Pulsed-perturbative QED

Moderne Lasereinrichtungen stellen hochintensives Licht mit sehr kurzer zeitlicher Struktur zur Verfügung. Damit bringen diese Einrichtungen die Phänomene in die Laboratorien, welche normalerweise nur in der Nähe von stark strahlenden Sternen im Weltall zu finden sind. Bezüglich der Streuprozesse von Teilchen innerhalb dieser extremen Lichtquellen gibt es eine Vielzahl an theoretischen Untersuchungen. Vorwiegend geschehen diese unter der Verwendung der Starkfeld-Quantenelektrodynamik, einer Theorie zur quanten- theoretischen Beschreibung von elektromagnetischen Wechselwirkungen innerhalb eines kohärenten hochintensiven Feldes, welches als semi-klassisches Hintergrundfeld beschrieben wird. Zum Beispiel zeigte die theoretische Behandlung des Compton-Prozesses (die inelastis- che Elektron-Photon-Streuung) oder des Breit-Wheeler-Prozesses (der Paarproduktion in der Kollision von zwei Photonen) innerhalb der Starkfeld-Quantenelektrodynamik eine große Menge an neuen nicht-linearen Effekten und Phänomen, welche stellenweise in zukun- ftsweisenden Experimenten nachgewiesen werden konnten. Von großem Interesse und auch zentrales Untersuchungsobjekt der vorliegenden Arbeit ist ebenso der Trident-Prozess: ein Prozess zweiter Ordnung in der (Starkfeld-) Quan- tenelektrodynamik, bei dem ein Elektron-Positron-Paar innerhalb der Kollision eines Photonstrahls (z.B. erzeugt von einem Laser) und eines gegenläufigen Elektronenstrahls entsteht. Allerdings ist der Trident-Prozess im Zusammenhang mit hochintensiven Feldern nicht ausschließlich das Produkt seiner Teile, den erwähnten Compton- und Breit-Wheeler- Prozessen, vielmehr erzeugt das Vorhandensein des intermediären Photons durch seine virtuellen und reellen Beträge überaus komplizierte Strukturen. In den letzten Jahren gab es daher eine große Menge an theoretischen Beiträgen zur nicht-linearen Behandlung des Trident-Prozesses bezüglich eines weiten Bereichs an Eigenschaften der verwendeten Lichtquelle. Jedoch ist der nicht-lineare Trident-Prozess wegen seiner anspruchsvollen mathematischen Natur bisher nicht als völlig verstanden anzusehen. In der vorliegen- den Arbeit liegt der Fokus auf der Abhängigkeit des Trident-Prozesses von den kurzen zeitlichen Strukturen der verwendeten Lichtquellen bei hohen Energien. Grob gesprochen bedeutet dies, dass die kurz gepulsten Strukturen der modernen Lichtquellen zu breiten Spektren der Photonstrahlen führen, welche sich dann auch in den betrachteten Prozessen widerspiegeln. Demfolgend wird in der vorliegenden Arbeit eine neue Approximation an die Starkfeld-Quantenelektrodynamik erarbeitet, welche in der Lage ist, die spektralen Abhängigkeiten in den Prozessen zu beschreiben, die in Laser-Elektron-Kollisionen bei hohen Energien vorzufinden sind. Diese neue Approximation wird dann auf den Trident- Prozess angewendet und es werden die neuen Strukturen herausgearbeitet, welche durch das breite Spektrum der betrachteten Lichtquelle entstehen. Ferner werden bestehende oder geplante extreme Lichtquellen dahingehend untersucht, in welcher Weise diese, kombiniert mit einem passendem Elektronenstrahl, sensitiv für die vorgestellten spektralen Effekte im Trident-Prozess sind. Abschließend werden weitere mögliche Anwendungsbereiche der neuen Approximation diskutiert.:1 Introduction 1 2 Strong-field quantum electrodynamics 11 2.1 Description of the laser field 12 2.2 Background field approximation 18 2.3 Momentum space rules of strong-field QED 25 2.4 Ward identity and gauge invariance 34 2.5 Strong-field trident process 36 3 Pulsed-perturbative quantum electrodynamics 43 3.1 Approaches and approximations to strong-field QED 43 3.2 Momentum space rules in pulsed-perturbative QED 46 3.3 Spectrum of the background field 52 4 Pulsed-perturbative trident process 57 4.1 Matrixelement and cross section 57 4.2 Total cross section 72 4.3 Inclusive positron distributions 75 4.4 Exclusive electron distributions 81 4.5 Experimental capability 93 5 Summary and Outlook 97 Appendix 101 A Relativistic Kinematics 103 A.1 Preliminary remarks 103 A.2 Coordinate systems 104 A.3 Frames of reference 109 A.4 Kinematics of 2→3 processes 111 B Feynman rules of QED 121 C Perturbative trident pair production 125 C.1 Matrixelement and cross section 125 C.2 Numerical implementation and comparison to literature 129 C.3 Differential cross sections in transverse coordinates 132 C.4 Darkphotons 134 D Useful mathematical statements 139 Bibliography 153Modern laser facilities provide highly intense light with a very short temporal structure, which brings the phenomena originally found near the strong radiating stars in the universe into the laboratory. Accordingly, there are, among others, wide theoretical investigations w.r.t. scattering processes of particles impinging this extreme light sources. This has been done by applying the strong-field quantum electrodynamics, which is a theory of electromagnetic interactions within coherent highly intense light treated as a semi-classical background field. For instance, the treatment of the Compton process (inelastic electron- photon scattering) and the Breit-Wheeler process (pair production of a collision of two photons) with strong-field quantum electrodynamics revealed a vast amount of novel non-linear structures and phenomena, which were to some extent experimentally verified. Of particular interest and the central object of investigation within this thesis is also the trident process: a second order process in (strong-field) quantum electrodynamics producing an electron-positron pair within the collision of a photon beam (e.g. produced by a laser) with a counter-propagating electron. However, in the context of highly intense fields, the trident process is more than the product of its parts, the mentioned Compton and Breit-Wheeler process, since the intermediate photon yields both virtual and real contributions producing exceedingly complicated structures. Over the last years, there are several theoretical contributions to the non-linear treatment of the trident process w.r.t. a wide range of laser properties, but the trident process has not yet been fully understood due to its demanding mathematical nature. Within the present thesis, we focus on the dependence of the trident process to the short temporal structures of the involved light source at high energies. Loosely speaking, this means the short pulsed structure of modern light sources provide a wide energy spectrum of the respective photons, which is imprinted on the considered scattering processes. Accordingly, we elaborate a new approximation to strong-field quantum electrodynamics capable to describe the spectral dependence of processes within laser-electron collisions at high energies. Then we apply this new approximation to the trident process and reveal the novel structures generated by the spectrum of the light source. Therefore, we provide an analysis of the spectral impact to the trident process involving the total cross section as well as several inclusive and exclusive distributions of its final particles. Consequently, we examine in principle the experimental capabilities of present or planed extreme light sources by combining them with a suitable electron beam, whether they are sensitive to the encountered spectral effects of the trident process and discuss further applications of the newly introduced approximation.:1 Introduction 1 2 Strong-field quantum electrodynamics 11 2.1 Description of the laser field 12 2.2 Background field approximation 18 2.3 Momentum space rules of strong-field QED 25 2.4 Ward identity and gauge invariance 34 2.5 Strong-field trident process 36 3 Pulsed-perturbative quantum electrodynamics 43 3.1 Approaches and approximations to strong-field QED 43 3.2 Momentum space rules in pulsed-perturbative QED 46 3.3 Spectrum of the background field 52 4 Pulsed-perturbative trident process 57 4.1 Matrixelement and cross section 57 4.2 Total cross section 72 4.3 Inclusive positron distributions 75 4.4 Exclusive electron distributions 81 4.5 Experimental capability 93 5 Summary and Outlook 97 Appendix 101 A Relativistic Kinematics 103 A.1 Preliminary remarks 103 A.2 Coordinate systems 104 A.3 Frames of reference 109 A.4 Kinematics of 2→3 processes 111 B Feynman rules of QED 121 C Perturbative trident pair production 125 C.1 Matrixelement and cross section 125 C.2 Numerical implementation and comparison to literature 129 C.3 Differential cross sections in transverse coordinates 132 C.4 Darkphotons 134 D Useful mathematical statements 139 Bibliography 15

Note on Klein-Nishina effect in strong-field QED: the case of nonlinear Compton scattering

Suitably normalized differential probabilities of one-photon emission in external electromagnetic fields are compared to quantify the transit of nonlinear Compton scattering to linear Compton scattering, described by the Klein-Nishina formula, and to constant crossed field treatment. The known Klein-Nishina suppression at large energies is further enforced by increasing field intensity. In view of the Ritus-Narozhny conjecture, we demonstrate that different paths in the field intensity vs. energy plane towards large values of the quantum non-linearity parameter $\chi$ facilitate significantly different asymptotic dependencies, both in the Klein-Nishina regime and the constant crossed field regime and in between.Comment: 18 pages, 5 figure

Is Julia ready to be adopted by HEP?

The Julia programming language was created 10 years ago and is now a mature and stable language with a large ecosystem including more than 8,000 third-party packages. It was designed for scientific programming to be a high-level and dynamic language as Python is, while achieving runtime performances comparable to C/C++ or even faster. With this, we ask ourselves if the Julia language and its ecosystem is ready now for its adoption by the High Energy Physics community. We will report on a number of investigations and studies of the Julia language that have been done for various representative HEP applications, ranging from computing intensive initial data processing of experimental data and simulation, to final interactive data analysis and plotting. Aspects of collaborative code development of large software within a HEP experiment has also been investigated: scalability with large development teams, continuous integration and code test, code reuse, language interoperability to enable an adiabatic migration of packages and tools, software installation and distribution, training of the community, benefit from development from industry and academia from other fields

Contributions of mean and shape of blood pressure distribution to worldwide trends and variations in raised blood pressure: A pooled analysis of 1018 population-based measurement studies with 88.6 million participants

© The Author(s) 2018. Background: Change in the prevalence of raised blood pressure could be due to both shifts in the entire distribution of blood pressure (representing the combined effects of public health interventions and secular trends) and changes in its high-blood-pressure tail (representing successful clinical interventions to control blood pressure in the hypertensive population). Our aim was to quantify the contributions of these two phenomena to the worldwide trends in the prevalence of raised blood pressure. Methods: We pooled 1018 population-based studies with blood pressure measurements on 88.6 million participants from 1985 to 2016. We first calculated mean systolic blood pressure (SBP), mean diastolic blood pressure (DBP) and prevalence of raised blood pressure by sex and 10-year age group from 20-29 years to 70-79 years in each study, taking into account complex survey design and survey sample weights, where relevant. We used a linear mixed effect model to quantify the association between (probittransformed) prevalence of raised blood pressure and age-group- and sex-specific mean blood pressure. We calculated the contributions of change in mean SBP and DBP, and of change in the prevalence-mean association, to the change in prevalence of raised blood pressure. Results: In 2005-16, at the same level of population mean SBP and DBP, men and women in South Asia and in Central Asia, the Middle East and North Africa would have the highest prevalence of raised blood pressure, and men and women in the highincome Asia Pacific and high-income Western regions would have the lowest. In most region-sex-age groups where the prevalence of raised blood pressure declined, one half or more of the decline was due to the decline in mean blood pressure. Where prevalence of raised blood pressure has increased, the change was entirely driven by increasing mean blood pressure, offset partly by the change in the prevalence-mean association. Conclusions: Change in mean blood pressure is the main driver of the worldwide change in the prevalence of raised blood pressure, but change in the high-blood-pressure tail of the distribution has also contributed to the change in prevalence, especially in older age groups

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018.

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field

Rising rural body-mass index is the main driver of the global obesity epidemic in adults

Body-mass index (BMI) has increased steadily in most countries in parallel with a rise in the proportion of the population who live in cities(.)(1,2) This has led to a widely reported view that urbanization is one of the most important drivers of the global rise in obesity(3-6). Here we use 2,009 population-based studies, with measurements of height and weight in more than 112 million adults, to report national, regional and global trends in mean BMI segregated by place of residence (a rural or urban area) from 1985 to 2017. We show that, contrary to the dominant paradigm, more than 55% of the global rise in mean BMI from 1985 to 2017-and more than 80% in some low- and middle-income regions-was due to increases in BMI in rural areas. This large contribution stems from the fact that, with the exception of women in sub-Saharan Africa, BMI is increasing at the same rate or faster in rural areas than in cities in low- and middle-income regions. These trends have in turn resulted in a closing-and in some countries reversal-of the gap in BMI between urban and rural areas in low- and middle-income countries, especially for women. In high-income and industrialized countries, we noted a persistently higher rural BMI, especially for women. There is an urgent need for an integrated approach to rural nutrition that enhances financial and physical access to healthy foods, to avoid replacing the rural undernutrition disadvantage in poor countries with a more general malnutrition disadvantage that entails excessive consumption of low-quality calories.Peer reviewe

Height and body-mass index trajectories of school-aged children and adolescents from 1985 to 2019 in 200 countries and territories: a pooled analysis of 2181 population-based studies with 65 million participants

Summary Background Comparable global data on health and nutrition of school-aged children and adolescents are scarce. We aimed to estimate age trajectories and time trends in mean height and mean body-mass index (BMI), which measures weight gain beyond what is expected from height gain, for school-aged children and adolescents. Methods For this pooled analysis, we used a database of cardiometabolic risk factors collated by the Non-Communicable Disease Risk Factor Collaboration. We applied a Bayesian hierarchical model to estimate trends from 1985 to 2019 in mean height and mean BMI in 1-year age groups for ages 5–19 years. The model allowed for non-linear changes over time in mean height and mean BMI and for non-linear changes with age of children and adolescents, including periods of rapid growth during adolescence. Findings We pooled data from 2181 population-based studies, with measurements of height and weight in 65 million participants in 200 countries and territories. In 2019, we estimated a difference of 20 cm or higher in mean height of 19-year-old adolescents between countries with the tallest populations (the Netherlands, Montenegro, Estonia, and Bosnia and Herzegovina for boys; and the Netherlands, Montenegro, Denmark, and Iceland for girls) and those with the shortest populations (Timor-Leste, Laos, Solomon Islands, and Papua New Guinea for boys; and Guatemala, Bangladesh, Nepal, and Timor-Leste for girls). In the same year, the difference between the highest mean BMI (in Pacific island countries, Kuwait, Bahrain, The Bahamas, Chile, the USA, and New Zealand for both boys and girls and in South Africa for girls) and lowest mean BMI (in India, Bangladesh, Timor-Leste, Ethiopia, and Chad for boys and girls; and in Japan and Romania for girls) was approximately 9–10 kg/m2. In some countries, children aged 5 years started with healthier height or BMI than the global median and, in some cases, as healthy as the best performing countries, but they became progressively less healthy compared with their comparators as they grew older by not growing as tall (eg, boys in Austria and Barbados, and girls in Belgium and Puerto Rico) or gaining too much weight for their height (eg, girls and boys in Kuwait, Bahrain, Fiji, Jamaica, and Mexico; and girls in South Africa and New Zealand). In other countries, growing children overtook the height of their comparators (eg, Latvia, Czech Republic, Morocco, and Iran) or curbed their weight gain (eg, Italy, France, and Croatia) in late childhood and adolescence. When changes in both height and BMI were considered, girls in South Korea, Vietnam, Saudi Arabia, Turkey, and some central Asian countries (eg, Armenia and Azerbaijan), and boys in central and western Europe (eg, Portugal, Denmark, Poland, and Montenegro) had the healthiest changes in anthropometric status over the past 3·5 decades because, compared with children and adolescents in other countries, they had a much larger gain in height than they did in BMI. The unhealthiest changes—gaining too little height, too much weight for their height compared with children in other countries, or both—occurred in many countries in sub-Saharan Africa, New Zealand, and the USA for boys and girls; in Malaysia and some Pacific island nations for boys; and in Mexico for girls. Interpretation The height and BMI trajectories over age and time of school-aged children and adolescents are highly variable across countries, which indicates heterogeneous nutritional quality and lifelong health advantages and risks

Worldwide trends in underweight and obesity from 1990 to 2022: a pooled analysis of 3663 population-representative studies with 222 million children, adolescents, and adults

Background Underweight and obesity are associated with adverse health outcomes throughout the life course. We estimated the individual and combined prevalence of underweight or thinness and obesity, and their changes, from 1990 to 2022 for adults and school-aged children and adolescents in 200 countries and territories. Methods We used data from 3663 population-based studies with 222 million participants that measured height and weight in representative samples of the general population. We used a Bayesian hierarchical model to estimate trends in the prevalence of different BMI categories, separately for adults (age ≥20 years) and school-aged children and adolescents (age 5–19 years), from 1990 to 2022 for 200 countries and territories. For adults, we report the individual and combined prevalence of underweight (BMI <18·5 kg/m2) and obesity (BMI ≥30 kg/m2). For schoolaged children and adolescents, we report thinness (BMI <2 SD below the median of the WHO growth reference) and obesity (BMI >2 SD above the median). Findings From 1990 to 2022, the combined prevalence of underweight and obesity in adults decreased in 11 countries (6%) for women and 17 (9%) for men with a posterior probability of at least 0·80 that the observed changes were true decreases. The combined prevalence increased in 162 countries (81%) for women and 140 countries (70%) for men with a posterior probability of at least 0·80. In 2022, the combined prevalence of underweight and obesity was highest in island nations in the Caribbean and Polynesia and Micronesia, and countries in the Middle East and north Africa. Obesity prevalence was higher than underweight with posterior probability of at least 0·80 in 177 countries (89%) for women and 145 (73%) for men in 2022, whereas the converse was true in 16 countries (8%) for women, and 39 (20%) for men. From 1990 to 2022, the combined prevalence of thinness and obesity decreased among girls in five countries (3%) and among boys in 15 countries (8%) with a posterior probability of at least 0·80, and increased among girls in 140 countries (70%) and boys in 137 countries (69%) with a posterior probability of at least 0·80. The countries with highest combined prevalence of thinness and obesity in school-aged children and adolescents in 2022 were in Polynesia and Micronesia and the Caribbean for both sexes, and Chile and Qatar for boys. Combined prevalence was also high in some countries in south Asia, such as India and Pakistan, where thinness remained prevalent despite having declined. In 2022, obesity in school-aged children and adolescents was more prevalent than thinness with a posterior probability of at least 0·80 among girls in 133 countries (67%) and boys in 125 countries (63%), whereas the converse was true in 35 countries (18%) and 42 countries (21%), respectively. In almost all countries for both adults and school-aged children and adolescents, the increases in double burden were driven by increases in obesity, and decreases in double burden by declining underweight or thinness. Interpretation The combined burden of underweight and obesity has increased in most countries, driven by an increase in obesity, while underweight and thinness remain prevalent in south Asia and parts of Africa. A healthy nutrition transition that enhances access to nutritious foods is needed to address the remaining burden of underweight while curbing and reversing the increase in obesit