145 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
Chasing a consistent picture for dark matter direct searches
In this paper we assess the present status of dark matter direct searches by
means of Bayesian statistics. We consider three particle physics models for
spin-independent dark matter interaction with nuclei: elastic, inelastic and
isospin violating scattering. We shortly present the state of the art for the
three models, marginalising over experimental systematics and astrophysical
uncertainties. Whatever the scenario is, XENON100 appears to challenge the
detection region of DAMA, CoGeNT and CRESST. The first aim of this study is to
rigorously quantify the significance of the inconsistency between XENON100 data
and the combined set of detection (DAMA, CoGeNT and CRESST together),
performing two statistical tests based on the Bayesian evidence. We show that
XENON100 and the combined set are inconsistent at least at 2 sigma level in all
scenarios but inelastic scattering, for which the disagreement drops to 1 sigma
level. Secondly we consider only the combined set and hunt the best particle
physics model that accounts for the events, using Bayesian model comparison.
The outcome between elastic and isospin violating scattering is inconclusive,
with the odds 2:1, while inelastic scattering is disfavoured with the odds of
1:32 because of CoGeNT data. Our results are robust under reasonable prior
assumptions. We conclude that the simple elastic scattering remains the best
model to explain the detection regions, since the data do not support extra
free parameters. Present direct searches therefore are not able to constrain
the particle physics interaction of the dark matter. The outcome of consistency
tests implies that either a better understanding of astrophysical and
experimental uncertainties is needed, either the dark matter theoretical model
is at odds with the data.Comment: 18 pages, 8 figures and 7 tables; minor revisions following referee
report. Accepted for publication in Phys.Rev.
Triplet seesaw model: from inflation to asymmetric dark matter and leptogenesis
The nature of dark matter (DM) particles and the mechanism that provides
their measured relic abundance are currently unknown. Likewise, the nature of
the inflaton is unknown as well. We investigate the triplet seesaw model in an
unified picture. At high energy scale, we consider Higgs inflation driven by an
admixture of standard model and triplet Higgs fields, both coupled
non-minimally to gravity. At intermediate and low energies we investigate
vector like fermion doublet DM candidates with a charge asymmetry in the dark
sector, which is generated by the same mechanism that provides the baryon
asymmetry, namely baryogenesis-via-leptogenesis induced by the decay of scalar
triplets. At the same time the model gives rise to neutrino masses in the
ballpark of oscillation experiments via type-II seesaw. We then apply Bayesian
statistics to infer the model parameters giving rise to the observed baryon
asymmetry and DM density, compatibly with inflationary and DM direct detection
constraints, updated with the CRESST-II excess, the new XENON100 data release
and KIMS exclusion limit.Comment: Contribution to the Proceedings of PASCOS2012 conference; 6 pages and
5 figure
Multi-lepton signatures at LHC from sneutrino dark matter
We investigate multi-lepton LHC signals arising from an extension at the
grand unification scale of the standard minimal supersymmetric model (MSSM)
involving right-handed neutrino superfields. In this framework neutrinos have
Dirac masses and the mixed sneutrinos are the lightest supersymmetric particles
and hence the dark matter candidates. We analyze the model parameter space in
which the sneutrino is a good dark matter particle and has a direct detection
cross-section compatible with the LUX bound. Studying the supersymmetric mass
spectrum of this region, we find several signatures relevant for LHC, which are
distinct from the predictions of the MSSM with neutralino dark matter. For
instance two opposite sign and different flavor leptons, three uncorrelated
leptons and long-lived staus are the most representative. Simulating both the
signal and expected background, we find that the multi-lepton signatures and
the long-lived stau are in the reach of the future run of LHC with a luminosity
of 100/fb. We point out that if one of these signatures is detected, it might
be an indication of sneutrino dark matter.Comment: 34 pages, 14 figures and 6 tables; this version matches the published
on
Constraints on Light WIMP candidates from the Isotropic Diffuse Gamma-Ray Emission
Motivated by the measurements reported by direct detection experiments, most
notably DAMA, CDMS-II, CoGeNT and Xenon10/100, we study further the constraints
that might be set on some light dark matter candidates, M_DM ~ few GeV, using
the Fermi-LAT data on the isotropic gamma-ray diffuse emission. In particular,
we consider a Dirac fermion singlet interacting through a new Z' gauge boson,
and a scalar singlet S interacting through the Higgs portal. Both candidates
are WIMP (Weakly Interacting Massive Particles), i.e. they have an annihilation
cross-section in the pbarn range. Also they may both have a spin-independent
elastic cross section on nucleons in the range required by direct detection
experiments. Although being generic WIMP candidates, because they have
different interactions with Standard Model particles, their phenomenology
regarding the isotropic diffuse gamma-ray emission is quite distinct. In the
case of the scalar singlet, the one-to-one correspondence between its
annihilation cross-section and its spin-independent elastic scattering
cross-section permits to express the constraints from the Fermi-LAT data in the
direct detection exclusion plot, sigma_n^0--M_DM. Depending on the
astrophysics, we argue that it is possible to exclude the singlet scalar dark
matter candidate at 95 % CL. The constraints on the Dirac singlet interacting
through a Z' are comparatively weaker.Comment: 18 pages, 13 figures, replaced to match with the published versio
Review on Dark Matter Tools
Whilst the need for dark matter was established almost a century ago, only
its gravitational interaction has been confirmed so far, allowing for plethora
of models for dark matter. The Weakly Interacting Massive Particles (WIMPs)
category has received by far the biggest attention, however despite the
enormous experimental efforts, these particles remain elusive. The attention of
the community has hence moved on to investigate the dark matter landscape over
a much larger number of models with varying degrees of resemblances and
differences in their predictions. This calls for the need to organise the
various facets of dark matter models and their signatures, in order to maximise
the experimental sensitivity and to select the models which are compatible with
existing data. In this paper, I provide a short review of the most widespread
public codes capable of computing dark matter observables. In particular, I
discuss what is the status of each numerical tool in terms of: (i) capturing
the WIMP phenomenology and (ii) accounting for new trend dark sector models
that might be weakly coupled to ordinary matter and/or be strongly
self-interacting. This short review has the aim of guiding the user towards
selecting the best suited public code to confront his/her model with the
largest variety of theoretical predictions and experimental data in order to
determine the parameter space consistent with observations for his/her
favourite dark matter model.Comment: 9 pages + references; matches the published version (only few
references added) into "Tools for High Energy Physics and Cosmology"
(TOOLS2020), 2-6 Nov. 2020, IP2I Lyon, Franc
Co-genesis of Matter and Dark Matter with Vector-like Fourth Generation Leptons
We propose a simple extension of the standard model by adding a fourth
generation vector-like lepton doublet and show that if the fourth neutrino is a
massive pseudo-Dirac fermion with mass in the few hundred GeV range and mass
splitting of about 100 keV, its lighter component can be a viable inelastic
dark matter candidate. Its relic abundance is produced by the CP violating
out-of-equilibrium decay of the type-II seesaw scalar triplet, which also gives
rise to the required baryon asymmetry of the Universe via type-II leptogenesis,
thus providing a simultaneous explanation of dark matter and baryon abundance
observed today. Moreover, the induced vacuum expectation value of the same
scalar triplet is responsible for the sub-eV Majorana masses to the three
active neutrinos. A stable fourth generation of neutrinos is elusive at
collider, however might be detected by current dark matter direct search
experiments.Comment: 7 pages, 5 figures and small corrections to match the version
accepted for publication in Physics Letters
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