Theses - Dept. of Physics
http://hdl.handle.net/1721.1/7608
2017-01-20T01:47:24ZLessons on interacting quantum field theories from string theory
http://hdl.handle.net/1721.1/106452
Lessons on interacting quantum field theories from string theory
Wang, Yifan, Ph. D. Massachusetts Institute of Technology
In this thesis, we use string theory constructions and dualities to explore various features of interacting quantum field theories. We begin with an overview in Chapter 1, of past and recent developments in quantum field theories, explaining the advantages of string theoretic techniques over traditional approaches in answering a range of questions about interacting dynamics. In Chapter 2 we study the holographic duality between the 6d (1, 1) Ak-1 little string theory (LST) and type II string theory in the double scaled limit. By identifying the low energy states, which are Cartan gluons in the 6d maximal super-Yang-Mills (SYM) that describes the massless sector of the LST, we compute the four-point amplitudes from both sides of the duality and demonstrate matching results. Since the two computations concern different regimes in the parameter space, their amazing agreement implies the presence of certain nonrenormalization theorems in the 6d SYM. In Chapter 3, motivated by the AdS/CFT duality, we develop a systematic procedure to derive an off-shell action for hydrodynamics from classical Einstein gravity. We first identity the boundary fluid degrees of freedom in the hydrodynamic regime, in terms of gapless modes of the metric in the bulk gravity. This allows us to derive an off-shell action, for relativistic fluids that have gravity duals, at leading order in derivative expansion, by explicitly integrating out gapped degrees of freedom in the bulk. We also explain the strategy to incorporate dissipation and higher order effects. In Chapter 4, we discuss 4d N = 2 superconformal field theories (SCFT) of the Argyres-Douglas (AD) type, which can be constructed in string/M theory by either wrapping M5 branes on punctured Riemann surface or probing 3-fold singularity by IIB string. We classify the punctures (irregular defects in Hitchin system) on the Riemann surface in the former construction, that will give rise to N = 2 SCFTs and demonstrate how to extract exact information about the Coulomb branch spectrum and central charges. We further identify these AD theories constructed from M5 branes with a special class of theories from IIB probing compound Du Val (cDV) singularities, thereby establishing a mathematical connection between singular Hitchin systems and cDV singularities through N = 2 SCFTs. We end with a short summary and outlook for future directions in Chapter 5.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 185-194).
2016-01-01T00:00:00ZRadial equilibrium of toroidal plasmas.
http://hdl.handle.net/1721.1/106036
Radial equilibrium of toroidal plasmas.
Pickrell, M. M. (Mark Manley)
Thesis. 1976. B.S.--Massachusetts Institute of Technology. Dept. of Physics.; Microfiche copy available in Archives and Science.
1976-01-01T00:00:00ZAutomatic detection of periodic sources in the K2 data sets
http://hdl.handle.net/1721.1/105653
Automatic detection of periodic sources in the K2 data sets
Molnar, Momchil Emil
We present an automated algorithm for the detection of periodic sources in the K2 data sets. Fast discreet Fourier transformations are used to compute the Fourier spectra of the targets and two different detection algorithms for identifying significant signals are used. The first technique searches through the DFT to identify peaks that are significantly above the background noise level, and which have at least one higher harmonic of the fundamental frequency. We show this approach to be relatively inefficient for detecting weaker sources with narrow features, such as transiting exoplanets. The second algorithm that we apply uses a summation of the DFT harmonics, which relies on the fact that typical planetary transits and binary eclipses have numerous harmonics in their Fourier spectra. In this method we sum the harmonics of the fundamental frequency, which increases the signal-to-noise ratio and substantially increases the detection efficiency of the algorithm. This latter technique yields a smaller number of false positives while having higher detection rates than the first approach. A discussion of the noise level and detection threshold is presented, with a derivation of the threshold for the algorithm based on the noise properties in the K2 data. Furthermore, a discussion of the performance of both algorithms is presented. We then apply this automated search algorithm to the sixth and seventh fields of the K2 mission. In all these fields contained some 45,000 stars that were monitored for nearly three months each. The automated search yielded about 2000 interesting periodic targets. We conclude with a short discussion of the more interesting objects detected in the C7 data release by the K2 team. Finally, we present a catalog of many of the periodic sources that we have detected using these algorithms in the Appendix.
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2016.; Cataloged from PDF version of thesis.; Includes bibliographical references.
2016-01-01T00:00:00ZImplementation of side-fringe locking in an SHG cavity
http://hdl.handle.net/1721.1/105652
Implementation of side-fringe locking in an SHG cavity
Moore, Sam, S.B. Massachusetts Institute of Technology
An alternative method for locking a second-harmonic generation (SHG) cavity on resonance is described and implemented. The usual method, Pound-Drever-Hall locking, is prone to long-term power fluctuations from power variations in the incident laser. When using the second harmonic field for squeezing, these power fluctuations need to be stabilized with an additional control loop (usually a Mach-Zender interferometer). The alternative method, side-fringe locking, involves a simple DC offset on the second-harmonic signal at the desired power to generate the error signal. This thesis demonstrates the insensitivity of side-fringe locking to such long-term power fluctuations and that the noise spectrum is comparable to PDH locking-explained largely due to PZT noise length fluctuations off-resonance..
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2016.; Pages 36-39 are missing. Cataloged from PDF version of thesis.; Includes bibliographical references (pages 40-41).
2016-01-01T00:00:00Z