Diffuse gamma-ray constraints on dark matter revisited I: the impact of subhalos

We make a detailed analysis of the indirect diffuse gamma-ray signals from dark matter annihilation in the Galaxy. We include the prompt emission, as well as the emission from inverse Compton scattering whenever the annihilation products contain light leptons. We consider both the contribution from the smooth dark matter halo and that from substructures. The main parameters for the latter are the mass function index and the minimal subhalo mass. We use recent results from N-body simulations to set the most reasonable range of parameters, and find that the signal can be boosted by a factor ranging from 2 to 15 towards the Galactic poles, slightly more towards the Galactic anticenter, with an important dependence on the subhalo mass index. This uncertainty is however much less than that of the extragalactic signal studied in the literature. We derive upper bounds on the dark matter annihilation cross section using the isotropic gamma-ray emission measured by Fermi-LAT, for two directions in the sky, the Galactic anticenter and the Galactic pole(s). The former represents the lowest irreducible signal from dark matter annihilation, and the latter is robust as the astrophysical background, dominated by the hadronic contribution, is rather well established in that direction. Finally, we show how the knowledge of the minimal subhalo mass, which formally depends on the dark matter particle interactions with normal matter, can be used to derive the mass function index.

Contribution of blazars to the extragalactic diffuse gamma-ray background and their future spatial resolution

Steve Blanchet

We examine the constraints on the luminosity-dependent density evolution model for the evolution of blazars given the observed spectrum of the diffuse gamma-ray background (DGRB), blazar source-count distribution, and the blazar spectral energy distribution sequence model, which relates the observed blazar spectrum to its luminosity. We show that the DGRB observed by the Large Area Telescope (LAT) aboard the Fermi Gamma-Ray Space Telescope can be produced entirely by gamma-ray emission from blazars and nonblazar active galactic nuclei, and that our blazar evolution model is consistent with and constrained by the spectrum of the DGRB and flux source-count distribution function of blazars observed by Fermi-LAT. Our results are consistent with previous work that used EGRET spectral data to forecast the Fermi-LAT DGRB. The model includes only three free parameters, and forecasts that 95% of the flux from blazars will be resolved into point sources by Fermi-LAT with 5 years of observation, with a corresponding reduction of the flux in the DGRB by a factor of ∼2 to 3 (95% confidence level), which has implications for the Fermi-LAT's sensitivity to dark matter annihilation photons. © 2011 American Physical Society.

2011

Baryogenesis, Dark Matter and Neutrino Oscillations from Right-Handed Neutrinos

Laurent Canetti

Our knowledge of our universe is deeply related to our understanding of physics at the sub- atomic scale. Indeed, at its early stage, our universe was so hot and so dense that the only relevant interactions were those between fundamental particles. Therefore, to improve our comprehension of the phenomena that take place over very large scales, we should improve our understanding of the physics at extremely small ones. The so-called Standard Model of particle physics (SM) provides us with a description of these fundamental particles and their interactions. Despite its enormous success, this model fails to explain several experimental evidences. In this thesis, we focus on the following three questions that are not answered by the SM. What is the so-called dark matter that is present in every galaxy? Why is our present universe made of matter with almost no trace of anti-matter? Finally, why can a neutrino of one family transform into a neutrino of another family? In this thesis, we show that the simple addition of three new neutrinos to the Standard Model allows us to answer the three questions above. The model that realizes this scenario is known as Neutrino Minimal Standard Model (νMSM). In this work, we give a comprehensive summary of all known constraints in the νMSM. We present the first complete quantitative study of the parameter space of the model where no physics beyond the νMSM is needed to simultaneously explain the three phenomena cited above. Moreover, these new particles can be looked for using current day experimental techniques and our results provide a guideline for future experimental searches.

EPFL2013

Exploring beyond the Standard Model: the Heavy and the Dark

Kin Shanho Eliaou Mimouni

Physics beyond the Standard Model can appear as new particles too heavy to be produced in experiments (the energy frontier) or interacting too weakly to be seen in our measurements (the intensity frontier). In the first part of this thesis, we study two dark matter models of electroweak WIMP coming from two limiting cases in the MSSM: the Higgsino and the Wino model. The dark matter candidate is a particle too heavy to be directly seen in colliders but it could be seen indirectly by astrophysical observations. Dark matter particles in the galaxy can annihilate to Standard Model particles and be detected by satellites. We consider the charged neutral mass splitting as a free parameter in the theory and investigate its effect on the Sommerfeld enhancement which gives an important boost to the annihilation cross-section, the main observable of indirect detection. In the second part of this thesis, we present an idea of a fixed target experiment so search for dark sector models, a class of model with very weakly interacting particles. This experiment uses the experimental setup needed for a future muon collider but is independent from the muon collider program. We study the reach of our experiment for three benchmark models, the dark photon, the dark Higgs, the heavy neutral lepton and we compare its expected performances to current and future experiments. In the third part of this thesis, we consider a more model-independent approach to the search for new physics. If new states are heavy, they can be integrated out and their leading effects are encoded in effective operators made of Standard Model fields. Assuming baryon and lepton number conservation, one can classify the effective operators of dimension-6 which give the leading contribution and constrain the coefficient of these operators by looking at precision observables. We compile results from LEP-I and LEP-II experiments as well as neutrino scattering and other low-energy observables. We allow all operators to be present with an arbitrary flavour structure. Our result can then be used to translate these constaints to specific models of new physics.

EPFL2019

Exploring beyond the Standard Model: the Heavy and the Dark

Kin Shanho Eliaou Mimouni

EPFL2019