Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005. / Includes bibliographical references (p. 133-144). / In this thesis we show how to calculate off-shell low energy effective actions and how to study the dynamics of the tachyon from string field theory. We discuss how to obtain an effective action for the massless field and we explain how to relate it to well known results. We then study the tachyon dynamics both in cubic and in boundary string field theory. / by Erasmo Coletti. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1995. / Includes bibliographical references (leaves 151-155). / by Sheperd S. Doeleman. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1997. / Includes bibliographical references (p. 163-165). / by James A. Quigley. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2004. / Includes bibliographical references (p. 135-142). / The Relativistic Heavy Ion Collider (RHIC) has provided its experiments with the most energetic nucleus-nucleus collisions ever achieved in a laboratory. These collisions allow for the study of the properties of nuclear matter at very high temperature and energy density, and may uncover new forms of matter created under such conditions. This thesis presents measurements of the elliptic flow amplitude, v₂, in Au+Au collisions at RHIC's top center of mass energy of 200 GeV per nucleon pair. Elliptic flow is interesting as a probe of the dynamical evolution of the system formed in the collision. The elliptic flow dependences on transverse momentum, centrality, and pseudorapidity were measured using data collected by the PHOBOS detector during the 2001 RHIC run. The reaction plane of the collision was determined using the multiplicity detector, and the azimuthal angles of tracks reconstructed in the spectrometer were then correlated with the found reaction plane. The v₂ values grow almost linearly with transverse momentum, up to P[sub]T of approximately 1.5 GeV, saturating at about 14%. As a function of centrality, v₂ is minimum for central events, as expected from geometry, and increases up to near 7% (for 0 < [eta] < 1) at (N[sub]part) = 83. The v2 dependence on pseudorapidity was measured over the range 0 < [eta] < 1.8 for three centrality rangess: 3-15%, 15-25% and 25-50%. For all but the most central of the three centrality ranges, v₂ is seen to decrease with increasing starting already near mid-rapidity. The results, their comparison to models and interpretation are discussed. / by Carla Manuel Vale. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 181-185). / Photonic band-gap (PBG) structures are promising candidates for electron accelerators capable of high-gradient operation because they have the inherent damping of high order modes required to avoid beam breakup due to instabilities. A key challenge for PBG structures is high-gradient operation without structure damage due to rf-field-induced breakdowns. This thesis reports theoretical results on the design of PBG structures and the generation of wakefields in such structures. It also reports experimental results on PBG structure breakdown testing at high power at both 11 and 17 GHz. A single-cell photonic band-gap (PBG) structure was designed with an inner row of elliptical rods (PBG-E) to reduce ohmic heating relative to a round-rod structure. The PBG-E structure was built and tested at high power at a 60 Hz repetition rate at X-Band (11.424 GHz) at the SLAC accelerator test stand, achieving a gradient of 128 MV/m at a breakdown probability of 3.6 x 10-3 per pulse per meter at a pulse length of 150 ns. The PBG-E structure showed major improvement in breakdown rate relative to a round-rod PBG structure designed at MIT and previously tested at SLAC. A test stand was designed and built at MIT for testing single-cell structures at 17.1 GHz, a frequency 50% higher than the SLAC frequency. This test stand provides comparable diagnostics to those used at SLAC, adding optical diagnostic access which can be used for open PBG structures. A conventional disc-loaded waveguide structure, MIT-DLWG, was tested at MIT at up to a 2 Hz repetition rate. This structure reached a maximum gradient of 87 MV/m at a breakdown probability of 1.19 x 10-1 per pulse per meter. A round-rod PBG structure, MIT-PBG-2, has also been tested at MIT at up to a 2 Hz repetition rate and 100 ns pulse length, demonstrating operation up to 89 MV/rn at a breakdown probability of 1.09 x 10-1 per pulse per meter. These test results show that a PBG structure can simultaneously operate at high gradients and low breakdown probability, while also providing wakefield damping. This makes PBG structures viable candidates for future collider applications. / by Brian J. Munroe. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Includes bibliographical references (p. 145-151). / by Christopher Russell Ekstrom. / Ph.D.

Massachusetts Institute of Technology. Dept. of Physics. Thesis. 1969. Ph.D. / Vita. / Bibliography: leaves 67-68. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1984. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Andrei Szilagyi. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Includes bibliographical references (leaves 157-161). / by Saúl González Martirena. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1997. / Includes bibliographical references (leaves 90-92). / by Matthew B. Hastings. / Ph.D.