206 research outputs found
Tests of a multichannel photometer based on silicon diode detectors
A breadboard photometer was constructed that demonstrates a precision of 2 times 10 to the 4th power in the laboratory and scintillation-limited performance when used with an 0.5 m aperture telescope. Because the detectors and preamps are not cooled, only stars with m sub v approx. less than 4 are bright enough to allow the photometer to attain a precision of 1 times 10 to the 3rd power for three minute observations with an 0.5 m aperature telescope. Cooling the telescope should allow much fainter stars to be observed. Increasing the aperture of the telescope will allow higher precision and the observation of fainter stars
The Energy Spectra and Relative Abundances of Electrons and Positrons in the Galactic Cosmic Radiation
Observations of cosmic-ray electrons and positrons have been made with a new
balloon-borne detector, HEAT (the "High-Energy Antimatter Telescope"), first
flown in 1994 May from Fort Sumner, NM. We describe the instrumental approach
and the data analysis procedures, and we present results from this flight. The
measurement has provided a new determination of the individual energy spectra
of electrons and positrons from 5 GeV to about 50 GeV, and of the combined
"all-electron" intensity (e+ + e-) up to about 100 GeV. The single power-law
spectral indices for electrons and positrons are alpha = 3.09 +/- 0.08 and 3.3
+/- 0.2, respectively. We find that a contribution from primary sources to the
positron intensity in this energy region, if it exists, must be quite small.Comment: latex2e file, 30 pages, 15 figures, aas2pp4.sty and epsf.tex needed.
To appear in May 10, 1998 issue of Ap.
A Measurement of the Angular Power Spectrum of the CMB from l = 100 to 400
We report on a measurement of the angular spectrum of the CMB between
and made at 144 GHz from Cerro Toco in the
Chilean altiplano. When the new data are combined with previous data at 30 and
40 GHz, taken with the same instrument observing the same section of sky, we
find: 1) a rise in the angular spectrum to a maximum with K at and a fall at , thereby localizing the peak
near ; and 2) that the anisotropy at has the
spectrum of the CMB.Comment: 4 pages, 2 figures. Revised version; includes Ned Wright's postscript
fix. Accepted by ApJL. Website at http://physics.princeton.edu/~cmb
WMAP constraint on the P-term inflationary model
In light of WMAP results, we examine the observational constraint on the
P-term inflation. With the tunable parameter , P-term inflation contains
richer physics than D-term and F-term inflationary models. We find the
logarithmic derivative spectral index with on large scales and on
small scales in agreement to observation. We obtained a reasonable range for
the choice of the gauge coupling constant in order to meet the requirements
of WMAP observation and the expected number of the e-foldings. Although tuning
and we can have larger values for the logarithmic derivative of the
spectral index, it is not possible to satisfy all observational requirements
for both, the spectral index and its logarithmic derivative at the same time.Comment: 6 pages, double column, 13 figures included. Version appearing in the
Physical Review
The Robustness of Quintessence
Recent observations seem to suggest that our Universe is accelerating
implying that it is dominated by a fluid whose equation of state is negative.
Quintessence is a possible explanation. In particular, the concept of tracking
solutions permits to adress the fine-tuning and coincidence problems. We study
this proposal in the simplest case of an inverse power potential and
investigate its robustness to corrections. We show that quintessence is not
affected by the one-loop quantum corrections. In the supersymmetric case where
the quintessential potential is motivated by non-perturbative effects in gauge
theories, we consider the curvature effects and the K\"ahler corrections. We
find that the curvature effects are negligible while the K\"ahler corrections
modify the early evolution of the quintessence field. Finally we study the
supergravity corrections and show that they must be taken into account as
at small red-shifts. We discuss simple supergravity
models exhibiting the quintessential behaviour. In particular, we propose a
model where the scalar potential is given by . We argue that the fine-tuning problem
can be overcome if . This model leads to
for which is in good agreement with the presently
available data.Comment: 16 pages, 7 figure
Cosmic microwave background anisotropy power spectrum statistics for high precision cosmology
As the era of high precision cosmology approaches, the empirically determined
power spectrum of the microwave background anisotropy, , will provide a
crucial test for cosmological theories. We present a unified semi-analytic
framework for the study of the statistical properties of the coefficients
computed from the results of balloon, ground based, and satellite experiments.
An illustrative application shows that commonly used approximations {\it bias}
the estimation of the baryon parameter at the 1% level even for a
satellite capturing as much as % of the sky.Comment: 4 pages, 3 figures. Also available at
http://www.tac.dk/~wandelt/downloads.htm
Energy Spectra, Altitude Profiles and Charge Ratios of Atmospheric Muons
We present a new measurement of air shower muons made during atmospheric
ascent of the High Energy Antimatter Telescope balloon experiment. The muon
charge ratio mu+ / mu- is presented as a function of atmospheric depth in the
momentum interval 0.3-0.9 GeV/c. The differential mu- momentum spectra are
presented between 0.3 and about 50 GeV/c at atmospheric depths between 13 and
960 g/cm^2. We compare our measurements with other recent data and with Monte
Carlo calculations of the same type as those used in predicting atmospheric
neutrino fluxes. We find that our measured mu- fluxes are smaller than the
predictions by as much as 70% at shallow atmospheric depths, by about 20% at
the depth of shower maximum, and are in good agreement with the predictions at
greater depths. We explore the consequences of this on the question of
atmospheric neutrino production.Comment: 11 pages, 8 figures, to appear in Phys. Rev. D (2000
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