1,638 research outputs found
Trans-Planckian signals from the breaking of local Lorentz invariance
This article examines how a breakdown of a locally Lorentz invariant,
point-like description of nature at tiny space-time intervals would translate
into a distinctive set of signals in the primordial power spectrum generated by
inflation. We examine the leading irrelevant operators that are consistent with
the spatial translations and rotations of a preferred, isotropically expanding,
background. A few of the resulting corrections to the primordial power spectrum
do not have the usual oscillatory factor, which is sometimes taken to be
characteristic of a "trans-Planckian" signal. Perhaps more interestingly, one
of these leading irrelevant operators exactly reproduces a correction to the
power spectrum that occurs in effective descriptions of the state of the field
responsible for inflation.Comment: 11 pages, no figures, uses ReVTe
Possible Constraints on the Duration of Inflationary Expansion from Quantum Stress Tensor Fluctuations
We discuss the effect of quantum stress tensor fluctuations in deSitter
spacetime upon the expansion of a congruence of timelike geodesics. We treat a
model in which the expansion fluctuations begin on a given hypersurface in
deSitter spacetime, and find that this effect tends to grow, in contrast to the
situation in flat spacetime. This growth potentially leads to observable
consequences in inflationary cosmology in the form of density perturbations
which depend upon the duration of the inflationary period. In the context of
our model, the effect may be used to place upper bounds on this duration.Comment: 21 pages, no figures; Sect. IV rewritten and expanded, several
comments and references adde
Are stealth scalar fields stable?
Non-gravitating (stealth) scalar fields associated with Minkowski space in
scalar-tensor gravity are examined. Analytical solutions for both non-minimally
coupled scalar field theory and for Brans-Dicke gravity are studied and their
stability with respect to tensor perturbations is assessed using a covariant
and gauge-invariant formalism developed for alternative gravity. For
Brans-Dicke solutions, the stability with respect to homogeneous perturbations
is also studied. There are regions of parameter space corresponding to
stability and other regions corresponding to instability.Comment: 10 pages, 1 table, no figures, to appear in Phys. Rev,
Can the Gravitational Wave Background from Inflation be Detected Locally?
The Cosmic Background Explorer (COBE) detection of microwave background
anisotropies may contain a component due to gravitational waves generated by
inflation. It is shown that the gravitational waves from inflation might be
seen using `beam-in-space' detectors, but not the Laser Interferometer Gravity
Wave Observatory (LIGO). The central conclusion, dependent only on weak
assumptions regarding the physics of inflation, is a surprising one. The larger
the component of the COBE signal due to gravitational waves, the {\em smaller}
the expected local gravitational wave signal.Comment: 8 pages, standard LaTeX (no figures), SUSSEX-AST 93/7-
Black holes and gravitational waves in string cosmology
Pre--big bang models of inflation based on string cosmology produce a
stochastic gravitational wave background whose spectrum grows with decreasing
wavelength, and which may be detectable using interferometers such as LIGO. We
point out that the gravitational wave spectrum is closely tied to the density
perturbation spectrum, and that the condition for producing observable
gravitational waves is very similar to that for producing an observable density
of primordial black holes. Detection of both would provide strong support to
the string cosmology scenario.Comment: 6 pages RevTeX fil
The dearth of halo dwarf galaxies: is there power on short scales?
N-body simulations of structure formation with scale-invariant primordial
perturbations show significantly more virialized objects of dwarf-galaxy mass
in a typical galactic halo than are observed around the Milky Way. We show that
the dearth of observed dwarf galaxies could be explained by a dramatic downturn
in the power spectrum at small distance scales. This suppression of small-scale
power might also help mitigate the disagreement between cuspy simulated halos
and smooth observed halos, while remaining consistent with Lyman-alpha-forest
constraints on small-scale power. Such a spectrum could arise in inflationary
models with broken scale invariance.Comment: 5 pages LaTeX, 3 figure
How long before the end of inflation were observable perturbations produced?
We reconsider the issue of the number of e-foldings before the end of
inflation at which observable perturbations were generated. We determine a
plausible upper limit on that number for the standard cosmology which is around
60, with the expectation that the actual value will be up to 10 below this. We
also note a special property of the model which reduces the
uncertainties in that case and favours a higher value, giving a fairly definite
prediction of 64 e-foldings for that model. We note an extreme (and highly
implausible) situation where the number of e-foldings can be even higher,
possibly up to 100, and discuss the shortcomings of quantifying inflation by
e-foldings rather than by the change in . Finally, we discuss the impact of
non-standard evolution between the end of inflation and the present, showing
that again the expected number of e-foldings can be modified, and in some cases
significantly increased.Comment: 7 pages RevTeX4 file with one figure incorporated. Minor updates to
match version accepted by Physical Review
On Metric Preheating
We consider the generation of super-horizon metric fluctuations during an
epoch of preheating in the presence of a scalar field \chi quadratically
coupled to the inflaton. We find that the requirement of efficient broad
resonance is concomitant with a severe damping of super-horizon \delta\chi
quantum fluctuations during inflation. Employing perturbation theory with
backreaction included as spatial averages to second order in the scalar fields
and in the metric, we argue that the usual inflationary prediction for metric
perturbations on scales relevant for structure formation is not strongly
modified.Comment: 5 latex pages, 1 postscript figure included, uses revtex.sty in two
column format and epsf.sty, some typos corrected and references added. Links
and further material at http://astro.uchicago.edu/home/web/sigl/r4.htm
Non-Singular Stationary Global Strings
A field-theoretical model for non-singular global cosmic strings is
presented. The model is a non-linear sigma model with a potential term for a
self-gravitating complex scalar field. Non-singular stationary solutions with
angular momentum and possibly linear momentum are obtained by assuming an
oscillatory dependence of the scalar field on t, phi and z. This dependence has
an effect similar to gauging the global U(1) symmetry of the model, which is
actually a Kaluza-Klein reduction from four to three spacetime dimensions. The
method of analysis can be regarded as an extension of the
gravito-electromagnetism formalism beyond the weak field limit. Some D=3
self-dual solutions are also discussed.Comment: 20 pages Latex, 12 PS figures included. Minor corrections. Version to
appear in Phys.Rev.
Dark Matter and Dark Energy via Non-Perturbative (Flavour) Vacua
A non-perturbative field theoretical approach to flavour physics
(Blasone-Vitiello formalism) has been shown to imply a highly non-trivial
vacuum state. In a previous work, we implemented the approach on a simple
supersymmetric model (free Wess-Zumino), with flavour mixing, which was
regarded as a model for free neutrinos and sneutrinos. The resulting effective
vacuum (called "flavour vacuum") was found to be characterized by a strong SUSY
breaking. In this paper we explore the phenomenology of the model and we argue
that the flavour vacuum is a consistent source for both Dark Energy (thanks to
the bosonic sector of the model) and Dark Matter (via the fermionic one). Quite
remarkably, besides the parameters connected with neutrino physics, in this
model no other parameters have been introduced, possibly leading to a
predictive theory of Dark Energy/Matter. Despite its oversimplification, such a
toy model already seems capable to shed some light on the observed energy
hierarchy between neutrino physics, Dark Energy and Dark Matter. Furthermore,
we move a step forth in the construction of a more realistic theory, by
presenting a novel approach for calculating relevant quantities and hence
extending some results to interactive theories, in a completely
non-perturbative way.Comment: 14 pages, 2 figure
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