1,535,493 research outputs found
Daemons and DAMA: Their Celestial-Mechanics Interrelations
The assumption of the capture by the Solar System of the electrically charged
Planckian DM objects (daemons) from the galactic disk is confirmed not only by
the St.Petersburg (SPb) experiments detecting particles with V<30 km/s. Here
the daemon approach is analyzed considering the positive model independent
result of the DAMA/NaI experiment. We explain the maximum in DAMA signals
observed in the May-June period to be associated with the formation behind the
Sun of a trail of daemons that the Sun captures into elongated orbits as it
moves to the apex. The range of significant 2-6-keV DAMA signals fits well the
iodine nuclei elastically knocked out of the NaI(Tl) scintillator by particles
falling on the Earth with V=30-50 km/s from strongly elongated heliocentric
orbits. The half-year periodicity of the slower daemons observed in SPb
originates from the transfer of particles that are deflected through ~90 deg
into near-Earth orbits each time the particles cross the outer reaches of the
Sun which had captured them. Their multi-loop (cross-like) trajectories
traverse many times the Earth's orbit in March and September, which increases
the probability for the particles to enter near-Earth orbits during this time.
Corroboration of celestial mechanics calculations with observations yields
~1e-19 cm2 for the cross section of daemon interaction with the solar matter.Comment: 12 pages including 5 figure
Characterization of a cryogenic beam source for atoms and molecules
We present a combined experimental and theoretical study of beam formation
from a cryogenic buffer gas cell. Atoms and molecules are loaded into the cell
by laser ablation of a target, and are cooled and swept out of the cell by a
flow of cold helium. We study the thermalization and flow dynamics inside the
cell and measure how the speed, temperature, divergence and extraction
efficiency of the beam are influenced by the helium flow. We use a finite
element model to simulate the flow dynamics and use the predictions of this
model to interpret our experimental results.Comment: 10 pages, 14 figure
How BAO measurements can fail to detect quintessence
We model the nonlinear growth of cosmic structure in different dark energy
models, using large volume N-body simulations. We consider a range of
quintessence models which feature both rapidly and slowly varying dark energy
equations of state, and compare the growth of structure to that in a universe
with a cosmological constant. The adoption of a quintessence model changes the
expansion history of the universe, the form of the linear theory power spectrum
and can alter key observables, such as the horizon scale and the distance to
last scattering. The difference in structure formation can be explained to
first order by the difference in growth factor at a given epoch; this scaling
also accounts for the nonlinear growth at the 15% level. We find that
quintessence models which feature late , rapid transitions towards
in the equation of state, can have identical baryonic acoustic
oscillation (BAO) peak positions to those in CDM, despite being very
different from CDM both today and at high redshifts .
We find that a second class of models which feature non-negligible amounts of
dark energy at early times cannot be distinguished from CDM using
measurements of the mass function or the BAO. These results highlight the need
to accurately model quintessence dark energy in N-body simulations when testing
cosmological probes of dynamical dark energy.Comment: 10 pages, 7 figures, to appear in the Invisible Univers International
Conference AIP proceedings serie
Soft X-ray Emission from the Spiral Galaxy NGC 1313
The nearby barred spiral galaxy NGC 1313 has been observed with the PSPC
instr- ument on board the ROSAT X-ray satellite. Ten individual sources are
found. Three sources (X-1, X-2 and X-3 [SN~1978K]) are very bright (~10^40
erg/s) and are unusual in that analogous objects do not exist in our Galaxy. We
present an X-ray image of NGC~1313 and \xray spectra for the three bright
sources. The emission from the nuclear region (R ~< 2 kpc) is dominated by
source X-1, which is located ~1 kpc north of the photometric (and dynamical)
center of NGC~1313. Optical, far-infrared and radio images do not indicate the
presence of an active galactic nucleus at that position; however, the compact
nature of the \xray source (X-1) suggests that it is an accretion-powered
object with central mass M >~ 10^3 Msun. Additional emission (L_X ~ 10^39
erg/s) in the nuclear region extends out to ~2.6 kpc and roughly follows the
spiral arms. This emission is from 4 sources with luminosity of several x 10^38
erg/s, two of which are consistent with emission from population I sources
(e.g., supernova remnants, and hot interstellar gas which has been heated by
supernova remnants). The other two sources could be emission from population II
sources (e.g., low-mass \xray binaries). The bright sources X-2 and SN~1978K
are positioned in the southern disk of NGC~1313. X-2 is variable and has no
optical counterpart brighter than 20.8 mag (V-band). It is likely that it is an
accretion-powered object in NGC~1313. The type-II supernova SN~1978K (Ryder
\etal 1993) has become extra- ordinarily luminous in X-rays 13 years
after optical maximum.Comment: to appear in 10 Jun 1995 ApJ, 30 pgs uuencoded compressed postscript,
25 pgs of figures available upon request from colbert, whole preprint
available upon request from Sandy Shrader ([email protected]),
hopefully fixed unknown problem with postscript fil
- …