Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1991. / Includes bibliographical references (leaves 149-156). / by Qing Ma. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005. / Includes bibliographical references (p. 49-50). / The X-ray intensities measured from 230 X-ray sources observed by the RXTE All-Sky Monitor (ASM) were analyzed for periodic behavior. The ASM has been observing sources for nine years in the 1.5-12 keV energy range. In this search, we investigated a frequency range of 5 d⁻¹ to 144 d⁻¹ for periodic modulation. The search was carried out by applying the Fast Fourier Transform on the ASM data and whitening the resulting power density spectrum using a local averaging technique. A power threshold was set to determine the statistical significance of a peak in the power density spectrum. The search verified the orbital frequencies of four known X-ray binaries and also identified four previously unreported periodicities. The 5.7232 d⁻¹ orbital frequency of GX 9+9 was observed for the first time in ASM data, although this modulation had been observed before. The 6.0999 d⁻¹ peak found for XTE J1723-376 has not been reported before and may be an orbital frequency. / y Vasudha B. Shivamoggi. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 253-273). / In this thesis, we build new Effective Field Theory tools to describe the propagation of energetic partons in hot and dense media, and we propose two new reactions for dark matter in the early universe. In the first part, we analyze the transverse momentum broadening in the absence of radiation of an energetic parton propagating through quark-gluon plasma via Soft Collinear Effective Theory (SCET). We show that the probability for picking up transverse momentum ki is given by the Fourier transform of the expectation value of two transversely separated light-like path-ordered Wilson lines. We evaluate the result for the strongly coupled plasma of N = 4 SYM theory by using gauge/gravity duality, and for the weakly coupled QCD plasma by using perturbation theory. In the second part, we introduce two new dark matter reactions, called "semi-annihilation" and "assimilation". The semi-annihilation reaction takes the schematic form [psi]i[psi]j -> [psi]k[psi], where [psi]i are stable dark matter particles and # is an unstable state. They lead to non-trivial dark matter dynamics in the early universe, and they might also take place today in the Milky Way, enriching the (semi-)annihilation final state spectrum observed in indirect detection experiments. The "assimilation" reaction efficiently destroy singlet dark matter particles, but dark matter number is stored in new quasi-stable heavy states which carry the baryon asymmetry. The subsequent annihilation and late-time decay of these heavy states yields (symmetric) dark matter as well as (asymmetric) standard model baryons. / by Francesco D'Eramo. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 199-204). / To measure the regeneration of electron neutrinos during passage through the Earth via the MSW effect, the difference in electron neutrino flux between day and night is measured at the Sudbury Neutrino Observatory (SNO). To be able to distinguish an actual discrepancy from an artifact, the detector properties and backgrounds are studied in regard to both a diurnal difference and a difference in the detector for upgoing v. downgoing neutrinos. This thesis focuses on the signal extraction part of this process, by which the neutrino fluxes are determined from the processed data by means of a Markov Chain Monte Carlo method. Recognizing that this effect is expected to have an energy dependence, the asymmetry is modeled as an affine function of energy. This measurement yields an asymmetry in the neutrino flux of ... measured in MeV. / by Richard Anthony Ott, III. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Studies of ion kinetic effects during the shock-convergence phase of inertial confinement fusion (ICF) implosions and magnetic reconnection in strongly-driven, laser-produced plasmas have been facilitated by the use of shock-driven ICF implosions and diagnosed using both mature and newly-developed nuclear diagnostics. Ion kinetic effects that are likely to be significant early in ICF implosions, as strong shocks create a high-temperature, moderate-density plasma with an ion mean free path approximately the size of the fuel region, have, for the first time, been explored in a comprehensive experimental campaign. These experiments at the OMEGA laser facility, in which the ion mean free path was systematically varied in a series of shock-driven implosions, have demonstrated that measured fusion yields are increasingly discrepant relative to the predictions of hydrodynamic codes with increasing ion mean free path. The enhanced transport of fuel ions out of the hot plasma region and the reduction in fusion reactivity due to the depletion of high-energy tail ions are responsible. These effects have also been inferred in shock-driven implosions at the National Ignition Facility. The universal plasma phenomenon of magnetic reconnection has been explored in strongly-driven, high-[beta] laser-produced plasmas, driving reconnection in a regime relevant to astrophysical environments, such as the Earth's magneto-pause. Using shock-driven ICF implosions as a proton source to probe magnetic fields, the first systematic laboratory experiments to study asymmetric magnetic reconnection have been conducted. These experiments have shown that the rate of reconnection in this strongly flow-driven system is dictated by the flow velocity and is largely insensitive to initial asymmetries in density, ram pressure, and geometry. Related experiments have probed the collision of parallel magnetic fields to assess the effect of strong flows on magnetic fields in the absence of reconnection. Experiments using high-resolution proton radiography have revealed small-scale electron jets that demonstrate the importance of two-fluid effects in permitting a fast reconnection even when reconnection is driven by strong plasma flows. This work has improved understanding and spurred further experimental and theoretical inquiry into kinetic ion behavior in ICF implosions and magnetic reconnection in regimes rarely accessed in the laboratory. / by Michael Jonathan Rosenberg. / Ph. D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2008. / Includes bibliographical references (p. 75-82). / In this thesis, I present a new determination of the cluster mass function in a volume ~107 h-03 70 Mpc3 using the ROSAT-2MASS-FAST Group Survey (R2FGS). R2FGS is an X-ray-selected sample of systems from the ROSAT All-Sky Survey in the region [delta] >/= 0° and 0.01 < z < 0.06, with target galaxies for each system compiled from the Two Micron All Sky Survey (2MASS). The sample is designed to focus on lowmass groups and clusters, so as to break a degeneracy between the cosmological parameters ,~ and as. In addition, R2FGS covers a very large area of sky (", 4.13 ster.), which is necessary given the low redshift limit of the survey. I acquire optical redshifts for the target galaxies in R2FGS from the literature and from new data collected with the FAST spectrograph on Mt. Hopkins. After removing foreground and background galaxies (interlopers) using a dynamical maximum-velocity criterion, I estimate the group and cluster masses using the full virial theorem, and subsequently verify the results using the projected mass estimator. I briefly investigate the [sigma]p - Lx and M - Lx scaling relations, as well as the halo occupation function. Due to interloper issues with some of the systems, I apply a luminosity-dependent correction to the virial masses, and subsequently use these masses to compute the virial mass function of the sample. By comparing this mass function to predictions from various cosmological models, I constrain the parameters , [omega]m and [sigma]s. I find m = 0.26 +0.07 -0.08 and [sigma]8 = 1.02 +0.30 -0.15; the R2FGS value for [omega]m agrees very well with the recent FiveYear WMAP (WMAP5) result, although the R2FGS value for [sigma]s is somewhat larger than that found by WMAP5. Future work will include an expansion of the survey to [delta] > -20° and z < 0.04, which will greatly increase its degeneracy-breaking power. / by James Colin Hill. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 45-46). / Through this thesis, heterostructures composed of a thin layer of hexagonal boron nitride atop a monolayer of molybdenum disulfide were fabricated with the goal of measuring quantum capacitance and probing the transition metal dichalcogenide's density of states. In the final devices, no modulation of the quantum-capacitance was observed due to large Schottky barriers between the metal contacts and the molybdenum disulfide. Lessons learned from this investigation inform improved fabrication and measurement techniques for future iterations of these fascinating devices. / by Alina Kononov. / S.B.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Physics, 1997. / Includes bibliographical references (leaf 48). / by Matthew Gray. / B.S.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2007. / Includes bibliographical references (p. 51-53). / This thesis is the beginning of a larger project to use BaBar to examine weak couplings through leptonic [tau] decay. I will use the ratio of Br... and Br... and the Michel parameters [rho] and [eta]. which describe the momenta spectrum of the daughter leptons. I studied using a simultaneous fit to the [tau] --> e and [tau] --> [mu] momentum spectra, using [rho], [eta], the ratio Br..., and total number of events as the fit variables. I created a simple Monte Carlo simulation which generated a. sample data spectrum and fit it for the Michel parameters [rho] and [eta]. I used the Monte Carlo to assess the impact of the uncertainties in the detector response function on the measurement of the ratio Br... My conclusion is that the three efficiency uncertainties equally have the greatest effect on the measurement of the number of events. The energy offset affects the measurement of Br... and that the energy scale and offset uncertainties have a non-negligible effect on [rho] and [eta]. / by Nicole Ackerman. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Includes bibliographical references (leaf 73). / by Yusuf İpekoğlu. / Ph.D.