Vacuum Radiation and Symmetry Breaking in Conformally Invariant Quantum Field Theory

The underlying reasons for the difficulty of unitarily implementing the whole conformal group $SO(4,2)$ in a massless Quantum Field Theory (QFT) are investigated in this paper. Firstly, we demonstrate that the singular action of the subgroup of special conformal transformations (SCT), on the standard Minkowski space $M$, cannot be primarily associated with the vacuum radiation problems, the reason being more profound and related to the dynamical breakdown of part of the conformal symmetry (the SCT subgroup, to be more precise) when representations of null mass are selected inside the representations of the whole conformal group. Then we show how the vacuum of the massless QFT radiates under the action of SCT (usually interpreted as transitions to a uniformly accelerated frame) and we calculate exactly the spectrum of the outgoing particles, which proves to be a generalization of the Planckian one, this recovered as a given limit.Comment: 29 pages, Latex, 1 figure, to appear in Commun. Math. Phy

Estudiar concepcions-idees d'estudiantes en ciències utilitzant teorias d'argumentació

Durant les últimes dècades, hi ha hagut un gran interès, en l'àrea de la didàctica de les ciències, per la investigació de les idees prèvies els alumnes en ciències. En el nostre treball no es tracta de trobar i identificar aquestes idees, sinó de trobar el sentit comú en què es basen aquestes idees. Ens proposem trobar esquemes de raonament, o argumentativos, espontanis que es troben detràs d'aquestes concepcions científiques d'estudiantes de Magisteri. El nostre marc analítico s'elabora a partir de la Teoria d'argumentació d'Aristòtil i de teorias més contemporànies com la de Perelman, Toulmin i Walton per a tenir un llistat el més ampli possible dels esquemes d'argumentació del nostre sentit comú actual

Two dimensional dynamical systems which admit Lie and Noether symmetries

We prove two theorems which relate the Lie point symmetries and the Noether symmetries of a dynamical system moving in a Riemannian space with the special projective group and the homothetic group of the space respectively. The theorems are applied to classify the two dimensional Newtonian dynamical systems, which admit a Lie point/Noether symmetry. Two cases are considered, the non-conservative and the conservative forces. The use of the results is demonstrated for the Kepler - Ermakov system, which in general is non-conservative and for potentials similar to the H\`enon Heiles potential. Finally it is shown that in a FRW background with no matter present, the only scalar cosmological model which is integrable is the one for which 3-space is flat and the potential function of the scalar field is exponential. It is important to note that in all applications the generators of the symmetry vectors are found by reading the appropriate entry in the relevant tables.Comment: 25 pages, 17 table

Estudiar concepcions-idees d'estudiantes en ciències utilitzant teorias d'argumentació

Durant les últimes dècades, hi ha hagut un gran interès, en l'àrea de la didàctica de les ciències, per la investigació de les idees prèvies els alumnes en ciències. En el nostre treball no es tracta de trobar i identificar aquestes idees, sinó de trobar el sentit comú en què es basen aquestes idees. Ens proposem trobar esquemes de raonament, o argumentativos, espontanis que es troben detràs d'aquestes concepcions científiques d'estudiantes de Magisteri. El nostre marc analítico s'elabora a partir de la Teoria d'argumentació d'Aristòtil i de teorias més contemporànies com la de Perelman, Toulmin i Walton per a tenir un llistat el més ampli possible dels esquemes d'argumentació del nostre sentit comú actual

Limited Ability to Activate Protein C Confers Left Atrial Endocardium A Thrombogenic Phenotype: A Role in Cardioembolic Stroke?

Background and Purpose—Atrial fibrillation is the most important risk factor for cardioembolic stroke. Thrombi form in the left atrial appendage rather than in the right. The causes of this different thrombogenicity are not well-understood. The goal herein was to compare the activation of the anticoagulant protein C and the thrombomodulin and endothelial protein C receptor/activated protein C receptor expression on the endocardium between right and left atria. Methods—We harvested the atria of 6 monkeys (Macaca fascicularis) and quantified their ability to activate protein C ex vivo and we measured the thrombomodulin and endothelial protein C receptor expression by immunofluorescence. Results—We found the ability to activate protein C decreased by half (P 0.028) and there was lower expression of thrombomodulin in the left atrial endocardium than the right (52.5 19.9 and 72.1 18.8 arbitrary intensity units, mean standard deviation; P 0.028). No differences were detected in endothelial protein C receptor expression. Conclusions—Impaired protein C activation on the left atrial endocardium attributable to low thrombomodulin expression may explain its higher thrombogenicity and play a role in cardioembolic stroke