88 research outputs found
Cosmic microwave background and large scale structure limits on the interaction between dark matter and baryons
We study the effect on the cosmic microwave background (CMB) anisotropy and
large scale structure (LSS) power spectrum of a scattering interaction between
cold dark matter and baryons. This scattering alters the CMB anisotropy and LSS
spectrum through momentum transfer between the cold dark matter particles and
the baryons. We find that current CMB observations can put an upper limit on
the scattering cross section which is comparable with or slightly stronger than
previous disk heating constraints at masses greater than 1 GeV, and much
stronger at smaller masses. When large-scale structure constraints are added to
the CMB limits, our constraint is more stringent than this previous limit at
all masses. In particular, a dark matter-baryon scattering cross section
comparable to the ``Spergel-Steinhardt'' cross section is ruled out for dark
matter mass greater than 1 GeV.Comment: 8 pages, 2 figures, use RevTeX4, submitted to PRD replaced with
revised versio
High-redshift objects and the generalized Chaplygin gas
Motivated by recent developments in particle physics and cosmology, there has
been growing interest in an unified description of dark matter and dark energy
scenarios. In this paper we explore observational constraints from age
estimates of high- objects on cosmological models dominated by an exotic
fluid with equation of state (the so-called generalized
Chaplygin gas) which has the interesting feature of interpolating between
non-relativistic matter and negative-pressure dark energy regimes. As a general
result we find that, if the age estimates of these objects are correct, they
impose very restrictive limits on some of these scenarios.Comment: 5 pages, 3 figures, to appear in Phys. Rev.
Definition and Calculation of Bottom Quark Cross-Sections in Deep-inelastic Scattering at HERA and Determination of their Uncertainties
The uncertainties involved in the calculation of bottom quark cross-sections
in deep-inelastic scattering at HERA are studied in different phase space
regions. Besides the inclusive bottom quark cross-section, definitions closer
to the detector acceptance requiring at least one high energetic muon from the
semi-leptonic \bquark decay or a jet with high transverse energy are
investigated. For each case the uncertainties due to the choice of the
renormalisation and factorisation scale as well as the \bquark mass are
estimated in the perturbative NLO QCD calculation and furthermore uncertainties
in the fragmenation of the bottom quark to a B-meson and in its semi-leptonic
decay are discussed
Is cosmology consistent?
We perform a detailed analysis of the latest CMB measurements (including
BOOMERaNG, DASI, Maxima and CBI), both alone and jointly with other
cosmological data sets involving, e.g., galaxy clustering and the Lyman Alpha
Forest. We first address the question of whether the CMB data are internally
consistent once calibration and beam uncertainties are taken into account,
performing a series of statistical tests. With a few minor caveats, our answer
is yes, and we compress all data into a single set of 24 bandpowers with
associated covariance matrix and window functions. We then compute joint
constraints on the 11 parameters of the ``standard'' adiabatic inflationary
cosmological model. Out best fit model passes a series of physical consistency
checks and agrees with essentially all currently available cosmological data.
In addition to sharp constraints on the cosmic matter budget in good agreement
with those of the BOOMERaNG, DASI and Maxima teams, we obtain a heaviest
neutrino mass range 0.04-4.2 eV and the sharpest constraints to date on gravity
waves which (together with preference for a slight red-tilt) favors
``small-field'' inflation models.Comment: Replaced to match accepted PRD version. 14 pages, 12 figs. Tiny
changes due to smaller DASI & Maxima calibration errors. Expanded neutrino
and tensor discussion, added refs, typos fixed. Combined CMB data, window and
covariance matrix at http://www.hep.upenn.edu/~max/consistent.html or from
[email protected]
The PHENIX Experiment at RHIC
The physics emphases of the PHENIX collaboration and the design and current
status of the PHENIX detector are discussed. The plan of the collaboration for
making the most effective use of the available luminosity in the first years of
RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program
available at http://www.rhic.bnl.gov/phenix
Dark Synergy: Gravitational Lensing and the CMB
Power spectra and cross-correlation measurements from the weak gravitational
lensing of the cosmic microwave background (CMB) and the cosmic shearing of
faint galaxies images will help shed light on quantities hidden from the CMB
temperature anisotropies: the dark energy, the end of the dark ages, and the
inflationary gravitational wave amplitude. Even with modest surveys, both types
of lensing power spectra break CMB degeneracies and they can ultimately improve
constraints on the dark energy equation of state w by over an order of
magnitude. In its cross correlation with the integrated Sachs-Wolfe effect, CMB
lensing offers a unique opportunity for a more direct detection of the dark
energy and enables study of its clustering properties. By obtaining source
redshifts and cross-correlations with CMB lensing, cosmic shear surveys provide
tomographic handles on the evolution of clustering correspondingly better
precision on the dark energy equation of state and density. Both can indirectly
provide detections of the reionization optical depth and modest improvements in
gravitational wave constraints which we compare to more direct constraints.
Conversely, polarization B-mode contamination from CMB lensing, like any other
residual foreground, darkens the prospects for ultra-high precision on
gravitational waves through CMB polarization requiring large areas of sky for
statistical subtraction. To evaluate these effects we provide fitting formula
for the evolution and transfer function of the Newtonian gravitational
potential.Comment: 16 pages, 11 figures submitted to PR
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