4,301 research outputs found
Prospects for direct detection of dark matter in an effective theory approach
We perform the first comprehensive analysis of the prospects for direct
detection of dark matter with future ton-scale detectors in the general
11-dimensional effective theory of isoscalar dark matter-nucleon interactions
mediated by a heavy spin-1 or spin-0 particle. The theory includes 8 momentum
and velocity dependent dark matter-nucleon interaction operators, besides the
familiar spin-independent and spin-dependent operators. From a variegated
sample of 27 benchmark points selected in the parameter space of the theory, we
simulate independent sets of synthetic data for ton-scale Germanium and Xenon
detectors. From the synthetic data, we then extract the marginal posterior
probability density functions and the profile likelihoods of the model
parameters. The associated Bayesian credible regions and frequentist confidence
intervals allow us to assess the prospects for direct detection of dark matter
at the 27 benchmark points. First, we analyze the data assuming the knowledge
of the correct dark matter nucleon-interaction type, as it is commonly done for
the familiar spin-independent and spin-dependent interactions. Then, we analyze
the simulations extracting the dark matter-nucleon interaction type from the
data directly, in contrast to standard analyses. This second approach requires
an extensive exploration of the full 11-dimensional parameter space of the dark
matter-nucleon effective theory. Interestingly, we identify 5 scenarios where
the dark matter mass and the dark matter-nucleon interaction type can be
reconstructed from the data simultaneously. We stress the importance of
extracting the dark matter nucleon-interaction type from the data directly,
discussing the main challenges found addressing this complex 11-dimensional
problem.Comment: 23 pages, 7 figures, replaced to match the published versio
Spherical collapse and halo mass function in the symmetron model
We study the gravitational clustering of spherically symmetric overdensities
and the statistics of the resulting dark matter halos in the "symmetron model",
in which a new long range force is mediated by a symmetric scalar field.
Depending on the initial radius of the overdensity, we identify two distinct
regimes: for small initial radii the symmetron mediated force affects the
spherical collapse at all redshifts; for initial radii larger than some
critical size this force vanishes before collapse because of the symmetron
screening mechanism. In both cases overdensities collapse earlier than in the
CDM and statistically tend to form more massive dark matter halos.
Regarding the halo-mass function of these objects, we observe order one
departures from standard CDM predictions. The formalism developed here
can be easily applied to other models where fifth-forces participate to the
dynamics of the gravitational collapse.Comment: 17 pages, 5 figures. Minor revisions to match published versio
Local transformations of units in Scalar-Tensor Cosmology
The physical equivalence of Einstein and Jordan frame in Scalar Tensor
theories has been explained by Dicke in 1962: they are related by a local
transformation of units. We discuss this point in a cosmological framework. Our
main result is the construction of a formalism in which all the physical
observables are frame-invariant. The application of this approach to CMB codes
is at present under analysis.Comment: To appear in the proceedings of IRGAC 2006, 2nd International
Conference on Quantum Theories and Renormalization Group in Gravity and
Cosmology, Barcelona, July 11-15 200
CMB Aberration and Doppler Effects as a Source of Hemispherical Asymmetries
Our peculiar motion with respect to the CMB rest frame represents a preferred
direction in the observed CMB sky since it induces an apparent deflection of
the observed CMB photons (aberration) and a shift in their frequency (Doppler).
Both effects distort the multipoles 's at all 's. Such
effects are real as it has been recently measured for the first time by Planck
according to what was forecast in some recent papers. However, the common lore
when estimating a power spectrum from CMB is to consider that Doppler affects
only the multipole, neglecting any other corrections. In this work we
use simulations of the CMB sky in a boosted frame with a peculiar velocity
in order to assess the impact of such
effect on power spectrum estimations in different regions of the sky. We show
that the boost induces a north-south asymmetry in the power spectrum which is
highly significant and non-negligible, of about (0.58 0.10)% for half-sky
cuts when going up to = 2500. We suggest that these effects are relevant
and may account for some of the north-south asymmetries seen in the Planck
data, being especially important at small scales. Finally we analyze the
particular case of the ACT experiment, which observed only a small fraction of
the sky and show that it suffers a bias of about 1% on the power spectrum and
of similar size on some cosmological parameters: for example the position of
the peaks shifts by 0.5% and the overall amplitude of the spectrum is about
0.4% lower than a full-sky case.Comment: 13 pages, 5 figure
SAMPEX
The DSN (Deep Space Network) mission support requirements for SAMPEX are summarized. SAMPEX is the first mission of the GSFC Small Explorer Satellite program (SMEX). Its primary scientific objectives are to measure the elemental and isotopic composition of solar energetic particles, anomalous cosmic rays, and galactic cosmic rays over the energy range from approximately one to several hundred MeV per nucleon. The SAMPEX mission objectives are outlined and the DSN support requirements are defined through the presentation of tables and narratives describing the spacecraft flight profile; DSN support coverage; frequency assignments; support parameters for telemetry, command and support systems; and tracking support responsibility
Aspects of a supersymmetric Brans-Dicke theory
We consider a locally supersymmetric theory where the Planck mass is replaced
by a dynamical superfield. This model can be thought of as the Minimal
Supersymmetric extension of the Brans-Dicke theory (MSBD). The motivation that
underlies this analysis is the research of possible connections between Dark
Energy models based on Brans-Dicke-like theories and supersymmetric Dark Matter
scenarios. We find that the phenomenology associated with the MSBD model is
very different compared to the one of the original Brans-Dicke theory: the
gravitational sector does not couple to the matter sector in a universal metric
way. This feature could make the minimal supersymmetric extension of the BD
idea phenomenologically inconsistent.Comment: 6 pages, one section is adde
Ab initio nuclear response functions for dark matter searches
We study the process of dark matter particles scattering off He with
nuclear wave functions computed using an ab initio many-body framework. We
employ realistic nuclear interactions from chiral effective field theory at
next-to-next-to-leading order (NNLO) and develop an ab initio scheme to compute
a general set of different nuclear response functions. In particular, we then
perform an accompanying uncertainty quantification on these quantities and
study error propagation to physical observables. We find a rich structure of
allowed nuclear responses with significant uncertainties for certain
spin-dependent interactions. The approach and results that are presented in
this Paper establish a new framework for nuclear structure calculations and
uncertainty quantification in the context of direct and (certain) indirect
searches for dark matter.Comment: version accepted for publication in Phys. Rev. D; figures revised
(incl. corrected labels); discussion of results extende
On inverted index compression for search engine efficiency
Efficient access to the inverted index data structure is a key aspect for a search engine to achieve fast response times to usersâ queries . While the performance of an information retrieval (IR) system can be enhanced through the compression of its posting lists, there is little recent work in the literature that thoroughly compares and analyses the performance of modern integer compression schemes across different types of posting information (document ids, frequencies, positions). In this paper, we experiment with different modern integer compression algorithms, integrating these into a modern IR system. Through comprehensive experiments conducted on two large, widely used document corpora and large query sets, our results show the benefit of compression for different types of posting information to the space- and time-efficiency of the search engine. Overall, we find that the simple Frame of Reference compression scheme results in the best query response times for all types of posting information. Moreover, we observe that the frequency and position posting information in Web corpora that have large volumes of anchor text are more challenging to compress, yet compression is beneficial in reducing average query response times
Signatures of Earth-scattering in the direct detection of Dark Matter
Direct detection experiments search for the interactions of Dark Matter (DM)
particles with nuclei in terrestrial detectors. But if these interactions are
sufficiently strong, DM particles may scatter in the Earth, affecting their
distribution in the lab. We present a new analytic calculation of this
`Earth-scattering' effect in the regime where DM particles scatter at most once
before reaching the detector. We perform the calculation self-consistently,
taking into account not only those particles which are scattered away from the
detector, but also those particles which are deflected towards the detector.
Taking into account a realistic model of the Earth and allowing for a range of
DM-nucleon interactions, we present the EarthShadow code, which we make
publicly available, for calculating the DM velocity distribution after
Earth-scattering. Focusing on low-mass DM, we find that Earth-scattering
reduces the direct detection rate at certain detector locations while
increasing the rate in others. The Earth's rotation induces a daily modulation
in the rate, which we find to be highly sensitive to the detector latitude and
to the form of the DM-nucleon interaction. These distinctive signatures would
allow us to unambiguously detect DM and perhaps even identify its interactions
in regions of the parameter space within the reach of current and future
experiments.Comment: 27 pages + appendices, 9 figures. Code (and animations) available at
https://github.com/bradkav/EarthShadow (Astrophysics Source Code Library,
record ascl:1611.012). v2: added references, matches version published in
JCA
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