[Show abstract][Hide abstract] ABSTRACT: The Cherenkov Telescope Array (CTA) will have a unique chance of discovery for a large range of masses in Weakly Interacting Massive Particles models of dark matter. The principal target for dark matter searches with CTA is the centre of the Galactic Halo. The best strategy is to perform CTA observations within a few degrees of the Galactic Centre, with the Galactic Centre itself and the most intense diffuse emission regions removed from the analysis. Assuming a cuspy dark matter density profile for the Milky Way, 500 hours of observations in this region provide sensitivities to and below the thermal cross-section of dark matter annihilations, for masses between a few hundred GeV and a few tens of TeV; therefore CTA will have a significant chance of discovery in some models. Since the dark matter density in the Milky Way is far from certain in the inner kpc region, other targets are also proposed for observation, like ultra-faint dwarf galaxies such as Segue 1 with 100 hours per year proposed. Beyond these two observational targets, further alternatives, such as Galactic dark clumps, will be considered closer to the actual date of CTA operations. Sensitivity predictions for dark matter searches are given on the various targets taking into account the latest instrument response functions expected for CTA together with a discussion on the systematic uncertainties from the backgrounds.
[Show abstract][Hide abstract] ABSTRACT: We review the current understanding of the diffuse gamma-ray background
(DGRB). The DGRB is what remains of the total measured gamma-ray emission after
the subtraction of the resolved sources and of the diffuse Galactic
foregrounds. It is interpreted as the cumulative emission of sources that are
not bright enough to be detected individually. Yet, its exact composition
remains unveiled. Well-established astrophysical source populations (e.g.
blazars, misaligned AGNs, star-forming galaxies and millisecond pulsars) all
represent guaranteed contributors to the DGRB. More exotic scenarios, such as
dark matter annihilation or decay, may contribute as well. In this review, we
describe how these components have been modeled in the literature and how the
DGRB can be used to provide valuable information on each of them. We summarize
the observational information currently available on the DGRB, paying
particular attention to the most recent measurement of its intensity energy
spectrum by the Fermi LAT Collaboration. We also discuss the novel analyses of
the auto-correlation angular power spectrum of the DGRB and of its
cross-correlation with tracers of the large-scale structure of the Universe.
New data sets already (or soon) available are expected to provide further
insight on the nature of this emission. By summarizing where we stand on the
current knowledge of the DGRB, this review is intended both as a useful
reference for those interested in the topic and as a means to trigger new ideas
for further research.
[Show abstract][Hide abstract] ABSTRACT: We recently proposed to cross-correlate the diffuse γ-ray emission with the gravita-tional lensing signal of cosmic shear. This represents a novel and promising strategy to search for annihilating or decaying dark matter (DM) candidates. In the present work, we demon-strate the potential of a tomographic-spectral approach: measuring the cross-correlation in separate bins of redshift and energy significantly improves the sensitivity to a DM signal. Indeed, the power of the proposed technique stems from the capability of simultaneously exploiting the different redshift scaling of astrophysical and DM components, their different energy spectra and their different angular shapes. The sensitivity to a particle DM signal is extremely promising even in the case the γ-ray emission induced by DM is a subdominant component in the isotropic γ-ray background. We quantify the prospects of detecting DM by cross-correlating the γ-ray emission from the Fermi large area telescope (LAT) with the cosmic shear measured by the Dark Energy Survey, using data sets that will be available in the near future. Under the hypothesis of a significant (but realistic) subhalo boost, such a measurement can deliver a 5σ detection of DM, if the DM particle has a mass lighter than 300 GeV and thermal annihilation rate. Data from the European Space Agency Euclid satellite (launch planned for 2020) will be even more informative: if used to reconstruct the properties of the DM particle, the cross-correlation of Euclid and Fermi-LAT will allow for a measurement of the DM mass within a factor of 1.5–2, even for moderate subhalo boosts, assuming the DM mass around 100 GeV and a thermal annihilation rate.
Full-text · Article · Nov 2014 · Journal of Cosmology and Astroparticle Physics
[Show abstract][Hide abstract] ABSTRACT: With positive signals from multiple direct detection experiments it will, in
principle, be possible to measure the mass and cross sections of
weakly-interacting massive particle (WIMP) dark matter. Recent work has shown
that, with a polynomial parameterisation of the WIMP speed distribution, it is
possible to make an unbiased measurement of the WIMP mass, without making any
astrophysical assumptions. However, direct detection experiments are not
sensitive to low-speed WIMPs and, therefore, any model-independent approach
will lead to a bias in the cross section. This problem can be solved with the
addition of measurements of the flux of neutrinos from the Sun. This is because
the flux of neutrinos produced from the annihilation of WIMPs which have been
gravitationally captured in the Sun is sensitive to low-speed WIMPs. Using mock
data from next-generation direct detection experiments and from the IceCube
neutrino telescope, we show that the complementary information from IceCube on
low-speed WIMPs breaks the degeneracy between the cross section and the speed
distribution. This allows unbiased determinations of the WIMP mass and
spin-independent and spin-dependent cross sections to be made, and the speed
distribution to be reconstructed. We use two parameterisations of the speed
distribution: binned and polynomial. While the polynomial parameterisation can
encompass a wider range of speed distributions, this leads to larger
uncertainties in the particle physics parameters.
Full-text · Article · Oct 2014 · Physical Review D
[Show abstract][Hide abstract] ABSTRACT: In the last decade direct detection Dark Matter (DM) experiments have
increased enormously their sensitivity and ton-scale setups have been proposed,
especially using germanium and xenon targets with double readout and background
discrimination capabilities. In light of this situation, we study the prospects
for determining the parameters of Weakly Interacting Massive Particle (WIMP) DM
(mass, spin-dependent (SD) and spin-independent (SI) cross section off
nucleons) by combining the results of such experiments in the case of a
hypothetical detection. In general, the degeneracy between the SD and SI
components of the scattering cross section can only be removed using targets
with different sensitivities to these components. Scintillating bolometers,
with particle discrimination capability, very good energy resolution and
threshold and a wide choice of target materials, are an excellent tool for a
multitarget complementary DM search. We investigate how the simultaneous use of
scintillating targets with different SD-SI sensitivities and/or light isotopes
(as the case of CaF2 and NaI) significantly improves the determination of the
WIMP parameters. In order to make the analysis more realistic we include the
effect of uncertainties in the halo model and in the spin-dependent nuclear
structure functions, as well as the effect of a thermal quenching different
Full-text · Article · Mar 2014 · International Journal of Modern Physics A
[Show abstract][Hide abstract] ABSTRACT: Dark Matter (DM) direct detection experiments usually assume the simplest
possible 'Standard Halo Model' for the Milky Way (MW) halo in which the
velocity distribution is Maxwellian. This model assumes that the MW halo is an
isotropic, isothermal sphere, hypotheses that are unlikely to be valid in
reality. An alternative approach is to derive a self-consistent solution for a
particular mass model of the MW (i.e. obtained from its gravitational
potential) using the Eddington formalism, which assumes isotropy. In this paper
we extend this approach to incorporate an anisotropic phase-space distribution
function. We perform Bayesian scans over the parameters defining the mass model
of the MW and parameterising the phase-space density, implementing constraints
from a wide range of astronomical observations. The scans allow us to estimate
the precision reached in the reconstruction of the velocity distribution (for
different DM halo profiles). As expected, allowing for an anisotropic velocity
tensor increases the uncertainty in the reconstruction of f(v) but the
distribution can still be determined with a precision of a factor of 4-5. The
mean velocity distribution resembles the isotropic case, however the amplitude
of the high-velocity tail is up to a factor of 2 larger. Our results agree with
the phenomenological parametrization proposed in Mao et al. (2013) as a good
fit to N-body simulations (with or without baryons), since their velocity
distribution is contained in our 68% credible interval.
Full-text · Article · Nov 2013 · Physical Review D
[Show abstract][Hide abstract] ABSTRACT: Both cosmic shear and cosmological gamma-ray emission stem from the presence of dark matter (DM) in the universe: DM structures are responsible for the bending of light in the weak-lensing regime and those same objects can emit gamma rays, either because they host astrophysical sources (active galactic nuclei or star-forming galaxies) or directly by DM annihilations (or decays, depending on the properties of the DM particle). Such gamma rays should therefore exhibit strong correlation with the cosmic shear signal. In this Letter, we compute the cross-correlation angular power spectrum of cosmic shear and gamma rays produced by the annihilation/decay of weakly interacting massive particle DM, as well as by astrophysical sources. We show that this observable provides novel information on the composition of the extragalactic gamma-ray background (EGB), since the amplitude and shape of the cross-correlation signal strongly depend on which class of sources is responsible for the gamma-ray emission. If the DM contribution to the EGB is significant (at least in a definite energy range), although compatible with current observational bounds, its strong correlation with the cosmic shear makes such signal potentially detectable by combining Fermi Large Area Telescope data with forthcoming galaxy surveys, like the Dark Energy Survey and Euclid. At the same time, the same signal would demonstrate that the weak-lensing observables are indeed due to particle DM matter and not to possible modifications of general relativity.
Full-text · Article · Jun 2013 · The Astrophysical Journal Letters
[Show abstract][Hide abstract] ABSTRACT: We study how the combined observation of dark matter in various direct
detection experiments can be used to determine the phenomenological properties
of WIMP dark matter: mass, spin-dependent (SD) and spin-independent (SI)
scattering cross section off nucleons. A convenient choice of target materials,
including nuclei that couple to dark matter particles through a significantly
different ratio of SD vs SI interactions, could break the degeneracies in the
determination of those parameters that a single experiment cannot discriminate.
In this work we investigate different targets that can be used as scintillating
bolometers and could provide complementary information to germanium and xenon
detectors. We observe that Al2O3 and LiF bolometers could allow a good
reconstruction of the DM properties over regions of the parameter space with a
SD scattering cross section as small as 10^(-5) pb and a SI cross section as
small as 5x10^(-10) pb for a 50 GeV WIMP. In the case of a CaWO4 bolometer the
area in which full complementarity is obtained is smaller but we show that it
can be used to determine the WIMP mass and its SI cross section. For each
target we study the required exposure and background.
Full-text · Article · Apr 2013 · Journal of Cosmology and Astroparticle Physics
[Show abstract][Hide abstract] ABSTRACT: The Cherenkov Telescope Array (CTA) is a project for a next-generation observatory for very high energy (GeV-TeV) ground-based gamma-ray astronomy, currently in its design phase, and foreseen to be operative a few years from now. Several tens of telescopes of 2-3 different sizes, distributed over a
large area, will allow for a sensitivity about a factor 10 better than current instruments such as H.E.S.S, MAGIC and VERITAS, an energy coverage from a few tens of GeV to several tens of TeV, and a field of view of up to 10 deg. In the following study, we investigate the prospects for CTA to study several science
questions that influence our current knowledge of fundamental physics. Based on conservative assumptions for the performance of the different CTA telescope configurations, we employ a Monte Carlo based approach to evaluate the prospects for detection. First, we discuss CTA prospects for cold dark matter searches, following different observational strategies: in dwarf satellite galaxies of the Milky Way, in the region close to the Galactic Centre, and in clusters of galaxies. The possible search for spatial signatures, facilitated by the larger field of view of CTA, is also discussed. Next we consider searches for axion-like particles which, besides being possible candidates for dark matter may also explain the unexpectedly low absorption by extragalactic background light of gamma rays from very distant blazars. Simulated light-curves of flaring sources are also used to determine the sensitivity to violations of Lorentz Invariance by detection of the possible delay between the arrival times of photons at different energies. Finally, we mention searches for other exotic physics with CTA.
Full-text · Article · Mar 2013 · Astroparticle Physics
[Show abstract][Hide abstract] ABSTRACT: The detailed origin of the diffuse gamma-ray background is still unknown.
However, the contribution of unresolved sources is expected to induce
small-scale anisotropies in this emission, which may provide a way to identify
and constrain the properties of its contributors. Recent studies have predicted
the contributions to the angular power spectrum (APS) from extragalactic and
galactic dark matter (DM) annihilation or decay. The Fermi-LAT collaboration
reported detection of angular power with a significance larger than $3\sigma$
in the energy range from 1 GeV to 10 GeV on 22 months of data [Ackermann et al.
2012]. For these preliminary results the already published Fermi-LAT APS
measurements [Ackermann et al. 2012] are compared to the accurate predictions
for DM anisotropies from state-of-the-art cosmological simulations as presented
in [Fornasa et al. 2013] to derive constraints on different DM candidates.
Full-text · Article · Mar 2013 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
[Show abstract][Hide abstract] ABSTRACT: The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project.
Full-text · Article · Mar 2013 · Astroparticle Physics
[Show abstract][Hide abstract] ABSTRACT: We present global fits of the constrained Minimal Supersymmetric Standard
Model (cMSSM) and the Non-Universal Higgs Model (NUHM), including the most
recent CMS constraint on the Higgs boson mass, 5.8/fb integrated luminosity
null Supersymmetry searches by ATLAS, the new LHCb measurement of the Bs to
mu+mu- branching ratio and the 7-year WMAP dark matter relic abundance
determination. We include the latest dark matter constraints from the XENON100
experiment, marginalising over astrophysical and particle physics
uncertainties. We present Bayesian posterior and profile likelihood maps of the
highest resolution available today, obtained from up to 350M points. We find
that the new constraint on the Higgs boson mass has a dramatic impact, ruling
out large regions of previously favoured cMSSM and NUHM parameter space. In the
cMSSM, light sparticles and predominantly gaugino-like dark matter with a mass
of a few hundred GeV are favoured. The NUHM exhibits a strong preference for
heavier sparticle masses and a Higgsino-like neutralino with a mass of 1 TeV.
The future ton-scale XENON1T direct detection experiment will probe large
portions of the currently favoured cMSSM and NUHM parameter space. The LHC
operating at 14 TeV collision energy will explore the favoured regions in the
cMSSM, while most of the regions favoured in the NUHM will remain inaccessible.
Our best-fit points achieve a satisfactory quality-of-fit, with p-values
ranging from 0.21 to 0.35, so that none of the two models studied can be
presently excluded at any meaningful significance level.
Full-text · Article · Dec 2012 · Journal of Cosmology and Astroparticle Physics
[Show abstract][Hide abstract] ABSTRACT: We study the effect that uncertainties in the nuclear spin-dependent
structure functions have in the determination of the dark matter (DM)
parameters in a direct detection experiment. We show that different nuclear
models that describe the spin-dependent structure function of specific target
nuclei can lead to variations in the reconstructed values of the DM mass and
scattering cross-section. We propose a parametrization of the spin structure
functions that allows us to treat these uncertainties as variations of three
parameters, with a central value and deviation that depend on the specific
nucleus. The method is illustrated for germanium and xenon detectors with an
exposure of 300 kg yr, assuming a hypothetical detection of DM and studying a
series of benchmark points for the DM properties. We find that the effect of
these uncertainties can be similar in amplitude to that of astrophysical
uncertainties, especially in those cases where the spin-dependent contribution
to the elastic scattering cross-section is sizable.
Full-text · Article · Aug 2012 · Physical review D: Particles and fields
[Show abstract][Hide abstract] ABSTRACT: The Fermi-LAT collaboration has recently reported the detection of angular
power above the photon noise level in the diffuse gamma-ray background between
1 and 50 GeV. Such signal can be used to constrain a possible contribution from
Dark-Matter-induced photons. We estimate the intensity and features of the
angular power spectrum (APS) of this potential Dark Matter (DM) signal, for
both decaying and annihilating DM candidates, by constructing template all-sky
gamma-ray maps for the emission produced in the galactic halo and its
substructures, as well as in extragalactic (sub)halos. The DM distribution is
given by state-of-the-art N-body simulations of cosmic structure formation,
namely Millennium-II for extragalactic (sub)halos, and Aquarius for the
galactic halo and its subhalos. We use a hybrid method of extrapolation to
account for (sub)structures that are below the resolution limit of the
simulations, allowing us to estimate the total emission all the way down to the
minimal self-bound halo mass. We describe in detail the features appearing in
the APS of our template maps and we estimate the effect of various
uncertainties such as the value of the minimal halo mass, the fraction of
substructures hosted in a halo and the shape of the DM density profile. Our
results indicate that the fluctuation APS of the DM-induced emission is of the
same order as the Fermi-LAT APS, suggesting that one can constrain this
hypothetical emission from the comparison with the measured anisotropy. We also
quantify the uncertainties affecting our results, finding "theoretical error
bands" spanning more than two orders of magnitude and dominated (for a given
particle physics model) by our lack of knowledge of the abundance of low-mass
Full-text · Article · Jul 2012 · Monthly Notices of the Royal Astronomical Society
[Show abstract][Hide abstract] ABSTRACT: The μνSSM is a supersymmetric model that has been proposed to solve the problems generated by other supersymmetric extensions of the standard model of particle physics. Given that R-parity is broken in the μνSSM, the gravitino is a natural candidate for decaying dark matter since its lifetime becomes much longer than the age of the Universe. In this model, gravitino dark matter could be detectable through the emission of a monochromatic gamma ray in a two-body decay. We study the prospects of the Fermi-LAT telescope to detect such monochromatic lines in 5 years of observations of the most massive nearby extragalactic objects. The dark matter halo around the Virgo galaxy cluster is selected as a reference case, since it is associated to a particularly high signal-to-noise ratio and is located in a region scarcely affected by the astrophysical diffuse emission from the galactic plane. The simulation of both signal and background gamma-ray events is carried out with the Fermi Science Tools, and the dark matter distribution around Virgo is taken from a N-body simulation of the nearby extragalactic Universe, with constrained initial conditions provided by the CLUES project. We find that a gravitino with a mass range of 0.6–2 GeV, and with a lifetime range of about 3 × 1027–2 × 1028 s would be detectable by the Fermi-LAT with a signal-to-noise ratio larger than 3. We also obtain that gravitino masses larger than about 4 GeV are already excluded in the μνSSM by Fermi-LAT data of the galactic halo.
Full-text · Article · Feb 2012 · Journal of Cosmology and Astroparticle Physics
[Show abstract][Hide abstract] ABSTRACT: We present updated global fits of the constrained Minimal Supersymmetric Standard Model (cMSSM), including the most recent constraints from the ATLAS and CMS detectors at the LHC, as well as the most recent results of the XENON100 experiment. Our robust analysis takes into account both astrophysical and hadronic uncertainties that enter in the calculation of the rate of WIMP-induced recoils in direct detection experiment.
We study the consequences for neutralino Dark Matter, and show that current direct detection data already allow to robustly rule out the so-called Focus Point region, therefore demonstrating the importance of particle astrophysics experiments in constraining extensions of the Standard Model of Particle Physics. We also observe an increased compatibility between results obtained from a Bayesian and a Frequentist statistical perspective.
We find that upcoming ton-scale direct detection experiments will probe essentially the entire currently favoured region (at the 99% level), almost independently of the statistical approach used. Prospects for indirect detection of the cMSSM are further reduced.
Full-text · Article · Jan 2012 · Journal of Cosmology and Astroparticle Physics
[Show abstract][Hide abstract] ABSTRACT: We present new global fits of the cMSSM, including LHC 1/fb integrated
luminosity SUSY exclusion limits, recent LHC 5/fb constraints on the mass of
the Higgs boson and XENON100 direct detection data. Our analysis fully takes
into account astrophysical and hadronic uncertainties that enter the analysis
when translating direct detection limits into constraints on the cMSSM
parameter space. We provide results for both a Bayesian and a Frequentist
statistical analysis. We find that LHC 2011 constraints in combination with
XENON100 data can rule out a significant portion of the cMSSM parameter space.
Our results further emphasise the complementarity of collider experiments and
direct detection searches in constraining extensions of Standard Model physics.
The LHC 2011 exclusion limit strongly impacts on low-mass regions of cMSSM
parameter space, such as the stau co-annihilation region, while direct
detection data can rule out regions of high SUSY masses, such as the
Focus-Point region, which is unreachable for the LHC in the near future. We
show that, in addition to XENON100 data, the experimental constraint on the
anomalous magnetic moment of the muon plays a dominant role in disfavouring
large scalar and gaugino masses. We find that, should the LHC 2011 excess
hinting towards a Higgs boson at 126 GeV be confirmed, currently favoured
regions of the cMSSM parameter space will be robustly ruled out from both a
Bayesian and a profile likelihood statistical perspective.
Full-text · Article · Dec 2011 · Journal of Cosmology and Astroparticle Physics
[Show abstract][Hide abstract] ABSTRACT: Even if Supersymmetric particles are found at the Large Hadron Collider
(LHC), it will be difficult to prove that they constitute the bulk of the Dark
Matter (DM) in the Universe using LHC data alone. We study the complementarity
of LHC and DM indirect searches, working out explicitly the reconstruction of
the DM properties for a specific benchmark model in the coannihilation region
of a 24-parameters supersymmetric model. Combining mock high-luminosity LHC
data with present-day null searches for gamma-rays from dwarf galaxies with the
Fermi LAT, we show that current Fermi LAT limits already have the capability of
ruling out a spurious Wino-like solution that would survive using LHC data
only, thus leading to the correct identification of the cosmological solution.
We also demonstrate that upcoming Planck constraints on the reionization
history will have a similar constraining power, and discuss the impact of a
possible detection of gamma-rays from DM annihilation in Draco with a CTA-like
experiment. Our results indicate that indirect searches can be strongly
complementary to the LHC in identifying the DM particles, even when
astrophysical uncertainties are taken into account.
Full-text · Article · Nov 2011 · Physical review D: Particles and fields