70 research outputs found
On T-duality transformations for the three-sphere
We study collective T-duality transformations along one, two and three
directions of isometry for the three-sphere with H-flux. Our aim is to obtain
new non-geometric backgrounds along lines similar to the example of the
three-torus. However, the resulting backgrounds turn out to be geometric in
nature. To perform the duality transformations, we develop a novel procedure
for non-abelian T-duality, which follows a route different compared to the
known literature, and which highlights the underlying structure from an
alternative point of view.Comment: 42 pages; v2: references added; v3: published versio
Nonassociative Gravity in String Theory?
In an on-shell conformal field theory approach, we find indications of a
three-bracket structure for target space coordinates in general closed string
backgrounds. This generalizes the appearance of noncommutative gauge theories
for open strings in two-form backgrounds to a putative
noncommutative/nonassociative gravity theory for closed strings probing curved
backgrounds with non-vanishing three-form flux. Several aspects and
consequences of the three-bracket structure are discussed and a new type of
generalized uncertainty principle is proposed.Comment: v2: references added, discussion in section 5 extended; v3: published
version, minor technical mistake corrected (discussion & conclusions
unchanged
Towards Universal Axion Inflation and Reheating in String Theory
The recent BICEP2 measurements of B-modes indicate a large tensor-to-scalar
ratio in inflationary cosmology, which points towards trans-Planckian evolution
of the inflaton. We propose possible string-theory realizations thereof.
Schemes for natural and axion monodromy inflation are presented in the
framework of the type IIB large volume scenario. The inflaton in both cases is
given by the universal axion and its potential is generated at subleading order
by F-terms. Our models are shown to feature a natural mechanism for inflaton
decay into predominantly Standard Model particles.Comment: 7 pages; v2: references and one paragraph added; v3: minor changes in
section
T-duality revisited
We revisit the transformation rules of the metric and Kalb-Ramond field under
T-duality, and express the corresponding relations in terms of the metric G and
the field strength H=dB. In the course of the derivation, we find an
explanation for potential reductions of the isometry group in the dual
background.
The formalism employed in this paper is illustrated with examples based on
tori and spheres, where for the latter we construct a new non-geometric
background.Comment: 43 pages, 5 figures; v2: references added, discussion clarified,
conclusions in section 2 changed; v3: published versio
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