Under the umbrella of Theoretical Physics, progress in ‘Beyond the Standard Model’ (BSM) physics proceeds broadly along two main avenues of investigation. The first is concerned with constructing theories that attempt to explain observations, or address theoretical problems, which cannot be explained within the tremendously successful Standard Model (SM) of particle physics. The second involves looking for new ways to observe or test BSM physics, and such tests are usually developed with current experimental hints, or attractive theoretical models, in mind. This thesis contains material which falls under both approaches. Part I is concerned with Supersymmetry (SUSY). We review the basics of SUSY, and the current state of this field, and then present a novel model for SUSY at the TeV scale. This model has a Higgs sector similar to the SM and possesses a continuous U(1)_R symmetry, dramatically suppressing contributions to flavour-changing neutral currents, which can be problematic in SUSY models. After this we demonstrate that if more than one SUSY-breaking sector is present then this could lead to a rich spectrum of states with mass roughly twice the gravitino mass. In particular, if SUSY-breaking in a hidden sector arises dynamically then multiple ‘Goldstini’ and ‘Modulini’ states can arise, which couple to visible sector fields via the ‘Goldstino Portal’. We also demonstrate a new phenomenon which can occur in the context of multiple hidden sectors. If one sector breaks SUSY then this can ‘stimulate’ other sectors into also breaking SUSY, even if they are incapable of doing so on their own. Part II focusses on the matter in our Universe. We review our current understand- ing of how the visible matter in our Universe came into existence, and our current understanding of the nature of dark matter (DM). Following this we describe how DM could potentially be indirectly observed through its effects on cold white dwarf stars. Alternatively, if DM were detected by independent means, then observed cold white dwarfs could be used to place limits on the DM density in globular clusters, giving clues as to how these clusters of stars formed. We then present a new model for the co-generation of both the visible and dark matter in our Universe. This proceeds by generating a particle anti-particle asymmetry in the dark sector, which is then shared with the visible sector. This model predicts the existence of a light, m ≲ 5 eV, scalar particle which derivatively couples to DM, and provides a final state for the symmetric DM component to annihilate away into. Work completed during the period of this D.Phil is contained in [1–8], however only material in [3–6, 8] is presented in this thesis.

The identification of the relic particles which presumably constitute cold dark matter is a key challenge for astroparticle physics. Indirect methods for their detection using high energy astro- physical probes such as cosmic rays have been much discussed. In particular, recent ‘excesses’ in cosmic ray electron and positron fluxes, as well as in microwave sky maps, have been claimed to be due to the annihilation or decay of dark matter. In this thesis, we argue however that these signals are plagued by irreducible astrophysical backgrounds and show how plausible con- ventional physics can mimic the alleged dark matter signals. In chapter 1, we review evidence of, and possible particle candidates for, cold dark matter, as well as our current understanding of galactic cosmic rays and the state-of-the-art in indirect detection. All other chapters contain original work, mainly based on the author’s journal publications. In particular, in chapter 2, we consider the possibility that the rise in the positron fraction observed by the PAMELA satellite is due to the production through (hadronic) cosmic ray spallation and subsequent acceleration of positrons, in the same sources as the primary cosmic rays. We present a new (unpublished) analytical estimate of the range of possible fluctuations in the high energy electron flux due to the discreteness of plausible cosmic ray sources such as supernova remnants. Fitting our result for the total electron-positron flux measured by the Fermi satellite allows us to fix the only free parameter of the model and make an independent prediction for the positron fraction. Our explanation relies on a large number of supernova remnants nearby which are accelerating hadronic cosmic rays. Turning the argument around, we find encouraging prospects for the observation of neutrinos from such sources in km^3-scale detectors such as IceCube. Chapter 3 presents a test of this model by considering similar effects expected for nuclear secondary-to-primary ratios such as B/C. A rise predicted above O(100)GeV/n would be an unique confirmation of our explanation for a rising positron fraction and rule out the dark matter explanation. In chapter 4, we review the assumptions made in the extraction of the `WMAP haze' which has also been claimed to be due to electrons and positrons from dark matter annihilation in the Galactic centre region. We argue that the energy-dependence of their diffusion means that the extraction of the haze through fitting to templates of low frequency diffuse galactic radio emission is unreliable. The systematic effects introduced by this can, under specific circumstances, reproduce the residual, suggesting that the ‘haze’ may be just an artefact of the template subtraction. We present a summary and thoughts about further work in the epilogue.

This thesis is concerned with the theoretical modelling of scattering processes as they are studied at high-energy collider experiments. Special attention is thereby given to an accurate simulation of multi-particle final states that are expected to constitute the key signatures for the existence of physics beyond the Standard Model of particle physics.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18447号 / 理博第4007号 / 新制||理||1578(附属図書館) / 31325 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 畑 浩之, 教授 川合 光, 准教授 市川 温子 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

This thesis is concerned with the theoretical modelling of scattering processes as they are studied at high-energy collider experiments. Special attention is thereby given to an accurate simulation of multi-particle final states that are expected to constitute the key signatures for the existence of physics beyond the Standard Model of particle physics.

This thesis concerns with numerical methods for a theoretical description of high energy particle scattering experiments. It focuses on fixed order perturbative calculations, i.e. on matrix elements and scattering cross sections at leading and next-to-leading order. For the leading order a number of algorithms for the matrix element generation and the numeric integration over the phase space are studied and implemented in a computer code, which allows to push the current limits on the complexity of the final state and the precision. For next-to-leading order calculations necessary steps towards a fully automated treatment are performed. A subtraction method that allows a process independent regularization of the divergent virtual and real corrections is implemented, and a new approach for a semi-numerically evaluation of one-loop amplitudes is investigated.

Cette thèse a pour but l'étude de théories diverses, toutefois interconnectées, décrivant la nouvelle physique au-delà du modèle standard de la physique des particules. Ces sont des théories d'un nouveau type de particules, les axions, d'un nouveau principe de symétrie, la supersymétrie, et d'une nouvelle description des degrés de liberté fondamentaux, la théorie des cordes. Les progrès instrumentaux et théoriques constamment fait au fil des ans ont confirmé que ces théories sont des candidates privilégiées pour une description de la physique au-delà du modèle standard.Les axions sont d'abord examinés et étudiés d'un point de vue phénoménologique: nous présentons des modèles qui désenchevêtrent les différentes échelles qui décrivent l'espace des paramètres des modèles d'axions, et nous discutons les axions présents dans des modèles de saveur. Inspirés par les recherches autour du swampland, nous nous imposons l'utilisation de symétries de jauge, et non globales, en tant que point de départ pour la construction de modèles.Notre intérêt se porte ensuite sur la supersymétrie. Nous étudions sa brisure, à la fois dans des modèles explicites dans l'ultraviolet qui génèrent une échelle de brisure de supersymétrie basse à partir de matière à haute échelle, et au niveau des théories effectives à l'aide de la supersymétrie non-linéaire. En ce qui concerne ce dernier thème, nous nous restreignons à l'approche des superchamps contraints. Enfin, nous présentons des solutions classiques exactes d'un modèle supersymétrique dont la portée est grande, le modèle de Wess-Zumino d'un superchamp chiral.Finalement, nous nous intéressons à la théorie des cordes. Nous calculons des spectres de cordes en guise d'illustration de la structure de la théorie et de point de départ pour le calcul d'amplitudes du vide à une boucle. Celles-ci nous permettent de tester l'une des conjectures du swampland, qui désigne la gravité comme la plus faible des forces, dans une configuration de théorie des cordes où la supersymétrie est brisée. Enfin, les axions en théorie des cordes sont analysés, en particulier lorsqu'ils sont chargés sous une symétrie de jauge abélienne anormale. / The aim of this thesis is to study various but interconnected theories for new physics beyond the standard model of particle physics. Those are theories of a new kind of particles, axions, a new symmetry principle, supersymmetry, and a new description of fundamental degrees of freedom, string theory. Constant instrumental and theoretical progresses made over the years maintain those already old subjects as leading BSM candidates.Axions are first reviewed and studied from a phenomenological perspective: we present models which disentangle the different scales which define the axion parameter space, and we discuss axions which arise in models of flavour physics. Motivated by swampland considerations, we insist on using gauge, and not global, symmetries as model building inputs.The focus then shifts to supersymmetry. We study its breaking, both in explicit ultraviolet models which generate a low supersymmetry breaking scale from high-scale matter, and at the effective field theory level using non-linearly realized supersymmetry. In our study of the latter topic, we focus on the constrained superfield approach. Finally, we present exact classical solutions of a supersymmetric model with broad application scope, the Wess-Zumino model of a chiral superfield.Last, we discuss string theory. We compute string spectra as illustrations of the structure of the theory and as starting points to compute one-loop vacuum amplitudes. Those are used to understand supersymmetry breaking in string theory, as well as brane interactions. Then, the latter enable us to test one of the swampland criteria, the weak gravity conjecture, in a string theory setup with broken supersymmetry. Finally, axions in string theory are scrutinized, in particular when they are charged under an anomalous abelian factor of the gauge group.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20168号 / 理博第4253号 / 新制||理||1611(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 福間 將文, 教授 川合 光, 教授 畑 浩之 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Die am LHC gewonnen Ergebnisse stimmen überwiegend mit den Vorhersagen des Standardmodells der Teilchenphysik (SM) überein, doch die Notwendigkeit von Physik jenseits des Standardmodells (BSM) bleibt. Allerdings führt kein klarer Weg zu einem Nachfolger des Standardmodells. In dieser Arbeit wird daher ein allgemeines theoretisches Werkzeug für die Erforschung der Grenzen des SM verwendet: die Effektiven Feldtheorien (EFTs). In dieser Arbeit wird die Standard Model Effective Field Theory (SMEFT) benutzt, um das Potential des zukünftigen Hadronenbeschleunigers FCC-hh zu beurteilen. Hierfür wird der Vh-Produktionsprozess untersucht. Die Sensitivität dieser Kanäle wird durch die Messung von doppelt differenziellen Wirkungsquerschnitten möglich. Die Abwesenheit von Eich-Anomalien ist nötig, um die Konsistenz einer Quantenfeldtheorie zu bewahren. Es wird gezeigt, dass die SMEFT bis zur Massendimension 6 für beliebige Werte seiner WCs frei von aus Dreiecks-Anomalien stammenden Eich-Anomalien ist. Die bosonischen EFT-Techniken werden auch benutzt, um die Beziehung zwischen gemischten globalen Eich-Anomalien und Axion-Kopplungen zu Vektorbosonen in Axion-EFTs zu analysieren. Es ergibt sich, dass diese in keiner Beziehung zueinander stehen, wenn schwere chirale Fermionen ausintegriert werden. Dieser Fakt verknüpft Axion-EFTs mit chiralen Erweiterungen des Standardmodells. Für nichtabelsche Eichbosonen werden IR-Summenregeln gefunden, deren Verletzung die Anwesenheit chiraler Felder im UV-Bereich anzeigen. Es wird eine minimale Erweiterung des Standardmodells als Beispiel studiert. Letztlich wird gezeigt, wie alte Formalismen zu neuen Einsichten führen können. Helizitäts-Spinoren und Streuamplituden werden eingeführt und es wird diskutiert, wie sie die Berechnung der Amplituden erleichtern und inwiefern sie eine Alternative zu EFTs darstellen. Die VVh- und VVhh-Amplituden werden studiert und ihre Hoch-Energie-Grenzwerte einschließlich verschiedener BSM-Beiträge berechnet. / The results obtained at the LHC agree well with the predictions of the Standard Model of particle physics (SM). However, the need for Beyond the Standard Model (BSM) physics remains. But there is no clear path towards a successor for the SM. Hence, we must prepare the tools needed to explore the frontiers of physics thoroughly. In this work, we study one of the main theoretical tools that can be used for such an exploration, Effective Field Theories (EFTs). We use the Standard Model Effective Field Theory (SMEFT) to study the Vh production process at FCC-hh, assessing the discovery potential of that future collider. The sensitivity to BSM effects is improved via the measurement of doubly-differential cross-sections. We also study the relation between EFTs and anomalies. The absence of gauge anomalies is required to preserve the consistency of a Quantum Field Theory. We prove that SMEFT at dimension 6 is free from gauge anomalies coming from triangle diagrams for any value of its WCs. Then, we analyse the relationship in axion EFTs between mixed global-gauge anomalies and axion couplings to vector bosons. They turn out to be unrelated when heavy chiral fermions are integrated out, linking axion EFTs to chiral extensions of the SM. We find IR sum rules whose violation indicate the presence of chiral fields in the UV. We show and study a minimal phenomenologically relevant model as an example. Finally, we explore how revisiting old formalisms can lead to new insights. We introduce the helicity spinor and scattering amplitudes formalisms and show how they facilitate the computation of cross sections and discuss how they constitute an alternative to EFTs as a parametrisation of BSM effects. We study the VVh and VVhh amplitudes, of which we compute the high-energy limit including different BSM contributions.

This thesis concerns with numerical methods for a theoretical description of high energy particle scattering experiments. It focuses on fixed order perturbative calculations, i.e. on matrix elements and scattering cross sections at leading and next-to-leading order. For the leading order a number of algorithms for the matrix element generation and the numeric integration over the phase space are studied and implemented in a computer code, which allows to push the current limits on the complexity of the final state and the precision. For next-to-leading order calculations necessary steps towards a fully automated treatment are performed. A subtraction method that allows a process independent regularization of the divergent virtual and real corrections is implemented, and a new approach for a semi-numerically evaluation of one-loop amplitudes is investigated.