Parton distributions in a constituent quark scenario

A simple picture of the constituent quark as a composite system of point-like partons is used to construct the unpolarized and polarized parton distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. We achieve good agreement with experiments in the unpolarized, as well as, in the polarized case. When our results are compared with similar calculations using non-composite constituent quarks, the accord with the experiments of the present scheme is impressive. We conclude that DIS data are consistent with a low energy scenario dominated by composite constituents of the nucleon.Comment: 4 pages; latex using espcrc1.sty; 4 postscript figures; Invited talk at the Workshop ``Nucleon '99'', Frascati; Italy 7-9 June 1999. Submitted to Nuc. Phys.

Generalized parton distributions of the nucleon in constituent quark models

Generalized parton distributions (GPDs) are studied at the hadronic (nonperturbative) scale within different assumptions based on a relativistic constituent quark model. In particular, by means of a meson-cloud model we investigate the role of nonperturbative antiquark degrees of freedom and the valence quark contribution. A QCD evolution of the obtained GPDs is used to add perturbative effects and to investigate the GPDs' sensitivity to the nonperturbative ingredients of the calculation at larger (experimental) scale.Comment: 4 pages, 1 figure, presented at the Baryon-04 Conference, Palaiseau (France), October 25-29, 2004. Nuclear Physics A, to be publishe

Spin force dependence of the parton distributions: the ratio F_2^n(x,Q^2)\/F_2^p(x,Q^2)

Light-front Hamiltonian dynamics is used to relate low-energy constituent quark models to deep inelastic unpolarized structure functions of the nucleon. The approach incorporates the correct Pauli principle prescription consistently and it allows a transparent investigation of the effects due to the spin-dependent SU(6)-breaking terms in the quark model Hamiltonian. Both Goldstone-boson-exchange interaction and hyperfine-potential models are discussed in a unified scheme and a detailed comparison, between the two(apparently) different potential prescriptions, is presented

I biglietti d’invito di Paolo Fabbri

Recensione del volume di Paolo Fabbri "Biglietti d’invito. Per una semiotica marcata", Milano, Bompiani, 2021

Comunicazioni emotive dei media nell’epoca della «post-verità»: le isole di plastica negli oceani raccontate da la Repubblica

Starting from the debate on the presence of plastic islands in the oceans, in this article I will report the findings of a semiotic analysis of ten articles of the “Usa e Rispetta” campaign against pollution and for a sustainable use of plastics, launched by La Repubblica newspaper on 22 April 2018. Then, I will focus on the analysis of a fanpage.it video about a mass of floating garbage in a corner of the Caribbean Sea, a video which became viral at the end of 2017. In both cases, the emotional component is strongly present, alongside with the following recurrent elements: effects of spatial decontextualization, effects of temporalization oriented towards an apocalyptic future, the use of actors with legitimizing functions (the experts). These analyses suggest the central role of emotions in mass media discourses. As a matter of facts, the appeal to emotions makes information more interesting and immediate to the public than logical and rational elements such as data, counterexamples, refutations and statistics, elements that would make the argumentation complex and articulated

La struttura assente e il principio di immanenza. Qualche riflessione sul metodo semiotico

Analytic semiotics has always created structures for describing and analysing texts. As was inevitable, ontological questions have emerged on these structures' modes of existence: are they real or abstract? Do they exist in texts, or inside people's heads? Umberto Eco reflected on the status and location of structures almost fifty years ago in his book La struttura assente, in a section of the book that became famous, Section D, which is dedicated to the epistemology of structural models (Eco 1968). In this article I take as my starting point some observations made by Eco at the end of the 1960s in order to see how some assumptions of structuralism influenced the development of semiotics over the decades that followed

Segreti, complotti e teorie semiotiche

Dealing with plots, conspiracies and secrets, Umberto Eco investigates those forms of reasoning that are based on the uncontrolled shift of meaning. This way, he first dwells on the historical-philosophical “precedents” of these forms of thought, describing the birth and developments of the “hermetic thought”. Then, he tries to describe the illogical shift of meanings as a pathological form of semiosis, using Peirce’s semiotic theory. He also uses the concept of connotation, defining the anomalous shift of meaning as a “connotative neoplasm”. Therefore, alongside an epistemologically-oriented semiotics (Peirce), it seems that Eco still feels the need to resort to an analysis-oriented semiotics (Hjelmslev, Barthes), despite having abandoned the structuralist paradigm for a long time, because of his philosophical propensity. Thus, moving among historical reconstructions, general philosophical theories and the application of analytical tools, Eco seems to give useful methodological suggestions for contemporary semiotics

Le muse fanno il girotondo: alcune considerazioni sulla semiotica delle arti di Lotman

Recensione del volume "Il girotondo delle muse. Semiotica delle arti", di Jurij Mihajlovič Lotman, Bompiani, 202