Flavorful BSM from Asymptotic Safety
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Date
2024
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Abstract
Diese Dissertation beinhaltet aktuelle Anwendungen des auf der Renormierungsgruppe (RG)
basierenden Konzepts der Planckskalensicherheit (PS) in der Modellbildung jenseits des Standardmodells
der Teilchenphysik (SM, BSM). PS bezeichnet dabei ein RG-Laufen aller Kopplungen
bis zum Quantengravitationsregime an der Planckskala ohne Vakuuminstabilitäten und
Landau-Pole. Dazu muss die Metastabilität des SM Higgspotentials behoben werden. Wir gehen
diese Aufgabe in minimalen SM-Erweiterungen mit vektorartigen Fermionen, Singulett-Skalaren
oder beiden, mit oder ohne flavour an. Dazu untersuchen wir die RG-Flüsse dieser Modelle in
höheren Schleifenordnungen sowie die gesamten durch BSM-Massen, -Multiplizitäten, -Ladungen
und -Kopplungen aufgespannten verfügbaren Parameterräume. Dabei enthüllen und charakterisieren
wir mehrere fundamentale RG-Mechanismen für PS, sowie deren Zusammenspiel. Die
Forderung nach PS impliziert dann Bedingungen an die BSM-Parameter. Wir studieren auch
die Beschleunigerphänomenologie unsere Modelle, insbesondere im Hinblick auf die Komplementarität
zwischen phänomenologischen und PS-Bedingungen an Parameter. Danach widmen
wir uns einer komplexeren Klasse von BSM Modellen, nämlich anomaliefreien, flavour-vollen
Z‘-Modellen. Das Z‘-Boson kann flavour-verändernde neutrale Ströme auf Baumgraphenniveau
induzieren, die im SM Schleifen- und Cabibbo-Kobayashi-Maskawa-unterdrückt sind. Daher sind
Z‘--Modelle natürliche Kandidaten um experimentell gemessene Abweichungen einiger flavour-
Observablen von ihrer SM-Vorhersage zu erklären. Insbesondere fokussieren wir uns dabei auf
die anhaltenden Anomalien im Zusammenhang mit b -> s μ+ μ- Übergängen sowie die unerwartet
große CP- und U-Spin-Verletzung in D0 -> K+ K- , π+ π- Zerfällen. Allerdings treten
in Z‘-Modellen typischerweise niederenergetische Landau-Pole auf, durch die die Theorien ihre
Vorhersagekraft verlieren. Wir zeigen, wie in Z‘-Modellen die Anomalien im beauty- und charm-
Sektor jeweils aufgelöst und gleichzeitig Landau-Pole hinter die Planckskala geschoben werden
können. Dadurch ergeben sich präzise Vorhersagen für charakteristische, phänomenologische
Signaturen, die an Beschleunigern gesucht werden können.
This thesis comprises recent applications of the renormalization group (RG) based concept of Planck safety (PS) in beyond the Standard Model of particle physics (SM, BSM) model building. PS refers to a RG flow of all couplings up to the quantum gravity regime at the Planck scale without any vacuum instabilities or Landau poles. This requires to cure the metastability of the SM Higgs potential. We tackle this task in several minimal SM extensions featuring vectorlike fermions, singlet scalars or both, with or without flavor. We investigate the higher looporder RG flows of these models, scrutinizing their complete available parameter spaces spanned by BSM masses, multiplicities, charges and couplings. Thereby, we unveil and characterize several fundamental mechanisms for PS as well as their interplay. Requiring PS then results in constraints on BSM parameters. We also study the collider phenomenology of our models, focusing in particular on the complementarity between phenomenological and PS constraints. We then turn to a class of more complex BSM models, namely flavorful, anomaly-free Z‘ models. The Z‘ boson can induce flavor-changing neutral current transitions at tree-level, which in the SM are loop- and Cabibbo-Kobayashi-Maskawa-suppressed. Therefore, Z‘ models are natural candidates to address several experimentally measured deviations from the SM in flavor observables. In particular, we focus on the persistent anomalies in b -> s μ+ μ- transitions as well as the large CP and U-spin breaking in D0 -> K+ K- , π+ π- decays. On the other hand, Z‘ models are generically plagued by low-energy Landau poles spoiling the predictivity of the theory. We show how the flavor anomalies in the beauty and charm sector can respectively be resolved in Z‘ models while the notorious Landau pole is simultaneously pushed beyond the Planck scale. This results in distinct predictions of characteristic phenomenological signatures that can be searched for at colliders.
This thesis comprises recent applications of the renormalization group (RG) based concept of Planck safety (PS) in beyond the Standard Model of particle physics (SM, BSM) model building. PS refers to a RG flow of all couplings up to the quantum gravity regime at the Planck scale without any vacuum instabilities or Landau poles. This requires to cure the metastability of the SM Higgs potential. We tackle this task in several minimal SM extensions featuring vectorlike fermions, singlet scalars or both, with or without flavor. We investigate the higher looporder RG flows of these models, scrutinizing their complete available parameter spaces spanned by BSM masses, multiplicities, charges and couplings. Thereby, we unveil and characterize several fundamental mechanisms for PS as well as their interplay. Requiring PS then results in constraints on BSM parameters. We also study the collider phenomenology of our models, focusing in particular on the complementarity between phenomenological and PS constraints. We then turn to a class of more complex BSM models, namely flavorful, anomaly-free Z‘ models. The Z‘ boson can induce flavor-changing neutral current transitions at tree-level, which in the SM are loop- and Cabibbo-Kobayashi-Maskawa-suppressed. Therefore, Z‘ models are natural candidates to address several experimentally measured deviations from the SM in flavor observables. In particular, we focus on the persistent anomalies in b -> s μ+ μ- transitions as well as the large CP and U-spin breaking in D0 -> K+ K- , π+ π- decays. On the other hand, Z‘ models are generically plagued by low-energy Landau poles spoiling the predictivity of the theory. We show how the flavor anomalies in the beauty and charm sector can respectively be resolved in Z‘ models while the notorious Landau pole is simultaneously pushed beyond the Planck scale. This results in distinct predictions of characteristic phenomenological signatures that can be searched for at colliders.
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Keywords
Physics beyond the standard model, Asymptotic safety, Renormalization group equations, Flavor physics