Double Field Theory

Bachelor thesis
Research group: 
String Cosmology
Hanne Hoitzing

In this thesis, a theory called double eld theory will be discussed. First, an introduction will be given into string theory. After this, compacti cations of dimensions will be discussed and with it the notion of winding. This winding gives rise to T-duality which is an important symmetry of double eld theory. We will discuss the weak constraint which says all elds and gauge parameters must be annihilated by the operator @i ~@i. An action to all orders in the elds will be constructed and it will turn out that a constraint stronger than the weak constraint is needed to ensure gauge invariance of the action and to keep T-duality as a symmetry. A possible stronger constraint is the strong constraint but it will be shown that upon satisfying this strong constraint it is always possible to perform an O(D,D) transformation after which our double eld theory has become a single eld theory. Finally, it is discussed what conditions are exactly needed to prove gauge invariance and to keep all the symmetries. These conditions are compared with the strong constraint and the possibility of an intermediate constraint will be discussed.

Publication date: 
July, 2012