognition. Although these heuristics are generally effective, they depend on many parameters that strongly affect their performances; therefore, a significant effort must be spent to understand how to let them express their full potentialities. This thesis describes a method to (i) automatically find good parameters for bio-inspired techniques, both for a specific problem and for more than one at the same time, and (ii) acquire more knowledge of a parameter's role in such algorithms. Then, it shows how bio-inspired techniques can be successfully applied to different object recognition tasks, and how it is possible to further improve their performances by means of automatic parameter tuning

Gravity in d=2+ϵd=2+\epsilon dimensions and realizations of the diffeomorphisms group

We discuss two distinct realizations of the diffeomorphism group for metric gravity, which give rise to theories that are classically equivalent, but quantum mechanically distinct. We renormalize them in $d=2+\epsilon$ dimensions, developing a new procedure for dimensional continuation of metric theories and highlighting connections with the constructions that previously appeared in the literature. Our hope is to frame candidates ultraviolet completions of quantum gravity in $d>2$ and give some perturbative mean to assess its existence in $d=4$, but also to speculate on some potential obstructions in the continuation of such candidates to finite values of $\epsilon$. Our results suggest the presence of a conformal window in $d$ which seems to extend to values higher than four.Comment: 17 pages, 1 figure; v2: improved draft in response to feedbac

Adsorption of water and organic solvents on the calcite [101¯4] surface: Implications for marble conservation treatments

When exposed outdoors, marble artefacts are subject to degradation caused by dissolution in rain. To improve acid-resistance of marble, surface treatments involving the in situ formation of a passivating calcium phosphate (CaP) layer have been developed. Adding alcohol to the treatment improves CaP coverage but the reason is still unclear. Here, we use computational and experimental studies to ascertain whether the interaction of the organic additives with the marble surface plays a role in determining the treatment outcome. Density functional theory calculations are employed to determine the binding energy of additives on the calcite [101¯4] surface and identify acetone as a promising new additive due to its weak adsorption. Molecular dynamics calculations show that ethanol and isopropanol displace water from the calcite [101¯4] surface forming an immobile, ordered, and hydrophobic layer, while acetone and water form a mixed, dynamic environment. In experimental trials, a continuous (yet cracked) layer of carbonate hydroxyapatite is formed after 24 h, with all organic additives improving the final coating. This result suggests that the interaction of the additive with the marble surface does not play a major role in determining treatment outcomes and other factors should be investigated for the design of improved treatments