Abstract:
Ohio-based, Chicago-born, gay, Puerto Rican author Rane Arroyo writes poetry in which ghosts and ghostliness serve as metaphors for identities that are present but not always represented in dominant U.S. literary history. This essay argues that in Arroyo′s mainly autobiographical poetry, ghosts, hauntings, and a broader concept of ghostliness are used to interrogate identifications that float between, around, and through socially constructed categories such as race, ethnicity, nationality, and sexuality. While the relationship between the poetic voice and his specters varies and is shown to be quite complex, Arroyo′s ghosts serve not only as constant inspiration for his poetry but also as vehicles for his meditations on identity.

Abstract:
An important form of transmission of knowledge about the Spanish nation is based on the continuous telling of stories in which the nation features as a suprahistorical, perennial entity. Myths of national origin, golden-age legends, and epics of national heroes are some of these stories. This mode of access to knowledge assumes a suspension of disbelief for the audience, and precludes other attempts to comprehend the nation through scientific research. Subjective national identities constructed upon such suspension of disbelief have a tendency to reify, personify or even deify the nation. In the struggle between mythic and objective knowledge, the question of authenticity becomes a hotly contested arena. This paper attempts to address questions of mythical national representation in Spanish films of 1975-2000.

Abstract:
When one uses the Dirac bracket, second class constraints become first class. Hence, they are amenable to the BRST treatment characteristic of ordinary first class constraints. This observation is the starting point of a recent investigation by Batalin and Tyutin, in which all the constraints are put on the same footing. However, because second class constraints identically vanish as operators in the quantum theory, they are quantum-mechanically reducible and require therefore ghosts of ghosts. Otherwise, the BRST cohomology would not yield the correct physical spectrum. We discuss how to incorporate this feature in the formalism and show that it leads to an infinite tower of ghosts of ghosts. An alternative treatment, in which the brackets of the ghosts are modified, is also mentioned.

Abstract:
We investigate the possibility that patches of old radio plasma (`radio ghosts') of former radio galaxies form a second distinct phase of the inter-galactic medium (IGM), not mixed with the thermal gas. The separation of this phase from the ambient gas and its resistance against eroding turbulent forces is given by magnetic fields, which are expected to be roughly in pressure equilibrium with the surrounding medium. Since patches of this plasma are largely invisible in the radio we use the term `radio ghost' to characterize their nature. Possibilities and difficulties of different detection strategies of ghosts are discussed. These involve radio emission, cosmic microwave background (CMB) and starlight Comptonization, and Faraday rotation. Re-activation of the electron population in shock waves of cosmological structure formation, which seems to lead to the cluster radio relic phenomena. We discuss the role radio ghosts can have: They are able to store relativistic particles for cosmological times, but are also able to release them under the influence of very strong turbulence. This might happen during a major merger event of clusters of galaxies. The released relativistic proton population could produce the observed radio halos of some cluster of galaxies via hadronic reactions with the background gas leading to the production of secondary electrons and positrons. Destroyed ghosts, mixed with the IGM can help to magnetize it. Finally, the strong field strength within ghosts should have a significant impact on the propagation of extragalactic high energy cosmic rays.

Abstract:
An inspection of the precise geometric constructions underlying fundamental notions in quantum gauge field theories sheds light on various aspects which tend to be obscured in the usual formalisms. Revising the notions of mutually conjugated "internal" bundles we propose a general rule for the constructions of free quantum fields and their conjugates, naturally yielding the needed fundamental properties with regard to contractions, super-commutators, field momentum and Hamiltonian, and other quantities. This scheme applies to fields of all types; in particular we examine consequences in relation to ghosts and anti-ghosts. Finally in the context of observer-independent Fr\"olicher-smooth quantum bundles we show how the antifield sectors naturally arise, and examine the precise relation among these and the BRST symmetry of a gauge field theory.

Abstract:
Suppose that $G$ is a finite group and $k$ is a field of characteristic $p>0$. A ghost map is a map in the stable category of finitely generated $kG$-modules which induces the zero map in Tate cohomology in all degrees. In an earlier paper we showed that the thick subcategory generated by the trivial module has no nonzero ghost maps if and only if the Sylow $p$-subgroup of $G$ is cyclic of order 2 or 3. In this paper we introduce and study some variations of ghosts maps. In particular, we consider the behavior of ghost maps under restriction and induction functors. We find all groups satisfying a strong form of Freyd's generating hypothesis and show that ghost can be detected on a finite range of Tate cohomology. We also consider maps which mimic ghosts in high degrees.

Abstract:
Perturbation theory for gravity in dimensions greater than two requires higher derivatives in the free action. Higher derivatives seem to lead to ghosts, states with negative norm. We consider a fourth order scalar field theory and show that the problem with ghosts arises because in the canonical treatment, $\phi$ and $\Box \phi $ are regarded as two independent variables. Instead, we base quantum theory on a path integral, evaluated in Euclidean space and then Wick rotated to Lorentzian space. The path integral requires that quantum states be specified by the values of $\phi$ and $\phi_{,\tau}$. To calculate probabilities for observations, one has to trace out over $\phi_{,\tau}$ on the final surface. Hence one loses unitarity, but one can never produce a negative norm state or get a negative probability. It is shown that transition probabilities tend toward those of the second order theory, as the coefficient of the fourth order term in the action tends to zero. Hence unitarity is restored at the low energies that now occur in the universe.

Abstract:
Distilling from a knowledge base only the part that is relevant to a subset of alphabet, which is recognized as forgetting, has attracted extensive interests in AI community. In standard propositional logic, a general algorithm of forgetting and its computation-oriented investigation in various fragments whose satisfiability are tractable are still lacking. The paper aims at filling the gap. After exploring some basic properties of forgetting in propositional logic, we present a resolution-based algorithm of forgetting for CNF fragment, and some complexity results about forgetting in Horn, renamable Horn, q-Horn, Krom, DNF and CNF fragments of propositional logic.

Abstract:
In questo intervento all’Accademia dei Lincei, l’Autore ripercorre il pensiero di Franco Modigliani,con particolare riguardo ai temi della moneta, della politica monetaria e, in generale, della politica economica, i cui aspetti salienti costituirono parte integrante del primo modello econometrico della Banca d’Italia. Sottolineando la posizione equilibrata di Modigliani nel dibattito macroeconomico,l’Autore mostra come, rifuggendo dalle logiche di schieramento, egli difese con argomentazioni penetranti la necessità delle politiche anticicliche. I numerosi contributi di Modigliani, sia teorici sia empirici, hanno costituito un utile strumento nelle mani del banchiere centrale; la sua lezione resta attuale, ponendo in luce il ruolo delle politiche di stabilizzazione in un sistema finanziario globale, i loro riflessi sulla competitività e sulla capacità di crescita delle economie.