Abstract
Non-perturbative phenomena have received much attention in string theory in the last years. M-Theory and F-Theory are the two main frameworks in which it is possible to explore such phenomena. This thesis focuses on aspects of both theories.In the first part of this thesis we study F-Theory compactifications with additional abelian gauge symmetries. This was motivated by problems affecting usual F-Theory compactifications and 4-dimensional Grand Uni ed Theories such as the presence of proton decay operators, which could in principle be resolved with additional abelian symmetries. In the F-Theory context, this translated into the novel analysis of elliptic brations with additional (two, in particular) rational sections. A systematic study of the possible degenerations of such elliptic brations through the application of Tate's algorithm was carried out and provided new insight into the phenomenology of F-Theory models with additional U(1) factors.
The second part of this thesis consists of the study of some aspects of membranes in M-Theory. D-branes in string theory are well understood thanks to a perturbative definition via open strings. On the contrary, membranes and vebranes in M-Theory lack such a description and their effective theories are not as well understood.
In particular the theory on parallel M5-branes, the so-called (2,0) theory, was studied in some detail. Following a number of results and dualities in lower dimensional field theories obtained in the last years starting from the (2,0) theory, the latter was compactified on a 2-dimensional sphere to obtain a 4-dimensional sigma model into the moduli space of monopoles. A supergravity background was turned on in order to preserve supersymmetry and an intermediate reduction to 5-dimensional N = 2 Super-Yang-Mills theory was used by considering the two-sphere as a circle bration over an interval.
Insight into the theory on parallel M5-branes was also gained by relating it to the better known dynamics on coincident M2-branes. This followed a recent proposal for the realization of the (2,0) algebra on a non-abelian tensor multiplet through the use of 3-algebras. In this thesis we generalize this proposal and nd an algebraic structure which describes two parallel M5-branes or two parallel M2-branes depending on whether a particular abelian three-form is turned on.
| Date of Award | 2017 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | affiliated academic (Supervisor) & Sakura Schafer-Nameki (Supervisor) |