Haßler, Falk (2015): Double field theory on group manifolds. Dissertation, LMU München: Faculty of Physics 

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Abstract
This thesis deals with Double Field Theory (DFT), an effective field theory capturing the low energy dynamics of closed strings on a torus. All observables arising from those dynamics match on certain families of background space times. These different backgrounds are connected by Tduality. DFT renders Tduality on a torus manifest by adding D windig coordinates in addition to the D space time coordinates. An essential consistency constraint of the theory, the strong constraint, only allows for fields which depend on half of the coordinates of the arising doubled space. An important application of DFT are generalized ScherkSchwarz compactifications. They give rise to halfmaximal, electrically gauged supergravities which are classified by the embedding tensor formalism, specifying the embedding of their gauge group into O(n,n). Because it is not compatible with all solutions of the embedding tensor, the strong constraint is replaced by the closure constraint of DFT's flux formulation. This allows for compactifications on backgrounds which are not Tdual to welldefined geometric ones. Their description requires nongeometric fluxes. Due to their special properties, they are also of particular phenomenological interest. However, the violation of the strong constraint obscures their uplift to full string theory. Moreover, there is an ambiguity in generalizing traditional ScherkSchwarz compactifications to the doubled space of DFT: There is a lack of a general procedure to construct the twist of the compactification. After reviewing DFT and generalized ScherkSchwarz compactifications, DFT_WZW, a generalization of the current formalism is presented. It captures the low energy dynamics of a closed bosonic string propagating on a compact group manifold and it allows to solve the problems mentioned above. Its classical action and the corresponding gauge transformations arise from Closed String Field Theory up to cubic order in the massless fields. These results are rewritten in terms of a generalized metric and extended to all orders in the fields. There is an explicit distinction between background and fluctuations. For the gauge algebra to close, the latter have to fulfill a modified strong constraint, while for the former the closure constraint is sufficient. Besides the generalized diffeomorphism invariance known from the traditional formulation, DFT_WZW is invariant under standard diffeomorphisms of the doubled space. They are broken by imposing the totally optional extended strong constraint. In doing so, the traditional formulation is restored. A flux formulation for the new theory is derived and its connection to generalized ScherkSchwarz compactifications is discussed. Further, a possible treelevel uplift of a genuinely nongeometric background (not Tdual to any geometric configuration) is presented. Finally, the ambiguity in constructing the compactification's twist is eliminated. Altogether, a more general picture of DFT and the structures it is based on emerges.
Item Type:  Thesis (Dissertation, LMU Munich) 

Subjects:  500 Natural sciences and mathematics 500 Natural sciences and mathematics > 530 Physics 
Faculties:  Faculty of Physics 
Language:  English 
Date of oral examination:  15. July 2015 
1. Referee:  Lüst, Dieter 
MD5 Checksum of the PDFfile:  48e6916130f309916f85ec493f2a377f 
Signature of the printed copy:  0001/UMC 23091 
ID Code:  18427 
Deposited On:  23. Jul 2015 08:35 
Last Modified:  20. Jul 2016 10:39 