Theses - Physics
http://hdl.handle.net/1721.1/7865
2014-10-30T10:59:17ZElectroweak symmetry breaking in the era of the Higgs boson discovery
http://hdl.handle.net/1721.1/91079
Electroweak symmetry breaking in the era of the Higgs boson discovery
Bertolini, Daniele, Ph. D. Massachusetts Institute of Technology
In this thesis we study possible deviations from the electroweak symmetry breaking mechanism as predicted by the Standard Model (SM), and we introduce a new framework to analyze hadronic final states at colliders. In the first part, we begin by considering supersymmetric extensions of the SM and by studying the connection between electroweak symmetry breaking and supersymmetry breaking. Contrary to the common lore, we show that a visible dynamics in the Higgs sector can contribute to supersymmetry breaking, as long as soft masses receive contributions also from one or more hidden sectors. A striking feature is the presence of a light pseudo-goldstino in the spectrum. We study potential collider signatures of visible supersymmetry breaking in Higgs and neutralino decays. Then, we move to a study of the Higgs data collected at the Large Hadron Collider (LHC). By using both measurements of the Higgs boson couplings, and limits on Higgs-like states at higher masses, we investigate whether the data support the possibility that the SM Higgs is mixed with another scalar. We consider fits to simplified models and we find that mixing angles with sin 2 6 > 0.2 are disfavored at 95% CL over a scalar mass range 200 - 1000 GeV. In the second part, we propose a new way to define inclusive jet (and subject) based observables at colliders. We introduce a new class of event shapes that characterize the jet-like structure of the event by using only information in the neighborhood of each particle. We show that conventional jet-based observables such as jet multiplicity, summed scalar transverse momentum, and missing transverse momentum can be recovered within this approach. We show that in this framework trimming can be recast as a particle weight assignment, without explicit jet identification. Finally, we comment on potential applications of the method both at trigger and analysis level.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014.; 166; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 115-125).
2014-01-01T00:00:00ZThe orbital dynamics and long-term stability of planetary systems
http://hdl.handle.net/1721.1/91078
The orbital dynamics and long-term stability of planetary systems
Deck, Katherine Michele
A large population of low-mass exoplanets with short orbital periods has been discovered using the transit method. At least 40% of these planets are actually part of compact systems with more than one planet. The closeness of the planetary orbits in these multi-planet systems leads to strong dynamical interactions that imprint themselves on the transit light curve as transit timing variations (TTVs). By modeling the orbital evolution of these planetary systems, one can fit the observed variations and strongly constrain the masses and orbits of the interacting planets, parameters which, given the faintness of the host stars, cannot be determined using other techniques. This type of analysis is performed for KOI- 984, a system with a single transiting planet perturbed by a non-transiting companion. By modeling the gravitational interaction between the planets using our code TTVFast, we are able to infer the masses and orbits of the two planets and to show that the orbits are distinctly non-coplanar. This discovery, a first for the low-mass multi-planet systems, indicates that dynamical processes that excite mutual inclinations can be important for such systems. The dynamical interactions that lead to observable TTVs can also lead to orbital instability and chaos. The Kepler 36 system has the closest confirmed pair of planets to date, with unique TTVs that tightly constrain the orbits, in turn allowing for detailed analysis of the long-term dynamics of the system. We find the system to be strongly chaotic, characterized by the very human timescale of -10 years. We are able to understand the source of this rapid chaos, and to show that despite its presence, the system can be long-lived. But how compact can two planetary orbits be before being unstable? We consider more generally the long-term stability of two-planet systems within the framework of first-order resonance overlap. We determine a stability criterion for close pairs of planets which we then compare to other analytic criteria and to numerical integrations. This work provides a step towards understanding the long-term evolution of more complex planetary systems.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 197-201).
2014-01-01T00:00:00ZStrings and monopoles in strongly interacting gauge theories
http://hdl.handle.net/1721.1/91077
Strings and monopoles in strongly interacting gauge theories
Dyer, Ethan Stanley
In this thesis we discuss aspects of strongly coupled gauge theories in two and three dimensions. In three dimensions, we present results for the scaling dimension and transformation properties of monopole operators in gauge theories with large numbers of fermions. In two dimensions, we study (0,2) gauge theories as a tool for constructing string backgrounds with non trivial H-flux. We demonstrate how chiral matter content in the gauge theory allows the construction of infrared fixed points outside of the usual Calabi-Yau framework, and further derive consistency relations for a special class of torsional models.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014.; 127; Title as it appears in MIT commencement exercises program, June 6, 2014: Few uses of low-dimensional gauge theory Cataloged from PDF version of thesis.; Includes bibliographical references (pages 201-209).
2014-01-01T00:00:00ZNon-equilibrium fluctuation induced-phenomena in quantum electrodynamics
http://hdl.handle.net/1721.1/91076
Non-equilibrium fluctuation induced-phenomena in quantum electrodynamics
Golyk, Vladyslav Alexander
We study fluctuation-induced phenomena in systems out of thermal equilibrium, resulting from the stochastic nature of quantum and thermal fluctuations of electromagnetic currents and waves. Specifically, we study radiative heat transfer and Casimir forces by applying the scattering formalism that expresses results solely in terms of the classical scattering matrices of the objects. For example, we obtain exact formulas for the heat radiation emitted by long cylindrical objects, as well as for Casimir forces that arise between them. We apply our results to explore the dependence of these phenomena on size and material properties of cylinders. While the scattering formalism is very general and technically can be employed for arbitrary shapes, in practice it is very time-consuming to apply it to the most experimentally-relevant and complex case of objects at close proximity. We examine easier ways to compute the heat transfer in such case. In particular, we develop a small distance expansion for the heat transfer between gently curved objects, in terms of the ratio of distance to radius of curvature. This expansion allows us to rigorously justify the widely used approach of "proximity transfer approximation", and to quantify corrections to it in the limit of small separation. Moreover, we study the role of surface roughness, and show that it may change the distance dependence of the heat transfer as well as Casimir forces between curved objects at proximity. Finally, as an alternative approach we construct general Green-Kubo relations that connect radiative heat transfer, non-equilibrium Casimir forces and vacuum friction between arbitrary objects to fluctuations in equilibrium which may be easier to consider from the perspective of experiment and simulations.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014.; 138; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 120-129).
2014-01-01T00:00:00Z