519 research outputs found
Misleading inferences from discretization of empty spacetime: Snyder-noncommutativity case study
No full textAlternative approaches to the study of the quantum gravity problem are handling the role of spacetime very differently. Some are focusing on the analysis of one or another novel formulation of empty spacetime, postponing to later stages the introduction of particles and fields, while other approaches assume that spacetime should only be an emergent entity. We here argue that recent progress in the covariant formulation of quantum mechanics, suggests that empty spacetime is not physically meaningful. We illustrate our general thesis in the specific context of the noncommutative Snyder spacetime, which is also of some intrinsic interest, since hundreds of studies were devoted to its analysis. We show that empty Snyder spacetime, described in terms of a suitable kinematical Hilbert space, is discrete, but this is only a formal artifact: the discreteness leaves no trace on the observable properties of particles on the physical Hilbert space
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Fantastic Architecture and the Building of Europe in Valerio Evangelisti's Eymerich Fiction
No full textConcomitant with the horizontal expansion of EU territory through physical and political enlargement is a genealogy narrative, which emphasizes the ostensible roots of Europeanness in classical antiquity and Christianity. In the face of this sanitized genealogy, which lies at the heart of the European constitutional project, a range of alternative and more inclusive narratives circulate in contemporary European popular fiction. This paper focuses on a series of fantasy novels by the Italian author Valerio Evangelisti, featuring Inquisitor Eymerich as hero-investigator. In his highly popular novels, Evangelisti seeks to uncover layers of shared historical memory untainted with post-Enlightenment rhetoric.
The central architectural tropes of Evangelisti’s imaginary world are those of a castle and a convent, epitomizing the temporal and sacral power in European history. Each isolated from its outside environment and built on layer upon layer of subterranean chambers and corridors, the castle and the convent conceal a past quite different from the one championed in the official European genealogy. Memories of pagan worship and Islamic or Judaic learning – banished from the official rhetoric – continue to thrive, dark and threatening, in the subterranean strata of Evangelisti’s European edifice. Evangelisti thus provides an incisive critique of the official European story of origin, which threatens to suppress any alternative visions of European history or unorthodox avenues for European identity formation
Relative locality in a quantum spacetime and the pregeometry of κ-Minkowski
No full textWe develop a description of the much-studied κ-Minkowski noncommutative spacetime, centered on representing on a single Hilbert space not only the κ-Minkowski coordinates, but also the κ-Poincaré symmetry generators and some suitable relativistic-transformation parameters. In this representation the relevant operators act on the kinematical Hilbert space of the covariant formulation of quantum mechanics, which we argue is the natural framework for studying the implications of the step from commuting spacetime coordinates to the κ-Minkowski case, where the spatial coordinates do not commute with the time coordinate. Within this kinematical-Hilbert-space representation we can give a crisp characterization of the "fuzziness" of points in κ-Minkowski spacetime, also allowing us to describe how the same fuzzy point is seen by different relativistic observers. The most striking finding of our analysis is a relativity of spacetime locality in κ-Minkowski. While previous descriptions of relative locality had been formulated exclusively in classical-spacetime setups, our analysis shows how relative locality in a quantum spacetime takes the shape of a dependence of the fuzziness of a spacetime point on the distance at which an observer infers properties of the event that marks the point. © 2013 Springer-Verlag Berlin Heidelberg and Società Italiana di Fisica
Relative locality and gravity's weight on worldline fuzziness
No full textWe use the example of the much-studied κ-Minkowski noncommutative spacetime for illustrating a novel approach toward the analysis of the possible implications of spacetime noncommutativity. Our starting point is the proposal that spacetime noncommutativity is most naturally introduced within the manifestly-covariant formulation of quantum mechanics. This allows us to obtain a crisp characterization of the relativity of spacetime locality present in κ-Minkowski theories. And we also develop a novel description of how κ-Minkowski noncommutativity affects the fuzziness of worldlines. © Published under licence by IOP Publishing Ltd
Efficient and accurate inference for mixtures of Mallows models with Spearman distance
No full textThe Mallows model occupies a central role in parametric modelling of ranking
data to learn preferences of a population of judges. Despite the wide range of
metrics for rankings that can be considered in the model specification, the
choice is typically limited to the Kendall, Cayley or Hamming distances, due to
the closed-form expression of the related model normalizing constant. This work
instead focuses on the Mallows model with Spearman distance. An efficient and
accurate EM algorithm for estimating finite mixtures of Mallows models with
Spearman distance is developed, by relying on a twofold data augmentation
strategy aimed at i) enlarging the applicability of Mallows models to samples
drawn from heterogeneous populations; ii) dealing with partial rankings
affected by diverse forms of censoring. Additionally, a novel approximation of
the model normalizing constant is introduced to support the challenging
model-based clustering of rankings with a large number of items. The
inferential ability of the EM scheme and the effectiveness of the approximation
are assessed by extensive simulation studies. Finally, we show that the
application to three real-world datasets endorses our proposals also in the
comparison with competing mixtures of ranking models.Comment: 20 pages, 6 Figures, 11 Table
Hermann Kant. Ein bio- bibliografisches Profil
No full textThe proximity to the power apparatus has cast dark shadows on the literary work of Hermann Kant, who is regarded as one of the most read authors of the GDR. Valerio Furneri embeds Kant's life and work in the all-German context of the 20th century and reinterprets his classics such as Die Aula or Der Aufenthalt. The author does not pursue the claim to rehabilitate the GDR, nor to trivialise Kant's role in it. Instead, the attempt is made to look at Kant's entire work from a temporal distance and to re-evaluate it. Through his works, Kant was able to accompany and depict not only the German-German history, but also European history.Die Nähe zum Machtapparat hat dunkle Schatten auf das literarische Werk von Hermann Kant, der als meistgelesener Schriftsteller der DDR gilt, geworfen. Valerio Furneri bettet Kants Leben und Werk in den gesamtdeutschen Kontext des 20. Jahrhunderts ein und interpretiert vor diesem Hintergrund Klassiker wie Die Aula oder Der Aufenthalt neu. Der Autor verfolgt dabei weder den Anspruch, die DDR zu rehabilitieren, noch Kants Rolle darin kleinzureden. Stattdessen wird der Versuch unternommen, Kants Gesamtwerk aus zeitlicher Distanz zu betrachten und neu zu bewerten. Durch seine Werke gelang es Kant nämlich nicht nur die deutsch-deutsche, sondern auch die europäische Geschichte zu begleiten und abzubilden
Hermann Kant. Ein bio- bibliografisches Profil
No full textThe proximity to the power apparatus has cast dark shadows on the literary work of Hermann Kant, who is regarded as one of the most read authors of the GDR. Valerio Furneri embeds Kant's life and work in the all-German context of the 20th century and reinterprets his classics such as Die Aula or Der Aufenthalt. The author does not pursue the claim to rehabilitate the GDR, nor to trivialise Kant's role in it. Instead, the attempt is made to look at Kant's entire work from a temporal distance and to re-evaluate it. Through his works, Kant was able to accompany and depict not only the German-German history, but also European history.Die Nähe zum Machtapparat hat dunkle Schatten auf das literarische Werk von Hermann Kant, der als meistgelesener Schriftsteller der DDR gilt, geworfen. Valerio Furneri bettet Kants Leben und Werk in den gesamtdeutschen Kontext des 20. Jahrhunderts ein und interpretiert vor diesem Hintergrund Klassiker wie Die Aula oder Der Aufenthalt neu. Der Autor verfolgt dabei weder den Anspruch, die DDR zu rehabilitieren, noch Kants Rolle darin kleinzureden. Stattdessen wird der Versuch unternommen, Kants Gesamtwerk aus zeitlicher Distanz zu betrachten und neu zu bewerten. Durch seine Werke gelang es Kant nämlich nicht nur die deutsch-deutsche, sondern auch die europäische Geschichte zu begleiten und abzubilden
Efficient estimation of finite mixtures of Mallows models with the Spearman distance
No full textThe class of Mallows models (MMs) occupy a central role in the literature for the analysis and learning of preferences from a sample of ranking data.
The MMs rely on the distance notion over the set of permutations but, despite the wide range of possible metrics, the choice is typically limited to
the Kendall or Cayley distances, due to the related analytical simplifications. We go beyond these conventional few options and explore the formal
properties of the MM with the Spearman distance, also referred to as the theta-model. The attractive feature of this model is its correspondence with
the restriction of the normal distribution over the permutation set such that, similarly to the Gaussian density, the theta model enjoys a convenient
closed-form expression for the critical estimation of the modal ranking. This means that, differently from the MMs with the other metrics, an
efficient and accurate inferential procedure can be developed, where the computational burden of inferring the discrete parameter is significantly
reduced. Additionally, an efficient estimation within the finite mixture framework is realized via the EM algorithm, for enlarging the applicability
of theta-models to samples of rankings characterized by a group structure. Finally, an application to a real-world dataset endorsing our proposals
in the comparison with competing mixtures of ranking models is provided
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