Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 02/05 Archiv

Studying the cosmic microwave background (CMB) has proven to be an immensely rich source of information about the Universe we live in. Many groups were and are intensely working on the interpretation of the large amount of CMB data, which has become available during the last decades and will be obtained with many new projects already observing at present or planned for the near future. The observations by COBE in the 90's have shown that the CMB is extremely uniform, with angular fluctuations of the temperature on the level of one part in 10^5 on angular scales larger than 7 degree. On the other hand on these scales no deviations of the CMB energy spectrum from a perfect blackbody were found. But today we do know that there exist spectral distortions of the CMB on arcminute scales due to the scattering of CMB photons off the hot electrons residing inside the deep potential well of clusters of galaxies, which leads to the so called thermal-SZ effect (th-SZ). The th-SZ effect has already been measured for several big cluster and within the next 5 years, many CMB experiments like ACBAR, SZA, PLANCK, SPT, ACT, APEX, AMI and QUIET will perform deep searches for clusters with very high sensitivity. Many tens of thousands of clusters will be detected allowing us to carry out detailed studies of cluster physics and to place constraints on parameters of the Universe. Due to this great advance in technology one can expect that small deviations from the main SZ cluster signal, e.g. related to relativistic corrections to Compton scattering for high electron temperature, will become observable. Motivated by this promising perspective here we studied the influence of the motion of the Solar System with respect to the CMB rest frame on the SZ cluster signature. This kind of contribution to the SZ signal has been neglected in the literature so far, but as we show here it is of the same order as other corrections under discussion. We found that this motion-induced SZ signal has a very strong spectral and spatial dependence and due to the great knowledge about the motion-induced CMB dipole it can be predicted with high precision, which makes it easy to account for it in the analysis of future SZ studies. Here one big problem naturally arises: any experiment trying to observe tiny frequency-dependent signals needs a cross calibration of the different frequency channels. Several different standard methods for calibration issues are known, e.g. based on the annual modulation of the CMB dipole, the microwave flux from planets like Jupiter or the comparison with CMB sky maps obtained by well calibrated experiments like WMAP, each with their own problems and drawbacks. However the achieved level of cross calibration is limited by the knowledge of the calibrator. Today scientists are already speaking about extremely small frequency-dependent features in the CMB temperature power spectrum resulting from the scattering of CMB photons in the fine structure lines of different atomic species during the dark ages. Obtaining these signals can in principle be used to answer some of the interesting questions about the history of chemical enrichment and reionization, but it is likely that the necessary level of cross calibration cannot be reached with the standard methods. In this context we considered the fact that the superposition of blackbodies with different temperatures is not again a blackbody. We show that in the limit of small temperature difference the superposition leads to a y-type spectral distortion. This kind of distortion arises whenever one in observing the CMB sky with finite angular resolution. We discuss the spectral distortions due to the primordial CMB temperature fluctuations and the motion-induced CMB dipole. Furthermore we considered possible applications for calibration issues. We show that within this context also clusters of galaxies, especially for experiments observing only small parts of the sky, in the future may become standard sources for calibration issues. Although the observations with COBE/FIRAS have proven that the CMB energy spectrum on large angular scales is extremely close to a pure blackbody one may still expect some deviations due to processes like the damping of acoustic waves, turbulent motion of the matter, the decay of unstable particles or annihilation of matter in the early Universe. Especially possible distortions from very early epochs (redshifts z> few x 10^5) lead to deviations of the CMB brightness temperature at frequencies (1-few x 10 GHz) well below the range of COBE/FIRAS. Currently people in the USA and especially at the NASA Goddard Space Flight Center are intensely working on experiments to measure the CMB temperature at these frequencies, where the largest distortions could be expected. One can therefore hope that in the near future also new constraints on the CMB energy spectrum will become available. Therefore in this thesis we also reexamined the thermalization of spectral distortions of the CMB in the early Universe. Due to the large entropy here one of the most important processes is the production of low frequency photons by double Compton scattering. Until now people were only using a description of this emission in the limit of cold electrons and soft initial photons, but especially for the thermalization of large distortions at very high redshifts (z > 10^6) the inclusion of relativistic corrections to the main processes at work may become necessary. Here we provide two steps towards a solution of this problem. First we discuss in detail the full kinetic equation for the time evolution of the photon field under double Compton scattering in a hot, isotropic thermal plasma, both numerically and analytically. We obtained accurate approximations for the effective double Compton Gaunt factor, which are applicable in a very broad range of physical situations. We then provide a reformulation of the thermalization problem with respect to relativistic corrections and discuss its solution in the limit of small chemical potential distortions at high redshifts. Our results indicate that due to relativistic corrections the thermalization at high redshifts slows down notably and therefore makes the CMB more vulnerable for distortions at epochs z > 10^6. Here we also report some of our attempts to solve the full problem numerically.

Die vorliegende Arbeit setzt sich aus zwei Teilen zusammen. Im ersten Teil wird exemplarisch dargelegt, wie man $q$-deformierte Superraeume konstruiert und darauf eine q-deformierte Superanalysis entwickeln kann. Dazu wird erst die Struktur des Superraumes an sich betrachtet, d.h. es werden die algebraischen Relationen zwischen den bosonischen und fermionischen Versionen fuer Koordinaten, Ableitungen und Differentiale angegeben. Danach werden die wichtigsten Elemente einer Superanalysis axiomatisch eingefuehrt und explizit berechnet, namentlich der Differentialkalkuel, Integrale, Exponentiale, Translationen sowie die nur fuer deformierte Raeume notwendigen Zopfprodukte. Im zweiten Teil wird gezeigt, dass es moeglich ist, die q-deformierten Symmetriealgebren von besonderem physikalischem Interesse, das sind die U_q(su(2)), U_q(so(4)) und die q-deformierte Lorentzalgebra, in weitgehender Analogie zum Undeformierten zu behandeln. Dazu wird der Begriff des q-Kommutators und der q-Liealgebra eingefuehrt. Auf diese Weise tritt die zum Undeformierten analoge Struktur der Quantenalgebren deutlich hervor, was bei der Konstruktion deformierter Quantenfeldtheorien hilfreich ist. Ergaenzend werden noch die Casimiroperatoren angegeben und fuer verschiedene Darstellungen spezifiziert.

Gegenstand dieser Arbeit ist die Inbetriebnahme SPIFFIs (Spectrograph for Integral Faint Field Imaging), des ersten abbildenden Nahinfrarot-Spektrographen an einem 8m-Klasse-Teleskop und die Demonstration der wissenschaftlichen Leistungsfähigkeit abbildender Nahinfrarot-Spektroskopie. Die Arbeit ist in zwei Teile gegliedert. Der erste Teil beschäftigt sich mit der Inbetriebnahme und Charakterisierung SPIFFIs im Labor und am Teleskop. Der zweite Teil dieser Arbeit beschäftigt sich mit der Analyse von K-Band-Daten der ultraleuchtkräftigen Galaxie IRAS06206-6315, die während des ersten Beobachtungslaufes SPIFFIs als Gast-Instrument im Februar 2003 am Very Large Telescope (VLT) genommen wurden.

This work has been carried out in the framework of the project GLOWA-Danube (GLObal WAter cycle) where a joint effort is made by several groups to model the interaction of the water cycle and society in the Upper Danube catchment area. In particular regional climate models are used to simulate and eventually predict precipitation in this research area, while other groups convert this information into river runoff estimates and groundwater fluxes. It has been agreed in the project that precipitation data and other meteorological data must be handed over to the hydrological groups with a spatial resolution of 1 km. Long term runs with regional climate models are, however, not feasible at 1 km resolution, because they would exceed available computer resources by far. Therefore, a pragmatic downscaling method for precipitation must be implemented which provides data of 1 km resolution on the basis of model results of fairly coarse resolution. This downscaling uses extensively climatological precipitation observations where such downscaling relations can be derived. These observed rates are then adapted to the model results. The data are provided by the German Weather Service (DWD) and the Austrian Weather Service (ZAMG). The years 1991-2000 have been chosen as a reference period for the analysis. The climate simulation is carried out by the mesoscale model MM5 at a resolution of 45 km. The model MM5 offers a wide range of parameterizations with respect to convective processes, the boundary layer, cloud microphysics, and the radiation balance, all directly or indirectly responsible for generating precipitation. Sensitivity studies are performed to find the best configuration for the research area and reference period. A variety of methods is tested to generate observed and simulated climatological time series of precipitation. In particular, a linear average, a running average, a Fourier analysis, and spline interpolation are intercompared. In the end, spline interpolation between monthly values showed the best results for both time series and is used as a basis for the downscaling method. The downscaling method has to correct two major discrepancies between the observed precipitation distribution at the 1 km resolution and the simulated distribution at the 45 km resolution. First, these are small scale details related to topography in the rainfall distribution at the 1 km resolution, which lack in the 45 km resolution. Second, there is an unrealistic southward shift of the rainfall maximum at the northern rim of the Alps in the simulations, which needs to be corrected. A specific correction factor is introduced for each problem. The correlation between the spatial distribution of observed and simulated distributions increases after using the correction factors. Due to the climatological relationships, the results time periods of 10 days and longer are superior to those for periods shorter than 10 days. The precipitation distribution depends, of course, on the wind direction in particular so near the Alps. Wind direction and wind speed are simulated by the MM5 model and combined with the correction factors described above. The correlation between the spatial distribution of observed and simulated precipitation increases more if the wind direction dependent correction factors are introduced. These improved correction factors depend less on climatological relationships and perform therefore better for shorter time periods. Additionally, they will be able to respond better on changes in the weather regime in future climates. Altogether, this investigation provides a new pragmatic method to downscale model simulations on the basis of observations. This method will be used in the project GLOWA-Danube.

Massive OB stars are the most luminous stellar objects (10e5 to a few 10e6 L⊙). Although being rare by number they play a dominant role in the chemical and dynamical evolution of galaxies through their input of energy, momentum, and nuclear processed material into the interstellar medium by means of stellar winds, eruptions, and (final) explosions. The luminosity of hot massive stars is the key ingredient to the driving of a dense (10e−6 - 10e−5 M⊙/yr) and fast (up to 3,000 km/s) outflow lasting a lifetime. This mass loss imprints unambiguous signatureson the spectral energy distribution and spectral lines received from these objects. The goal of this thesis was to investigate and to apply recent, improved methods for spectral diagnostics in the optical and the infrared by means of unified model atmospheres, comprising the entire sub- and supersonic structure from the pseudo-hydrostatic photosphere to the stellar wind. In particular, we used the nlte-model atmospheres code fastwind, which is highly computational efficient and updated to comprise an adequate though approximate treatment of metal line opacity effects, i.e., metal line-blocking/-blanketing. First we have tested this code by a comparison with alternative codes (e.g., cmfgen by Hillier & Miller 1998 and WM-Basic by Pauldrach et al. 2001), particularly in terms of temperature stratification, fluxes, and number of ionizing photons. In almost all cases we obtained very similar results. Also for the H/He lines which could be only compared to cmfgen, the coincidence between the codes is remarkable, except for a subtle discrepancy concerning the He i singlets, where, in a restricted temperature range, cmfgen predicts weaker singlet lines. Having tested the improved model atmospheres code we began our study with a re-analysis of the Galactic O-star sample presented by Puls et al. 1996 (at that time using pure H/He models) to investigate the influence of line-blocking/-blanketing. This re-analysis (by means of profile fitting of photospheric and wind lines from H and He) resulted in a significant re-definition of the effective temperature scale due to this line-blanketing effect. We obtain lower effective temperatures (up to 8,000 K, depending on spectral type and luminosity class) in combination with a reduction in either gravity or helium abundance, thus, making it possible to assign a new Teff - log g and Teff - spectral type calibration as a function of luminosity class. Further, by calculating new spectroscopic masses and comparing them with previous results we find a significant reduction in the so-called mass discrepancy (Herrero et al. 1992), where the latter describes the unfortunate situation that spectroscopically derived masses are lower than those resulting from stellar evolution calculations. For stars below 50 M⊙ a systematic trend is retained such that the spectroscopically derived masses are smaller by approx. 10 M⊙ compared to the evolutionary ones. Moreover, the wind momentum luminosity relation (WLR) changes because of lower luminosities and almost unmodified wind-momentum rates. Still present, however, is a separation of the WLR as a function of luminosity class, in contrast to theoretical simulations which do not predict such a dependence. From simple arguments and using stellar samples of different sizes, we find strong indications that for most supergiants the mass-loss rate is over-estimated by a factor of 2 to 3, whereas the mass-loss-estimates for luminosity class III and V objects are consistent with our own theoretical expectations and those by others. The over-estimate is interpreted as an effect of wind-clumping, and our argumentation is based on the assumption that the material in the lower wind region is un-clumped, in accordance with theoretical predictions. As a final step we have analyzed a large sample of OB stars by means of H and K band spectroscopy in the infrared (IR) regime, with the primary goal to investigate to what extent a lone near IR-spectroscopy is able to recover stellar and wind parameters derived in the optical. Due to the substantial progress in ground-based IR instrumentation in the past decade and the extension of model atmosphere codes to the infrared wavelength regime, IR spectroscopy has become a powerful diagnostics for the investigation of young and massive stars lying deeply embedded in the dust-enshrouded environment of molecular clouds or the Galactic centre, allowing us to take a first step in the direction of a pure IR analysis. For the stars analyzed we obtain well-agreeing results between the optical and the infrared, except for the line cores of Br gamma in early O stars with significant mass loss, which, again, might indicate the presence of clumping effects. Having derived the stellar and wind parameters from the IR, we are now able to constrain the observational requirements to perform a pure IR-analysis. Most important is a very high S/N ratio, as the lines to be investigated are extremely shallow, and a very good resolution, in addition to an adequately large set of strategic lines. Given this prerequisite, spectral analyses based on pure IR data could, indeed, be successfully used as an alternative or support to traditional methods, and will allow us to proceed towards our ultimate goal of analyzing very young and highly obscured objects just emanating from their birth places.

Three-dimensional data-based master equations are developed and subsequently used to study climate variability in the stratosphere. Master equations are used to develop understanding of observed systems where no dynamic equations are available. Master equations are used in this thesis as prognostic equations for the probability density in a discretized phase space spanned by climate variables. The evolution of the probability density may then reveal information about the relationship between these variables. The phase space is partitioned into several hundred boxes of equal grid size representing at any one time states that the system can assume. In this discretized version of the phase space, the coefficients of a master equation may be estimated from the relative frequencies of transitions observed in a time series of the variables obtained from observations or numerical model runs. Data-based master equations are numerical structures whose success depends among other things on the resolution and volume of the available time series. These dependencies are studied on the basis of data from the famous three-component Lorenz convection model extended with a stochastic forcing. Time series of the desired length and time resolution can thus be generated easily. Furthermore, the results can be compared directly. Best results are obtained through the combination of a long data record and a coarse time resolution. The choice of the variables and their number also play a crucial role in the success of a master equation. Time series of stratospheric climate indices obtained from the reanalyses ERA-40 lead also to these last results. The stratosphere serves now as an implementation area. The master equation shows that during the eastern phase of the quasi-biennial oscillation (QBO) of equatorial zonal wind the arctic stratosphere is about 2 K warmer than during the western phase. Thus the relationship between QBO and arctic stratosphere can be quantified. The influence of the 11-year solar cycle is described by the master equation. It emerges that the relationship between QBO and temperature anomaly of the arctic stratosphere shows a dependence on solar variability. The implications of stratospheric processes on the climate in the troposphere are analysed with a master equation for a time series of an index of the Arctic Oscillation (AO) at stratospheric and tropospheric pressure levels. The master equation captures the main features of this interaction between stratosphere and troposphere. It is shown that anomalies of the AO in the middle stratospere propagate deeply into the troposphere with a time scale of 4 weeks. Furthermore the master equation shows that the influence of strong tropospheric AO-anomalies remains confined to the lower stratosphere.

In 1935 Einstein, Podolsky and Rosen used the assumption of local realism to conclude in a Gedankenexperiment with two entangled particles that quantum mechanics is not complete. For this reason EPR motivated an extension of quantum mechanics by so-called local hidden variables. Based on this idea in 1964 Bell constructed a mathematical inequality whereby experimental tests could distinguish between quantum mechanics and local-realistic theories. Many experiments have since been done that are consistent with quantum mechanics, disproving the concept of local realism. But all these tests suffered from loopholes allowing a local-realistic explanation of the experimental observations by exploiting either the low detector efficiency or the fact that the detected particles were not observed space-like separated. In this context, of special interest is entanglement between different quantum objects like atoms and photons, because it allows one to entangle distant atoms by the interference of photons. The resulting space-like separation together with the almost perfect detection efficiency of the atoms allows a first loophole-free test of Bell's inequality. The primary goal of the present thesis is the experimental realization of entanglement between a single localized atom and a single spontaneously emitted photon at a wavelength suitable for the transport over long distances. In the experiment a single optically trapped Rb87 atom is excited to a state which has two selected decay channels. In the following spontaneous decay a photon is emitted coherently with equal probability into both decay channels. This accounts for perfect correlations between the polarization state of the emitted photon and the Zeeman state of the atom after spontaneous decay. Because these decay channels are spectrally and in all other degrees of freedom indistinguishable, the spin state of the atom is entangled with the polarization state of the photon. To verify entanglement, appropriate correlation measurements in complementary bases of the photon polarization and the internal quantum state of the atom are performed. It is shown, that the generated atom-photon state yields an entanglement fidelity of 0.82. The experimental results of this work mark an important step towards the generation of entanglement between space-like separated atoms for a first loophole-free test of Bell's inequality. Furthermore entanglement between a single atom and a single photon is an important tool for new quantum communication and information applications, e.g. the remote state preparation of a single atom over large distances.

Im Myonspektrometer des ATLAS-Detektors am LHC, bei dem Protonen mit einer Schwerpunktsenergie von 14~TeV kollidieren, werden Kammern aus Hochdruckdriftrohren zur Vermessung der Trajektorien der Myonen verwendet. Um den Impuls der Myonen aus der Krümmung ihrer Spur in dem 0.4~T starken Magnetfeld mit hinreichender Genauigkeit vermessen zu können, müssen zum einen die Driftrohre eine Ortsauflösung von $\sigma_{r} \leq 100\; \mu \text{m}$ liefern und zum anderen muss die Position jedes Annodendrahtes, also auch die Geometrie jeder Kammer, mit einer Genauigkeit von deutlich besser als 100~$\mu$m bekannt sein. Die Arbeit beschäftigt sich mit diesem Problem an zwei Fronten. Wegen der hohen Luminosität des Beschleunigers und des großen Wirkungsquerschnittes für Proton-Proton-Kollisionen, herrscht im Myonspektrometer ein erheblicher Untergrund an Photonen und Neutronen. Um das Verhalten der Driftrohre bei hoher Untergrundzählrate zu untersuchen, wurde eine Teststrahlmessung durchgeführt, bei der neben einem hochenergetischen Myonstrahl (100~GeV) auch eine 740~GBq starke $\gamma$-Quelle die Kammer beleuchtete. Mittels eines hochauflösenden Referenzdetektors aus Silizium-Streifenzählern wurden Ortsauflösung und Effizienz bei unterschiedlichen Untergrundstrahlungsniveaus untersucht. Eine Möglichkeit die Ortsauflösung zu verbessern, in dem mittels einer in die Ausleseelektronik integrierten Pulshöhenmessung die Abhängigkeit zwischen Signalzeit und Pulshöhe betrachtet wird, wurde untersucht und weiterentwickelt. Damit konnte die Auflösung unabhängig von der Photonenbestrahlung um 13~$\%$ verbessert und die angestrebte Ortsauflösung von 100~$\mu$m selbst beim Dreifachen der erwarteten Untergrundstrahlung erreicht werden. In Zusammenarbeit mit dem Max-Plank-Institut für Physik in München und dem Joint Institute for Nuclear Research in Dubna werden 88 der 1226 Myonkammern gebaut. Zur ersten Inbetriebnahme und Überprüfung der Qualität dieser Kammern wurde der Höhenstrahlmessstand eingerichtet. Insbesondere kann dort die Geometrie einer Kammer bestimmt werden, in dem sie zwischen zwei Referenzkammern eingebaut wird, deren Geometrie mit einem Röntegentomographen genau vermessen wurde. Mit Hilfe dieser Kammern wird die Spur des kosmischen Myons bestimmt. Aus systematischen Abweichungen zwischen dieser Referenzspur und den Messungen in der zu testenden Kammer, kann die Position eines jeden Drahtes mit einer Genauigkeit in der Größenordnung 10~$\mu$m bestimmt werden. Diesbezüglich wird die Arbeit von Oliver Kortner~\cite{olivers_dis} fortgesetzt, also der Messstand hin zu drei vollständig ausgelesenen Kammern ausgebaut und seine Leistungsfähigkeit überprüft. Der Messstand erlaubt es, mechanische Ungenauigkeiten der Kammern, die allerdings nur selten vorkommen, zuverlässig zu finden und zu quantifizieren. Dadurch sind auch Kammern die von der Normgeometrie abweichen vollständig beim ATLAS-Experiment einsetzbar, wenn die im Messstand ermittelten Geometrieparameter in der Spurrekonstruktion berücksichtigt werden.

The main theme of this PhD-thesis is the observation of clusters of galaxies at submillimetric wavelengths. The Sunyaev-Zel'dovich (SZ) effect due to interaction of cosmic microwave background (CMB) photons with electrons of the hot intra-cluster medium causes a distinct modulation in the spectrum of the CMB and is a very promising tool for detecting clusters out to very large distances. Especially the European PLANCK-mission, a satellite dedicated to the mapping of CMB anisotropies, will be the first experiment to routinely detect clusters of galaxies by their SZ-signature. This thesis presents an extensive simulation of PLANCK's SZ-capabilities, that combines all-sky maps of the SZ-effect with a realisation of the fluctuating CMB and submillimetric emission components of the Milky Way and of the Solar system, and takes instrumental issues such as the satellite's point-spread function, the frequency response, scan paths and detector noise of the receivers into account. For isolating the weak SZ-signal in the presence of overwhelming spurious components with complicated correlation properties across PLANCK's channels, multifrequency filters based on matched and scale-adaptive filtering have been extended to spherical topologies and applied to simulated data. These filters were shown to efficiently amplify and extract the SZ-signal by combining spatial band-filtering and linear combination of observations at different frequencies, where the filter shapes and the linear combination coefficients follow from the cross- and autocorrelation properties of the sky maps, the anticipated profile of SZ clusters and the known SZ spectral dependence. The characterisation of the resulting SZ-sample yielded a total number of 6000 detections above a statistical significance of 3 sigma and the distribution of detected clusters in mass, redshift, and position on the sky. In a related project, a method of constructing morphological distance estimators for resolved SZ cluster images is proposed. This method measures a cluster's SZ-morphology by wavelet decomposition. It was shown that the spectrum of wavelet moments can be modeled by elementary functions and has characteristic properties that are non-degenerate and indicative of cluster distance. Distance accuracies following from a maximum likelihood approach yielded values as good as 5% for the relative deviation, and deteriorate only slightly when noise components such as instrumental noise or CMB fluctuations were added. Other complications like cool cores of clusters and finite instrumental resolution were shown not to affect the wavelet distance estimation method significantly. Another line of research is the Rees-Sciama (RS) effect, which is due to gravitational interaction of CMB photons with non-stationary potential wells. This effect was shown to be a second order gravitational lensing effect arising in the post-Newtonian expansion of general relativity and measures the divergence of gravitomagnetic potentials integrated along the line-of-sight. The spatial autocorrelation function of the Rees-Sciama effect was derived in perturbation theory and projected to yield the angular autocorrelation function while taking care of the differing time evolution of the various terms emerging in the perturbation expansion. The RS-effect was shown to be detectable by PLANCK as a correction to the primordial CMB power spectrum at low multipoles. Within the same perturbative formalism, the gravitomagnetic corrections to the autocorrelation function of weak gravitational lensing observables such as cosmic shear could be determined. It was shown that those corrections are most important on the largest scales beyond 1~Gpc, which are difficult to access observationally. For contemporary weak lensing surveys, gravitomagnetic corrections were confirmed not play a significant role. A byproduct of the simulation of CMB fluctuations on the basis of Gaussian random fields was a new way of generating coded mask patterns for X-ray and gamma-ray imaging. Coded mask cameras observe a source by recording the shadow cast by a mask onto a position-sensitive detector. The distribution of sources can be reconstructed from this shadowgram by correlation techniques. By using Gaussian random fields, coded mask patterns can be specifically tailored for a predefined point-spread function which yields significant advantages with respect to sensitivity in the observation of extended sources while providing a moderate performance compared to traditional mask generation schemes in the observation of point sources. Coded mask patterns encoding Gaussian point-spread functions have been subjected to extensive ray-tracing studies where their performance has been evaluated.

The CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) Dark Matter search is aiming to directly detect Weakly Interacting Massive Particles (WIMPs) via their elastic scattering off nuclei in a target. Due to the low event rate expected for WIMP-nucleus scattering the suppression of background which would hide or mimic the WIMP signal is of crucial importance. Moreover, since the energy transferred to a nucleus in a WIMP-nucleus elastic scattering is extremely low (a few tens of keV), the energy threshold and the sensitivity of detectors are additional fundamental issues in a Dark Matter search. CRESST detectors consist of a 300g CaWO4 scintillating crystal operated as a cryogenic calorimeter in close proximity to a second much smaller cryogenic calorimeter used to detect the scintillation light produced in the target crystal. The lower light yield of nuclear recoils, caused by neutrons and WIMPs, with respect to electron recoils resulting from alpha, beta and gamma interactions is used to identify the event in the scintillating absorber. In the second phase of the CRESST experiment, active background suppression is achieved by the simultaneous measurement of a phonon and a light signal from a scintillating cryogenic calorimeter. Passive background suppression is achieved by operating CRESST detectors in a low background facility located in a deep underground site. About 1% of the energy deposited in CaWO4 by beta or gamma interactions can be detected as scintillation light; therefore the sensitivity of light detectors is a fundamental issue for the discrimination of electron recoils from nuclear recoils at energies relevant for WIMP searches. This work reports on the development of extremely sensitive cryogenic calorimeters for the detection of the scintillation light. These detectors applied a new thermometer geometry characterized by phonon collectors and a thin film thermal coupling to the heat sink. This concept allows a high sensitivity by decoupling the area required for the collection of non-thermal phonons and the heat capacity of the sensor and permits to make the thermal relaxation time of the thermometer long enough to allow for the integration of the scintillation light, despite the slow light emission of CaWO4 at low temperature. Results on new materials to be used as absorbers for a new generation of light detectors are presented. First competitive limits on WIMP Dark Matter established by the CRESST experiment running scintillating CaWO4 cryogenic detectors in association with the light detectors developed in the course of this work are reported together with main results of the detector prototyping phase.

In dieser Arbeit wurde die Femtosekunden (fs)-Frequenzkammtechnik, die in der Arbeitsgruppe von Prof. T. W. Hänsch entwickelt wurde, angewendet, um die Genauigkeit nichtlinearer Prozesse zu überprüfen und eine mögliche zeitliche Veränderung von Naturkonstanten nachzuweisen. Ein Frequenzkamm ist das Spektrum eines regelmäßigen kohärenten Pulszugs, der von einem modengekoppelten Laser ausgesendet wird. Die Frequenzen f_n der Kammoden sind durch f_n=f_ce+n*f_r gegeben. Dabei ist n eine natürliche Zahl der Größenordnung 10^6, f_r die Pulswiederholrate des Lasers und f_ce eine für alle Moden gleiche Frequenzverschiebung. Wird das Spektrum eines fs-Lasers mit Hilfe einer mikrostrukturierten Glasfaser auf eine Oktave verbreitert, so können die beiden Radiofrequenzen f_r und f_ce auf einfache Weise gemessen und kontrolliert werden. Einen fs-Frequenzkamm kann man sich dabei anschaulich als Getriebe vorstellen, der optische Frequenzen und Radiofrequenzen phasengenau miteinander verbindet. Das oktavenbreite Spektrum nach einer mikrostrukturierten Glasfaser wurde in dieser Arbeit dazu verwendet, um in einem nichtlinearen Kristall durch Summenfrequenzmischung (SFG) bzw. Differenzfrequenzmischung (DFG) zwei neue Frequenzkämme zu erzeugen, deren Frequenzverschiebung 2*f_ce (SFG) bzw. f_ce=0 (DFG) beträgt. Durch das Verschwinden von f_ce eignet sich der DFG-Kamm als stabiles Uhrwerk für zukünftige optische Uhren, von denen eine relative Genauigkeit von 10^(-18) erwartet wird, was etwa 1000 mal genauer ist als die besten Cs-Atomuhren der Welt. Ein Vergleich des erzeugten SFG- und DFG-Kamms mit dem Originalkamm gestattet darüber hinaus die Überprüfung der Genauigkeit nichtlinearer Prozesse mit einer relativen Genauigkeit von 6,6*10^(-21), was verglichen mit früheren Arbeiten eine 100 fache Verbesserung darstellt. Eine Abweichung von den erwarteten Werten konnte im Rahmen der Meßgenauigkeit nicht beobachtet werden. In Zusammenarbeit mit dem Wasserstofflabor in unserer Arbeitsgruppe wurde die Frequenz des 1S-2S Übergangs in atomarem Wasserstoff zu 2466061413187087+-34 Hz gemessen, was einer relativen Genauigkeit von 1,4*10^(-14) entspricht. Damit gehört die 1S-2S Frequenz zu den am besten bekannten optischen Frequenzen. Für ihre Messung wurde ein fs-Frequenzkammgenerator verwendet, der mit Hilfe der transportablen Cs-Fontänenuhr FOM des BNM-SYRTE/ENS, Paris stabilisiert wurde. Ein Vergleich mit der Messung aus dem Jahr 1999 ergibt eine relative zeitliche Änderung der 1S-2S Frequenz von (-3,2+-6,3)*10^(-15)/Jahr. Mit diesem Wert und optischen Frequenzmessungen am 199Hg+ bzw. 171Yb+ Ion, die am NIST in Boulder/Colorado bzw. an der PTB in Braunschweig durchgeführt wurden, konnte eine Obergrenze für die gegenwärtige zeitliche Änderung der Feinstrukturkonstante von (d/dt)alpha/alpha=(-0,3+-2,0)*10^(-15)/Jahr angegeben werden. Dieser Wert ist mit Null verträglich. Für seine Herleitung wurden keine Annahmen über das zeitliche Verhalten der anderen Kopplungskonstanten gemacht. Die ermittelten Obergrenzen sind daher weitgehend modellunabhängig.

We consider the brane world picture in the context of higher-derivative theories of gravity and tackle the problematic issues fine-tuning and brane-embedding. First, we give an overview of extra-dimensional physics, from the Kaluza-Klein picture up to modern brane worlds with large extra dimensions. We describe the different models and their physical impact on future experiments. We work within the framework of Randall-Sundrum models in which the brane is a gravitating object, which warps the background metric. We add scalar fields to the original model and find new and self-consistent solutions for quadratic potentials of the fields. This gives us the tools to investigate higher-derivative gravity theories in brane world models. Specifically, we take gravitational Lagrangians that depend on an arbitrary function of the Ricci scalar only, so-called $f(R)$-gravity. We make use of the conformal equivalence between $f(R)$-gravity and Einstein-Hilbert gravity with an auxiliary scalar field. We find that the solutions in the higher-derivative gravity framework behave very differently from the original Randall-Sundrum model: the metric functions do not have the typical kink across the brane. Furthermore, we present solutions that do not rely on a cosmological constant in the bulk and so avoid the fine-tuning problem. We address the issue of brane-embedding, which is important in perturbative analyses. We consider the embedding of codimension one hypersurfaces in general and derive a new equation of motion with which the choice for the embedding has to comply. In particular, this allows for a consistent consideration of brane world perturbations in the case of higher-derivative gravity. We use the newly found background solutions for quadratic potentials and find that gravity is still effectively localized on the brane, i.e that the Newtonian limit holds.

Die Verwendung akustischer Oberflächenwellen (OFW) zum Transport kleinster Flüssigkeitsmengen stellt eine besonders elegante Methode dar ein mikrofluidisches System zu realisieren. Der Transport kleinster Flüssigkeitsmengen durch eine OFW bringt große Vorteile mit sich. Das System besitzt keine beweglichen Bauteile, ist von außen leicht zugänglich und wird ausschließlich durch Planartechnologie hergestellt. Ein wesentlicher Bestandteil zur Anfertigung dieser Arbeit war die Untersuchung akustisch induzierter Mischvorgänge. Die Fluidik im flüssigkeitsgefüllten Spalt und speziell der Mischvorgang in einem engen Spalt wurde betrachtet. Mit diesen Betrachtungen erhielt man die Möglichkeit, die Wirkung des elektrischen Feldes der OFW, das bei Ausbreitung einer OFW auf einem piezoelektrischen Substrat vorhanden ist, zu untersuchen. Durch die Verringerung des mechanischen Einfluss' auf die Flüssigkeit ergab sich die Möglichkeit die Wirkung des elektrischen Feldes der OFW auf eine im Spalt befindliche Nanotubelösung zu beobachten. Füllte man eine Nanotubelösung in den Spalt, erfuhren die Nanotubes Kräfte durch die Fluidik und das elektrische Feld. Das Zusammenspiel der beiden Kräfte bietet die Möglichkeit Nanotubes auszurichten. Wie Nanotubes wurden auch Flüssigkristallmoleküle ausgerichtet und der dazu notwendige Aufbau in eine geeignete Optik integriert. Bei den Untersuchungen erwiesen sich Scherwellenbauteile als geeignete Testsysteme die Ergebnisse einer weiteren Prüfung zu unterziehen. Mit Untersuchung der Eigenschaften der Scherwellenbauteile, zeigte sich ihre Einsatzmöglichkeit in der Mikrofluidik für Aktorik und Sensorik. Mit Verwendung der Scherwellenbauteile bot sich im weiteren an Volumenmoden und Modenkonversion zu studieren. Es zeigte sich, dass Volumenmoden in der akustisch getriebenen Fluidik sehr vorteilhaft eingesetzt werden können, um kleinste Mengen Flüssigkeiten zu mischen. Dazu zeigte sich die Möglichkeit auf, die Technik der akustisch getriebenen Fluidik auf beliebige Materialien zu erweitern und für Mischeraufbauten zu nutzen. Neben dem Mischen verschiedener Bestandteile ist die Trennung verschiedener Inhalte einer Flüssigkeit betrachtet worden. Unter Verwendung elektrischer Felder wurde Separation eines elektrophoretisch beweglichen Farbstoffs aus einem akustisch getriebenen Fluss in einem kontinuierlich fließenden System betrachtet. Bei diesen Untersuchungen wurde auch die Verwendbarkeit planarer Elektroden gezeigt und die Übertragbarkeit der Ergebnisse von Wasser auf Elektrolyte. Mit den Erfahrungen dieser Untersuchungen wurde zum Abschluss eine Gelelektrophorese für einen Chip mit akustisch getriebener Fluidik entwickelt. Das System lies sich ohne Technologiebruch in ein Gesamtsystem integrieren. Dieses Beispiel für eine Anwendung des Systems zeigt die Verwendbarkeit für Alltagsprobleme wie der Analyse.