45 research outputs found
WIMP Annual Modulation with Opposite Phase in Late-Infall Halo Models
We show that in the late-infall model of our galactic halo by P. Sikivie the
expected phase of the annual modulation of a WIMP halo signal in direct
detection experiments is opposite to the one usually expected. If a
non-virialized halo component due to the infall of (collisionless) dark matter
particles cannot be rejected, an annual modulation in a dark matter signal
should be looked for by experimenters without fixing the phase a-priori.
Moreover, WIMP streams coming to Earth from directions above and below the
galactic plane should be expected, with a characteristic pattern of arrival
directions.Comment: 15 pages, 5 figure
Assessing Big-Bang Nucleosynthesis
Systematic uncertainties in the light-element abundances and their evolution
make a rigorous statistical assessment difficult. However, using Bayesian
methods we show that the following statement is robust: the predicted and
measured abundances are consistent with 95\% credibility only if the
baryon-to-photon ratio is between and
and the number of light neutrino species is less than 3.9. Our analysis
suggests that the He abundance may have been systematically underestimated.Comment: 7 pages, LaTeX(2.09), 6 postscript figures (attached). A postscript
version with figures can be found at
ftp://astro.uchicago.edu/pub/astro/copi/assessing_BBN . (See the README file
for details
How Sensitive is the CMB to a Single Lens?
We study the imprints of a single lens, that breaks statistical isotropy, on
the CMB and calculate the signal to noise ratio (S/N) for its detection. We
emphasize the role of non-Gaussianities induced by LCDM weak lensing in this
calculation and show that typically the S/N is much smaller than expected. In
particular we find that the hypothesis that a void (texture) is responsible for
the WMAP cold spot can barely (cannot) be tested via weak lensing of the CMB.Comment: Accepted for publication in JCAP, 24 pages, 5 figure
Cosmological constant, violation of cosmological isotropy and CMB
We suggest that the solution to the cosmological vacuum energy puzzle does
not require any new field beyond the standard model, but rather can be
explained as a result of the interaction of the infrared sector of the
effective theory of gravity with standard model fields. The cosmological
constant in this framework can be presented in terms of QCD parameters and the
Hubble constant as follows, \epsilon_{vac} \sim H \cdot m_q\la\bar{q}q\ra
/m_{\eta'} \sim (4.3\cdot 10^{-3} \text{eV})^4, which is amazingly close to
the observed value today. In this work we explain how this proposal can be
tested by analyzing CMB data. In particular, knowing the value of the observed
cosmological constant fixes univocally the smallest size of the spatially flat,
constant time 3d hypersurface which, for instance in the case of an effective
1-torus, is predicted to be around 74 Gpc. We also comment on another important
prediction of this framework which is a violation of cosmological isotropy.
Such anisotropy is indeed apparently observed by WMAP, and will be confirmed
(or ruled out) by future PLANCK data.Comment: uses revtex4 - v2 as publishe
Generalized Analysis of Weakly-Interacting Massive Particle Searches
We perform a generalized analysis of data from WIMP search experiments for
point-like WIMPs of arbitrary spin and general Lorenz-invariant WIMP-nucleus
interaction. We show that in the non-relativistic limit only spin-independent
(SI) and spin-dependent (SD) WIMP-nucleon interactions survive, which can be
parameterized by only five independent parameters. We explore this
five-dimensional parameter space to determine whether the annual modulation
observed in the DAMA experiment can be consistent with all other experiments.
The pure SI interaction is ruled out except for very small region of parameter
space with the WIMP mass close to 50 GeV and the ratio of the WIMP-neutron to
WIMP-proton SI couplings . For the predominantly SD
interaction, we find an upper limit to the WIMP mass of about 18 GeV, which can
only be weakened if the constraint stemming from null searches for energetic
neutrinos from WIMP annihilation the Sun is evaded. None of the regions of the
parameter space that can reconcile all WIMP search results can be easily
accommodated in the minimal supersymmetric extension of the standard model.Comment: 27 pages, 3 figure
Scalar-Tensor Gravity and Quintessence
Scalar fields with inverse power-law effective potentials may provide a
negative pressure component to the energy density of the universe today, as
required by cosmological observations. In order to be cosmologically relevant
today, the scalar field should have a mass
, thus potentially inducing sizable
violations of the equivalence principle and space-time variations of the
coupling constants. Scalar-tensor theories of gravity provide a framework for
accommodating phenomenologically acceptable ultra-light scalar fields. We
discuss non-minimally coupled scalar-tensor theories in which the scalar-matter
coupling is a dynamical quantity. Two attractor mechanisms are operative at the
same time: one towards the tracker solution, which accounts for the accelerated
expansion of the Universe, and one towards general relativity, which makes the
ultra-light scalar field phenomenologically safe today. As in usual
tracker-field models, the late-time behavior is largely independent on the
initial conditions. Strong distortions in the cosmic microwave background
anisotropy spectra as well as in the matter power spectrum are expected.Comment: 5 pages, 4 figure
Light Unstable Sterile Neutrino
The three massless active (doublet) neutrinos may mix with two heavy and one
\underline {light} sterile (singlet) neutrinos so that the induced masses and
mixings among the former are able to explain the present data on atmospheric
and solar neutrino oscillations. If the LSND result is also to be explained,
one active neutrino mass eigenstate must mix with the light sterile neutrino. A
specific model is proposed with the spontaneous and soft explicit breaking of a
new global symmetry so that a sterile neutrino will decay into an
active antineutrino and a nearly massless pseudo-Majoron.Comment: Discussion and references adde
Effect of halo modelling on WIMP exclusion limits
WIMP direct detection experiments are just reaching the sensitivity required
to detect galactic dark matter in the form of neutralinos. Data from these
experiments are usually analysed under the simplifying assumption that the
Milky Way halo is an isothermal sphere with maxwellian velocity distribution.
Observations and numerical simulations indicate that galaxy halos are in fact
triaxial and anisotropic. Furthermore, in the cold dark matter paradigm
galactic halos form via the merger of smaller subhalos, and at least some
residual substructure survives. We examine the effect of halo modelling on WIMP
exclusion limits, taking into account the detector response. Triaxial and
anisotropic halo models, with parameters motivated by observations and
numerical simulations, lead to significant changes which are different for
different experiments, while if the local WIMP distribution is dominated by
small scale clumps then the exclusion limits are changed dramatically.Comment: 9 pages, 9 figures, version to appear in Phys. Rev. D, minor change
Scalar cosmological perturbations from inflationary black holes
We study the correction to the scale invariant power spectrum of a scalar
field on de Sitter space from small black holes that formed during a
pre-inflationary matter dominated era. The formation probability of such black
holes is estimated from primordial Gaussian density fluctuations. We determine
the correction to the spectrum by first deriving the Keldysh propagator for a
massless scalar field on Schwarzschild-de Sitter space. Our results suggest
that the effect is strong enough to be tested -- and possibly even ruled out --
by observations.Comment: 41 pages, 11 figures, published versio
Solar Wakes of Dark Matter Flows
We analyze the effect of the Sun's gravitational field on a flow of cold dark
matter (CDM) through the solar system in the limit where the velocity
dispersion of the flow vanishes. The exact density and velocity distributions
are derived in the case where the Sun is a point mass. The results are extended
to the more realistic case where the Sun has a finite size spherically
symmetric mass distribution. We find that regions of infinite density, called
caustics, appear. One such region is a line caustic on the axis of symmetry,
downstream from the Sun, where the flow trajectories cross. Another is a
cone-shaped caustic surface near the trajectories of maximum scattering angle.
The trajectories forming the conical caustic pass through the Sun's interior
and probe the solar mass distribution, raising the possibility that the solar
mass distribution may some day be measured by a dark matter detector on Earth.
We generalize our results to the case of flows with continuous velocity
distributions, such as that predicted by the isothermal model of the Milky Way
halo.Comment: 30 pages, 8 figure