10,305 research outputs found
Axion Inflation in F-theory
We study the dynamics of axion-like fields in F-theory and suggest that they
can serve as inflatons in models of natural inflation. The axions arise from
harmonic three-forms on the F-theory compactification space and parameterize a
complex torus that varies over the geometric moduli space. In particular, this
implies that the axion decay constants depend on the complex structure moduli
that can be fixed by background fluxes. This might allow tuning them to be
super-Planckian in a controlled way and allow for interesting single field
inflationary models. We argue that this requires a localization of the
three-forms near regions of strong string coupling, analogously to the
reasoning that GUT physics requires the use of F-theory. These models can admit
a tensor to scalar ratio r>0.1.Comment: 9 pages, 1 figure; v2: added clarifying remarks and reference
Challenges Facing Judges Regarding Expert Evidence in Criminal Cases
With regard to criminal cases, the focus of this Article, judges face significant challenges in ruling on the admissibility of expert testimony that do not occur in most civil cases. This Article starts by describing these challenges and then offers some suggestions about what can be done to address them
The N=1 effective action of F-theory compactifications
The four-dimensional N=1 effective action of F-theory compactified on a
Calabi-Yau fourfold is studied by lifting a three-dimensional M-theory
compactification. The lift is performed by using T-duality realized via a
Legendre transform on the level of the effective action, and the application of
vector-scalar duality in three dimensions. The leading order Kahler potential
and gauge-kinetic coupling functions are determined. In these compactifications
two sources of gauge theories are present. Space-time filling non-Abelian
seven-branes arise at the singularities of the elliptic fibration of the
fourfold. Their couplings are included by resolving the singular fourfold.
Generically a U(1)^r gauge theory arises from the R-R bulk sector if the base
of the elliptically fibered Calabi-Yau fourfold supports 2r harmonic
three-forms. The gauge coupling functions depend holomorphically on the complex
structure moduli of the fourfold, comprising closed and open string degrees of
freedom. The four-dimensional electro-magnetic duality is studied in the
three-dimensional effective theory obtained after M-theory compactification. A
discussion of matter couplings transforming in the adjoint of the seven-brane
gauge group is included.Comment: 59 pages, v2: references added, typos correcte
On Mirror Symmetry for Calabi-Yau Fourfolds with Three-Form Cohomology
We study the action of mirror symmetry on two-dimensional N=(2,2) effective
theories obtained by compactifying Type IIA string theory on Calabi-Yau
fourfolds. Our focus is on fourfold geometries with non-trivial three-form
cohomology. The couplings of the massless zero-modes arising by expanding in
these forms depend both on the complex structure deformations and the Kahler
structure deformations of the Calabi-Yau fourfold. We argue that two
holomorphic functions of the deformation moduli capture this information. These
are exchanged under mirror symmetry, which allows us to derive them at the
large complex structure and large volume point. We discuss the application of
the resulting explicit expression to F-theory compactifications and their weak
string coupling limit. In the latter orientifold settings we demonstrate
compatibility with mirror symmetry of Calabi-Yau threefolds at large complex
structure. As a byproduct we find an interesting relation of no-scale like
conditions on Kahler potentials to the existence of chiral and twisted-chiral
descriptions in two dimensions.Comment: 36 page
Self-Dual Tensors and Partial Supersymmetry Breaking in Five Dimensions
We study spontaneous supersymmetry breaking of five-dimensional supergravity
theories from sixteen to eight supercharges in Minkowski vacua. This N=4 to N=2
breaking is induced by Abelian gaugings that require the introduction of
self-dual tensor fields accompanying the vectors in the gravity multiplet and
vector multiplets. These tensor fields have first-order kinetic terms and can
become massive by a Stueckelberg-like mechanism. We identify the general class
of N=2 vacua and show how the N=4 spectrum splits into massless and massive N=2
multiplets. In particular, we find a massive gravitino multiplet, containing
two complex massive tensors, and a number of massive tensor multiplets and
hypermultiplets. We determine the resulting N=2 effective action for the
massless multiplets obtained by integrating out massive fields. We show that
the metric and Chern-Simons terms of the vectors are corrected at one-loop by
massive tensors as well as spin-1/2 and spin-3/2 fermions. These contributions
are independent of the supersymmetry-breaking scale and thus have to be
included at arbitrarily low energies.Comment: 33 page
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