In this thesis various aspects of target-space duality in closed bosonic string theory are studied. It begins by introducing generalized geometry as the main mathematical framework. In analogy to general relativity with the Riemannian metric as dynamical quantity, a unified description for string backgrounds – Riemannian metrics together with Kalb-Ramond two-form fields – is approached via Courant algebroids on the generalized tangent bundle equipped with a generalized metric. The dual background configuration, i.e. a metric and a bivector field, is described by the generalized cotangent bundle. The absence of a conventional curvature tensor and consequently the problem of defining generalized gravity theories on Courant algebroids is investigated in detail. This leads to the introduction of Lie algebroids whose differential geometry is suitable for the formulation of gravity theories. Different such theories are shown to be interrelated by appropriate homomorphisms. This proves to be useful for describing non-geometric backgrounds. Target-space duality is introduced in terms of O(d,d)-duality which identifies two-dimensional non-linear sigma models for different string backgrounds as physically equivalent under certain conditions: The backgrounds and coordinates of the dual theories have to be related by certain O(d, d) transformations. In particular, integrability conditions of the dual coordinates are formulated in terms of Courant algebroids. Apart from (non-abelian) T-duality, O(d,d)-duality contains the novel Poisson-duality induced by Poisson structures. T- and Poisson-duality are applied to the three-torus with constant H-flux which shows the existence of non-geometric backgrounds. The latter exceed conventional conceptions of geometry as they cannot be described globally. The problem of describing non-geometric backgrounds is approached with generalizes geometry. A unified description of T-dual backgrounds is given in terms of proto-Lie bialgebroids – one for the geometric sector and another for the non-geometric one. They combine into a Courant algebroid whose anomalous Jacobi identity provides conditions for the concurrent appearance of dual fluxes. The absence of a gravity theory leads to the restriction to Lie algebroids. Their gravity theories allow for a global description of non-geometric backgrounds by an exact prescription for the patching of these backgrounds. The description extends to all possible supergravity theories. The question whether a unified description of dual backgrounds is possible is reconsidered in a manifestly T-duality invariant conformal field theory approach. Dual coordinates are treated on equal footing. Modular invariance of the one-loop partition function together with the premise of physical intermediate states in four-tachyon scattering inevitably leads to the appearance of the strong constraint of double field theory on non-compact spaces. Toroidally compactified directions do not require a constraint. This explains the appearance of the strong constraint and justifies possible attenuations.

The development of renewable energy sources depicts a constantly growing interdisciplinary research field. Beyond photovoltaics chemical photocatalysis plays a small role, but is gaining more and more importance. In photocatalysis, light serves as an energy source for the chemical conversion of certain molecules. However, not only the application of photocatalysis as energy source but also the utilization of photocatalysis in chemical synthesis has attracted a deep scien- tific interest. For the optimization of photocatalytic systems a fundamental understanding oft the underlying processes is more than essential. Thereby, transient absorption spectroscopy has proved to be a very useful tool. On the one hand, the operation of a setup for transient absorption spectroscopy and on the other hand the systematic data evaluation requires physical and mathe- matical skills whereas the results cannot be interpreted without deep chemical knowledge. With- in the framework of the present thesis the cooperation between the fields of organic chemistry and physics has turned out as a very productive cooperation. Sensitizing mechanisms, reaction mechanisms and reactive intermediate states in photocatalytic reactions on time scales from femto- to microseconds are the object of the present work. The present thesis will prove that the analysis of measurement data on the basis of established standard methods, such as the fitting of a sum of exponential functions to the temporal evolution of the measured signal, often is not sufficient for a complete interpretation of the data. Only a data analysis precisely adapted to the problem can lead to a fundamental understanding of the underlying processes. In the first part of the present thesis, the focus lies on light-induced intramolecular charge transfer processes. Marcus Theory, which depicts the theoretical background, will be briefly in- troduced. On the basis of a molecular donor-bridge-acceptor system it will be shown that the damping coefficient β is not sufficient to differ unambiguously between coherent tunneling and incoherent hopping mechanism. Flavin-capped DNA hairpins serve as a model for the investigation of intramolecular charge transfer processes. After photo-excitation, flavin induces a hole which migrates through the DNA strand. It will be shown that an adapted base sequence allows for quantum yields of ΦCS = 14% for long-lived charge separated states. In the next section it will be discussed if the building blocks of the DNA are adapted to serve as chiral backbone for enantioselective photocatalysis. The conformation-dependent charge- transfer dynamics in benzophenone-DNA dinucleotides will be put on solid ground with the help of Marcus Theory. It will be shown that these dinucleotides are generally not suited to serve as an inert backbone for every kind of photochemical reaction. In the following section a true bimolecular photocatalytic reaction will be discussed. Flavin serves as photocatalyst for the conversion of an alcohol to the corresponding aldehyde. A pre- cisely adapted data analysis allows and exact quantification of the diffusion controlled reaction dynamics on the ps time scale. The understanding of the process allows optimizing the reaction conditions. The targeted utilization of triplet chemistry within this reaction can help to increase the quantum yield for product formation. As photo-induced charge transfer processes have been intensively discussed, the focus in the second part of the thesis lies on the [2+2] photocycloaddition. As basis for the interpretation of subsequent measurements, the [2+2] photocycloaddition of substituted quinolones will be inves- tigated. The formation of the cyclobutane ring in which the quinolone triplet state plays the cen- tral role will be characterized and quantified on the time scale from ps to ns. Afterwards the [2+2] photocycloaddition of substituted quinolones will be initiated by a chiral xanthone-based photocatalyst. It will be shown that within this catalyst-substrate complex in which both constit- uents have a distance of only few Ångströms, new electronic properties appear. The photo- excitation of a new electronic state not only initiates the [2+2] photocycloaddition of the quino- lone but also depicts a new sensitizing mechanism, which has to the author’s best knowledge not been observed in photocatalysis of organic molecules. The quinolone triplet state does not appear in this mechanism. The question, if this mechanism can be transferred to other photocatalytic systems has to be answered within the framework of further studies. / Die Erforschung nachhaltiger und ressourcenschonender Energiequellen bildet ein stetig wachsendes, interdisziplinäres Forschungsfeld. Neben der Photovoltaik, die inzwischen eine etablierte Energiequelle darstellt, ist die chemische Photokatalyse noch ein kleines, aber stets wachsendes Teilgebiet. In der Photokatalyse dient das einfallende Licht dazu, chemische Ver- bindungen umzuformen. Nicht nur die Anwendung der Photokatalyse für die Energiegewinnung, sondern auch der Einsatz in der chemischen Synthese stößt dabei auf wachsendes Interesse. Um photokatalytische Systeme zu optimieren ist ein fundamentales Verständnis der Prozesse erfor- derlich. Die transiente Absorptionsspektroskopie hat sich dabei als geeignetes Werkzeug erwie- sen. Der Betrieb eines Aufbaus zur Messung transienter Spektren auf verschiedenen Zeitskalen und die gezielte Datenauswertung erfordert fundiertes physikalisches und mathematisches Ver- ständnis, wohingegen die Interpretation der Ergebnisse nicht ohne chemisches Wissen erfolgen kann. Im Rahmen dieser Arbeit hat sich die Kooperation zwischen der organischen Chemie und der Physik als erfolgreiche Zusammenarbeit erwiesen. Gegenstand der vorliegenden Arbeit sind die Sensibilisierungsmechanismen, die Reaktionsmechanismen und die reaktiven Intermediate in photokatalytischer Reaktionen auf Zeitskalen von Femto- bis Mikrosekunden. Es wird gezeigt, dass die Auswertung von Datensätzen mit Standardmethoden, wie der Anpas- sung einer Summe von Exponentialfunktionen an die zeitliche Entwicklung des Signals oft nicht ausreichend ist, um die Messdaten hinreichend zu interpretieren. Erst eine der Problemstellung exakt angepasste Datenanalyse führt zum Verständnis der zugrundeliegenden Prozesse. Zunächst werden lichtinduzierte intramolekulare Ladungstransferprozesse behandelt. Die the- oretische Basis für die Beschreibung solcher Prozesse bildet die Marcus-Theorie, die kurz einge- führt wird. Anhand eines molekularen Donor-Bridge-Acceptor-Systems wird gezeigt, dass der exponentielle Dämpfungskoeffizient β oft ungeeignet ist um der Reaktion einen kohärenten Tun- nelprozess oder einen inkohärenten Transfermechanismus zuzuweisen. DNS-Haarnadelstrukturen, welche kovalent mit einem Flavin-Chromophor verbunden sind, dienen als Modellsystem für die Untersuchung intramolekularer Ladungstransferprozesse. Nach Anregung induziert Flavin eine Elektronenfehlstelle in dem benachbarten DNS-Strang, die den Strang entlangwandern kann. Es wird gezeigt, dass durch die geeignete Wahl der Basensequenz eine Quantenausbeute von ΦCS = 14 % für langlebige ladungsgetrennte Zustände erreicht wird. In einem weiteren Abschnitt wird untersucht, ob die Bausteine der DNS als chirale Umgebung für die enantioselektive Photokatalyse geeignet sind. Mit Hilfe einer auf der Marcus-Theorie basierenden Interpretation der Messergebnisse wird die konformationsabhängige Ladungstrans- ferdynamik in Benzophenon-DNS-Dinukleotiden beschrieben. Es wird gezeigt, dass die Dinuk- leotide nicht uneingeschränkt für die enantioselektive Photokatalyse geeignet sind. Schließlich wird eine echte bimolekuare photokatalytische Reaktion untersucht. Dabei wird mit Hilfe von Flavin ein Alkohol in ein Aldehyd umgesetzt. Mit einer angepassten Datenauswer- tung werden diffusive Prozesse auf der ps-Zeitskala genau quantifiziert. Die gewonnen Informa- tionen dienen dazu, die Reaktionsbedingungen zu optimieren um über einen Triplett- Reaktionsmechanismus höhere Quantenausbeuten zu erzielen. Nachdem photoinduzierte Ladungstransferprozesse ausgiebig diskutiert wurden, liegt der Fo- kus im zweiten Teil auf der [2+2] Photocycloaddition: Als Grundlage für die Interpretation spä- terer Messungen wird zunächst die [2+2] Photocykloaddition an substituierten Chinolonen unter- sucht. Die einzelnen Reaktionsschritte der Ringbildung werden auf der Zeitskala von ps bis ns quantifiziert und charakterisiert, wobei der Triplettzustand den zentralen Zustand bildet. An- schließend wird die [2+2] Photocycloaddition an substituierten Chinolonen durch einen chiralen, auf dem organischen Chromophor Xanthon basierenden Photokatalysator initiiert. Es wird ge- zeigt, dass innerhalb des Katalysator-Substrat-Komplexes, in dem beide Moleküle einen Abstand von wenigen Ångström haben, neue elektronische Eigenschaften auftreten. Die Anregung eines neuen Zustands initiiert nicht nur die [2+2] Photocycloaddition sondern stellt auch einen neuen Sensibilisierungsmechanismus dar, der bisher in photokatalytischen Reaktion organischer Mole- küle nicht beobachtet wurde. Der Triplettzustand des Chinolons tritt hierbei nicht mehr auf. Ob sich dieser Sensibilisierungsmechanismus auch auf andere Systeme übertragen lässt, muss durch weitere Arbeiten auf diesem Gebiet geklärt werden.

Diese Arbeit befasst sich mit dem Einfluss von Sternen, deren Masse acht Sonnenmassen übersteigt, auf das Interstellare Medium in ihrer Umgebung. Solche massereiche Sterne beenden ihr Dasein mit einer Supernovaexplosion und verlieren im Laufe ihrer - verglichen mit massearmen Sternen - raschen Entwicklung einen großen Teil ihrer Masse über ihre starken Sternwinde. Beispielsweise gibt ein Stern mit 60 Sonnenmassen Anfangsmasse mehr als die doppelte Supernovaenergie über die kinetische Energie seiner Winde in seine Umgebung ab. Sterne entstehen in Regionen mit kaltem, dichtem Gas, den sogenannten Molekülwolken. Beobachtungen zeigen, dass diese Gaswolken turbulent sind. Es ist allerdings noch ungeklärt, woher die beobachtete Turbulenz im Interstellaren Medium ihre Energie bezieht. Die Energieabgabe von massereichen Sternen ist - neben großskaligen gravitativen Instabilitäten in der Scheibe der Milchstraße - eine der möglichen Erklärungen. Beobachtungen erlauben Rückschlüsse auf die eingebrachte Energiemenge und die Längenskalen des Energie liefernden Prozesses. Daher ist es relevant, zu bestimmen, wie viel kinetische Energie ein massereicher Stern in der ihn umgebenden Molekülwolke deponieren kann. Der Schwerpunkt dieser Arbeit sind hydrodynamische Simulationen, die diese Energieeffizienz testen. Dazu wurden aktuelle Sternentwicklungsmodelle in die frei zugänglichen Eulerschen Gittercodes Pluto und Ramses eingebaut. Die Simulationen verwenden das von Eva Ntormousi erstellte Modul für die Berechnung der Heiz- und Kühlprozesse eines Multiphasenmediums. Die Modellrechnungen führten zur Erkenntnis, dass in jener Phase der Simulation, in der die räumliche Auflösung der Modellrechnung die Eneergieeffizienz stark beeinflusst, der größte Energieverlust durch Strahlung an jener Stelle auftritt, an der das vom Stern ausgestoßene Material auf das aufgesammelte Umgebungsgas trifft. An dieser Kontaktfläche treten Mischungsprozesse auf, welche die Energieverluste steigern. Somit können unsere Simulationen in Kombination mit einer Abschätzung der Effizienz und Skalenlänge dieser Mischprozesse eine Aussage treffen, wie viel Energie massereiche Sterne zur Aufrechterhaltung der Turbulenz beitragen können. Für diese Abschätzung der Mischprozesse liefert die Literatur auf Beobachtungen und numerischen Simulationen basierende Richtwerte. Als Anwendungsbeispiel wird in dieser Arbeit die Orion-Eridanus Region diskutiert. In dieser Region wird das radioaktive Isotop 26-Al beobachtet. Dieses Isotop wird vorrangig in massereichen Sternen gebildet. Es kann daher als Indikator für von Sternen ausgestoßene Materie verwendet werden. Interessanterweise zeigen die Beobachtungen dieser Region nur in einem Teil des Gebiets mit Röntgenemission ein 26-Al Signal. Unsere Ramses Modelle berücksichtigen 26-Al und können daher auf Gebiete mit (fehlenden) Korrelationen zwischen Röntgenemission und 26-Al Signal durchsucht werden.

Galaxy clusters, the massive systems host hundreds of galaxies, are invaluable cosmological probes and astrophysical laboratories. Besides these fascinating galaxies, the concentration of dark matter creates a deep gravitational potential well, where even light passing by is bended and the background image is distorted. The baryonic gas falling into the potential well is heated up to more than 10^7 K that free electrons start to emitting in X-ray. Observing those phenomena leads to a throughout understanding of gravity, particle physics and hydrodynamics. In addition, residing on the top of the density perturbations, clusters are sensitive to the initial condition of the Universe, such that they are complimentary tools for cosmology studies. In this thesis we first introduce the basic framework of the Universe and supporting observational evidence. Following that, we sketch the principle to use clusters for cosmology study via their redshift and mass distribution. However cluster mass is not a direct observable, so we need to estimate it by other channels. We briefly exhibit cluster observations in optical, X-ray and microwave bands and discuss the challenges in estimating the underlying cluster mass with them. After this introduction, we present our results on three aspects of the cluster cosmology study. First, we present a study of Planck Sunyaev-Zel’dovich effect (SZE) selected galaxy cluster candidates using Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) imaging data. To fulfil the strength of SZE survey, the redshifts of clusters are required. In this work we examine 237 Planck cluster candidates that have no redshift in the Planck source catalogue. Among them, we confirmed 60 galaxy clusters and measure their redshifts. For the remaining sample, 83 candidates are so heavily contaminated by stars due to their location near the Galactic plane that we do not identify galaxy members and assign reliable redshifts. For the rest 94 candidates we find no optical counterparts. By examining with 150 Planck confirmed clusters with spectroscopy redshifts, our redshift estimations have an accuracy of σ_{z/(1+z)}~0.022. Scaling for the already published Planck sample, we expect the majority of the unconfirmed candidates to be noise fluctuations, except a few at high redshift that the Pan-STARRS1 (PS1) data are not sufficiently deep for confirmation. Thus we use the depth of the optical imaging for each candidate together with a model of the expected galaxy population for a massive cluster to estimate a redshift lower limit, beyond which we would not have expected to detect the optical counterpart. Second, we use 95GHz, 150GHz, and 220GHz observations from South Pole Telescope (SPT) to study the SZE signatures of a sample of 46 X-ray selected groups and clusters drawn from ~6 deg^2 of the XMM-Newton Blanco Cosmology Survey (XMM-BCS). The wide redshift range and low masses make this analysis complementary to previous studies. We develop an analysis tool that using X-ray luminosity as a mass proxy to extract selection-bias corrected constraints on the SZE significance- and Y_{SZ}-mass relations. The SZE significance- mass relation is in good agreement with an extrapolation of the relation obtained from high mass clusters. However, the fit to the Y_{SZ}-mass relation at low masses, while in agreement with the extrapolation from high mass SPT sample, is in tension at 2.8σ with the constraints from the Planck sample. We examine the tension with the Planck relation, discussing sample differences and biases that could contribute. We also analyse the radio galaxy point source population in this ensemble of X-ray selected systems. We find 18 of our systems have 1 GHz Sydney University Molonglo Sky Survey (SUMSS) sources within 2 arcmin of the X-ray centre, and three of these are also detected at significance >4 by SPT. Among these three, two are associated with the brightest cluster galaxies, and the third is a likely unassociated quasar candidate. We examined the impact of these point sources on our SZE scaling relation result and find no evidence of biases. We also examined the impact of dusty galaxies. By stacking the 220 GHz data, we found 2.8σ significant evidence of flux excess, which would correspond to an average underestimate of the SZE signal that is (17±9) % in this sample of low mass systems. Finally we predict a factor of four to five improvements on these SZE mass-observable relation constraints based on future data from SPTpol and XMM-XXL. In the end we present a study using clusters as tools to probe deviations from adiabatic evolution of the Cosmic Microwave Background (CMB) temperature. The expected adiabatic evolution is a key prediction of standard cosmology. We measure the deviation of the form T(z)=T_0(1+z)^{1-α} using measurements of the spectrum of the SZE with SPT. We present a method using the ratio of the SZE signal measured at 95 and 150 GHz in the SPT data to constrain the temperature of the CMB. We validate that this approach provides unbiased results using mock observations of cluster from a new set of hydrodynamical simulations. Applying this method to a sample of 158 SPT-selected clusters, we measure α=0.017^{+0.030}_{−0.028} consistent with the standard model prediction of α=0. Combining with other published results, we find α=0.005±0.012, an improvement of ~ 10% over published constraints. This measurement also provides a strong constraint on the effective equation of state, w_{eff}=−0.994±0.010, which is presented in models of decaying dark energy.

No description available.

This thesis investigates bulk continuum generation. A full study of all relevant parameter is given. In addition, its application in ultrafast and widly tunable amplifiers and spectrometers is shown.

No description available.

No description available.

In der vorliegenden Dissertation werden Eigenschaften stark gekoppelter hydrodynamischer Theorien untersucht, die mittels einer dualen Beschreibung als höherdimensionale gravitative Systeme aufgefasst werden können. Besonderes Augenmerk liegt hierbei auf der Berechnung physikalischer Größen wie Viskositäten oder Diffusionskonstanten. Diese werden hinsichtlich der Frage betrachtet, ob sie allgemeingültigen, universellen Gesetzmäßigkeiten folgen, die man aus der Beschreibung mittels einer Gravitationstheorie ableiten kann. Die theoretische Grundlage bildet hierbei die Dualität konformer Quantenfeldtheorien im Minkowski Raum und höherdimensionaler Stringtheorien im Anti-de Sitter Raum, die AdS/CFT Korrespondenz. Einen besonders interessanten Grenzfall stellt der Limes starker Kopplung und hoher Anzahl von Freiheitsgraden der konformen Feldtheorie dar, in dem sich die duale Beschreibung zu klassischer Gravitationstheorie im AdS Raum vereinfacht. Mittels störungstheoretischer Betrachtung der Fluktuationen von Schwarzen Loch Lösungen der Gravitationstheorie lassen sich universelle hydrodynamische Eigenschaften der stark gekoppelten Feldtheorie beschreiben. Eines der Hauptergebnisse dieses Forschungsgebietes ist der Nachweis, dass Fluide, die durch eine einfache duale Gravitationstheorie mit ungebrochener Rotationsinvarianz beschrieben werden können, ein universelles Verhältnis aus Scherviskosität und Entropiedichte besitzen. Erstaunlicherweise stimmt dieses Verhältnis parametrisch mit dem gemessenen Wert des stark gekoppelten Quark-Gluonen-Plasmas überein, ohne dass eine direkte Beschreibung dieser QCD Phase momentan möglich ist. In der vorliegenden Arbeit wird die Konstruktion eines ähnlichen, universellen Zusammenhangs beschrieben. In der hydrodynamischen Beschreibung supersymmetrischen Feldtheorien existiert eine Diffusionskonstante, die, ähnlich der Scherviskosität, den spurfreien Teil der Konstitutivgleichung des Supersymmetriestroms beschreibt. Wir berechnen diese Konstante in supersymmetrischen Theorien allgemeiner Dimension mittels verschiedener unabhängiger Rechnungen. Dazu betrachten wir als duale Gravitationstheorie eine generische Supergravitationstheorie. Die Bewegungsgleichung des zum Supersymmetriestrom dualen Gravitinos in Schwarzen Loch Hintergründen wird gelöst und erlaubt die Berechnung der retardierten Greenschen Funktion des Supersymmetriestroms der Feldtheorie. Diese besitzt einen Pol, der die charakteristische Schalldispersionsrelation des Phoninos beschreibt, des Goldstonefermions spontan gebrochener Supersymmetrie aufgrund endlicher Temperatur. In dieser Dispersionsrelation findet sich die besagte Diffusionskonstante, die sich auch mittels einer neuartigen Kubo-Formel direkt aus der Greenschen Funktion berechnen lässt. Das Hauptergebnis der Arbeit bildet hierbei die Etablierung eines Zusammenhangs dieser Diffusionskonstante und eines universell gültigen Absorptionsquerschnitts auf der dualen Seite der Gravitationstheorie, der die Absorption von Spinoren von einem Schwarzen Loch Hintergrund beschreibt. Eine weitere bedeutende Entwicklung besteht in der Entdeckung eines neuartigen Transportkoeffizienten, der einen beobachtbaren induzierten Strom aufgrund der Vortizität eines Fluids beschreibt. Dieser stellt die klassische Manifestation eines quantenmechanischen Effektes dar, der entsteht, wenn die zugrunde liegende mikroskopische Theorie eine quantenmechanische chirale Anomalie aufweist. Wir untersuchen diesen Effekt mithilfe eines theoretischen Ansatzes, der verschiedene Zugänge zum Verhältnis von Hydrodynamik und Gravitation miteinander vereint. Dazu werden rotierende D3-Branen effektiv als asymptotisch flache Verallgemeinerungen von fünf-dimensionalen AdS Reissner-Nordström Schwarzen Löchern beschrieben. Die Fluktuationen dieses Hintergrundes beschreiben nun eine effektive hydrodynamische Theorie auf einer Fläche in festem Abstand zur Singularität des Schwarzen Lochs, auf der die Fluktuationen Dirichlet Randbedingungen annehmen. Diese Herangehensweise erlaubt es uns den erwähnten Quanteneffekt nicht nur am Rand des AdS Raums zu betrachten, sondern auch am Horizont des Schwarzen Lochs, auf jeder Fläche mit konstantem Radius dazwischen oder sogar im asymptotisch flachen Raum. / In the present thesis we study properties of strongly coupled hydrodynamic theories which may be described in terms of a dual higher dimensional gravitational system. Particular attention is given to the computation of physical quantities like the theories' viscosities and diffusion constants. These are analysed with regard to the question of whether they follow generally applicable, universal laws which may be derived from the description in terms of a gravitational theory. The theoretical foundation for this is laid by the duality between conformal quantum field theories in Minkowski space and higher-dimensional string theories on Anti-de Sitter space, the AdS/CFT correspondence. A particularly interesting simplification is given by the limit of strong coupling and large number of degrees of freedom of the conformal field theory in which the dual description reduces to a classical theory of gravity on AdS space. By using a perturbative treatment of fluctuations of the gravitational theory's black hole solutions one may describe universal hydrodynamic properties of the strongly coupled field theory. One of the main results within this area of research is the proof that fluids which may be described by a simple dual gravitational theory with unbroken rotational invariance possess a universal ratio of shear viscosity and entropy density. Astonishingly, this ratio parametrically agrees with the value measured for the strongly-coupled quark gluon plasma, although a direct treatment of this QCD phase is at present not available. In the following work we describe the construction of a similar, universal relation. In the hydrodynamic description of supersymmetric field theories there exists a further diffusion constant which, similarly to the shear viscosity, appears in the traceless part of the constitutive relation of the supersymmetry current. We compute this constant in supersymmetric theories of arbitrary dimension via different independent calculations. For doing so we look at a generic supergravity theory as the gravitational dual. The equation of motion of a gravitino, which is the dual field to the supersymmetry current, is solved in a black hole background and allows for the computation of retarded Green's functions of the field theory's supersymmetry current. This has a pole which describes the characteristic sound dispersion relation of the phonino, the Goldstone fermion of spontaneously broken supersymmetry due to finite temperature. In this dispersion relation we find the aforementioned diffusion constant which we also obtain directly from the correlator via a new Kubo formula. The main result of this project is the establishment of a relation of the supersound diffusion constant and a universally applicable absorption cross section on the dual gravitational side which describes the absorption of spinors by a black hole. A further important development is the discovery of a new transport coefficient which describes the observable current that is induced by the vorticity of a fluid. This illustrates the classical manifestation of a quantum mechanical effect which appears when the underlying microscopic theory possesses a quantum mechanical chiral anomaly. We investigate this effect within a theoretical framework which unifies several different approaches at the interplay of hydrodynamics and gravitational physics. We effectively describe rotating D3-branes as asymptotically flat generalisations of five-dimensional AdS Reissner-Nordström black holes. The fluctuations of this background describe an effective hydrodynamical theory on a surface at a finite distance from the black hole's singularity, on which the fluctuations satisfy Dirichlet boundary conditions. This approach allows us to study the mentioned quantum effect not only at the boundary of AdS space, but also at the black hole's horizon, at a surface in between at finite radius, or even in asymptotically flat space.

Markarian 421 (Mrk~421) is one of the classical blazars at X-ray and very high energies (VHE; $>$100 GeV). Its spectral energy distribution (SED) can be accurately characterized by current instruments because of its close proximity, which makes Mrk~421 one of the best sources to study the nature of blazars. The goal of this PhD thesis is to better understand the mechanisms responsible for the broadband emission and the temporal evolution of Mrk~421. The results might be applied to other blazars which cannot be studied with this level of detail because their emissions are weaker, or they are located further away. This thesis reports results from $\sim$70 hours of observations with MAGIC in 2010 and 2011 (the first two years of the operation of the MAGIC stereo telescopes), as well as the results from the multi-wavelength (MW) observation campaigns in 2010 and 2011, where more than 20 instruments participated, covering energies from radio to VHE. The MW data from the 2010 and 2011 campaigns show that, for both years, the fractional variability $F_{\rm var}$ increases with the energy for both the low-energy and the high-energy bumps in the SED of Mrk~421. Furthermore, $F_{\rm var}(\text{optical})$ was similar to $F_{\rm var}(\text{HE-$\gamma$-ray;$>$100 MeV})$, and $F_{\rm var}(\text{X-ray})$ was similar to $F_{\rm var}(\text{VHE-$\gamma$-ray})$. This observed characteristic is expected from the strong correlation between the synchrotron photons and the up-scattered photons by inverse-Compton effect within the synchrotron self-Compton (SSC) emission model, thus allowing for the first time of the consistency test on this widely used theoretical model. During the MW campaign in 2010, we measured the decay of a flaring activity during 13 days in March. We could perform MW observations every day, which enables an unprecedented characterization of the time-evolution of the radio to $\gamma$-ray emission of Mrk~421. The broadband SEDs during this flaring episode, resolved on timescales of one day, were characterized with two leptonic scenarios: a one-zone SSC model, and a two-zone SSC model where one zone is responsible for the quiescent emission while the other (smaller) zone, which is spatially separated from the former one, contributes to the daily-variable emission occurring mostly at X-rays and VHE $\gamma$ rays. Both the one-zone SSC and the two-zone SSC models can describe the daily SEDs. However, the two-zone SSC model provides a better agreement to the observed SED at the narrow peaks of the low- and high-energy bumps during the highest activity. The proposed two-zone scenario would naturally lead to the correlated variability in the X-ray and VHE bands without variability in the optical/UV band, as well as to shorter timescales for the variability in the X-ray and VHE bands with respect to the variability in the other bands. This concept of a second small emission region containing a narrow electron spectrum in order to explain the short timescale flaring activity in the X-ray and VHE bands could be generalized to other blazars. The results from the 2010 March flaring activity of Mrk~421 are reported in Sections~\ref{LightCurves} -- \ref{Discussion}, and they are the main scientific achievement of this PhD thesis. Preliminary results were reported (as an oral contribution) in the 33rd International Cosmic Ray Conference (Rio de Janeiro, July 2013), one of the most prestigious conferences in the field of the VHE astronomy and astro-particle physics in general. The final results (reviewed and approved within the \Fermic, MAGIC, and VERITAS Collaborations) have been submitted for publication in the Astronomy and Astrophysics journal in 2014 June. During the MW campaign in 2011, Mrk~421 had an atypically high activity in the optical band, together with a very low state in the X-ray/VHE band. Typically, blazar emission models for Mrk~421 focus on the explanation of the variability in the X-ray and $\gamma$-ray bands. This data set is suitable for examining emission models and estimate if they can describe the evolution of the whole broadband SEDs including the variabilities in optical, X-ray, and $\gamma$-ray bands. We found that the one-zone SSC model can describe the relatively slow variation of the 2011 broadband SEDs. The modeling of these SEDs shows that the main factor dominating the spectral evolution could be the electron energy distribution (EED), instead of the environmental parameters like the blob size and the Doppler factor. To explain the featured high optical state together with the low X-ray/VHE state, several changes were needed in comparison to the typical state from 2009: a harder power-law index in the first segment in the EED, a lower first break in the EED, and a softer power-law index in the second segment in the EED. Besides, these optical high states had synchrotron peak frequencies 10 times lower than the typical state, while their synchrotron peak energy-fluxes were similar to those of the typical state. On the contrary, the 2010~March flaring activity showed that a high peak energy-flux was accompanied by a high peak frequency in comparison to the typical state, which has also been observed on several other blazars. This contrast showed that the broadband variability in the emission of Mrk~421 during 2011 had a different \emph{flavor} with respect to the typical blazar broadband flaring activity. This PhD thesis shows that most variations in the SED of Mrk~421 can be produced through changes in the EED, which could shed light into how particles get accelerated in the vicinity of super-massive black holes, or within the relativistic jets of the active galactic nuclei. However, the results also show a large complexity in the evolution of the broadband (radio to VHE $\gamma$-rays) SED. Thus longer and deeper observations are needed to understand what characteristics get repeated over time and hence typical, what characteristics are atypical, and ultimately, whether the lessons learned with Mrk~421 can be extended to high-synchrotron-peaked blazars in general.