4,605 research outputs found
False Vacuum Chaotic Inflation: The New Paradigm?
Recent work is reported on inflation model building in the context of
supergravity and superstrings, with special emphasis on False Vacuum (`Hybrid')
Chaotic Inflation. Globally supersymmetric models do not survive in generic
supergravity theories, but fairly simple conditions can be formulated which do
ensure successful supergravity inflation. The conditions are met in some of the
versions of supergravity that emerge from superstrings.Comment: 4 pages, LATEX, LANCASTER-TH 94-1
Cosmological perturbation spectra from SL(4,R)-invariant effective actions
We investigate four-dimensional cosmological vacuum solutions derived from an
effective action invariant under global SL(n,R) transformations. We find the
general solutions for linear axion field perturbations about homogeneous
dilaton-moduli-vacuum solutions for an SL(4,R)-invariant action and find the
spectrum of super-horizon perturbations resulting from vacuum fluctuations in a
pre big bang scenario. We show that for SL(n,R)-invariant actions with n>3
there exists a regime of parameter space of non-zero measure where all the
axion field spectra have positive spectral tilt, as required if light axion
fields are to provide a seed for anisotropies in the microwave background and
large-scale structure in the universe.Comment: 8 pages, 3 figures, revtex plus epsf, minor typos corrected, version
to appear in Physical Review
Dilaton and axion bremsstrahlung from collisions of cosmic (super)strings
We calculate dilaton and axion radiation generated in the collision of two
straight initially unexcited strings and give a rough cosmological estimate of
dilaton and axion densities produced via this mechanism in the early universe.Comment: 7 pages, to appear in Proceedings of the 2nd International conference
On quantum theories and renormalization group in gravity and cosmology (IRGAC
2006), 11-15 Jul 2006, Barcelona, Spai
wormholes and topological charge
I investigate solutions to the Euclidean Einstein-matter field equations with
topology in a theory with a massless periodic scalar
field and electromagnetism. These solutions carry winding number of the
periodic scalar as well as magnetic flux. They induce violations of a
quasi-topological conservation law which conserves the product of magnetic flux
and winding number on the background spacetime. I extend these solutions to a
model with stable loops of superconducting cosmic string, and interpret them as
contributing to the decay of such loops.Comment: 18 pages (includes 6 figs.), harvmac and epsf, CU-TP-62
Generalized Assisted Inflation
We obtain a new class of exact cosmological solutions for multi-scalar fields
with exponential potentials. We generalize the assisted inflation solutions
previously obtained, and demonstrate how they are modified when there exist
cross-couplings between the fields, such as occur in supergravity inspired
cosmological models.Comment: 5 page
Fanny Copeland and the geographical imagination
Raised in Scotland, married and divorced in the English south, an adopted Slovene, Fanny Copeland (1872 – 1970) occupied the intersection of a number of complex spatial and temporal conjunctures. A Slavophile, she played a part in the formation of what subsequently became the Kingdom of Yugoslavia that emerged from the First World War. Living in Ljubljana, she facilitated the first ‘foreign visit’ (in 1932) of the newly formed Le Play Society (a precursor of the Institute of British Geographers) and guided its studies of Solčava (a then ‘remote’ Alpine valley system) which, led by Dudley Stamp and commended by Halford Mackinder, were subsequently hailed as a model for regional studies elsewhere. Arrested by the Gestapo and interned in Italy during the Second World War, she eventually returned to a socialist Yugoslavia, a celebrated figure. An accomplished musician, linguist, and mountaineer, she became an authority on (and populist for) the Julian Alps and was instrumental in the establishment of the Triglav National Park. Copeland’s role as participant observer (and protagonist) enriches our understanding of the particularities of her time and place and illuminates some inter-war relationships within G/geography, inside and outside the academy, suggesting their relative autonomy in the production of geographical knowledge
Reconstructing the Equation of State of Tachyon
Recent progress in theoretical physics suggests that the dark energy in the
universe might be resulted from the rolling tachyon field of string theory.
Measurements to SNe Ia can be helpful to reconstruct the equation of state of
the rolling tachyon which is a possible candidate of dark energy. We present a
numerical analysis for the evolution of the equation of state of the rolling
tachyon and derive the reconstruction equations for the equation of state as
well as the potential.Comment: 6 pages, 3 figures, to appear Phys. Rev.
Growth of Inflaton Perturbations and the Post-Inflation Era in Supersymmetric Hybrid Inflation Models
It has been shown that hybrid inflation may end with the formation of
non-topological solitons of inflaton field. As a first step towards a fully
realistic picture of the post-inflation era and reheating in supersymmetric
hybrid inflation models, we study the classical scalar field equations of a
supersymmetric hybrid inflation model using a semi-analytical ansatz for the
spatial dependence of the fields. Using the minimal D-term inflation model as
an example, the inflaton field is evolved using the full 1-loop effective
potential from the slow-rolling era to the U(1)_{FI} symmetry-breaking phase
transition. Spatial perturbations of the inflaton corresponding to quantum
fluctuations are introduced for the case where there is spatially coherent
U(1)_{FI} symmetry breaking. The maximal growth of the dominant perturbation is
found to depend only on the ratio of superpotential coupling \lambda to the
gauge coupling g. The inflaton condensate fragments to non-topological solitons
for \lambda/g > 0.09. Possible consequences of non-topological soliton
formation in fully realistic SUSY hybrid inflation models are discussed.Comment: 27 pages LaTeX, 8 figures. Additional references and discussio
Anisotropic String Cosmology at Large Curvatures
We study the effect of the antisymmetric tensor field on the
large curvature phase of string cosmology. It is well-known that a
non-vanishing value of leads to an anisotropic expansion of the spatial
dimensions. Correspondingly, in the string phase of the model, including
corrections, we find anisotropic fixed points of the evolution,
which act as regularizing attractors of the lowest order solutions. The
attraction basin can also include isotropic initial conditions for the scale
factors. We present explicit examples at order for different values
of the number of spatial dimensions and for different ans\"{a}tze for .Comment: 16 pages, Latex, 2 figure
Curvaton reheating: an application to braneworld inflation
The curvaton was introduced recently as a distinct inflationary mechanism for
generating adiabatic density perturbations. Implicit in that scenario is that
the curvaton offers a new mechanism for reheating after inflation, as it is a
form of energy density not diluted by the inflationary expansion. We consider
curvaton reheating in the context of a braneworld inflation model, {\em steep
inflation}, which features a novel use of the braneworld to give a new
mechanism for ending inflation. The original steep inflation model featured
reheating by gravitational particle production, but the inefficiency of that
process brings observational difficulties. We demonstrate here that the
phenomenology of steep inflation is much improved by curvaton reheating.Comment: 8 pages RevTeX4 file with two figures incorporated. Improved
referencing, matches PRD accepted versio
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