18,628 research outputs found
Widening the Axion Window via Kinetic and St\"uckelberg Mixings
We point out that kinetic and St\"uckelberg mixings that are generically
present in the low energy effective action of axions can significantly widen
the window of axion decay constants. We show that an effective super-Planckian
decay constant can be obtained even when the axion kinetic matrix has only
sub-Planckian entries. Our minimal model involves only two axions, a
St\"uckelberg U(1) and a modest rank instanton generating non-Abelian group.
Below the mass of the St\"uckelberg U(1), there is only a single axion with a
non-perturbatively generated potential. In contrast to previous approaches, the
enhancement of the axion decay constant is not tied to the number of degrees of
freedom introduced. We also discuss how kinetic mixings can lower the decay
constant to the desired axion dark matter window. String theory embeddings of
this scenario and their phenomenological features are briefly discussed.Comment: v2: published version (references and clarifying comments added); v1:
5 pages, 2 figure
Large Field Inflation from Axion Mixing
We study the general multi-axion systems, focusing on the possibility of
large field inflation driven by axions. We find that through axion mixing from
a non-diagonal metric on the moduli space and/or from St\"uckelberg coupling to
a U(1) gauge field, an effectively super-Planckian decay constant can be
generated without the need of "alignment" in the axion decay constants. We also
investigate the consistency conditions related to the gauge symmetries in the
multi-axion systems, such as vanishing gauge anomalies and the potential
presence of generalized Chern-Simons terms. Our scenario applies generally to
field theory models whose axion periodicities are intrinsically sub-Planckian,
but it is most naturally realized in string theory. The types of axion mixings
invoked in our scenario appear quite commonly in D-brane models, and we present
its implementation in type II superstring theory. Explicit stringy models
exhibiting all the characteristics of our ideas are constructed within the
frameworks of Type IIA intersecting D6-brane models on T6/OR and Type IIB
intersecting D7-brane models on Swiss-Cheese Calabi-Yau orientifolds.Comment: v2: references added, typos corrected; v1: 1+85 pages, 4 figure
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