3,121 research outputs found
Cosmological Recombination of Lithium and its Effect on the Microwave Background Anisotropies
The cosmological recombination history of lithium, produced during Big--Bang
nucleosynthesis, is presented using updated chemistry and cosmological
parameters consistent with recent cosmic microwave background (CMB)
measurements. For the popular set of cosmological parameters, about a fifth of
the lithium ions recombine into neutral atoms by a redshift . The
neutral lithium atoms scatter resonantly the CMB at 6708 \AA and distort its
intensity and polarization anisotropies at observed wavelengths around m, as originally suggested by Loeb (2001). The modified anistropies
resulting from the lithium recombination history are calculated for a variety
of cosmological models and found to result primarily in a suppression of the
power spectrum amplitude. Significant modification of the power spectrum occurs
for models which assume a large primordial abundance of lithium. While
detection of the lithium signal might prove difficult, if offers the
possibility of inferring the lithium primordial abundance and is the only probe
proposed to date of the large-scale structure of the Universe for .Comment: 20 pages, 7 figure
Measuring the 3D Clustering of Undetected Galaxies Through Cross Correlation of their Cumulative Flux Fluctuations from Multiple Spectral Lines
We discuss a method for detecting the emission from high redshift galaxies by
cross correlating flux fluctuations from multiple spectral lines. If one can
fit and subtract away the continuum emission with a smooth function of
frequency, the remaining signal contains fluctuations of flux with frequency
and angle from line emitting galaxies. Over a particular small range of
observed frequencies, these fluctuations will originate from sources
corresponding to a series of different redshifts, one for each emission line.
It is possible to statistically isolate the fluctuations at a particular
redshift by cross correlating emission originating from the same redshift, but
in different emission lines. This technique will allow detection of clustering
fluctuations from the faintest galaxies which individually cannot be detected,
but which contribute substantially to the total signal due to their large
numbers. We describe these fluctuations quantitatively through the line cross
power spectrum. As an example of a particular application of this technique, we
calculate the signal-to-noise ratio for a measurement of the cross power
spectrum of the OI(63 micron) and OIII(52 micron) fine structure lines with the
proposed Space Infrared Telescope for Cosmology and Astrophysics. We find that
the cross power spectrum can be measured beyond a redshift of z=8. Such
observations could constrain the evolution of the metallicity, bias, and duty
cycle of faint galaxies at high redshifts and may also be sensitive to the
reionization history through its effect on the minimum mass of galaxies. As
another example, we consider the cross power spectrum of CO line emission
measured with a large ground based telescope like CCAT and 21-cm radiation
originating from hydrogen in galaxies after reionization with an interferometer
similar in scale to MWA, but optimized for post-reionization redshifts.Comment: 21 pages, 6 figures; Replaced with version accepted by JCAP; Added an
example of cross correlating CO line emission and 21cm line emission from
galaxies after reionizatio
A new, simple electrostatic-acoustic hybrid levitator
Battelle has developed a hybrid levitator by combining the known single-axis acoustic standing wave levitator with a coaxial DC electric field. The resulting Coulomb forces on the charged liquid or solid sample support its weight and, together with the acoustic force, center the sample. Liquid samples with volumes approximately less than 100 micro-liters are deployed from a syringe reservoir into the acoustic pressure node. The sample is charged using a miniature high voltage power supply (approximately less than 20 kV) connected to the syringe needle. As the electric field, generated by a second miniature power supply, is increased, the acoustic intensity is reduced. The combination of both fields allows stable levitation of samples larger than either single technique could position on the ground. Decreasing the acoustic intensity reduces acoustic convection and sample deformation. Neither the electrostatic nor the acoustic field requires sample position sensing or active control. The levitator, now used for static and dynamic fluid physics investigations on the ground, can be easily modified for space operations
Ethyl Orthocarbonate [Orthocarbonic acid, tetrahethyl ester]
A solution of sodium ethoxide is prepared under nitrogen from 70 g. (3.04 g. atoms) of sodium and 2 l. of absolute ethanol (Note 1) in a 3-l. three-necked flask which is equipped with mechanical stirrer, efficient reflux condenser, dropping funnel, and a thermometer which dips below the level of the liquid in the flask. Chloropicrin (100 g., 0.61 mole) (Note 2) is placed in the dropping funnel, and the stirred solution is heated to 58–60° with a water bath. The chloropicrin is added at a rate of 30–35 drops per minute until the reaction becomes self-sustaining (about 20 minutes), at which point the water bath is removed and the balance of the chloropicrin is added at a rate sufficient to maintain the temperature at 58–60° (Note 3). When the addition, which requires nearly 2 hours, is complete, the stirrer is stopped and the mixture is allowed to stand overnight
Measuring the Small-Scale Power Spectrum of Cosmic Density Fluctuations Through 21 cm Tomography Prior to the Epoch of Structure Formation
The thermal evolution of the cosmic gas decoupled from that of the cosmic
microwave background (CMB) at a redshift z~200. Afterwards and before the first
stars had formed, the cosmic neutral hydrogen absorbed the CMB flux at its
resonant 21cm spin-flip transition. We calculate the evolution of the spin
temperature for this transition and the resulting anisotropies that are
imprinted on the CMB sky due to linear density fluctuations during this epoch.
These anisotropies at an observed wavelength of 10.56[(1+z)/50] meters, contain
an amount of information that is orders of magnitude larger than any other
cosmological probe. Their detection, although challenging, could tightly
constrain any possible running of the spectral index from inflation (as
suggested by WMAP), small deviations from Gaussianity, or any significant
contribution from neutrinos or warm dark matter to the cosmic mass budget.Comment: 4 pages, 3 figures, accepted for publication in Physical Review
Letter
Observing GRBs with EXIST
We describe the Energetic X-ray Imaging Survey Telescope EXIST, designed to carry out a sensitive all-sky survey in the 10 keV – 600 keV band. The primary goal of EXIST is to find black holes in the local and distant universe. EXIST also traces cosmic star formation via gamma-ray bursts and gamma-ray lines from radioactive elements ejected by supernovae and novae
Decompositions of Bn and \u3a0n using symmetric chains
We review the Green/Kleitman/Leeb interpretation of de Bruijn\u2019s symmetric chain decomposition of Bn, and explain how it can be used to find a maximal collection of disjoint symmetric chains in the nonsymmetric lattice of partitions of a set
Cosmology with X-ray Cluster Baryons
X-ray cluster measurements interpreted with a universal baryon/gas mass
fraction can theoretically serve as a cosmological distance probe. We examine
issues of cosmological sensitivity for current (e.g. Chandra X-ray Observatory,
XMM-Newton) and next generation (e.g. Con-X, XEUS) observations, along with
systematic uncertainties and biases. To give competitive next generation
constraints on dark energy, we find that systematics will need to be controlled
to better than 1% and any evolution in f_gas (and other cluster gas properties)
must be calibrated so the residual uncertainty is weaker than (1+z)^{0.03}.Comment: 6 pages, 5 figures; v2: 13 pages, substantial elaboration and
reordering, matches JCAP versio
Coherent Neutrino Interactions in a Dense Medium
Motivated by the effect of matter on neutrino oscillations (the MSW effect)
we study in more detail the propagation of neutrinos in a dense medium. The
dispersion relation for massive neutrinos in a medium is known to have a
minimum at nonzero momentum p \sim (G_F\rho)/\sqrt{2}. We study in detail the
origin and consequences of this dispersion relation for both Dirac and Majorana
neutrinos both in a toy model with only neutral currents and a single neutrino
flavour and in a realistic "Standard Model" with two neutrino flavours. We find
that for a range of neutrino momenta near the minimum of the dispersion
relation, Dirac neutrinos are trapped by their coherent interactions with the
medium. This effect does not lead to the trapping of Majorana neutrinos.Comment: 28 pages, 6 figures, Latex; minor changes, one reference added;
version to appear in Phys. Rev.
- …