42 research outputs found
Cold + Hot Dark Matter and the Cosmic Microwave Background
We examine the cosmic microwave background power spectrum for adiabatic
models with a massive neutrino component. We present the results of a detailed
numerical evolution of cold + hot dark matter (CHDM) models and compare with
the standard cold dark matter (CDM) spectrum. The difference is of order
for for currently popular CHDM models. With
semi-analytic approximations, we also discuss the relevant physics involved.
Finally we remark on the ability of future experiments to differentiate between
these models. An all-sky experiment with a beam size smaller than 30 arcminutes
can distinguish between CHDM and CDM if other cosmological parameters are
known. Even allowing other parameters to vary, it may be possible to
distinguish CDM from CHDM.Comment: Compressed uuencoded postscript, 26 pages including figures. Color
version available at http://www-astro-theory.fnal.gov
Comment on "Dispersion velocity of galactic dark matter particles"
A Comment on the Letter by R. Cowsiki Charu Ratnam, and P. Bhattacharjee, Phys. Rev. Lett. 76, 3886 (1996). The authors of the Letter offer a Reply
Solar Neutrino Data, Solar Model Uncertainties and Neutrino Oscillations
We incorporate all existing solar neutrino flux measurements and take solar
model flux uncertainties into account in deriving global fits to parameter
space for the MSW and vacuum solutions of the solar neutrino problem.Comment: 10 pages, latex, 3 figures (not included
Monopole annihilation at the electroweak scale---Not!
We examine the issue of monopole annihilation at the electroweak scale
induced by flux tube confinement, concentrating first on the simplest
possibility---one which requires no new physics beyond the standard model.
Monopoles existing at the time of the electroweak phase transition may trigger
condensation which can confine magnetic flux into flux tubes. However we
show on very general grounds, using several independent estimates, that such a
mechanism is impotent. We then present several general dynamical arguments
constraining the possibility of monopole annihilation through any confining
phase near the electroweak scale.Comment: 15 p
Additional Ultracool White Dwarfs Found in the Sloan Digital Sky Survey
We identify seven new ultracool white dwarfs discovered in the Sloan Digital
Sky Survey (SDSS). The SDSS photometry, spectra, and proper motions are
presented, and additional BVRI data are given for these and other previously
discovered ultracool white dwarfs. The observed colors span a remarkably wide
range, qualitatively similar to colors predicted by models for very cool white
dwarfs. One of the new stars (SDSS J1251+44) exhibits strong collision-induced
absorption (CIA) in its spectra, while the spectra and colors of the other six
are consistent with mild CIA. Another of the new discoveries (SDSS J2239+00A)
is part of a binary system -- its companion is also a cool white dwarf, and
other data indicate that the companion exhibits an infrared flux deficiency,
making this the first binary system composed of two CIA white dwarfs. A third
discovery (SDSS J0310-00) has weak Balmer emission lines. The proper motions of
all seven stars are consistent with membership in the disk or thick disk.Comment: Accepted for Astrophysical Journal. 16 pages (includes 3 figures