The optical properties of matter are determined by the coupling of the incident electromagnetic radiation to oscillators within the material. The oscillators can be electrons, ions or molecules. Close to a resonance the dielectric function exhibits strong dispersion and may be negative. A negative dielectric function gives rise to a complex wave vector which is associated with no allowed states for photons, i.e. high extinction and bulk reflectance, as well as the possibility to support surface waves. It is possible to manufacture a dielectric material that generates a complex wave vector. Such materials are called photonic crystals and they may exhibit a frequency range without allowed states for photons, i.e. an energy gap. A photonic crystal has a periodically varying dielectric function and the lattice constant is of the same order of magnitude as the wavelengths of the gap. In this thesis, two optical phenomena causing a complex wave vector are combined. Polar materials, which have lattice resonance in the thermal infrared causing strong dispersion, are studied in combination with a periodic structure. The periodicity introduced is achieved using another material, but also by structuring of the polar material. One, two and three dimensional structures are considered. The polar materials used are silicon dioxide and silicon carbide. It is shown, both by calculations and experiments that the two optical phenomena can co-exist and interact, both constructively and destructively. A possible application for the combination of the two phenomena is discussed: Selective emittance in the thermal infrared. It is also shown that a polar material can be periodically structured by a focused ion beam in such way that it excites surface waves.

The existence of charged electroweak-scale particles in the early universe can drastically affect the evolution of elemental abundances. Through the formation of Coulombic bound states with light nuclei, these exotic relic particles (hereafter referred to as X–) act to catalyze nuclear reactions by reducing their threshold energies. This thesis examines the properties of the X– bound states, and uses primordial element observations to constrain the abundance, lifetime, and mass of this exotic particle species. If the X– is a Dirac Fermion, its abundance relative to baryons is found to be YX- ~ 0.01, with a lifetime of 1500s ≤ τX- ≤ 3000s, and a mass of order 100 GeV. Assuming that the X– is a Scalar particle that decays into gravitinos, the resulting bounds become, 5x10-4 ≤ YX- ≤ 0.07, 1600s ≤ τX- ≤ 7000s, and 60GeV ≤ mX- ≤ 1000GeV. These ranges are consistent with Dark Matter constraints.

We investigate the decay mode τ − → π − π + π − ηντ , where the η subsequently decays to π + π − π 0 using 232 fb−1 data acquired by the BABAR detector. The branching fraction of τ − → π − π + π − ηντ is found to be (1.88 ± 0.14 ± 0.11) × 10−4 . The first error on the is measurement is purely statistical and the second error is estimated systematic error. This measurement is consistent with the prior experimental mesaurements at CLEO and BABAR.

A prototype time projection chamber has been designed and constructed to study the performance that can be expected by the large scale time projection chambers in the ND280m detector of the Tokai to Kamioka (T2K) neutrino oscillation experiment. Tests using the prototype will indicate any changes necessary to the fullscale design in order to meet the physics goals of the detectors. Some TPC gas parameters are measured, including the drift velocity, diffusion constant, and electron attachment coefficient. The spatial resolution of the TPC is also measured, and results are presented for two candidate TPC gasses.

As an alternative to dark matter, Modified Newtonian Dynamics (MOND) can explain dynamical measurements of galaxies on small scales. It is, however, unclear whether MOND still works for galaxies on the large scale. In this study, we use galaxy- galaxy (g-g) weak lensing measurements to examine MOND in the outer regions of galaxies. First, we study the amplitude of the weak gravitational lensing signal as a function of stellar mass around relatively isolated galaxies. We find that our measurements are inconsistent with the predictions from MOND. Second, we examine whether MOND can produce an anisotropic lensing signal as observed in the real data. Starting with a mass distribution of an extremely high ellipticity, we find it is very hard for MOND to reproduce the observed extensive anisotropic lensing signal from only the visible mass. Because the g-g lensing is measured at radii of up to hundreds of kiloparsecs, these two tests indicate that MOND does not work in outer regions of galaxies. Our study casts serious doubt on the notation that MOND can convincingly prove itself as a viable alternative to dark matter.

Chiral perturbation theory is a useful tool in the study of low energy reactions involving light particles. However the inclusion of heavy particles in chiral perturbation theory results in large contributions from loop diagrams which violate the standard power counting scheme. We review two methods, referred to as heavy baryon chiral perturbation theory and infrared regularization, which remove the high energy effects of the heavy particles and which therefore do not violate the power counting scheme. We then use these two methods to calculate the amplitude for pion photoproduction to fourth order and prove that the two amplitudes are equivalent.

Polymer gel dosimetry, in conjunction with x-ray computed tomography (x-ray CT) imaging, is a three-dimensional dosimetric tool that shows promise in the verification of complex radiation therapy treatments. Previous studies have shown that x-ray CT imaging of gel dosimeters is robust, easy-to-use, and has wide clinical accessibility. The effects of x-ray CT dose imparted to the gel dosimeter, during imaging of the delivered therapy dose distributions, is not well understood. This thesis quantifies the effects of CT dose on normoxic polyacrylamide gel (nPAG) dosimeters. The investigation is comprised of four parts. First, quantification of the x-ray CT dose given during CT imaging of nPAG gels was measured using ion chamber measurements and filmed dose profiles for a range of typical gel dosimetry imaging protocols (200 mAs (current-time), 120-140 kVp (peak potential energy of photons), 2-10 mm slice thickness). It was found that CT doses ranged from 0.007 Gy/slice (120 kVp, 2 mm) to 0.021 Gy/slice (140 kVp, 10 mm) for volumetric phantoms. Second, Raman spectroscopy was used to determine the effect of photon energy on the dose response of nPAG dosimeters exposed to photon energies from a CT scanner (140 kVp photons) and from a Linac (6 MV photons). A weaker response was exhibited within the gels irradiated with kV photons than MV photons. Thirdly, the measurements of the given x-ray CT dose as established in the first study and the dose response of the polymer gel to different photon energies in the second study were correlated to estimate the induced changes of the nPAG CT number ("NCT ), caused by x-ray CT imaging of the polymer gel. (CT number is defined to be the measured attenuation coefficient normalized to water.) For typical gel imaging protocols (as above with 16-32 image averages), it was found that "NCT <0.2 H is induced in active nPAG gel dosimeters. This "NCT is below the current threshold of detectability of CT nPAG gel dosimetry. Finally, the traditional method of chemically fixing the dose response mechanism of nPAG gels by passive oxygenation of the gel, is investigated to determine if oxygenation would mitigate the changes caused by x-ray CT imaging of the gels. It was determined that oxygen diffusion was too slow to cause fixation of nPAG dosimeters, as the diffusion constant was 1.2 ± 0.2 × 10−6cm2/s, or 25% of the diffusion constant for anoxic PAG gel dosimeters. In conclusion, it was found that x-ray CT dose in polymer gel dosimeters is not a concern for standard gel imaging protocols. X-ray CT dose can potentially be a concern when large numbers of image averages (e.g. >60 image averages) are utilized, as in gel imaging protocols for high-resolution scans.

I examine the observational effects of a light scalar field with a scalar coupling to masses and a pseudoscalar coupling to light and particle spins. The pseudoscalar coupling to light induces a coupling to atomic spins both by inducing a coupling to particle spins directly, and by interactions with electromagnetic fields in the atom. Experiments measuring the interaction of spins to the gradient of the field are the only known way to measure the strength of the interaction with spins. However, limits on the interaction with light derived from these experiments are barely competitive with the separate astronomical limits on the scalar interaction and the interaction with light. Assuming a low mass of the field, as would be the case if the field acts as quintessence, the polarization rotation of the CMB provides a much tighter limit on the product of the pseudoscalar and scalar interaction strengths.

Read-out channels in the liquid argon (LAr) calorimeter of the ATLAS detector are susceptible to various kinds of faults, which can impair the selection of events made by the trigger system. General-purpose software tools have been developed for dealing with problematic calorimeter channels. In order to give High-Level Trigger (HLT) algorithms robustness against detector problems, these tools have been applied in the HLT calorimeter data preparation code to mask problematic channels in the LAr calorimeter. Timing measurements and optimizations have been conducted to assess and minimize the impact of these operations on the execution speed of HLT algorithms. The efficacy of the bad-channel masking has been demonstrated using cosmic-ray data.

A search is done on the entire BaBar data set for the neutrino-less tau decay tau->e gamma. No evidence for the decay is found and a 90% confidence level upper limit is determined to be 3.3 * 10^(-8) including systematic uncertainty. This measurement is a factor of three improvement from the previous best result from BaBar.