In this thesis I present research in neutrino physics utilizing tools from both atomic physics and astrophysics. Recent advances in atomic physics enable a new type of beta decay experiment to measure the absolute mass scale of the neutrino using a sample of ultracold atomic tritium. These initial conditions enable the detection of the helium ion in coincidence with the beta. I construct a two-dimensional fit incorporating both the shape of the beta spectrum and the direct reconstruction of the neutrino mass peak. I present simulation results of the feasible limits on the neutrino mass achievable in this new type of tritium beta decay experiment. The same advances in atomic physics that enable the creation of an atomic source for tritium beta decay also suggest a new method of achieving large-scale isotope separation. Multiple experiments that are investigating the absolute mass scale of the neutrino through neutrinoless double beta decay could benefit from this new technique, which applies generally to many elements, including the double beta emitter Nd-150 that is particularly difficult to separate in large quantities. The method is based on an irreversible change of the mass-to-magnetic moment ratio of a particular isotope in a supersonic atomic beam, followed by a magnetic multipole whose gradients deflect and guide the atoms. I present numerical simulations of isotope separation for a range of examples and demonstrate that large-scale isotope separation should be possible using ordinary inexpensive magnets and the existing technologies of supersonic beams and lasers. Additionally I report results from a search for low-multiplicity neutrino bursts in the Sudbury Neutrino Observatory (SNO). Such bursts could indicate detection of a nearby core-collapse supernova explosion. The data were taken from November 1999 to May 2001 when the detector was filled with heavy water (Phase I), as well as data from July 2001 to August 2003 when NaCl was added to the detector (Phase II). The search was a blind analysis in which the potential backgrounds were estimated and analysis cuts were developed to eliminate such backgrounds with 90% confidence before the data were examined. The search maintained a greater than 50% detection probability for standard supernovae occurring at a distance of up to 60 kpc for Phase I and up to 70 kpc for Phase II. No low-multiplicity bursts were observed during the data-taking period. / text

Supernova explosions are among the most energetic events known in the universe, leaving supernova remnants (SNRs) as their relics. The cores of massive stars collapse to form neutron stars, among the most compact and strongest magnets in the cosmos. The thesis studies a sample of such magnetic "beauties" in X-rays, the magnetars and high-magnetic field pulsars (HBPs), with the motivation to understand their evolutionary links. We also address the connection between these sources by investigating their environs through their securely associated SNRs. Magnetars have ultra-high magnetic fields B ~ 10^{14} - 10^{15} Gauss (G) and include the soft-gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs). The HBPs have magnetic fields B ~ 10^{13} - 10^{14} G, intermediate between the classical rotation-powered pulsars (B ~ 10^{12} G) and magnetars. We focussed on two HBPs: J1119-6127 and J1846-0258, with similar spin-properties and associated with the SNRs G292.2-0.5 and Kes 75, respectively. In our studies, magnetar-like behavior was discovered from the Crab-like pulsar J1846-0258, clearly establishing a connection between the HBPs and magnetars for the first time, while no such behavior has been observed from PSR J1119-6127 so far. J1119-6127's overall X-ray properties together with its compact pulsar wind nebula resemble more the classical rotation-powered pulsars. We studied two magnetars, one from each sub-class: SGR 0501+4516 and AXP 1E 1841-045. The spectral and statistical analysis of the bursts and the persistent X-ray emission properties observed from them were found consistent with the magnetar model predictions as well as those seen in other SGRs. Finally, we probed the environment of these stellar magnets by performing a detailed X-ray imaging and spatially resolved spectroscopic study of two SNRs: G292.2-0.5 and Kes 73 associated with J1119-6127 and 1E 1841-045, respectively. We found that both SNRs point to very massive progenitors (>~25 solar masses), further supporting the growing evidence for magnetars originating from massive progenitors using other multiwavelength studies.

Supernova explosions are among the most energetic events known in the universe, leaving supernova remnants (SNRs) as their relics. The cores of massive stars collapse to form neutron stars, among the most compact and strongest magnets in the cosmos. The thesis studies a sample of such magnetic "beauties" in X-rays, the magnetars and high-magnetic field pulsars (HBPs), with the motivation to understand their evolutionary links. We also address the connection between these sources by investigating their environs through their securely associated SNRs. Magnetars have ultra-high magnetic fields B ~ 10^{14} - 10^{15} Gauss (G) and include the soft-gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs). The HBPs have magnetic fields B ~ 10^{13} - 10^{14} G, intermediate between the classical rotation-powered pulsars (B ~ 10^{12} G) and magnetars. We focussed on two HBPs: J1119-6127 and J1846-0258, with similar spin-properties and associated with the SNRs G292.2-0.5 and Kes 75, respectively. In our studies, magnetar-like behavior was discovered from the Crab-like pulsar J1846-0258, clearly establishing a connection between the HBPs and magnetars for the first time, while no such behavior has been observed from PSR J1119-6127 so far. J1119-6127's overall X-ray properties together with its compact pulsar wind nebula resemble more the classical rotation-powered pulsars. We studied two magnetars, one from each sub-class: SGR 0501+4516 and AXP 1E 1841-045. The spectral and statistical analysis of the bursts and the persistent X-ray emission properties observed from them were found consistent with the magnetar model predictions as well as those seen in other SGRs. Finally, we probed the environment of these stellar magnets by performing a detailed X-ray imaging and spatially resolved spectroscopic study of two SNRs: G292.2-0.5 and Kes 73 associated with J1119-6127 and 1E 1841-045, respectively. We found that both SNRs point to very massive progenitors (>~25 solar masses), further supporting the growing evidence for magnetars originating from massive progenitors using other multiwavelength studies.

Extensions to general relativity are often considered as possibilities in the quest for a quantum theory of gravity on one hand, or to resolve anomalies within cosmology on the other. Scalar fields, found in many areas of physics, are frequently studied in this context. This is partly due to their manifestation in the effective four dimensional theory of a number of underlying fundamental theories, most notably string theory. This thesis is concerned with the effects of scalar fields on cosmological and black hole solutions. By comparison, an analysis of an inhomogeneous cosmological model which requires no extensions to general relativity is also undertaken. In chapter three, examples of numerical solutions to black hole solutions, which have previously been shown to be linearly stable, are found. The model includes at least two scalar fields, non-minimally coupled to electromagnetism and hence possesses non-trivial contingent primary hair. We show that the extremal solutions have finite temperature for an arbitrary coupling constant. Chapter four investigates the effects of higher order curvature corrections and scalar fields on the late-time cosmological evolution. We find solutions which mimic many of the phenomenological features seen in the post-inflation Universe. The effects due to non-minimal scalar couplings to matter are also shown to be negligible in this context. Such solutions can be shown to be stable under homogeneous perturbations. Some restrictions on the value of the slope of the scalar coupling to the Gauss-Bonnet term are found to be necessary to avoid late-time superluminal behaviour and dominant energy condition violation. A number of observational tests are carried out in chapter five on a new approach to averaging the inhomogeneous Universe. In this "Fractal Bubble model" cosmic acceleration is realised as an apparent effect, due to quasilocal gravitational energy gradients. We show that a good fit can be found to three separate observations, the type Ia supernovae, the baryon acoustic oscillation scale and the angular scale of the sound horizon at last scattering. The best fit to the supernovae data is χ² ≃ 0:9 per degree of freedom, with a Hubble parameter at the present epoch of H0 = 61:7+1:4 -1:3 km sec⁻¹ Mpc⁻¹ , and a present epoch volume void fraction of 0:76 ± 0:05.

A sample of 9 small-diameter radio sources has been selected from the Molonglo Galactic Plane Survey (MGPS) and observed with the Australia Telescope Compact Array (ATCA) in the radio recombination line (RRL) at 5 GHz, in a search for young Galactic SNRs. Since the RRL emission is an unambiguous indicator of a thermal source, this method has been used to eliminate HII regions from the selected sample. In addition, the IRAS and MSX infrared data and spectral index measurements have been combined with the RRL studies to distinguish thermal and non-thermal sources in the selected sample. One source (G282.8-1.2) is identified here as a possible new young Galactic supernova remnant, based on its relatively weak infrared emission, steep radio spectrum and possible x-ray emission. However, the ATCA data are inconclusive and further studies are needed to confirm this result. Radio recombination line emission (H107 alpha) has been detected in 3 of the selected sources, eliminating them from the sample of SNR candidates. In addition, the parameters of the RRL emission from the identified HII regions have been used to estimate their properties. The RRL data are inconclusive for the remaining low brightness, extended sources in the sample. However, some of these sources are likely to be thermal HII regions according to the infrared and spectral index data. The selected method for distinguishing thermal and non-thermal Galactic radio sources seems promising. The selected ATCA configuration was appropriate for imaging relatively bright, compact sources, but a slightly modified observing technique is needed to successfully image low surface brightness, extended sources.

Thesis (Ph.D.)--McMaster University (Canada), 1988. / Source: Dissertation Abstracts International, Volume: 49-08, Section: B, page: 3250.

Heidelberg, Univ., Dipl.-Arb., 2006.

Techn. University, Diss., 2005--München.

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics, August 1997. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph.D.) - University of Buenos Aires, 2005. / PDF copy of thesis. Includes bibliographic references.