Experiments on neutrino oscillations have confirmed that neutrinos have small, but non-zero masses, and that the interacting neutrino states do not have definite masses, but are mixtures of such states.The seesaw models make up a group of popular models describing the small neutrino masses and the corresponding mixing.In these models, new, heavy fields are introduced and the neutrino masses are suppressed by the ratio between the electroweak scale and the large masses of the new fields. Usually, the new fields introduced have masses far above the electroweak scale, outside the reach of any foreseeable experiments, making these versions of seesaw models essentially untestable. However, there are also so-called low-scale seesaw models, where the new particles have masses above the electroweak scale, but within the reach of future experiments, such as the LHC.In quantum field theories, quantum corrections generally introduce an energy-scale dependence on all their parameters, described by the renormalization group equations. In this thesis, the energy-scale dependence of the neutrino parameters in two low-scale seesaw models, the low-scale type I and inverse seesaw models, are considered. Also, the question of whether the neutrinos are Majorana particles, \ie , their own antiparticles, has not been decided experimentally. Future experiments on neutrinoless double beta decay could confirm the Majorana nature of neutrinos. However, there could also be additional contributions to the decay, which are not directly related to neutrino masses. We have investigated the possible future bounds on the strength of such additional contributions to neutrinoless double beta decay, depending on the outcome of ongoing and planned experiments related to neutrino masses. / QC 20110812

This report discusses higher differential forms with applications in the study of topological phenomena. The integer quantum Hall effect is first discussed, demonstrating a connection between models on a lattice and quantum field theories bridged by a topological invariant, namely the Chern number. Next, for parametrized models on a lattice, the higher Berry curvature is described. This is a rank-(d + 2) differential form on a (d + 2)-dimensional parameter manifold which provides a relation between models in a bulk and on a lower-dimensional interface. Finally, a family of quantum field theories connected to a (d + 1)-dimensional manifold, termed a target space, is constructed. This connection is realized through the incorporation of a set of classical fields, and the effective action of the full field theories all contain a Wess-Zumino-Witten term given by the pullback of a rank-(d + 1) differential form from the target space to spacetime. By performing an extension of spacetime, a (d + 2)-form on a (d + 2)-dimensional target space is constructed in a similar way. Extending a theory in d dimensions thus yields a form on a target space of the same dimension as that of a (d + 1)-dimensional theory without extension, defining a dimensional hierarchy. The dimensional relations inherent in the two higher forms studied indicate the possibility of a relation between them. / Denna rapport beskriver högre ordningens differentialformer med tillämpningar inom topologiska fenomen. Den heltaliga kvantmekaniska Halleffekten beskrivs först, som ett exempel på ett samband mellan modeller på ett gitter och kvantfältteorier som förbindas av topologiska invarianter, specifikt Chern-talet. För parametriserade modeller på ett gitter beskrivs därefter den högre Berrykrökningen. Detta är en differentialform av ordning (d + 2) definierad på en (d + 2)-dimensionell parametermångfald som ger en koppling mellan modeller i en kropps inre och på dens gränsskikt, som är i en lägre dimension. Slutligen konstrueras en familj av kvantfältteorier som är kopplade till en (d + 1)-dimensionell mångfald kallad modellens målrum. Denna koppling realiseras genom introduktionen av ett antal klassiska fält, och den effektiva verkan för den fullständiga teorin innehåller en Wess-Zumino-Witten-term som ges av en tillbakadragen (d + 1)-form från målrummet till rumtiden. Genom att utvidga rumtiden kan även en (d + 2)-form på en (d + 2)-dimensionellt målrum konstrueras på ett motsvarande sätt. Utvidgningen av en teori i d dimensioner ger därmed en differentialform på ett målrum med samma dimension som målrummet för en (d + 1)-dimensionell teori utan utvidning, vilket definierar en dimensionell hierarki. Dimensionsrelationerna inbyggda i dessa två differentialformer indikerar den möjliga existensen av en relation mellan dem.

Nuclear electromagnetic breakup processes at low energy are particularly relevant in the astrophysical context. In this Thesis we analyse the Beryllium-9 photodisintegration reaction, whose inverse process, under certain astrophysical conditions, is related to the Carbon-12 formation. A preliminary study of the Carbon-12 photodisintegration is also carried out. The interaction of these nuclei with a low-energy photon induces a transition to a state consisting of cluster sub-units, the alpha-particles, and possibly a neutron, n. The theoretical study of the cross section in the low-energy regime is conducted by using a three-body ab initio approach. Beryllium-9 exhibits a clear separation of energy scales, since its alpha-alpha-n three-body binding energy is shallow compared to the binding of the alpha-particle. Within this framework a halo/cluster Effective Field Theory (EFT) can be developed. The alpha-alpha and alpha-n effective interactions are defined in momentum space as a series of contact terms, regularized by a momentum-regulator function. The Low Energy Constants are expressed in terms of scattering observables, i.e. scattering length and effective range. A three-body potential is also introduced in the model. Carbon-12 is studied on the same footing. By means of an integral transform approach, the problem of the transition to a state in the continuum can be advantageously reformulated in terms of a bound-state problem: in the calculations we use the Lorentz Integral Transform method, in conjunction with the Non-Symmetrized Hyperspherical Harmonics method. In determining the low-energy photodisintegration cross section, the nuclear current matrix element is evaluated through the electric dipole, or quadrupole, transition operator (Siegert theorem). Since the continuity equation is used explicitly, the contribution of the one-body and the many-body current operators is implicitly included in the calculation. By comparing the results with those obtained by using a one-body convection current, the effect of the many-body terms can be quantified. The dependence of the results on different EFT parameters is discussed, always in connection with the experimental data available in the literature. By following the power counting dictated by the EFT approach for Beryllium-9, the inclusion of different partial waves in the potential model is explored. In addition to a alpha-alpha S-wave, a alpha-n P-wave and a three-body effective interaction, a alpha-n S-wave term is also required to obtain results more consistent with the experimental data. The contribution of the many-body currents to the cross section is found to be non-negligible. Although at an early stage, Carbon-12 results show interesting features. The formalism presented in this Thesis can be extended to study the photodisintegration of Oxygen-16 within a fully four-body ab initio approach.

In dieser Arbeit verwenden wir Flavourinvarianten, um systematisch Lösungen für Probleme des Standardmodells (SM) der Teilchenphysik mit Hilfe verschiedener effektiver Feldtheorien (EFTs) zu untersuchen. In Teil I untersuchen wir die CP-Verletzung im SM und in der SM EFT erweitert mit leichten, sterilen Neutrinos. Wir konstruieren die erzeugende Menge von Flavourinvarianten im νSM, mit der jede Observable als Polynom der Invarianten, sowie die Bedingungen für die CP-Verletzung auf flavourinvariante Weise ausgedrückt werden können. Anschließend weiten wir die Ergebnisse auf die EFT-Wechselwirkungen für verschiedene Szenarien der Neutrinomassen aus. Hier ändert sich die Form der EFT-Flavourinvarianten und ihre Unterdrückung mit der Skala der neuen Physik drastisch mit der untersuchten Art der Neutrinomassen. In Teil II untersuchen wir verschiedene Aspekte der Symmetriebrechung in EFTs von axionartigen Teilchen (ALPs). Wegen ihrer pseudo-Nambu–Goldstone-Natur ist eine wesentliche Eigenschaft der ALPs ihre Shiftsymmetrie (ShS). Wir formulieren flavourinvariante Ordnungsparameter der ShS, die das Powercounting der EFT führender Ordnung bei einer leicht gebrochenen ShS korrekt implementieren lassen. Mit der Hilbertreihe zählen wir die Anzahl der Operatoren, die in der ALP EFT mit und ohne ShS oberhalb und unterhalb der elektroschwachen Skala auftreten, womit wir Operatorbasen konstruieren, die Beziehungen der ShS auf höhere Ordnung verallgemeinern und die CP-verletzenden Flavourinvarianten führender Ordnung konstruieren. Die Axionlösung des starken CP-Problems kann durch neue CP-Verletzung im Ultravioletten durch kleine Instantonen gestört werden. Mit einer SMEFT-Parametrisierung der neuen CP-Verletzung zeigen wir, dass neu konstruierte CP-verletzende SMEFT-Flavourinvarianten explizit in den Instantonberechnungen auftauchen und zur Systematisierung der Berechnungen verwendet werden können, wodurch wir bessere Limits für kleine Instanton- und Flavourszenarien ableiten. / In this thesis, we use flavour invariants to systematically study solutions to problems of the Standard Model (SM) of particle physics with different effective field theories (EFTs). In Part I, we study Charge–Parity (CP) violation in the SM and SM EFT extended with light sterile neutrinos. We construct the generating set of flavour invariants in the νSM allowing us to express any observable as a polynomial of those invariants. In addition, the invariants enable us to express the conditions for CP violation in a flavour-invariant way. We extend the results to the EFT interactions with different scenarios for the neutrino masses. Here, the form of the EFT flavour invariants and their suppression with the scale of new physics changes drastically depending on the nature of the neutrino masses. In Part II, we study different aspects of symmetry breaking in the EFTs of axionlike particles (ALPs). An essential property of ALPs is their shift symmetry (ShS) due to their pseudo-Nambu–Goldstone nature. We formulate flavour-invariant order parameters of ShS, which allow us to properly impose the power counting of the leading order EFT in the presence of a softly broken ShS. Using the Hilbert series, we count the number of operators appearing in the ALP EFT with and without a ShS above and below the electroweak scale. We use this information to construct operator bases, generalise the relations imposing ShS to higher orders and construct the leading order CP-odd flavour invariants. The axion solution to the strong CP problem can be spoiled by new CP violation in the ultraviolet in the presence of small instantons. Parameterising the new CP violation in the SMEFT, we show that newly constructed CP-odd SMEFT flavour invariants, featuring the strong CP angle, explicitly appear in the instanton computations and vice-versa that they can be used to systematise the computations. Using these results, we derive bounds on different small instanton and SMEFT flavour scenarios.

Gittersimulationen der Quantenchromodynamik ermöglichen eine vollständig nichtperturbative Berechnung hadronischer Korrelationsfunktionen, allerdings müssen die Beiträge angeregter Zustände unter Kontrolle sein um verlässlich physikalische Größen wie Teilchenenergien und Matrixelemente extrahieren zu können. In dieser Arbeit wird eine effektive Feldtheorie, die Chirale Störungstheorie Schwerer Mesonen (ChSTSM), verwendet um die dominanten Beiträge der angeregten Zustände in B Meson Korrelationsfunktionen, die zur Extraktion von CKM Matrixelementen verwendet werden, analytisch zu bestimmen. Zuerst werden die Analoga der Quarkbilineare, die als interpolierende Felder in Gittersimulationen verwendet werden, in der ChSTSM hergeleitet. Diese hängen von Niedrig-Energie-Konstanten (NEKs) ab, deren Werte für lokale Felder bekannt sind. Geschmierte interpolierende Felder kann man andererseits durch verändern dieser numerischen Werte beschreiben. Dies wird im Laufe der Arbeit mehrfach genutzt um den Einfluss des Schmierens zu untersuchen. Mit den Feldern kann die Zweipunkt-Funktion des B Meson berechnet werden, aus der seine Masse und Zerfallskonstante sowie die jeweiligen Beiträge der angeregten Zustände bestimmt werden können. Aus Quotienten von passend gewählten Drei- und Zweipunkt-Funktionen werden weiterhin die ChSTSM NEK g, die Formfaktoren des semileptonischen B Zerfalls und die Matrixelemente, die neutrale B Oszillationen beschreiben, sowie die dominanten Beiträge der angeregten Zustände bestimmt. Letztere führen, abhängig von den Werten der NEKs, meist zu einem um ein paar Prozent höheren Wert für die Quotienten. Einige Ergebnisse hängen zusätzlich von weiteren unbekannten NEKs ab. Für diese werden Korrelationsfunktionen angegeben aus denen sie mittels Gitterrechnungen bestimmt werden können. Im Gegensatz zu den vorherigen Ergebnissen sind die Beiträge der angeregten Zustände für einen der semileptonischen Formfaktoren eine Größenordnung größer und negativ. / Lattice simulations of Quantum Chromodynamics allow for a fully non-perturbative computation of hadronic correlation functions, but for a reliable extraction of physical quantities such as particle energies and matrix elements the contribution of excited states needs to be under control. In this thesis, an effective field theory known as Heavy Meson Chiral Perturbation Theory (HM ChPT) is used to analytically compute the dominant excited states contamination of B meson correlators which are relevant for the extraction of CKM matrix elements. First, the analogues of the quark bilinears which are used as interpolating fields in lattice simulations are derived in HM ChPT. These depend on a set of low energy constants (LECs) which are known for local fields. On the other hand, smeared interpolating fields can be incorporated in the effective theory by changing the values of these LECs, a fact that will be used throughout this thesis for investigating the effect of smearing. The interpolating fields are used to compute the B meson two-point function from which the B meson mass and decay constant as well as the respective excited states contamination can be extracted. From suitably chosen ratios of three-point functions and two-point functions, the HM ChPT LEC g, the form factors of semileptonic B meson decay, and the matrix elements of neutral B meson oscillations were determined. The computed excited states contamination of these ratios usually leads to an overestimation of the order of a few percent, depending on the values chosen for the LECs. Some results depend on so far unknown LECs, for which suitable correlation functions for a lattice determination are presented. In contrast, the excited states contamination of one of the semileptonic form factors is an order of magnitude larger and negative.

In dieser Arbeit wird der Ansatz der Weltlinienquantenfeldtheorie (WQFT) zur Berechnung von Observablen des klassischen allgemeinen relativistischen Zweikörpersystems vorgestellt. Kompakte Körper wie Schwarze Löcher oder Neutronensterne werden im Rahmen einer effektiven Feldtheorie mit Weltlinienfeldern beschrieben. Die WQFT behandelt alle Weltlinienfelder gleichberechtigt mit dem Gravitationsfeld und ist definiert als die tree-level-Beiträge eines Pfadintegrals auf diesen Feldern. Zuerst wird die effektive feldtheoretische Beschreibung von kompakten Körpern mit Weltlinien und die post-Minkowski'schen Approximation der Streuung dieser Körpern vorgestellt. Die Einbeziehung des Spins wird mit besonderem Augenmerk auf ihre supersymmetrische Beschreibung in Form von antikommutierenden Grassmann-Variablen analysiert. Anschließend wird die WQFT mit einer Diskussion ihrer in-in Schwinger-Keldysh-Formulierung, ihrer Feynman-Regeln und Graphengenerierung sowie ihrer on-shell Einpunktfunktionen vorgestellt. Die Berechnung von Streuobservablen erfordert im Allgemeinen die Auswertung von Multi-Loop-Integralen, und wir analysieren die Zwei-Loop-Integrale, die in der dritten post-Minkowski'schen Ordnung der Weltlinienobservablen auftreten. Schließlich wenden wir uns den Ergebnissen der WQFT zu und beginnen mit der gravitativen Bremsstrahlung bei der Streuung zweier rotierender Körper. Diese Wellenform wird zusammen mit der Strahlungsinformation der Linear- und Drehimpulsflüsse diskutiert. Der gesamte abgestrahlte Drehimpuls führender post-Minkowski'schen Ordnung wird abgeleitet. Wir präsentieren dann die Ergebnisse des konservativen und strahlenden Impulses und des Spin-Kicks bei dritter post-Minkowski'scher Ordnung und quadratischer Ordnung in Spins zusammen mit der Abbildung der ungebundenen Ergebnisse auf einen konservativen (gebundenen) Hamiltonian bei der entsprechenden perturbativen Ordnung. / In this work the worldline quantum field theory (WQFT) approach to computing observables of the classical general relativistic two-body system is presented. Compact bodies such as black holes or neutron stars are described in an effective field theory by worldline fields with spin degrees of freedom efficiently described by anti-commuting Grassmann variables. Novel results of the WQFT include the gravitational bremsstrahlung at second post-Minkowskian order and the impulse and spin kick at third post-Minkowskian order all at quadratic order in spins. Next, the WQFT is presented with a comprehensive discussion of its in-in Schwinger-Keldysh formulation, its Feynman rules and graph generation and its on-shell one-point functions which are directly related to the scattering observables of unbound motion. Here, we present the second post-Minkowskian quadratic-in-spin contributions to its free energy from which the impulse and spin kick may be derived to the corresponding order. The computation of scattering observables requires the evaluation of multi-loop integrals and for the computation of observables at the third post-Minkowskian order we analyze the required two-loop integrals. Our discussion uses retarded propagators which impose causal boundary conditions of the observables. Finally we turn to results of the WQFT starting with the gravitational bremsstrahlung of the scattering of two spinning bodies. This waveform is discussed together with its radiative information of linear and angular momentum fluxes. Lastly we present the conservative and radiative impulse and spin kick at third post-Minkowskian order and quadratic order in spins together with the a conservative Hamiltonian at the corresponding perturbative order. The results obey a generalized Bini-Damour radiation-reaction relation and their conservative parts can be parametrized in terms of a single scalar.

This thesis is devoted to the rare decay π0 → e+ e− . We firstly introduce all theoretical knowledge necessary for the description of the vertices used in this work. Subsequently, we introduce three two-loop chiral Feynman diagrams, which are of order O(α2 p4 ). These diagrams are firstly decomposed to Master integrals by Laporta algorithm. After that, we calculate each Master integral individually by the differential equation technique. We also focus on the renormalization of the process. Since we are working with the effective field theory, finite corrections χ from counterterm diagrams naturally appear. With use of the calculations listed in this thesis, the determination of the parameter χR could be further improved taking into account the whole two-loop correction. 1

Dans cette thèse, nous nous intéressons à certains aspects concernant les phénomènes hadroniques à basse énergie sous 1 GeV, en dessous de laquelle la symétrie chirale de la Chromodynamique Quantique (QCD) est spontanément brisée. En dessous de cette échelle d'énergie, le spectre de QCD se réduit à un octet de mésons légers pseudo-scalaires (π, K and η). Mais à cause du confinement, QCD sous 1 GeV devient hautement non perturbative – il n'est donc plus possible de décrire à basse énergie la dynamique de ces mésons en termes de gluons et de quarks (ici seuls les quarks légers u, d et s sont concernés). Deux alternatives principales à cet obstacle majeur existent néanmoins: la QCD sur réseau ainsi que les Théories Effectives des Champs. La QCD sur réseau consiste à calculer de manière numériques les diverses observables hadroniques, alors que les théories effectives permettent de nouveau une approche analytique (et perturbative) adaptée à une échelle d'énergie donnée. Dans le cas de QCD à basse énergie, c'est la Théorie Chirale des Perturbations (ChiPT) qui joue le rôle de théorie effective. Cette théorie peut être construite à partir de deux saveurs de quarks légers (u et s) ou trois (u,d, et s). Il est alors possible d'utiliser certains résultats de calculs sur réseau (ainsi que certains résultats expérimentaux) afin d'extraire des valeurs numériques pour les divers paramètres libres que contient la théorie chirale. Il fut néanmoins observé que le développement en séries chirales de quelques observables hadroniques sont numériquement “malades” dans le cadre de la théorie à trois saveurs. En effet, des travaux antérieurs montrent qu'il pourrait exister une possible compétition numérique entre l'Ordre Dominant (LO) et l'Ordre Sous-Dominant (NLO): en place de la hiérarchie usuelle LO>>NLO, l'équivalence LO~NLO prévalerait. La partie principale de la thèse consiste ainsi à la description et l'utilisation d'une version alternative de ChiPT, nommée Théorie Chirale des Perturbations Ressommée (ReChiPT ). Quelques observables hadroniques de basse energie sont calculées puis étudiées dans ce cadre “ressommé”, puis nous procédons à l'ajustement de certaines données de QCD sur réseau obtenues par des simulations à 2+1 quarks dynamiques sur ces observables exprimées en ReChiPT: les constantes de désintégrations et les masses de l'octet (π, K, η), ainsi que les facteurs de forme Kl3. Nous testons ensuite la validité de notre assertion concernant la possible compétition numérique observée dans les séries chirales. Enfin, dans la dernière partie, nous discutons plusieurs aspects analytiques et numériques concernant certaines quantités topologiques liées de manière intrinsèque à la très complexe structure du vide de QCD, dans le cadre de ChiPT (ressommé), et nous confrontons de nouveau cette étude à des données réseau 2+1. / In this thesis, we focus on some aspects concerning hadronic phenomena at low energy, below 1 GeV, under which the spontaneous breaking of chiral symmetry takes place. Under this scale, the spectrum of Quantum Chromodynamics reduces to an octet of light pseudo-scalar mesons (π, K and η). But because of the confinement property, QCD under 1 GeV is highly non-perturbative, it is thus not possible to describe at low energy the dynamics of these mesons in terms of gluons and quarks (in that case the three light quarks u,d, and s). Two main alternatives exist to circumvent this major obstacle: Lattice QCD and Effective Field Theories. Lattice QCD is concerned with the numerical computations of various hadronic observables, while Effective Field Theories correspond to analytical frameworks adapted to a particular energy scale. In the case of QCD at low energy, this role is devoted to Chiral Perturbation Theory (ChiPT). This theory can be built either from two quark flavours (u and d), or three (u,d, and s). Using the numerical results from Lattice QCD, it is possible to obtain numerical values for the unknown parameters that ChPT contains. It was however observed that the series expansions of hadronic observables stemming from ChiPT calculations do not “behave well” numerically in the three-flavour case. Indeed, previous works shown that there could exists at the numerical level a competition between the Leading and the Next-to- Leading order (LO and NLO); i.e., instead of the usually expected hierarchy LO>>NLO, one would have LO~NLO. The main part of the thesis work consists in the description and the use of a modified version of ChiPT allowing this numerical competition in the chiral series that was called “Resummed ChiPT”. Within this “Resummed” framework, we proceed to fitting data from 2+1 lattice calculations to hadronic observables computed in ChiPT: decay constants and masses of π, K and η, and Kl3 form factors, and check the consistency of our claim about the numerical competition in ChiPT expansions. In the last part, we discuss topological quantities that are intrinsically tied to the very complex structure of the QCD vacuum, in the (resummed) ChiPT framework and in the light of 2+1 lattice data, in their analytical and numerical aspects.

The standard model of particle physics can excellently describe the vast majorityof data of particle physics experiments. However, in its simplest form, it cannot account for the fact that the neutrinos are massive particles and lepton flavorsmixed, as required by the observation of neutrino oscillations. Hence, the standardmodel must be extended in order to account for these observations, opening up thepossibility to explore new and interesting physical phenomena. There are numerous models proposed to accommodate massive neutrinos. Thesimplest of these are able to describe the observations using only a small numberof effective parameters. Furthermore, neutrinos are the only known existing particleswhich have the potential of being their own antiparticles, a possibility that isactively being investigated through experiments on neutrinoless double beta decay.In this thesis, we analyse these simple models using Bayesian inference and constraintsfrom neutrino-related experiments, and we also investigate the potential offuture experiments on neutrinoless double beta decay to probe other kinds of newphysics. In addition, more elaborate theoretical models of neutrino masses have beenproposed, with the seesaw models being a particularly popular group of models inwhich new heavy particles generate neutrino masses. We study low-scale seesawmodels, in particular the resulting energy-scale dependence of the neutrino parameters,which incorporate new particles with masses within the reach of current andfuture experiments, such as the LHC. / Standardmodellen för partikelfysik beskriver den stora majoriteten data från partikelfysikexperimentutmärkt. Den kan emellertid inte i sin enklaste form beskrivadet faktum att neutriner är massiva partiklar och leptonsmakerna är blandande,vilket krävs enligt observationerna av neutrinooscillationer. Därför måste standardmodellenutökas för att ta hänsyn till detta, vilket öppnar upp möjligheten att utforska nya och intressanta fysikaliska fenomen. Det finns många föreslagna modeller för massiva neutriner. De enklaste av dessakan beskriva observationerna med endast ett fåtal effektiva parametrar. Dessutom är neutriner de enda kända befintliga partiklar som har potentialen att vara sinaegna antipartiklar, en möjlighet som aktivt undersöks genom experiment på neutrinolöst dubbelt betasönderfall. I denna avhandling analyserar vi dessa enkla modellermed Bayesisk inferens och begränsningar från neutrinorelaterade experiment och undersöker även potentialen för framtida experiment på neutrinolöst dubbelt betasönderfall att bergänsa andra typer av ny fysik. Även mer avancerade teoretiska modeller för neutrinomassor har föreslagits, med seesawmodeller som en särskilt populär grupp av modeller där nya tunga partiklargenererar neutrinomassor. Vi studerar seesawmodeller vid låga energier, i synnerhetneutrinoparametrarnas resulterande energiberoende, vilka inkluderar nya partiklarmed massor inom räckh°all för nuvarande och framtida experiment såsom LHC. / <p>QC 20130830</p>

Cette thèse est dédiée à l’étude des désintégrations B0 s → φγ au LHCb afin de mesurer la polarisation du photon . Au niveau des quarks, ces désintégrations procèdent via une transition pingouin b→ sγ et sont sensibles aux éventuelles contributions virtuelles de Nouvelle Physique. La mesure de la polarisation du photon permet de tester la structure V – A du couplage du Modèle Standard dans les processus des diagrammes de boucles de pingouin. Cette mesure peut être réalisée en étudiant le taux de désintégration dépendant du temps des mésons B. Une analyse délicate a été faite pour comprendre la distribution du temps propre et l’acceptance de sélection qui affecte cette distribution. Afin de contrôler l’acceptance de temps propre, des méthodes basées sur les données ont été développées. Plusieurs stratégies utilisées dans la mesure de la polarisation des photons sont introduites et des résultats préliminaires sont présentés. De plus, une étude de certains effets systématiques est discutée. Dans le cadre de l’étude des désintégrations radiatives, une nouvelle procédure d’identification de photons a été développée et nous avons fourni un outil pour calibrer la performance de la variable de séparation photon/pion neutre sur la simulation. Ces outils sont d’intérêt général pour la collaboration LHCb et sont largement utilisés. / This thesis is dedicated to the study of the photon polarization in B0 s → φγ decays at LHCb. At the quark level, such decays proceed via a b→ sγ penguin transition and are sensitive to possible virtual contributions from New Physics. The measurement of the photon polarization stands also as a test of the V – A structure of the Standard Model coupling in the processes mediated by loop penguin diagrams. The measurement of the photon polarization can be done through a study of the time-dependent decay rate of the B meson. A delicate treatment has been done to understand the proper time distribution and the selection acceptance affecting it. To control the proper time acceptance, data driven control methods have been developed. Several possible strategies to measure the photon polarization are introduced and preliminary blinded results are presented. A study of some of the systematic effects is discussed. In the context of studying radiative decays, the author has developed a new photon identification procedure and has provided a tool to calibrate the performance of the photon/neutral pion separation variable on simulation. Those tools are of general interest for the LHCb collaboration and are widely used.