arXiv subjects

M. Fornasa

Publications and source records attributed to M. Fornasa.

13 recordsLinked to original sources

arXiv2015

Prospects for Indirect Dark Matter Searches with the Cherenkov Telescope Array (CTA)

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.

astro-ph.HE↗

arXiv2014

Scintillating bolometers: a key for determining WIMP parameters

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 from 1.

astro-ph.IM↗

arXiv2013

A novel approach in the WIMP quest: Cross-Correlation of Gamma-Ray Anisotropies and Cosmic Shear

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 (WIMP) DM, as well as from astrophysical sources. We show that this observable provides novel information on the composition of the Extra-galactic Gamma-ray Background (EGB), since the amplitude and shape of the cross-correlation signal strongly depends on which class of source 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-LAT data with forthcoming galaxy surveys, like 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.

astro-ph.CO↗

arXiv2013

Complementarity of dark matter direct detection: the role of bolometric targets

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.

hep-ph↗

arXiv2013

Dark Matter implications of Fermi-LAT measurement of anisotropies in the diffuse gamma-ray background

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 $3σ$ 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.

astro-ph.HE↗

arXiv2012

Global Fits of the cMSSM and NUHM including the LHC Higgs discovery and new XENON100 constraints

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.

hep-ph↗

arXiv2012

Dark Matter and Fundamental Physics with the Cherenkov Telescope Array

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.

astro-ph.IM↗

arXiv2012

Updated global fits of the cMSSM including the latest LHC SUSY and Higgs searches and XENON100 data

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.

hep-ph↗

arXiv2012

Global fits of the cMSSM including the first LHC and XENON100 data

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.

hep-ph↗

arXiv2012

CLUES on Fermi-LAT prospects for the extragalactic detection of munuSSM gravitino Dark Matter

The munuSSM 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 munuSSM, 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 to 2 GeV, and with a lifetime range of about 3x10^27 to 2x10^28 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 munuSSM by Fermi-LAT data of the galactic halo

astro-ph.HE↗

arXiv2011

Complementarity of Indirect and Accelerator Dark Matter Searches

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.

astro-ph.HE↗

arXiv2011

Searches for Dark Matter signatures in the Segue 1 dwarf spheroidal galaxy with the MAGIC-I telescope

Despite the interest in Dark Matter (DM) searches is currently more focused on underground experiments, a signature of DM annihilation/decay in gamma-rays from the space would constitute a smoking gun for its identification. Here, we present the results of the survey of Segue1 by the MAGIC-I telescope performed in 2008 and 2009. This source is considered by many as the most DM dominated Milky Way satellite galaxy known so far. The nearly 43 hours of data taken constitute the deepest observation ever made on a single dwarf galaxy by Cherenkov telescopes. No significant gamma-ray emission was found above an energy threshold of 100 GeV. Integral upper limits on the gamma-ray flux were calculated assuming various power-law spectra for the possible emission spectrum and for different energy thresholds. We also discuss a novel analysis that fully takes into account the spectral features of the gamma-ray spectrum of specific DM models in a SuperSymmetric scenario.

astro-ph.HE↗

arXiv2011

Segue 1: the best dark matter candidate dwarf galaxy surveyed by MAGIC

Despite the interest in Dark Matter (DM) searches is currently more focused on underground experiments, a signature of DM annihilation/decay in gamma-rays from space would constitute a smoking gun for its identification. In this contribution, we start with a brief review of the efforts of the ground-based MAGIC Cherenkov telescopes system to detect DM signatures from dwarf satellite galaxies orbiting the Milky Way halo. We then present the recent survey of Segue 1, considered by many as possibly the most DM dominated satellite galaxy known in our galaxy. No significant gamma-ray emission was found above the background in around 30 hours of observation. This is the largest survey ever made on a single dwarf by Cherenkov telescopes. We present a novel analysis that fully takes into account the spectral features of the gamma-ray spectrum of specific DM models in a Supersymmetric scenario. We also discuss the prospects of detection after the Fermi observation of similar objects at lower energies.

astro-ph.CO↗