http://hdl.handle.net/1721.1/7867 2013-05-26T03:29:19Z http://hdl.handle.net/1721.1/78551 The DarkLight experiment : searching for the dark photon Katzin, Dustin R We describe a setup to search for the existence of a massive gauge boson A', the "dark photon," mediating dark matter interactions with coupling strength [alpha]'. In certain models, the A' decays promptly but invisibly and might be discoverable in high luminosity collider experiments. Following a proposed setup by Wojtsekhowski et al. to use the VEPP-3 electron-positron storage ring at the Budker Institute for Nuclear Physics, we study whether an e+ + e- - A'+ -[gamma] signal could be seen over the quantum electrodynamic background. The proposed VEPP-3 setup is sensitive to an A' within the mass range mA = 5-20 MeV. Out of the two backgrounds, e++e- - 3[gamma] and e+ + e- - e+ + e- + [gamma], we find that the former process provides the dominant background for the A' signal. While positron bremsstrahlung events can be detected and suppressed in Wojtsekhowski's apparatus, the 3[gamma] cross-section has a large cross section in this range, "faking" an A'. We use Monte Carlo numerical integration techniques to calculate the cross sections and obtain reach plots, determining which values of mA' and a' could be discovered at 5[sigma] confidence. This background study can be used to improve the VEPP-3 proposal, and provides a valuable comparison study with the MIT-led DarkLight proposal to search for a dark photon in the same mass range. Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 53-54). 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78550 Testing and modeling of photo-electric modulators Weaver, Matthew J. (Matthew James) Optical links are a promising alternative to the electrical interconnects that are currently used between chips within a computer. A crucial part of an optical link is a modulator, a device that converts an electrical signal into an optical signal. This thesis explores the physics of how these modulators operate. I built a general purpose optical and electrical testing station to perform these measurements. The optical transmission spectra of the set of modulators studied had extinction ratios in the range of 5 to 27 dB, which is sufficient for modulation. I developed analytical and T-Matrix models to extract physical parameters from the transmission scans, such as light transmission, loss in the ring, and index of refraction of the contact section. The modulators worked with an open eye up to frequencies of 600 MHz. A theoretical model was developed to match the data and experiment with injection and recombination dynamics. Finally, several design solutions are suggested to further improve the modulators and to move towards the goal of modulators that operate at 5 Gb/s. Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 65-66). 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78543 An algorithm for rapid measurement of aberrations in pairs of out-of-focus images Janish, Ryan J. (Ryan Joseph) In this thesis, I present a new technique for measuring the optical aberrations produced by a telescope, with an eye towards future use of these aberration measurements to align wide-field telescopes. This method determines the aberrations by simultaneously fitting a pair of oppositely defocused images to a mostly analytic model. I develop the model and describe its software implementation in detail, and then report on the results of tests with simulated and real data. This technique is able to extract the aberrations from simulated data rapidly and accurately, and it has been used with mixed success to analyze data from the VISTA telescope. With the VISTA data, the algorithm is unable to match small-scale brightness variations in the images. However, it was able to determine aberrations with median accuracies of 0.08 um for coma, 0.08 um for astigmatism, 0.9 um for tilt, and 0.3 um for defocus. It was also quite fast, with an average of 34 iterations until convergence. Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 57). 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78542 Refining the multi-field effects of Higgs inflation Greenwood, Ross Norman In this thesis, I investigated the extent to which the inclusion of multiple scalar fields in models of Higgs inflation produces observable departures from the single field case. I designed simulations to numerically solve the differential equations of motion in the Einstein frame governing the evolution of two nonminimally coupled fields in a quartic potential. Determining the behavior of the Hubble parameter, I found that successful inflation results in this model from a range of initial conditions. Based on calculations of the evolution of field perturbations by Courtney Peterson and Max Tegmark [6], the results suggest that the turn rate of the fields' combined velocity through field space has been sufficiently small since Hubble crossing that it may be excluded as a source of the amplification of perturbations in the Cosmic Microwave Background to their present size. Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 37). 2012-01-01T00:00:00Z