2,119 research outputs found
Uranium triamidoamine chemistry
Uranium triamidoamine chemistry is reviewed.</p
Inflation during oscillations of the inflaton
Damour and Mukhanov have recently devised circumstances in which inflation
may continue during the oscillatory phase which ensues once the inflaton field
reaches the minimum of its potential. We confirm the existence of this
phenomenon by numerical integration. In such circumstances the quantification
of the amount of inflation requires particular care. We use a definition based
on the decrease of the comoving Hubble length, and show that Damour and
Mukhanov overestimated the amount of inflation occurring. We use the numerical
calculations to check the validity of analytic approximations.Comment: 5 pages RevTeX file with 5 figures incorporated using eps
Is there an imprint of Planck scale physics on inflationary cosmology?
We study the effects of the trans-Planckian dispersion relation on the
spectrum of the primordial density perturbations during inflation. In contrast
to the earlier analyses, we do not assume any specific form of the dispersion
relation and allow the initial state of the field to be arbitrary. We obtain
the spectrum of vacuum fluctuations of the quantum field by considering a
scalar field satisfying the linear wave equation with higher spatial derivative
terms propagating in the de Sitter space-time. We show that the power spectrum
does not strongly depend on the dispersion relation and that the form of the
dispersion relation does not play a significant role in obtaining the
corrections to the scale invariant spectrum. We also show that the signatures
of the deviations from the flat scale-invariant spectrum from the CMBR
observations due to quantum gravitational effects cannot be differentiated from
the standard inflationary scenario with an arbitrary initial state.Comment: 6 pages, uses RevTex4; References added; Final versio
Inflation in Gauged 6D Supergravity
In this note we demonstrate that chaotic inflation can naturally be realized
in the context of an anomaly free minimal gauged supergravity in D=6 which has
recently been the focus of some attention. This particular model has a unique
maximally symmetric ground state solution, which leaves
half of the six-dimensional supersymmetries unbroken. In this model, the
inflaton field originates from the complex scalar fields in the D=6
scalar hypermultiplet. The mass and the self couplings of the scalar field are
dictated by the D=6 Lagrangian. The scalar potential has an absolute munimum at
with no undetermined moduli fields. Imposing a mild bound on the
radius of enables us to obtain chaotic inflation. The low eenrgy
equations of motion are shown to be consistent for the range of scalar field
values relevant for inflation.Comment: one reference adde
The inflationary prediction for primordial non-gaussianity
We extend the \delta N formalism so that it gives all of the stochastic
properties of the primordial curvature perturbation \zeta if the initial field
perturbations are gaussian. The calculation requires only the knowledge of some
family of unperturbed universes. A formula is given for the normalisation \fnl
of the bispectrum of \zeta, which is the main signal of non-gaussianity.
Examples of the use of the formula are given, and its relation to cosmological
perturbation theory is explained.Comment: Revtex Latex file. 4 pages, no figures. v4: minor changes, typos
corrected, references added and updated. Version published in Physical Review
Letter
Processing Issues in Top-Down Approaches to Quantum Computer Development in Silicon
We describe critical processing issues in our development of single atom
devices for solid-state quantum information processing. Integration of single
31P atoms with control gates and single electron transistor (SET) readout
structures is addressed in a silicon-based approach. Results on electrical
activation of low energy (15 keV) P implants in silicon show a strong dose
effect on the electrical activation fractions. We identify dopant segregation
to the SiO2/Si interface during rapid thermal annealing as a dopant loss
channel and discuss measures of minimizing it. Silicon nanowire SET pairs with
nanowire width of 10 to 20 nm are formed by electron beam lithography in SOI.
We present first results from Coulomb blockade experiments and discuss issues
of control gate integration for sub-40nm gate pitch levels
Anisotropic evolution of 5D Friedmann-Robertson-Walker spacetime
We examine the time evolution of the five-dimensional Einstein field
equations subjected to a flat, anisotropic Robertson-Walker metric, where the
3D and higher-dimensional scale factors are allowed to dynamically evolve at
different rates. By adopting equations of state relating the 3D and
higher-dimensional pressures to the density, we obtain an exact expression
relating the higher-dimensional scale factor to a function of the 3D scale
factor. This relation allows us to write the Friedmann-Robertson-Walker field
equations exclusively in terms of the 3D scale factor, thus yielding a set of
4D effective Friedmann-Robertson-Walker field equations. We examine the
effective field equations in the general case and obtain an exact expression
relating a function of the 3D scale factor to the time. This expression
involves a hypergeometric function and cannot, in general, be inverted to yield
an analytical expression for the 3D scale factor as a function of time. When
the hypergeometric function is expanded for small and large arguments, we
obtain a generalized treatment of the dynamical compactification scenario of
Mohammedi [Phys.Rev.D 65, 104018 (2002)] and the 5D vacuum solution of Chodos
and Detweiler [Phys.Rev.D 21, 2167 (1980)], respectively. By expanding the
hypergeometric function near a branch point, we obtain the perturbative
solution for the 3D scale factor in the small time regime. This solution
exhibits accelerated expansion, which, remarkably, is independent of the value
of the 4D equation of state parameter w. This early-time epoch of accelerated
expansion arises naturally out of the anisotropic evolution of 5D spacetime
when the pressure in the extra dimension is negative and offers a possible
alternative to scalar field inflationary theory.Comment: 20 pages, 4 figures, paper format streamlined with main results
emphasized and details pushed to appendixes, current version matches that of
published versio
Sunyaev-Zel'dovich Predictions for the Planck Surveyor Satellite using the Hubble Volume Simulations
We use the billion-particle Hubble Volume simulations to make statistical
predictions for the distribution of galaxy clusters that will be observed by
the Planck Surveyor satellite through their effect on the cosmic microwave
background -- the Sunyaev-Zel'dovich effect. We utilize the lightcone datasets
for both critical density (tauCDM) and flat low-density (LambdaCDM)
cosmologies: a `full-sky' survey out to , two `octant' datasets out
to beyond and a 100 square degree dataset extending to . Making
simple, but robust, assumptions regarding both the thermodynamic state of the
gas and the detection of objects against an unresolved background, we present
the expected number of SZ sources as a function of redshift and angular size,
and also by flux (for both the thermal and kinetic effects) for 3 of the
relevant HFI frequency channels. We confirm the expectation that Planck will
detect around clusters, though the exact number is sensitive to
the choice of several parameters including the baryon fraction, and also to the
cluster density profile, so that either cosmology may predict more clusters. We
also find that the majority of detected sources should be at , and we
estimate that around one per cent of clusters will be spatially resolved by
Planck, though this has a large uncertainty.Comment: 11 pages LaTeX file with six figures incorporated, using mn.st
Power Spectrum in Krein Space Quantization
The power spectrum of scalar field and space-time metric perturbations
produced in the process of inflation of universe, have been presented in this
paper by an alternative approach to field quantization namely, Krein space
quantization [1,2]. Auxiliary negative norm states, the modes of which do not
interact with the physical world, have been utilized in this method. Presence
of negative norm states play the role of an automatic renormalization device
for the theory.Comment: 8 pages, appear in Int. J. Theor. Phy
Bayesian analysis of Friedmannless cosmologies
Assuming only a homogeneous and isotropic universe and using both the 'Gold'
Supernova Type Ia sample of Riess et al. and the results from the Supernova
Legacy Survey, we calculate the Bayesian evidence of a range of different
parameterizations of the deceleration parameter. We consider both spatially
flat and curved models. Our results show that although there is strong evidence
in the data for an accelerating universe, there is little evidence that the
deceleration parameter varies with redshift.Comment: 7 pages, 3 figure
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