14,690 research outputs found
The anisotropy of a three- and a one-form
We calculate the anisotropic signal associated with the coupling of a
three-form with an Abelian vector gauge field. In the simplest examples of
three-form inflation the amplification of the vector fluctuations is
exponential; this makes it almost certain that a large anisotropy will develop,
severely constraining the viability of the coupling
Pseudoscalar N-flation and axial coupling revisited
We revisit the dynamics of the axial coupling between many N-flatons and an
Abelian gauge field, with special attention to its statistically anisotropic
signal. The anisotropic power spectrum of curvature perturbations associated to
the large wavelength modes of the gauge vector field is generally undetectable,
since the anisotropy is confined to small scales. If the gauge field is the
electromagnetic field, provided that the number of fields participating in the
exponential expansion is large, it could be possible to generate sizable large
scale magnetic fields. However, its spectrum is blue, and appreciable power on
large scales implies an overly strong field on smaller scales, incompatibly
with observations. Furthermore, the anisotropy is also markedly enhanced, and
might be at odds with the isotropic observed sky. These aspects further demand
that the scale of inflation is kept to a minimum.Comment: 14 pages - v2 with minor changes in the conclusions, v3 to match
published versio
Critical Theory of Two-Dimensional Mott Transition: Integrability and Hilbert Space Mapping
We reconsider the Mott transition in the context of a two-dimensional fermion
model with density-density coupling. We exhibit a Hilbert space mapping between
the original model and the Double Lattice Chern-Simons theory at the critical
point by use of the representation theory of the q-oscillator and Weyl
algebras. The transition is further characterized by the ground state
modification. The explicit mapping provides a new tool to further probe and
test the detailed physical properties of the fermionic lattice model considered
here and to enhance our understanding of the Mott transition(s)
Three-magnetic fields
A completely new mechanism to generate the observed amount of large-scale
cosmological magnetic fields is introduced in the context of three-form
inflation. The amplification of the fields occurs via fourth order dynamics of
the vector perturbations and avoids the backreaction problem that plagues most
previously introduced mechanisms.Comment: 4 pages, 2 figures -- v2 as published (title changed in the published
version to "Cosmic magnetization in three-form inflation"
Doubly-boosted vector cosmologies from disformal metrics
A systematic dynamical system approach is applied to study the cosmology of
anisotropic Bianchi I universes in which a vector field is assumed to operate
on a disformal frame. This study yields a number of new fixed points, among
which anisotropic scaling solutions. Within the simplifying assumption of
(nearly) constant-slope potentials these are either not stable attractors, do
not describe accelerating expansion or else they feature too large anisotropies
to be compatible with observations. Nonetheless, some solutions do have an
appeal for cosmological applications in that isotropy is retained due to rapid
oscillations of the vector field.Comment: 11 pages, 4 figures, prepared during the NORDITA Extended Theories of
Gravity program. arXiv admin note: substantial text overlap with
arXiv:1407.344
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