Theoretische Physik IV
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Item Flavorful BSM from Asymptotic Safety(2024) Höhne, Tim Fabian; Hiller, Gudrun; Stamou, EmmanuelDiese 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.Item Rare radiative charm decays in and beyond the standard model(2022) Adolph, Nico; Hiller, Gudrun; Stamou, EmmanuelThis thesis comprises a study of rare radiative |Δc| = |Δu| = 1 transitions within and beyond the standard model of particle physics. For the 18 three-body decays D → P1 P2 ɣ with 𝑃 = π, K decay amplitudes are derived using Low’s theorem, QCD factorization and heavy hadron chiral perturbation theory. Standard model predictions for branching ratios, CP asymmetries as well as forward-backward asymmetries are determined. Moreover, the effects of new physics in the coefficients of the electromagnetic dipole operators are investigated respecting the current constraints. The photon polarization in Ds→ K1(→ Kπ π) ɣ decays is studied with respect to new physics effects in the dipole coefficients. Within the standard model, the polarization parameter agrees with the SM- like partner decay 𝐷+ → 𝐾1 (→ 𝐾π π)) ɣ up to U-spin breaking corrections. The existence of partner decays allows to construct a null test which does not require precise knowledge of the hadronic K1 → Kπ π decay. Finally, different ways to test the standard model with rare radiative decays of charm baryons are discussed. Based on the approximate SU(3)𝐹 symmetry of QCD as well as its subgroups, relations between partner decays are worked out. Branching ratios, CP asymmetries as well as the photon polarizations are considered as observables and the potential of new physics effects is estimated. Methods for the extraction of the photon polarization from two-body decays Bc → B ɣ of polarized charm baryons as well as from decay chains Bc → B(→ B′ 𝑃 ) ɣ with self-analyzing hyperons 𝐵 are presented.Item Exploiting the phenomenology of flavourful Z′ models(2022) Bause, Rigo; Hiller, Gudrun; Stamou, EmmanuelThis thesis comprises recent studies on extensions of the standard model (SM) involving a heavy Z’ boson. In the SM, flavour-changing neutral current (FCNC) quark transitions only appear at loop level and are highly suppressed. This puts forward flavourful Z’ models, where the new gauge boson couples non-universally to the known quarks and leptons at tree level. The models are able address the persistent deviations of the SM seen in observables of rare B-meson decays referred to as the B-anomalies. By supplementing the particle content of the SM with new scalars and vector-like fermions, the occurrence of putative Landau poles present in general Z’ scenarios can be averted. We discuss dedicated models in the context of the B-anomalies that allow for a stable and predictive theory up to the Planck scale. Moreover, flavour rotations also enable FCNC transitions in the charm sector, where the resonance pollution in branching ratios of semileptonic decays demands null test observables sensitive to physics beyond the SM. We investigate effects in such decays and present unique correlations to CP-violating observables in hadronic decays, accessible with future measurements by the LHCb and Belle II experiments. Recent studies involving dineutrino modes are discussed as well. We exploit an interplay between neutrino and charged lepton couplings within the SM effective field theory approach that connects decays of opposite flavour sectors. In doing so, we derive limits on diverse sets of dineutrino branching ratios and find novel tests of lepton universality using data from global fits of the B-anomalies.Item |Δc| = |Δu| = 1 transitions in and beyond the standard model(2022) Golz, Marcel; Hiller, Gudrun; Stamou, EmmanuelThis thesis comprises a study of rare semileptonic |Δc|=|Δu|=1 transitions in the Standard Model and beyond. The Standard Model phenomenology of three-body meson decays D→ Pll, as well as three- and four-body charmed baryon decays B0 → B1 (→ B2 π) ll, is analyzed and branching ratios are found to be dominated by resonances. Physics effects beyond the Standard Model are studied model-independently as well as in the framework of leptoquark- and flavorful, anomaly-free Z’-models. Resonance dominance is shown to be overcome or even used as a catalyst in analyses of clean null-test observables, where any signal indicates new physics. Null tests are based on angular observables, CP-conservation, lepton flavor universality and charged lepton flavor conservation. Already a subset of four angular observables in three- and four-body rare charm baryon decays are sufficient to disentangle beyond Standard Model effects in dipole and (axial) vector Wilson coefficients, whereas (semi-)leptonic rare meson decays D→ (P)ll are shown to control (pseudo-)scalar and (pseudo-)tensor effects. A global view on connections between different flavor sectors is put forward in the context of flavor summed dineutrino branching ratios. Indirect tests of lepton flavor universality and charged lepton flavor conservation are presented for the charm sector, where dineutrino modes already pose null tests of the Standard Model. In |Δb|=|Δs|=1 transitions, the first evidence for the violation of lepton flavor universality is found in muon over electron ratios of B-meson branching fractions. Complementing the direct probes, dineutrino modes are shown to test charged lepton flavor indirectly in the correlation of B → Pνν and B → Vνν. Similarly, indirect flavor probes in other quark sectors are also commented on.Item Flavorful new physics models in the light of the B decay anomalies(2021) Loose, Dennis; Hiller, Gudrun; Päs, HeinrichCurrent experimental data on the flavor observables R_K and R_K^* shows evidence for a violation of lepton universality – an essential feature of the Standard Model of particle physics. Together with several deviations seen in other b -> sµ^+ µ^− observables as well as R_D and R_D^*, these results constitute the so-called B decay anomalies. In this thesis we investigate new physics models that provide potential solutions to these anomalies and put a special emphasis on their flavor structure. To this end, we consider an A4 x U(1)_FN based flavor symmetry, which addresses the SM flavor puzzle, and study patterns that it imposes on the couplings of leptoquark models. We find that flavorful leptoquarks provide good explanations of R_K^(*) , while constraints from rare kaon decays and charged lepton flavor violating processes are too strong to allow to accommodate the deviations in R_D^(*). As another consequence of the imposed flavor structure, flavorful leptoquarks are light enough to be produced at current and future hadron colliders. We compute estimates for the production cross sections of the S_3 , V_1 and V_3 leptoquarks in different flavor scenarios, focusing on single production, which is sensitive to the leptoquark coupling and its flavor structure. We find that future hadron colliders with higher center of mass energies are needed to cover the full parameter space and determine leptoquark mass bound for benchmark scenarios.Item Flavorful models for asymptotic safety(2021) Hormigos Feliu, Clara; Hiller, Gudrun; Brod, JoachimIn this thesis we study asymptotically safe models with implications for flavor physics. We show that the Yukawa couplings necessary to generate ultraviolet fixed points could link a new sector to the Standard Model, generating a rich phenomenology. Most prominently, we find that for theories with heavy vector-like leptons and singlet scalars the discrepancies in the anomalous magnetic moments of the electron and the muon can be simultaneously explained without explicitly breaking lepton flavor universality. We study implications for the models at colliders, and propose targeted observables and null tests which exploit the flavor structure of the new sector. We finally show that, in asymptotically safe theories where the Standard Model is extended with an additional U(1) gauge symmetry, large hierarchies in the Yukawa sector can be generated through renormalization group running. Employing non-universal charge assignments, we find that the observed fermion masses and quark mixing patterns can be reproduced to the order of magnitude.Item Synergies of flavor anomalies with top-quark physics in the Standard Model Effective Field Theory and direct searches(2021) Bißmann, Stefan; Hiller, Gudrun; Kröninger, KevinThis thesis comprises a study on opportunities for physics beyond the Standard Model (BSM) guided by the flavor anomalies. Aiming at linking the top-quark sector of the Standard Model Effective Field Theory (SMEFT) to the anomalies in b → s transitions, we perform a global fit to top-quark data detailing on the validity of the SMEFT framework, and highlight benefits and challenges of combining multiple measurements in a combined fit. To combine top-quark and beauty data we perform a first joined fit of three SMEFT Wilson coefficients to tt̄γ and b → sγ data. We work out the steps needed for linking top-quark and B physics within SMEFT, and demonstrate how the complementarity of both sectors enhances constraints significantly. Extending our setup, we analyze semileptonic four-fermion operators, which are of high interest in the context of anomalies seen in b → sμ+μ− data, in a combined fit to top-quark, Zbb, and B-physics observables using present data as well as future scenarios of HL-LHC, Belle II, and a future lepton collider. We observe powerful synergies between top-quark and beauty physics, which open new directions for model-independent searches. To complement our analysis, we investigate the possibility that BSM physics can be well within the reach of the LHC while still accommodating the anomalies within the lepton anomalous magnetic moments and lifting several shortcomings of the Standard Model (SM). The models are an asymptotically safe extension of the SM featuring potentially light vector-like leptons and additional scalars with a non-trivial flavor structure. We perform a detailed study of implications for discovery at the LHC exploiting unique flavor signatures to construct null- tests of the SM, and find that Run 2 data can be sufficient to detect BSM physics, indicating that new physics might be just around the corner.Item Fixed points in supersymmetric extensions of the Standard Model(2020) Moch, Kevin; Hiller, Gudrun; Litim, Daniel F.In this work, we are searching for supersymmetric extensions of the Standard Model (SM) of particle physics which are asymptotically safe. Such models are well-defined at all energy scales and provide hints for the scale at which supersymmetry gets broken. The combination of supersymmetry and asymptotic safety hereby turns out to strongly restrict the space of possible models. Within extensions of the minimal supersymmetric SM (MSSM), we perturbatively find candidates which all have a specific field content and low supersymmetry-breaking scales. For extensions of the MSSM with an extended gauge sector, we find models for which these scales appear at much larger energies. We then investigate whether the perturbatively found models are in agreement with non-perturbative results obtained from superconformal field theories. The exact supersymmetric Novikov-Shifman-Vainshtein-Zakharov beta functions suggest that these models are not asymptotically safe beyond perturbation theory. Finally, we present a model for which the non-perturbative results suggests that the SM can be UV-completed by this model. We also study perturbatively whether the fixed point needed for this UV-completion is physical.Item Massive two- and three-loop calculations in QED and QCD(2019-10-15) Schönwald, Kay; Blümlein, Johannes; Hiller, GudrunThis thesis is devoted to the study of mass effects in higher order radiative corrections within QED and QCD. The first part of the thesis deals with the process of deep-inelastic scattering. We compute the full mass dependence of the pure singlet Wilson coefficient in the polarized and unploarized case to next-to-leading order using iterated integrals over square root valued letters. Through explicit expansion in the asymptotic limit we proof the factorization of the heavy Wilson coefficient into massless Wilson coefficient and massive operator matrix element and additionally derive improved asymptotic expressions. We then turn to the calculation of massive operator matrix elements with two masses. We compute missing two-mass contributions to unpolarized operator matrix elements at next-to-next-to-leading order and extend the calculation to polarized operator matrix elements at next-to-leading and next-to-next-to-leading order in the single and two-mass case. For the calculation of these processes we set up new calculational methods. In the second part of the thesis we deal with QED initial state radiation in electron-positron annihilation into a neutral vector boson at next-to-next-to-leading order. With the new calculation, which is based on an exact integration of the phase space and a subsequent expansion, we proof the asymptotic factorization of massive external particles for this process and clarify results in the literature.Item Probing the standard model with rare charm decays(2017) Boer, Stefan de; Hiller, Gudrun; Brod, Joachim; Fajfer, SvjetlanaThis thesis comprises a study of rare charm decays in the standard model (SM) and beyond. Within an effective theory framework, we calculate the SM Wilson coefficients to (partly) next-to-next-to leading logarithmic order in quantumchromodynamics. The calculation includes matching conditions and the running of the Wilson coefficients in the renormalization group-improved perturbation theory, thereby correcting expressions used in the literature. Furthermore, a calculation of phenomenological relevant two loop matrix elements of current-current operators is presented. We work out the phenomenology in the SM for radiative and semileptonic inclusive decays as well as the exclusive decays D -> Pll and D -> V gamma, including non-perturbative effects. The branching ratios are dominated by resonances, yet we can construct various observables which cleanly probe the SM, e.g. asymmetries, angular observables and lepton flavor violating decays are (approximate) SM null tests. Beyond the SM physics effects are analyzed model-independently and via leptoquark models, where various constraints and correlations, e.g. through flavor patterns, are worked out. In addition, we probe the SM by means of the decay Lambda_c -> p gamma, which is accessible at (future) colliders, and investigate the radiative decays in supersymmetric models.Item Three-loop QCD corrections from massive quarks to deep-inelastic structure functions and operator matrix elements(2016) Behring, Arnd; Blümlein, Johannes; Hiller, GudrunThis thesis discusses higher-order contributions from heavy quarks to inclusive deep-inelastic lepton-nucleon scattering. In this context, massive operator matrix elements play an important role: they enter into the heavy flavour Wilson coefficients through a factorisation relation in the asymptotic limit of large virtualities. Furthermore, they also enter into the definition of the variable flavour number scheme for parton distributions. Here, we present the analytic calculation of of several such massive operator matrix elements at the 3-loop level in perturbative quantum chromodynamics. In particular, we review the necessary mathematical and computational methods for these calculations and give results for the non-singlet and pure-singlet operator matrix elements including their applications in the structure functions, sum rules and and the variable flavour number scheme. Through this calculation we also obtain the pure-singlet and non-singlet anomalous dimensions at 3-loop order. Moreover, we discuss the calculation of certain representative Feynman diagrams with ladder and V-topologies, which serve as a testing ground for the calculational tools. Finally, also all Feynman diagrams of the gluonic operator matrix element are calculated, which is required in a 3-loop description of the variable flavour number scheme.Item O(α 3 s) contributions to the heavy flavor Wilson coefficients of the structure function F 2(χ, Q²) at Q² >> m²(2015) Wißbrock, Fabian Philipp; Blümlein, Johannes; Hiller, GudrunAt $O(\alpha_s^3)$ the contribution of a single heavy quark to the unpolarized structure function $F_2(x,Q^2)$ in the asymptotic region $Q^2\gg m^2$ is written as a convolution of the light flavor Wilson coefficents and the process independent massive operator matrix elements. This thesis extends the present description to allow for the presence of two heavy quark flavors and presents the respective renormalization prescription and first analytic results for these contributions. Furthermore the remaining $O(C_{A,F} T_F^2 N_F)$ contributions and various diagrams of more complex topologies have been computed analytically. On the mathematical side different evaluation techniques based on representations in terms of special functions, Mellin-Barnes representations and Hyperlogarithms have been worked out.Item Collider physics in anticipation of new TeV-scale phenomena(2014-03-27) Sedello, Henning; Hiller, Gudrun; Päs, HeinrichItem 3-loop contributions to heavy flavor Wilson coefficients of neutral and charged current DIS(2014-01-13) Hasselhuhn, Alexander; Blümlein, Johannes; Hiller, GudrunDie vorliegende Dissertation behandelt die Berechnung höherer Korrekturen zu den Strukturfunktionen der tiefinelastischen Streuung. Insbesondere werden Effekte schwerer Quarks in QCD-Korrekturen auf dem Drei-Schleifen-Niveau bestimmt. In dem asymtotischen Bereich Q^2 >>m^2 ergeben sich die schweren Wilsonkoeffizienten aus den leichten Wilsonkoeffizienten und den massiven Operatormatrixelementen (OMEs). Es werden neue Beiträge zu den OMEs A_{gq,Q} und A_{gg,Q} berechnet. Ferner werden Methoden für die computeralgebraische Berechnung von Leiterdiagrammen angegeben, wobei von Darstellungen generalisierter hypergeometrischer Funktionen und Appell-Funktionen Gebrauch gemacht wird. Hierbei kommen symbolische Summationstechniken zum Einsatz. Für die Berechnung von Graphen mit zwei disjunkten massiven Zyklen werden diese Methoden erweitert um Mellin-Barnes-Integrale und Eigenschaften iterierter Integrale. Schliesslich werden für den Fall der tiefinelastischen Streuung im geladenen Strom die kompletten Zwei-Schleifen-Korrekturen für die schweren Wilsonkoeffizienten konstruiert und im x- und N-Raum angegeben. Die Ergebnisse sind notwendig für eine präzise Bestimmung der Partondichten (PDFs) und der starken Kopplungskonstante zu Drei-Schleifen-Präzision.Item Probing Flavor and CP in Decays of Beauty and Charm(2013-07-16) Schacht, Stefan; Hiller, Gudrun; Päs, HeinrichItem Mellin moments of heavy flavor contributions to F 2 (x, Q 2 ) at NNLO(2009-11-16T14:13:16Z) Klein, Sebastian; Bluemlein, Johannes; Reya, EwaldItem Dynamical parton distributions of the nucleon up to NNLO of QCD(2009-03-12T10:30:08Z) Jiménez Delgado, Pedro; Reya, E.; Glück, M.Item The polarized and unpolarized photon content of the nucleon(2005-09-06T05:28:56Z) Pisano, Cristian; Reya, Ewald; Glück, MosheItem NLO QCD corrections to the polarized photo- and hadroproduction of heavy quarks(Universität Dortmund, 2000-05-22) Bojak, IngoThis thesis presents the complete details of our calculation of the next-to-leading order (NLO) QCD corrections to heavy flavor photo- and hadroproduction with longitudinally (circularly) polarized photons and hadrons. The main motivation for investigating these processes is the determination of the polarized gluon density. Corresponding measurements will be available from the COMPASS and RHIC experiments, respectively, in the near future. All methods used in the computation are extensively documented and explained, providing a self-contained introduction to this type of NLO calculations. Some of the employed mathematical tools also may be of general interest, e.g., the series expansion of hypergeometric functions. The relevant parton level results are collected and plotted in the form of scaling functions. However, the simplification of the obtained gluon-gluon virtual contributions has not been completed yet. Thus NLO phenomenological predictions at the hadron level are only given in the case of photoproduction. The theoretical uncertainties of these predictions, in particular with respect to the size of the heavy quark mass, are carefully considered. Also it is shown that cuts on the transverse momentum of the produced heavy flavor can considerably enhance the measured production asymmetries. Finally unpolarized heavy quark production is briefly reviewed in order to derive conditions for a successful extraction of the polarized gluon density from future spin-dependent experimental data.