Electromagnetic self-force in curved spacetime: New insights from the Janis-Newman algorithm

We present an original approach to compute the electromagnetic self-force acting on a static charge in Kerr spacetime. Our approach is based on an improved version of the Janis-Newman algorithm and extends its range of applicability. It leads to a closed expression which generalizes the existing one and, since it does not involve the electromagnetic potential, it simplifies the calculation of the self-force.Comment: 4 pages. Minor corrections, added references. Version accepted by Physical Review

Irrelevant Operators and their Holographic Anomalies

Irrelevant operators in a CFT modify the usual Weyl transformation of the metric. A metric beta-function turns on, which modifies the Weyl anomalies as well. In this paper, we study the relation between bulk diffeomorphisms and Weyl transformation at the boundary when a massive scalar field, which sources irrelevant operators at the boundary, is coupled to the bulk metric. Considering the effect of the backreaction generated by the scalar field, we provide a holographic description of the boundary metric beta-function and anomalies. Our results represent an additional test of the AdS/CFT correspondence

Aspects of Conformal Field Theory

In dieser Dissertation analysieren wir drei Aspekte von Konforme Feldtheorien (CFTs). Erstens betrachten wir Korrelationsfunktionen von sekundären Zuständen (SZ) in zweidimensionalen CFTs. Wir diskutieren eine rekursive Formel zu ihrer Berechnung und erstellen eine Computerimplementierung dieser Formel. Damit können wir jede Korrelationsfunktion von SZ des Vakuums erhalten und für Nicht-Vakuum-SZ den Korrelator als Differentialoperator, der auf den jeweiligen primären Korrelator wirkt, ausdrücken. Mit diesem Code untersuchen wir dann einige Verschränkungs- und Unterscheidbarkeitsmaße zwischen SZ, i.e. die Rényi-Entropie, den Spurquadratabstand und die Sandwich-Rényi-Divergenz. Mit unseren Ergebnissen können wir die Rényi Quanten-Null-Energie-Bedingung testen und stellen neue Werkzeuge zur Analyse der holographischen Beschreibung von SZ bereit. Zweitens untersuchen wir vierdimensionale Weyl-Fermionen auf verschiedenen Hintergründen. Unser Interesse gilt ihrer Spuranomalie, und der Frage, ob die Pontryagin-Dichte auftritt. Deshalb berechnen wir die Anomalien von Dirac-Fermionen, die an vektorielle und axiale Eichfelder gekoppelt sind, und dann auf einem metrisch-axialen Tensor Hintergrund. Geeignete Grenzwerte der Hintergründe erlauben es dann, die Anomalien von Weyl-Fermionen, die an Eichfelder gekoppelt sind, und in einer gekrümmten Raumzeit zu berechnen. Wir bestätigen das Fehlen der Pontryagin-Dichte in den Spuranomalien. Drittens liefern wir die holographische Beschreibung einer vierdimensionalen CFT mit einem irrelevanten Operator. Wenn der Operator eine ganzzahlige konforme Dimension hat, modifiziert sein Vorhandensein in der CFT die Weyl-Transformation der Metrik, was wiederum die Spuranomalie ändert. Unter Ausnutzung der Äquivalenz zwischen Diffeomorphismen im Inneren und Weyl-Transformationen auf dem Rand, berechnen wir diese Modifikationen mithilfe der dualen Gravitationstheorie. Unsere Ergebnisse repräsentieren einen weiteren Test der AdS/CFT-Korrespondenz.Conformal field theories (CFTs) are amongst the most studied field theories and they offer a remarkable playground in modern theoretical physics. In this thesis we analyse three aspects of CFTs in different dimensions. First, we consider correlation functions of descendant states in two-dimensional CFTs. We discuss a recursive formula to calculate them and provide a computer implementation of it. This allows us to obtain any correlation function of vacuum descendants, and for non-vacuum descendants to express the correlator as a differential operator acting on the respective primary correlator. With this code, we study some entanglement and distinguishability measures between descendant states, i.e. the Rényi entropy, trace square distance and sandwiched Rényi divergence. With our results we can test the Rényi Quantum Null Energy Condition and provide new tools to analyse the holographic description of descendant states. Second, we study four-dimensional Weyl fermions on different backgrounds. Our interest is in their trace anomaly, where the Pontryagin density has been claimed to appear. To ascertain this possibility, we compute the anomalies of Dirac fermions coupled to vector and axial non-abelian gauge fields and then in a metric-axial-tensor background. Appropriate limits of the backgrounds allow to recover the anomalies of Weyl fermions coupled to non-abelian gauge fields and in a curved spacetime. In both cases we confirm the absence of the Pontryagin density in the trace anomalies. Third, we provide the holographic description of a four-dimensional CFT with an irrelevant operator. When the operator has integer conformal dimension, its presence in the CFT modifies the Weyl transformation of the metric, which in turns modifies the trace anomaly. Exploiting the equivalence between bulk diffeomorphisms and boundary Weyl transformations, we compute these modifications from the dual gravity theory. Our results represent an additional test of the AdS/CFT conjecture

On the trace anomaly of a Weyl fermion in a gauge background

In this thesis we study the trace anomaly of a Weyl fermion in an abelian gauge background. We first introduce the topic of anomaly in Quantum Fields Theory and provide case studies of a global and a gauge anomaly. Then, we review the lagrangians of the Weyl fermion and Dirac fermion, the models that are the focus of our chiral and trace anomaly computations. Since we evaluate the anomalies using Pauli-Villars (PV) regularization, we present different PV masses and discuss the classical symmetries they break. We identify the differential operators that enter our regularization schemes and we review the method that we use to evaluate anomalies: we read them from the path integral à la Fujikawa and compute them with heat kernel formulas. Then, we evaluate the chiral and trace anomaly of the models we are interested in. The chiral anomaly is well studied in the literature and we reproduce the standard result. The trace anomaly is our original result and, although the presence of the chiral anomaly implies a breakdown of gauge invariance, we find that the trace anomaly can be cast in a gauge invariant form. The issue is analogous to the one recently discussed in the literature about a conjectured contribution of an odd-parity term to the trace anomaly of a Weyl fermion in curved backgrounds. With an abelian gauge background, this odd-parity term would be a Chern-Pontryagin density, that does not appear in our final results

Community-based perceptions of emergency care in communities lacking formalised emergency medicine systems

Kenya and Zambia face an increasing burden of emergent disease, with a high incidence of communicable diseases, increasing prevalence of non-communicable diseases and traumatic injuries. However, neither country has an integrated emergency care system that provides community access to high-quality emergency services. There has been recent interest in strengthening the emergency care systems in these countries, but before any interventions are implemented, an assessment of the current need for emergency care must be conducted, as the burden of acute disease and barriers to accessing emergency care in Zambia and Kenya remain largely undocumented. Aims and Objectives: The aim of this project was to ascertain community-based perceptions of the critical interventions necessary to improve access to emergency care in Zambia and Kenya, with the following objectives: 1. Determine the current pattern of out-of-hospital emergency care delivery at the community level. 2. Identify the communities’ experiences with emergency conditions and the barriers they face when trying to access care. 3. Discover community-generated solutions to the paucity of emergency care in urban and rural settings. Methods: Semi-structured focus groups were piloted in Zambia with 200 participants. Results were analysed with subsequent tool refinement for Kenya. Data were collected via focus groups with 600 urban and rural community members in cities and rural villages in the 8 Kenyan provinces. Thematic analysis of community member focus groups identified frequency of emergencies, perceptions of emergency care, perceived barriers to emergency care, and ideas for potential interventions. Results: Analysis of the focus group data identified several common themes. Community members in Zambia and Kenya experience a wide range of medical emergencies, and they rely on family members, neighbours, and Good Samaritans for assistance. These community members frequently provide assistance with transportation to medical facilities, and also attempt some basic first aid. These communities are already assisting one another during emergencies, and are willing to help in the future. Participants in this study also identified several barriers to emergency care : a lack of community education, absent or non-functional communication systems, insufficient transportation, no triage system, a lack of healthcare providers trained in emergency care, and inadequate equipment and supplies. Conclusions: Community members in Zambia and Kenya experience a wide range of medical emergencies. There is substantial reliance on family members and neighbours for assistance, commonly with transportation. Creating community education initiatives, identifying novel transportation solutions, implementing triage in healthcare facilities, and improving receiving facility care were community-identified solutions to barriers to emergency care

Microgravity, Stem Cells, and Embryonic Development: Challenges and Opportunities for 3D Tissue Generation

Space is a challenging environment for the human body, due to the combined effects of reduced gravity (microgravity) and cosmic radiation. Known effects of microgravity range from the blood redistribution that affects the cardiovascular system and the eye to muscle wasting, bone loss, anemia, and immune depression. About cosmic radiation, the shielding provided by the spaceship hull is far less efficient than that afforded at ground level by the combined effects of the Earth atmosphere and magnetic field. The eye and its nervous layer (the retina) are affected by both microgravity and heavy ions exposure. Considering the importance of sight for long-term manned flights, visual research aimed at devising measures to protect the eye from environmental conditions of the outer space represents a special challenge to meet. In this review we focus on the impact of microgravity on embryonic development, discussing the roles of mechanical forces in the context of the neutral buoyancy the embryo experiences in the womb. At variance with its adverse effects on the adult human body, simulated microgravity may provide a unique tool for understanding the biomechanical events involved in the development and assembly in vitro of three-dimensional (3D) ocular tissues. Prospective benefits are the development of novel safety measures to protect the human eye from cosmic radiation in microgravity during long-term manned spaceflights in the outer space, as well as the generation of human 3D-retinas with its supporting structures to develop innovative and effective therapeutic options for degenerative eye diseases

On the trace anomaly of a Weyl fermion in a gauge background

We study the trace anomaly of a Weyl fermion in an abelian gauge background. Although the presence of the chiral anomaly implies a breakdown of gauge invariance, we find that the trace anomaly can be cast in a gauge invariant form. In particular, we find that it does not contain any odd-parity contribution proportional to the Chern-Pontryagin density. The latter would be allowed by the consistency conditions. We perform our calculations using Pauli-Villars regularization and heat kernel methods. The issue is analogous to the one recently discussed in the literature about a conjectured contribution of an odd-parity term to the trace anomaly of a Weyl fermion in curved backgrounds.Comment: 26 pages, minor changes and reference adde

Correlation functions and quantum measures of descendant states

We discuss a computer implementation of a recursive formula to calculate correlation functions of descendant states in two-dimensional CFT. This allows us to obtain any N-point function of vacuum descendants, or to express the correlator as a differential operator acting on the respective primary correlator in case of non-vacuum descendants. With this tool at hand, we then study some entanglement and distinguishability measures between descendant states, namely the Renyi entropy, trace square distance and sandwiched Renyi divergence. Our results provide a test of the conjectured Renyi QNEC and new challenges for the holographic description of descendant states at large c

The Effects of the Laurentide Ice Sheet on North American Climate during the Last Glacial Maximum

A climate model, consisting of an atmospheric general circulation model coupled with a simple model of the oceanic mixed layer, is used to investigate the effects of the continental ice distribution of the last glacial maximum (LGM) on North American climate. This model has previously been used to simulate the LGM climate, producing temperature changes reasonably in agreement with paleoclimatic data. The LGM distribution of continental ice according to the maximum reconstruction of HUGHES et al. (1981) is used as input to the model. In response to the incorporation of the expanded continental ice of the LGM, the model produces major changes in the climate of North America. The ice sheet exerts an orographic effect on the tropospheric flow, resulting in a splitting of the midlatitude westerlies in all seasons but summer. Winter temperatures are greatly reduced over a wide region south of the Laurentide ice sheet, although summer cooling is less extensive. An area of reduced soil moisture develops in the interior of North America just south of the ice margin. At the same time, precipitation increases in a belt extending from the extreme southeastern portion of the ice sheet eastward into the North Atlantic. Some of these findings are similar to paleoclimatic inferences based on geological evidence.Un modèle climatique, composé d'un modèle de circulation atmosphérique général associé à un modèle simple de la couche océanique mixte, a servi à étudier l'influence de la répartition des glaciers continentaux sur le climat de l'Amérique du Nord au dernier pléniglaciaire. Ce modèle avait déjà servi pour simuler le climat au dernier pléniglaciaire; il a montré des changements de températures concordant assez bien avec les données paléoclimatiques. La répartition des glaces continentales pendant le pléniglaciaire selon l'hypothèse d'extension maximale de HUGHES et al. (1981) a servi à la modélisation. En réponse à l'incorporation des données de cette hypothèse, le modèle fait voir des changements majeurs dans le climat de l'Amérique du Nord. La présence de la calotte glaciaire fait ressortir l'influence de l'orographie sur le flux troposphérique qui se concrétise par une séparation des vents d'ouest aux latitudes moyennes durant toutes les saisons, sauf l'été. Les températures hivernales s'abaissent substantiellement dans une vaste région située au sud de la calotte laurentidienne, bien que le refroidissement soit moindre durant l'été. Une zone sèche se développe immédiatement au sud de la marge glaciaire. Au même moment, les précipitations augmentent dans la région qui s'étend de l'extrémité sud-est de la calotte glaciaire jusque dans l'Atlantique Nord, à l'est. Certains de ces résultats sur la nature du paléoclimat sont similaires aux déductions que les données géologiques ont inspirées.Um die Auswirkungen der kontinentalen Eisverbreitung im jüngsten glazialen Maximum auf das nordamerikanische Klima zu erforschen, wird ein Klima-Modell benutzt. das aus einem Modell der Hauptluftströmung in Verbindung mit einem einfachen Modell der gemischten ozeanischen Schicht besteht. Frùher wurde dieses Modell benutzt, um das Klima im jüngsten glazialen Maximum zu simulieren. Die Ergebnisse haben Temperaturschwankungen ergeben, die einigermapen genau mit den paleoklimatischen Daten übereinstimmten. Ausgegangen wurde bei dem Modell von der Verteilung des kontinentalen Eises im jüngsten glazialen Maximum entsprechend der Maximum-Rekonstruktion von HUGHES et al. (1981). AIs Antwort auf die Einverleibung des ausgedehnten kontinentalen Eises im jüngsten glazialen Maximum produziert das Modell bedeutende Veränderungen im nordamerikanischen Klima. Die Eisdecke übt eine orographische Wirkung auf die troposphärische Luftströmung aus, was zu einer Aufsplitterung der westlichen Winde mittlerer Breite in alien Jahreszeiten auBer im Sommer führt. Die Winter-Temperaturen sinken stark in einem weiten Gebiet südlich der laurentischen Eisdecke, während die sommerliche Abkühlung weniger stark ausfällt. Im Innern Nordamerikas südlich der Eisgrenze entwickelt sich ein Gebiet verringerter Bodenfeuchtigkeit. Gleichzeitig nehmen die Niederschläge innerhalb eines Gürtels zu, der von dem äupersten südöstlichen Teil der Eisdecke ostwärts in den Nordatlantik reicht. Einige dieser Ergebnisse decken sich mit paleoklimatischen Folgerungen, die sich auf geologische Nachweise stützen