683 research outputs found
Duality Invariance of Cosmological Perturbation Spectra
I show that cosmological perturbation spectra produced from quantum
fluctuations in massless or self-interacting scalar fields during an
inflationary era remain invariant under a two parameter family of
transformations of the homogeneous background fields. This relates slow-roll
inflation models to solutions which may be far from the usual slow-roll limit.
For example, a scale-invariant spectrum of perturbations in a minimally
coupled, massless field can be produced by an exponential expansion with
, or by a collapsing universe with .Comment: 5 pages, Latex with Revtex. Hamiltonian formulation added and
discussion expanded. Version to appear in Phys Rev
Profile Characteristics of Cut Tooth Surfaces Developed by Rotating Instruments
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68018/2/10.1177_00220345570360062301.pd
CBR Anisotropy and the Running of the Scalar Spectral Index
Accurate () predictions for the anisotropy of the Cosmic
Background Radiation (CBR) are essential for using future high-resolution
() CBR maps to test cosmological models. In many inflationary
models the variation (``running'') of the spectral index of the spectrum of
density perturbations is a significant effect and leads to changes of around
1\% to 10\% in the CBR power spectrum. We propose a general method for taking
running into account which uses the derivative of the spectral index (). Conversely, high-resolution CBR maps may be able to determine ,
giving important information about the inflationary potential.Comment: Discussion of calculation clarified; error corrected which reduces
estimated effect for chaotic inflatio
Tunneling and propagation of vacuum bubbles on dynamical backgrounds
In the context of bubble universes produced by a first-order phase transition
with large nucleation rates compared to the inverse dynamical time scale of the
parent bubble, we extend the usual analysis to non-vacuum backgrounds. In
particular, we provide semi-analytic and numerical results for the modified
nucleation rate in FLRW backgrounds, as well as a parameter study of bubble
walls propagating into inhomogeneous (LTB) or FLRW spacetimes, both in the
thin-wall approximation. We show that in our model, matter in the background
often prevents bubbles from successful expansion and forces them to collapse.
For cases where they do expand, we give arguments why the effects on the
interior spacetime are small for a wide range of reasonable parameters and
discuss the limitations of the employed approximations.Comment: 29 pages, 8 figures, typos corrected, matches published versio
Localisation of Fermions to brane: Codimension
We investigate dimensional fermionic models in which the system in
codimension- supports a topologically stable solution, and in which the
fermion may be localised to the brane, with power law in 'instanton'
backgrounds and exponentially in 'soliton' backgrounds. When the fermions are
isoscalars, the mechanism fails, while for isospinor fermions it is successful.
As backgrounds we consider instantons of Yang--Mills and sigma models in even
codimensions, solitons of sigma models in odd codimensions, as well as solitons
of Higgs and Goldstone models in all codimensions.Comment: 20 pages latex; expande
Developmental contexts and features of elite academy football players: Coach and player perspectives
Player profiling can reap many benefits; through reflective coach-athlete dialogue that produces a profile the athlete has a raised awareness of their own development, while the coach has an opportunity to understand the athlete's viewpoint. In this study, we explored how coaches and players perceived the development features of an elite academy footballer and the contexts in which these features are revealed, in order to develop a player profile to be used for mentoring players. Using a Delphi polling technique, coaches and players experienced a number of 'rounds' of expressing their opinions regarding player development contexts and features, ultimately reduced into a consensus. Players and coaches had differing priorities on the key contexts of player development. These contexts, when they reflect the consensus between players and coaches were heavily dominated by ability within the game and training. Personal, social, school, and lifestyle contexts featured less prominently. Although 'discipline' was frequently mentioned as an important player development feature, coaches and players disagreed on the importance of 'training'
The Detectability of Departures from the Inflationary Consistency Equation
We study the detectability, given CMB polarization maps, of departures from
the inflationary consistency equation, r \equiv T/S \simeq -5 n_T, where T and
S are the tensor and scalar contributions to the quadrupole variance,
respectively. The consistency equation holds if inflation is driven by a
slowly-rolling scalar field. Departures can be caused by: 1) higher-order terms
in the expansion in slow-roll parameters, 2) quantum loop corrections or 3)
multiple fields. Higher-order corrections in the first two slow-roll parameters
are undetectably small. Loop corrections are detectable if they are nearly
maximal and r \ga 0.1. Large departures (|\Delta n_T| \ga 0.1) can be seen if r
\ga 0.001. High angular resolution can be important for detecting non-zero
r+5n_T, even when not important for detecting non-zero r.Comment: 7 pages, 4 figures, submitted to PR
Gravitational waves in non-singular string cosmologies
We study the evolution of tensor metric fluctuations in a class of
non-singular models based on the string effective action, by including in the
perturbation equation the higher-derivative and loop corrections needed to
regularise the background solutions. We discuss the effects of such
higher-order corrections on the final graviton spectrum, and we compare the
results of analytical and numerical computations.Comment: 24 pages, 7 figure
Collider signals from slow decays in supersymmetric models with an intermediate-scale solution to the mu problem
The problem of the origin of the mu parameter in the Minimal Supersymmetric
Standard Model can be solved by introducing singlet supermultiplets with
non-renormalizable couplings to the ordinary Higgs supermultiplets. The
Peccei-Quinn symmetry is broken at a scale which is the geometric mean between
the weak scale and the Planck scale, yielding a mu term of the right order of
magnitude and an invisible axion. These models also predict one or more singlet
fermions which have electroweak-scale masses and suppressed couplings to MSSM
states. I consider the case that such a singlet fermion, containing the axino
as an admixture, is the lightest supersymmetric particle. I work out the
relevant couplings in several of the simplest models of this type, and compute
the partial decay widths of the next-to-lightest supersymmetric particle
involving leptons or jets. Although these decays will have an average proper
decay length which is most likely much larger than a typical collider detector,
they can occasionally occur within the detector, providing a striking signal.
With a large sample of supersymmetric events, there will be an opportunity to
observe these decays, and so gain direct information about physics at very high
energy scales.Comment: 24 pages, LaTeX, 4 figure
Dynamics of tachyonic preheating after hybrid inflation
We study the instability of a scalar field at the end of hybrid inflation,
using both analytical techniques and numerical simulations. We improve previous
studies by taking the inflaton field fully into account, and show that the
range of unstable modes depends sensitively on the velocity of the inflaton
field, and thereby on the Hubble rate, at the end of inflation. If topological
defects are formed, their number density is determined by the shortest unstable
wavelength. Finally, we show that the oscillations of the inflaton field
amplify the inhomogeneities in the energy density, leading to local symmetry
restoration and faster thermalization. We believe this explains why tachyonic
preheating is so effective in transferring energy away from the inflaton zero
mode.Comment: 12 pages, 10 figures, REVTeX. Minor changes, some references added.
To appear in PR
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