Search results for "ALTER"
showing 10 items of 2368 documents
Massless positivity in graviton exchange
2021
We formulate Positivity Bounds for scattering amplitudes including exchange of massless particles. We generalize the standard construction through dispersion relations to include the presence of a branch cut along the real axis in the complex plane for the Maldestam variable $s$. In general, validity of these bounds require the cancellation of divergences in the forward limit of the amplitude, proportional to $t^{-1}$ and $\log(t)$. We show that this is possible in the case of gravitons if one assumes a Regge behavior of the amplitude at high energies below the Planck scale, as previously suggested in the literature, and that the concrete UV behaviour of the amplitude is uniquely determined…
Infrared lessons for ultraviolet gravity: the case of massive gravity and Born-Infeld
2014
We generalize the ultraviolet sector of gravitation via a Born-Infeld action using lessons from massive gravity. The theory contains all of the elementary symmetric polynomials and is treated in the Palatini formalism. We show how the connection can be solved algebraically to be the Levi-Civita connection of an effective metric. The non-linearity of the algebraic equations yields several branches, one of which always reduces to General Relativity at low curvatures. We explore in detail a {\it minimal} version of the theory, for which we study solutions in the presence of a perfect fluid with special attention to the cosmological evolution. In vacuum we recover Ricci-flat solutions, but also…
On gravitational waves in Born-Infeld inspired non-singular cosmologies
2017
We study the evolution of gravitational waves for non-singular cosmological solutions within the framework of Born-Infeld inspired gravity theories, with special emphasis on the Eddington-inspired Born-Infeld theory. We review the existence of two types of non-singular cosmologies, namely bouncing and asymptotically Minkowski solutions, from a perspective that makes their features more apparent. We study in detail the propagation of gravitational waves near these non-singular solutions and carefully discuss the origin and severity of the instabilities and strong coupling problems that appear. We also investigate the role of the adiabatic sound speed of the matter sector in the regularisatio…
Correlation patterns from massive phonons in 1+1 dimensional acoustic black holes: A toy model
2018
Transverse excitations in analogue black holes induce a mass like term in the longitudinal mode equation. With a simple toy model we show that correlation functions display a rather rich structure characterized by groups of parallel peaks. For the most part the structure is completely different from that found in the massless case.
Abjection and alterity in the imagining of transgender in physical education and sport: a pedagogical approach in higher education
2014
In physical education (PE) and sports there is little theoretical and empirical knowledge about transgender people, and particularly, on how they are and can be imagined within this context. In this paper, we present and analyze a pedagogical activity based on the reading and discussion of a fictional representation of a transgender person within a group of undergraduate students of Sport Sciences. Our theoretical frame situates abjection and alterity as opposing concepts on a continuum. Results show several ways in which a transgender person is imagined by students, as well as constraints and possibilities for the pedagogical proposal to promote moral imagining of transgender. Students sit…
Comment: What is Alternative Technology? A Reply to Professor Stanley Carpenter
1983
Modern man is dissatisfied with the technology we have and would replace it with another. Three very different reasons are given for this. I will divide my treatment of them under three headings, listing the reason in each case together with a reply.
Intersecciones críticas. Experiencias y estrategias desde la museología y el feminismo gitano, bajo el prisma del covid-19 = Critical Intersections. …
2020
La pandemia de 2020 enfrentó las áreas que tratan la memoria desde los márgenes con la necesidad de transformar sus experiencias en estrategias con potencial de futuro. El artículo busca reflejar la intersección entre dos campos de acción cultural comprometida: el de algunos museos valencianos y el de las asociaciones de mujeres gitanas, vistas también desde el ámbito local. El objeto de nuestro análisis son dos vertientes de la actuación cultural emancipadora: las experiencias, fenómenos a menudo caóticos y coyunturales, y las estrategias razonadas, que unen prácticas del conocimiento crítico hasta ahora no contiguas. El estado de alarma definió estas ramas estratégicas como inclusión digi…
Carlo Ginzburg. Cuando el historiador amoneda un símbolo
2020
Resumen En este artículo pretendemos analizar la trayectoria, la contribución, los resultados y la influencia de un historiador de renombre mundial, Carlo Ginzburg. La suya es una investigación de largo recorrido, cuya influencia se ha dado no sólo en esta rama del saber, sino también en muy distintos ámbitos de las humanidades, de las ciencias, de las artes. Carlo Ginzburg ha sido reconocido e identificado principalmente a partir de dos logros historiográficos: la microhistoria y El queso y los gusanos. Por un lado, se le ve como el máximo representante de la microhistoria, la corriente de origen italiano que se expande principalmente en los años ochenta del siglo XX. Por otro lado, a este…
Implicaciones de la evolución histórica de algunos conceptos en la enseñanza de la Relatividad
2006
La relatividad es una parte importante de la fisica moderna. En este articulo se analiza el debate en torno a la utilizacion de la historia de la ciencia para orientar la didactica de la relatividad en la ensenanza secundaria. Se repasa la evolucion historica de algunos conceptos clave de la relatividad especial y se muestra su implicacion en la ensenanza-aprendizaje.Palabras clave: ensenanza-aprendizaje; relatividad; historia de la ciencia.Implications of the historical evolution of some concepts in the teaching of relativityThe relativity is an important part the modern physics. In this article we analyze the discussion around the use of the history of science to guide the didactics of th…
Technological differences and convergence in the OECD
2000
Abstract. In this paper we test the homogeneity of the technological parameters among OECD countries, which is the maintained hypothesis in most of the empirical growth literature. We first identify differences in the constant term of the convergence equation estimated for the OECD 1960/1990 sample using a fixed- effects estimator. Then we provide a formal test of the homogeneity of technological parameters across groups of countries. We identify at least two different groups within the OECD, with significantly different technologies. Convergence within each group is fast, supporting the notion of club convergence. Nevertheless, the implausible parameter values obtained for the leading tech…