163,851 research outputs found
Bayesian analysis of multiple direct detection experiments
Bayesian methods offer a coherent and efficient framework for implementing
uncertainties into induction problems. In this article, we review how this
approach applies to the analysis of dark matter direct detection experiments.
In particular we discuss the exclusion limit of XENON100 and the debated hints
of detection under the hypothesis of a WIMP signal. Within parameter inference,
marginalizing consistently over uncertainties to extract robust posterior
probability distributions, we find that the claimed tension between XENON100
and the other experiments can be partially alleviated in isospin violating
scenario, while elastic scattering model appears to be compatible with the
frequentist statistical approach. We then move to model comparison, for which
Bayesian methods are particularly well suited. Firstly, we investigate the
annual modulation seen in CoGeNT data, finding that there is weak evidence for
a modulation. Modulation models due to other physics compare unfavorably with
the WIMP models, paying the price for their excessive complexity. Secondly, we
confront several coherent scattering models to determine the current best
physical scenario compatible with the experimental hints. We find that
exothermic and inelastic dark matter are moderatly disfavored against the
elastic scenario, while the isospin violating model has a similar evidence.
Lastly the Bayes' factor gives inconclusive evidence for an incompatibility
between the data sets of XENON100 and the hints of detection. The same question
assessed with goodness of fit would indicate a 2 sigma discrepancy. This
suggests that more data are therefore needed to settle this question.Comment: 29 pages, 8 figures; invited review for the special issue of the
journal Physics of the Dark Universe; matches the published versio
Aspects of the Stueckelberg Extension
A detailed analysis of a Stueckelberg extension of the electro-weak gauge
group with an extra U(1) factor is presented for the Standard Model as well as
for the MSSM. The extra gauge boson gets massive through a Stueckelberg type
coupling to a pseudo-scalar, instead of a Higgs effect. This new massive
neutral gauge boson Z' has vector and axial vector couplings uniquely different
from those of conventional extra abelian gauge bosons, such as appear e.g. in
GUT models. The extended MSSM furthermore contains two extra neutralinos and
one extra neutral CP-even scalar, the latter with a mass larger than that of
the Z'. One interesting scenario that emerges is an LSP that is dominantly
composed out of the new neutralinos, leading to a possible new superweak
candidate for dark matter. We investigate signatures of the Stueckelberg
extension at a linear collider and discuss techniques for the detection of the
expected sharp Z' resonance. It turns out that the substantially modified
forward-backward asymmetry around the Z' pole provides an important signal.
Furthermore, we also elaborate on generalizations of the minimal Stueckelberg
extension to an arbitrary number of extra U(1) gauge factors.Comment: 49 pages, 13 figures; to appear in JHE
TeV Scale Singlet Dark Matter
It is well known that stable weak scale particles are viable dark matter
candidates since the annihilation cross section is naturally about the right
magnitude to leave the correct thermal residual abundance. Many dark matter
searches have focused on relatively light dark matter consistent with weak
couplings to the Standard Model. However, in a strongly coupled theory, or even
if the coupling is just a few times bigger than the Standard Model couplings,
dark matter can have TeV-scale mass with the correct thermal relic abundance.
Here we consider neutral TeV-mass scalar dark matter, its necessary
interactions, and potential signals. We consider signals both with and without
higher-dimension operators generated by strong coupling at the TeV scale, as
might happen for example in an RS scenario. We find some potential for
detection in high energy photons that depends on the dark matter distribution.
Detection in positrons at lower energies, such as those PAMELA probes, would be
difficult though a higher energy positron signal could in principle be
detectable over background. However, a light dark matter particle with
higher-dimensional interactions consistent with a TeV cutoff can in principle
match PAMELA data.Comment: 30 pages, 11 figures. Minor changes, references adde
Dark Matter Blind Spots at One-Loop
We evaluate the impact of one-loop electroweak corrections to the
spin-independent dark matter (DM) scattering cross-section with nucleons
(), in models with a so-called blind spot for direct
detection, where the leading-order prediction for the relevant DM coupling to
the Higgs boson, and therefore , are vanishingly small.
Adopting a simple illustrative scenario in which the DM state results from the
mixing of electroweak singlet and doublet fermions, we compute the relevant
higher order corrections to the scalar effective operator contributions to
, stemming from both triangle and box diagrams involving the
SM and dark sector fields. It is observed that in a significant region of the
singlet-doublet model-space, the one-loop corrections ``unblind'' the
tree-level blind spots and lead to detectable SI scattering rates at future
multi-ton scale liquid Xenon experiments, with reaching
values up to a few times , for a weak scale DM with
Yukawa couplings. Furthermore, we find that there always
exists a new SI blind spot at the next-to-leading order, which is
perturbatively shifted from the leading order one in the singlet-doublet mass
parameters. For comparison, we also present the tree-level spin-dependent
scattering cross-sections near the SI blind-spot region, that could lead to a
larger signal. Our results can be mapped to the blind-spot scenario for
bino-Higgsino DM in the MSSM, with other sfermions, the heavier Higgs boson,
and the wino decoupled.Comment: 20 pages, 5 figures; Minor corrections, references updated, version
published in JHE
Can WIMP Dark Matter overcome the Nightmare Scenario?
Even if new physics beyond the Standard Model (SM) indeed exists, the energy
scale of new physics might be beyond the reach at the Large Hadron Collider
(LHC) and the LHC could find only the Higgs boson but nothing else. This is the
so-called "nightmare scenario". On the other hand, the existence of the dark
matter has been established from various observations. One of the promising
candidates for thermal relic dark matter is a stable and electric
charge-neutral Weakly Interacting Massive Particle (WIMP) with the mass below
the TeV scale. In the nightmare scenario, we introduce a WIMP dark matter
singlet under the SM gauge group, which only couples to the Higgs doublet at
the lowest order, and investigate a possibility that such WIMP dark matter can
be a clue to overcome the nightmare scenario via various phenomenological tests
such as the dark matter relic abundance, the direct detection experiments for
the dark matter particle, and the production of the dark matter particle at the
LHC.Comment: 14 pages, 10 figure
Rician MIMO Channel- and Jamming-Aware Decision Fusion
In this manuscript we study channel-aware decision fusion (DF) in a wireless
sensor network (WSN) where: (i) the sensors transmit their decisions
simultaneously for spectral efficiency purposes and the DF center (DFC) is
equipped with multiple antennas; (ii) each sensor-DFC channel is described via
a Rician model. As opposed to the existing literature, in order to account for
stringent energy constraints in the WSN, only statistical channel information
is assumed for the non-line-of sight (scattered) fading terms. For such a
scenario, sub-optimal fusion rules are developed in order to deal with the
exponential complexity of the likelihood ratio test (LRT) and impractical
(complete) system knowledge. Furthermore, the considered model is extended to
the case of (partially unknown) jamming-originated interference. Then the
obtained fusion rules are modified with the use of composite hypothesis testing
framework and generalized LRT. Coincidence and statistical equivalence among
them are also investigated under some relevant simplified scenarios. Numerical
results compare the proposed rules and highlight their jammingsuppression
capability.Comment: Accepted in IEEE Transactions on Signal Processing 201
Exploring the BWCA (Bino-Wino Co-Annihilation) Scenario for Neutralino Dark Matter
In supersymmetric models with non-universal gaugino masses, it is possible to
have opposite-sign SU(2) and U(1) gaugino mass terms. In these models, the
gaugino eigenstates experience little mixing so that the lightest SUSY particle
remains either pure bino or pure wino. The neutralino relic density can only be
brought into accord with the WMAP measured value when bino-wino co-annihilation
(BWCA) acts to enhance the dark matter annihilation rate. We map out parameter
space regions and mass spectra which are characteristic of the BWCA scenario.
Direct and indirect dark matter detection rates are shown to be typically very
low. At collider experiments, the BWCA scenario is typified by a small mass gap
m_{\tilde Z_2}-m_{\tilde Z_1} ~ 20-80 GeV, so that tree level two body decays
of \tilde Z_2 are not allowed. However, in this case the second lightest
neutralino has an enhanced loop decay branching fraction to photons. While the
photonic neutralino decay signature looks difficult to extract at the Fermilab
Tevatron, it should lead to distinctive events at the CERN LHC and at a linear
e^+e^- collider.Comment: 44 pages, 21 figure
Estimation of the Number of Sources in Unbalanced Arrays via Information Theoretic Criteria
Estimating the number of sources impinging on an array of sensors is a well
known and well investigated problem. A common approach for solving this problem
is to use an information theoretic criterion, such as Minimum Description
Length (MDL) or the Akaike Information Criterion (AIC). The MDL estimator is
known to be a consistent estimator, robust against deviations from the Gaussian
assumption, and non-robust against deviations from the point source and/or
temporally or spatially white additive noise assumptions. Over the years
several alternative estimation algorithms have been proposed and tested.
Usually, these algorithms are shown, using computer simulations, to have
improved performance over the MDL estimator, and to be robust against
deviations from the assumed spatial model. Nevertheless, these robust
algorithms have high computational complexity, requiring several
multi-dimensional searches.
In this paper, motivated by real life problems, a systematic approach toward
the problem of robust estimation of the number of sources using information
theoretic criteria is taken. An MDL type estimator that is robust against
deviation from assumption of equal noise level across the array is studied. The
consistency of this estimator, even when deviations from the equal noise level
assumption occur, is proven. A novel low-complexity implementation method
avoiding the need for multi-dimensional searches is presented as well, making
this estimator a favorable choice for practical applications.Comment: To appear in the IEEE Transactions on Signal Processin
Mixed Higgsino Dark Matter from a Reduced SU(3) Gaugino Mass: Consequences for Dark Matter and Collider Searches
In gravity-mediated SUSY breaking models with non-universal gaugino masses,
lowering the SU(3) gaugino mass |M_3| leads to a reduction in the squark and
gluino masses. Lower third generation squark masses, in turn, diminish the
effect of a large top quark Yukawa coupling in the running of the higgs mass
parameter m_{H_u}^2, leading to a reduction in the magnitude of the
superpotential mu parameter (relative to M_1 and M_2). A low | mu | parameter
gives rise to mixed higgsino dark matter (MHDM), which can efficiently
annihilate in the early universe to give a dark matter relic density in accord
with WMAP measurements. We explore the phenomenology of the low |M_3| scenario,
and find for the case of MHDM increased rates for direct and indirect detection
of neutralino dark matter relative to the mSUGRA model. The sparticle mass
spectrum is characterized by relatively light gluinos, frequently with
m(gl)<<m(sq). If scalar masses are large, then gluinos can be very light, with
gl->Z_i+g loop decays dominating the gluino branching fraction. Top squarks can
be much lighter than sbottom and first/second generation squarks. The presence
of low mass higgsino-like charginos and neutralinos is expected at the CERN
LHC. The small m(Z2)-m(Z1) mass gap should give rise to a visible
opposite-sign/same flavor dilepton mass edge. At a TeV scale linear e^+e^-
collider, the region of MHDM will mean that the entire spectrum of charginos
and neutralinos are amongst the lightest sparticles, and are most likely to be
produced at observable rates, allowing for a complete reconstruction of the
gaugino-higgsino sector.Comment: 35 pages, including 26 EPS figure
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