1,750 research outputs found
Simple route to non-Gaussianity in inflation
We present a simple way to calculate non-Gaussianity in inflation using fully
non-linear equations on long wavelengths with stochastic sources to take into
account the short-wavelength quantum fluctuations. Our formalism includes both
scalar metric and matter perturbations, combining them into variables which are
invariant under changes of time slicing in the long-wavelength limit. We
illustrate this method with a perturbative calculation in the single-field
slow-roll case. We also introduce a convenient choice of variables to
graphically present the full momentum dependence of the three-point correlator.Comment: 6 pages, 2 figures. v2: Updated formalism to version described in
astro-ph/0504508, leading to dropping of one unnecessary approximation. Final
results not significantly changed. Extended discussion of calculation and
added graphical presentation of full momentum dependence. References
corrected and added. v3: Final version, only small textual change
Quantitative bispectra from multifield inflation
After simplifying and improving the non-Gaussian formalism we developed in
previous work, we derive a quantitative expression for the three-point
correlator (bispectrum) of the curvature perturbation in general multiple-field
inflation models. Our result describes the evolution of non-Gaussianity on
superhorizon scales caused by the nonlinear influence of isocurvature
perturbations on the adiabatic perturbation during inflation. We then study a
simple quadratic two-field potential and find that when slow roll breaks down
and the field trajectory changes direction in field space, the non-Gaussianity
can become large. However, for the simple models studied to date, the magnitude
of this non-Gaussianity decays away after the isocurvature mode is converted
into the adiabatic mode.Comment: 7 pages, 1 figure. v4: Added remarks on momentum dependence, minor
textual changes, matches published versio
Cosmic Microwave Background Radiation Anisotropy Induced by Cosmic Strings
We report on a current investigation of the anisotropy pattern induced by
cosmic strings on the cosmic microwave background radiation (MBR). We have
numerically evolved a network of cosmic strings from a redshift of to
the present and calculated the anisotropies which they induce. Based on a
limited number of realizations, we have compared the results of our simulations
with the observations of the COBE-DMR experiment. We have obtained a
preliminary estimate of the string mass-per-unit-length in the cosmic
string scenario.Comment: 8 pages of TeX - [Color] Postscript available by anonymous ftp at
ftp://fnas08.fnal.gov:/pub/Publications/Conf-94-197-A, FERMILAB-Conf-94/197-
The contemporary landscape of occupational bladder cancer within the United Kingdom: a meta-analysis of risks over the last 80 years.
OBJECTIVE: To profile the contemporary risks of occupational bladder in the UK, as this is a common malignancy that arises through occupational carcinogen exposure. MATERIALS AND METHODS: A systematic review using PubMed, Medline, Embase and Web of Science was performed in March 2016. We selected reports of British workers in which bladder cancer or occupation were the main focus, with sufficient cases or with confidence intervals (CIs). We used the most recent data in populations with multiple reports. We combined odds ratios and risk ratios (RRs) to provide pooled RRs of incidence and disease-specific mortality (DSM). We tested for heterogeneity and publication bias. We extracted bladder cancer mortality from Office of National Statistics death certificates. We compered across regions and with our meta-analysis. RESULTS: We identified 25 articles reporting risks in 702 941 persons. Meta-analysis revealed significantly increased incidence for 12/37 and DSM for five of 37 occupational classes. Three classes had reduced bladder cancer risks. The greatest risk of bladder cancer incidence occurred in chemical process (RR 1.87, 95% CI 1.50-2.34), rubber (RR 1.82, 95% CI 1.4-2.38), and dye workers (RR 1.8, 95% CI 1.07-3.04). The greatest risk of DSM occurred in electrical (RR 1.49, 95% CI 1.19-1.87) and chemical process workers (RR 1.35, 95% CI 1.09-1.68). Bladder cancer mortality was higher in the North of England, probably reflecting smoking patterns and certain industries. Limitations include the lack of sufficient robust data, missing occupational tasks, and no adjustment for smoking. CONCLUSION: Occupational bladder cancer occurs in many workplaces and the risks for incidence and DSM may differ. Regional differences may reflect changes in industry and smoking patterns. Relatively little is known about bladder cancer within British industry, suggesting official data underestimate the disease
Universal Non-Gaussian Initial Conditions for N-body Simulations
In this paper we present the implementation of an efficient formalism for the
generation of arbitrary non-Gaussian initial conditions for use in N-body
simulations. The methodology involves the use of a separable modal approach for
decomposing a primordial bispectrum or trispectrum. This approach allows for
the far more efficient generation of the non-Gaussian initial conditions
already described in the literature, as well as the generation for the first
time of non-separable bispectra and the special class of diagonal-free
trispectra. The modal approach also allows for the reconstruction of the
spectra from given realisations, a fact which is exploited to provide an
accurate consistency check of the simulations.Comment: 7 pages, 3 figure
Non-linear inflationary perturbations
We present a method by which cosmological perturbations can be quantitatively
studied in single and multi-field inflationary models beyond linear
perturbation theory. A non-linear generalization of the gauge-invariant
Sasaki-Mukhanov variables is used in a long-wavelength approximation. These
generalized variables remain invariant under time slicing changes on long
wavelengths. The equations they obey are relatively simple and can be
formulated for a number of time slicing choices. Initial conditions are set
after horizon crossing and the subsequent evolution is fully non-linear. We
briefly discuss how these methods can be implemented numerically in the study
of non-Gaussian signatures from specific inflationary models.Comment: 10 pages, replaced to match JCAP versio
Coupled currents in cosmic strings
We first examine the microstructure of a cosmic string endowed with two
simple Abelian currents. This microstructure depends on two state parameters.
We then provide the macroscopic description of such a string and show that it
depends on an additional Lorentz-invariant state parameter that relates the two
currents. We find that in most of the parameter space, the two-current string
is essentially equivalent to the single current-carrying string, i.e., only one
field condenses onto the defect. In the regions where two currents are present,
we find that as far as stability is concerned, one can approximate the dynamics
with good accuracy using an analytic model based on either a logarithmic (on
the electric side, i.e., for timelike currents) or a rational (on the magnetic
side, i.e., for spacelike currents) worldsheet Lagrangian.Comment: 25 pages, 9 figure
Waveforms for Gravitational Radiation from Cosmic String Loops
We obtain general formulae for the plus- and cross- polarized waveforms of
gravitational radiation emitted by a cosmic string loop in transverse,
traceless (synchronous, harmonic) gauge. These equations are then specialized
to the case of piecewise linear loops, and it is shown that the general
waveform for such a loop is a piecewise linear function. We give several simple
examples of the waveforms from such loops. We also discuss the relation between
the gravitational radiation by a smooth loop and by a piecewise linear
approximation to it.Comment: 16 pages, 6 figures, Revte
Analytic Results for the Gravitational Radiation from a Class of Cosmic String Loops
Cosmic string loops are defined by a pair of periodic functions and
, which trace out unit-length closed curves in three-dimensional
space. We consider a particular class of loops, for which lies along
a line and lies in the plane orthogonal to that line. For this class
of cosmic string loops one may give a simple analytic expression for the power
radiated in gravitational waves. We evaluate exactly in
closed form for several special cases: (1) a circle traversed
times; (2) a regular polygon with sides and interior vertex angle
; (3) an isosceles triangle with semi-angle .
We prove that case (1) with is the absolute minimum of within
our special class of loops, and identify all the stationary points of
in this class.Comment: 15 pages, RevTex 3.0, 7 figures available via anonymous ftp from
directory pub/pcasper at alpha1.csd.uwm.edu, WISC-MILW-94-TH-1
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