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General Relativity Resolves Galactic Rotation Without Exotic
Dark Matter
Authors: F.
I. Cooperstock, S.
Tieu
Comments: Submitted to the Astrophysical Journal, 23
pages, 7 figures, 4 tables
A galaxy is modeled as a stationary axially symmetric pressure-free
fluid in
general relativity. For the weak gravitational fields under
consideration, the
field equations and the equations of motion ultimately lead to one
linear and
one nonlinear equation relating the angular velocity to the fluid
density. It
is shown that the rotation curves for the Milky Way, NGC 3031, NGC 3198
and NGC
7331 are consistent with the mass density distributions of the visible
matter
concentrated in flattened disks. Thus the need for a massive halo of
exotic
dark matter is removed. For these galaxies we determine the mass
density for
the luminous threshold as 10^{-21.75} kg.m$^{-3}.
Presence of exotic matter in the Cooperstock and Tieu galaxy
model
Authors: D.
Vogt, P.
S. Letelier
Comments: 4 pages
We analyze the presence of an additional singular thin disk in the
recent
General Relativistic model of galactic gravitational field proposed by
Cooperstock and Tieu. The physical variables of the disk's
energy-momentum
tensor are calculated. We show that the disk is made of exotic matter,
either
cosmic strings or struts with negative energy density.
Singular disk of matter in the Cooperstock and Tieu galaxy
model
Authors: Mikolaj
Korzynski
Comments: 5 pages, no figures
Recently a new model of galactic gravitational field, based on ordinary
General Relativity, has been proposed by Cooperstock and Tieu in which
no
exotic dark matter is needed to fit the observed rotation curve to a
reasonable
ordinary matter distribution. We argue that in this model the
gravitational
field is generated not only by the galaxy matter, but by a thin,
singular disk
as well. The model should therefore be considered unphysical.
See also Online
Discussion
Implications of the DAMA/NaI and CDMS experiments for mirror
matter-type dark matter
Authors: R.
Foot
Comments: about 15 pages, some references added
We re-analyse the implications of the DAMA/NaI experiment for mirror
matter-type dark matter, taking into account information from the
energy
dependence of the DAMA annual modulation signal. This is combined with
the null
results from the CDMS experiment, leading to fairly well defined
allowed
regions of parameter space. The allowed regions of parameter space will
be
probed in the near future by the DAMA/LIBRA, CDMS, and other
experiments, which
should either exclude or confirm this explanation of the DAMA/NaI
annual
modulation signal. In particular, we predict that the CDMS experiments
should
find a positive signal around the threshold recoil energy region, E_R
< 15 keV
in the near future.
Low energy antideuterons: shedding light on dark matter
Authors: Howard
Baer, Stefano
Profumo
Comments: 24 pages, 7 figures
Report-no: FSU-HEP-051030
Low energy antideuterons suffer a very low secondary and tertiary
astrophysical background, while they can be abundantly synthesized in
dark
matter pair annihilations, therefore providing a privileged indirect
dark
matter detection technique. The recent publication of the first upper
limit on
the low energy antideuteron flux by the BESS collaboration, a new
evaluation of
the standard astrophysical background, and remarkable progresses in the
development of a dedicated experiment, GAPS, motivate a new and
accurate
analysis of the antideuteron flux expected in particle dark matter
models. To
this extent, we consider here supersymmetric, universal
extra-dimensions (UED)
Kaluza-Klein and warped extra-dimensional dark matter models, and
assess both
the prospects for antideuteron detection as well as the various related
sources
of uncertainties. The GAPS experiment, even in a preliminary
balloon-borne
setup, will explore many supersymmetric configurations, and,
eventually, in its
final satellite-borne configuration, the whole cosmologically allowed
UED
parameter space, providing a search technique which is highly
complementary
with other direct and indirect dark matter detection experiments.
ArDM: a ton-scale liquid Argon experiment for direct
detection of Dark Matter in the Universe
Authors: A.
Rubbia
Comments: 5 pages, 3 figures, Talk given at IXth
international conference on Topics in Astroparticle and Underground
Physics (TAUP05), Zaragoza, (Spain)
The ArDM project aims at developing and operating large noble liquid
detectors to search for direct evidence of Weakly Interacting Massive
Particle
(WIMP) as Dark Matter in the Universe. The initial goal is to design,
assemble
and operate a $\approx$1 ton liquid Argon prototype to demonstrate the
feasibility of a ton-scale experiment with the required performance to
efficiently detect and sufficiently discriminate backgrounds for a
successful
WIMP detection. Our design addresses the possibility to detect
independently
ionization and scintillation signals. In this paper, we describe this
goal and
the conceptual design of the detector.
Super-acceleration as Signature of Dark Sector Interaction
Authors: Subinoy
Das, Pier
Stefano Corasaniti, Justin
Khoury
Comments: 9 pages, 4 figures
We show that an interaction between dark matter and dark energy
generically
results in an effective dark energy equation of state of w<-1. This
arises
because the interaction alters the redshift-dependence of the matter
density.
An observer who fits the data treating the dark matter as
non-interacting will
infer an effective dark energy fluid with w<-1. We argue that the
model is
consistent with all current observations, the tightest constraint
coming from
estimates of the matter density at different redshifts. Comparing the
luminosity and angular-diameter distance relations with LambdaCDM and
phantom
models, we find that the three models are degenerate within current
uncertainties but likely distinguishable by the next generation of dark
energy
experiments.
Authors: Katherine
Benson
Comments: 13 pages, PoS proceeding for 28th Johns Hopkins
Workshop on Current Problems in Particle Theory June 2004
Warped extra dimension claims remarkable success:
solving the hierarchy
problem; explaining hierarchies in particle phenomenology; yielding
standard
cosmology, plus interesting nonstandard scenarios. Yet it has marked
shortcomings: we over-rely on a single toy model, Randall-Sundrum; we
treat
matter and gravity in an ad hoc, asymmetric way; and we conceptualize
integrated 4D effective field theory inconsistently. I here construct
sounder
4D effective field theories for matter and gravity in warped extra
dimension --
whether Randall-Sundrum or higher codimension. I track both Planck and
particle
scales through brane formation, beginning with fully extradimensional
matter
and gravity, at unified scale, in gravitationally warped backgrounds
with bulk
electroweak symmetry-breaking. This validates hierarchy solution, as
warp
generically drives 4D effective Planck and particle scales apart. It
evades
classic obstacles to warped confinement of matter: colocalizing
particles and
assuring effective charge universality. Diverse particles do fail to
colocalize, generically and in discussed models; however, aggregate 4D
effective field theory still holds, since hierarchy solution fixes
unresolvably
small extradimensional radius. Electromagnetic charge universality
emerges
generically, and weak charge universality in the Randall-Sundrum case.
The footprint of large scale cosmic structure on the
ultra-high energy cosmic ray distribution
Authors: A.
Cuoco, R.
D' Abrusco, G.
Longo, G.
Miele, P.
D. Serpico
Comments: 20 pages, 14 figures
Report-no: DSF-37-2005, MPP-2005-121
Current experiments collecting high statistics in ultra-high energy
cosmic
rays (UHECRs) are opening a new window on the universe. In this work we
discuss
a large scale structure model for the UHECR origin which evaluates the
expected
anisotropy in the UHECR arrival distribution starting from a given
astronomical
catalogue of the local universe. The model takes into account the main
selection effects in the catalogue and the UHECR propagation effects.
By
applying this method to the IRAS PSCz catalogue, we derive the minimum
statistics needed to significatively reject the hypothesis that UHECRs
trace
the baryonic distribution in the universe, in particular providing a
forecast
for the Auger experiment.
Spectral distortions to the Cosmic Microwave Background from
the recombination of hydrogen and helium
Authors: Wan
Yan Wong, Sara
Seager, Douglas
Scott
Comments: 12 pages, 12 figures, submitted to MNRAS
The recombination of hydrogen and helium at z~1000-7000 gives
unavoidable
distortions to the Cosmic Microwave Background (CMB) spectrum. We
present a
detailed calculation of the line intensities arising from the Ly-alpha
(2p-1s)
and two-photon (2s-1s) transitions for the recombination of hydrogen,
as well
as the corresponding lines from helium. We give an approximate formula
for the
strength of the main recombination line distortion on the CMB in
different
cosmologies, this peak occurring at about 170 microns. We also find a
previously undescribed long wavelength peak (which we call the
pre-recombination peak) from the lines of the 2p-1s transitions, which
are
formed before significant recombination of the corresponding atoms
occurred.
Detailed calculations of the two-photon emission line shapes are
presented here
for the first time. The frequencies of the photons emitted from the
two-photon
transition have a wide spectrum and this causes the location of the
peak of the
two-photon line of hydrogen to be located almost at the same wavelength
as the
main Ly-alpha peak. The helium lines also give distortions at similar
wavelengths, so that the combined distortion has a complex shape. The
detection
of this distortion would provide direct supporting evidence that the
Universe
was indeed once a plasma. Moreover, the distortions are a sensitive
probe of
physics during the time of recombination. Although the spectral
distortion is
overwhelmed by dust emission from the Galaxy, and is maximum at
wavelengths
roughly where the cosmic far-infrared background peaks, it may be able
to
tailor an experiment to detect its non-trivial shape.
Distribution of Damped Lyman-alpha Absorbers in a Lambda Cold
Dark Matter Universe
Authors: Kentaro
Nagamine (1), Arthur
M. Wolfe (1), Lars
Hernquist (2), Volker
Springel (3) ((1)UCSD, (2)Harvard, (3)MPA)
Comments: 29 pages, 7 figures, submitted to ApJ. Errors on
mean DLA halo masses corrected
We examine the `rate-of-incidence' distribution for damped Lyman-alpha
absorbers (DLAs) as a function of halo mass, galaxy apparent magnitude,
and
impact parameter using a series of cosmological Smoothed Particle
Hydrodynamics
simulations. Our simulations include radiative cooling and heating by a
UV
background, star formation, and feedback from supernovae and galactic
winds. We
find the DLA rate-of-incidence in our simulations at z=3 is dominated
(80-90%)
by faint galaxies with apparent magnitude R_AB < 25.5. However,
interestingly
in a `strong wind' run, we find that the differential distribution of
DLA
sight-lines is peaked at M_halo=10^{12} Msun/h (R_AB ~ 27) and the mean
DLA
halo mass is M_mean=10^{12.4} Msun/h (R_AB ~ 26). These mass-scales are
much
larger than those if we ignore winds, because galactic feedback
suppresses the
DLA cross section in low mass halos and increases the relative
contribution to
the DLA incidence from more massive halos. But we caution that the mean
DLA
mass is biased towards a high value and is very different from the
median halo
mass unless the DLA distribution is highly peaked. The simulations also
suggest
that DLAs at z=3 are more compact than present-day disk galaxies, and
the
impact parameter distribution is very narrow unless we limit searches
for the
galaxy hosting a DLA to only bright Lyman-break galaxies (LBGs). We
find that
the comoving number density of DLAs is higher than that of LBGs down to
the
magnitude limit of R_AB=30 mag if the physical radius of each DLA is
smaller
than 5 kpc/h_70. We discuss conflicts between current simulations and
observations, and potential problems with hydrodynamic simulations
based on the
cold dark matter model.
Constraints on changes in fundamental constants from a
cosmologically distant OH absorber/emitter
Authors: N.
Kanekar (NRAO), C.
L. Carilli (NRAO), G.
I. Langston (NRAO), G.
Rocha (Cambridge), F.
Combes (Observatoire de Paris - LERMA), R.
Subrahmanyan (ATNF), J.
T. Stocke (University of Colorado), K.
M. Menten (MPIfR), F.
H. Briggs (ATNF/ANU), T.
Wiklind (STScI/Onsala)
Comments: 4 pages, 3 figures. Accepted for publication in
Physical Review Letters
We have detected the four 18cm OH lines from the $z \sim 0.765$
gravitational
lens toward PMN J0134-0931. The 1612 and 1720 MHz lines are in
conjugate
absorption and emission, providing a laboratory to test the evolution
of
fundamental constants over a large lookback time. We compare the HI and
OH
main-line absorption redshifts of the different components in the $z
\sim
0.765$ absorber and the $z \sim 0.685$ lens toward B0218+357 to place
stringent
constraints on changes in $F \equiv g_p [\alpha^2/\mu]^{1.57}$. We
obtain
$[\Delta F/F] = (0.44 \pm 0.36^{\rm stat} \pm 1.0^{\rm syst}) \times
10^{-5}$,
consistent with no changes in these constants over the redshift range
$0 < z <
0.7$. The measurements have a $2 \sigma$ sensitivity of $[\Delta
\alpha/\alpha]
< 6.7 \times 10^{-6}$ and $[\Delta \mu/\mu] < 1.4 \times 10^{-5}$
to fractional
changes in $\alpha$ and $\mu$, over a period of $\sim 6.5$ Gyr, half
the age of
the Universe. These are among the most sensitive current constraints on
changes
in $\mu$.
A search for the most massive galaxies: Double Trouble?
Authors: M.
Bernardi, R.
K. Sheth, R.
C. Nichol, C.
J. Miller, D.
Schlegel, J.
Frieman, D.
P. Schneider, M.
Subbarao, D. G.
York, J.
Brinkmann
Comments: 20 pages, 8 figures. Accepted by AJ. The full
set of figures in Appendix B is available at this
http URL
We describe the results of a search for galaxies with large (> 350
km/s)
velocity dispersions. The largest systems we have found appear to be
the
extremes of the early-type galaxy population: compared to other
galaxies with
similar luminosities, they have the largest velocity dispersions and
the
smallest sizes. However, they are not distant outliers from the
Fundamental
Plane and mass-to-light scaling relations defined by the bulk of the
early-type
galaxy population. They may host the most massive black holes in the
Universe,
and their abundance and properties can be used to constrain galaxy
formation
models. Clear outliers from the scaling relations tend to be objects in
superposition (angular separations smaller than 1 arcsec), evidence for
which
comes sometimes from the spectra, sometimes from the images, and
sometimes from
both. The statistical properties of the superposed pairs, e.g., the
distribution of pair separations and velocity dispersions, can be used
to
provide useful information about the expected distribution of image
multiplicities, separations and flux ratios due to gravitational
lensing by
multiple lenses, and may also constrain models of their interaction
rates.
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