# Master Projects in Astroparticle Physics and Cosmology (2015-2016)

Eight topics are proposed by the group of Astroparticle Physics and Cosmology, by Pr. Julien Lesgourgues and the three post-doc of the group:

- Maria Archidiacono (starting date 01.10.2015, will visit on the 18.06.2015, archi@phys.au.dk)
- Sebastien Clesse (starting date 01.10.2015, will visit on the 18.06.2015, sebastien.clesse@unamur.be)
- Alessandro Cuoco (already started, office MBP 115, alessandro.cuoco@physik.rwth-aachen.de)

Please take contact with us if you are interested. Note that all these projects require a significant amount of numerical work and coding.

Project 1: Investigating annihilating and decaying Dark Matter with polarised radio/microwave observations.

**Field:** astroparticle physics

**Main supervisor:** Alessandro Cuoco

**Other supervisor:** Julien Lesgourgues

**Abstract:**

Annihilation/decay of Dark Matter in our Galaxy produces electrons which interacting with the Galactic magnetic field can then produce synchrotron radiation in the radio/microwave frequencies. The predicted radio/microwave emission can then be compared with observations, in order to derive DM constraints or search for DM signatures. So far, only the synchrotron intensity has been used to search for DM. On the other hand, thanks to the PLANCK satellite, precise maps of the the radio/microwave polarisation are now available. The project will focus on deriving predictions for the DM synchrotron polarisation signal and on using the PLANCK polarisation observations to put novel constraints on the DM properties.

Project 2: Dark Energy signatures in the extra-galactic gamma-ray background

**Fields:** cosmology and gamma-ray astroparticle physics

**Main supervisor:** Alessandro Cuoco

**Other supervisor:** Julien Lesgourgues

**Abstract:**

The imprint that Dark Energy leaves in the Cosmic Microwave Background can typically be searched through the cross-correlation with tracers of the cosmological gravitational potential, like galaxy catalogues. For this project, we plan to use gamma-ray maps from the Fermi satellite as gravitational tracer, and correlate them with CMB maps from the Planck satellite. The project will involve learning and using the typical tools used for cross-correlation analyses, i.e. cross-correlation functions and angular power spectra, which will be then applied to the Fermi-Planck cross-correlation. The cross-correlation results will be then used to constrain the Dark Energy properties.

Project 3: Investigating Galactic Cosmic Rays and Dark Matter with AMS02

**Field:** astroparticle physics

**Main supervisor:** Alessandro Cuoco

**Other supervisor:** Julien Lesgourgues

**Abstract:**

The project will consist in using the recent precise Cosmic Rays measurements performed by AMS02 to investigate the yet not well known properties of galactic cosmic rays, like the propagation properties and the distribution of the sources. In addition, Dark Matter can be studied through its imprint in the spectrum of positrons and antiprotons. Modelling of the propagation of Cosmic Rays from galactic sources and from Dark Matter will be performed through the use of the code Galprop. Dark Matter and Cosmic Rays will be then constrained through a fit to the AMS02 data.

Project 4: Dealing with models of inflation generating features in the primordial spectrum

**Field:** cosmology (inflation in the early universe)

**Main supervisor:** Julien Lesgourgues

**Other supervisor:** Sebastien Clesse

**Abstract:**

Recently there has be a revival of interest for models of inflation in the early universe having a complicated potential that generates wiggles in the primordial spectrum of fluctuations. There have been two motivations: one theoretical (string-inspired models leading to so-called ???axion monodromy inflation???) and one phenomenological (attempts to fit anomalies in the Planck CMB data). In most of the recent literature, people have studied these models using analytical approximations for the computation of the primordial slow-roll spectrum. It is however likely that these models violate the conditions under which these analytical approximations can be used. Hence we will study these models with an already existing inflation simulation code, to check the solidity of recent published results.

Project 5: Inhomogeneous initial conditions for inflation

**Field:** Cosmology (inflation in the early Universe)

**Main supervisor:** Sebastien Clesse

**Other supervisor:** Julien Lesgourgues

**Abstract:**

The question of how homogeneous must have been the initial conditions for cosmological inflation to be triggered has been tackled for about twenty years. For the simplest single field potentials, the Universe must have been initially homogeneous on scales larger than the Hubble radius. Thus inflation merely transforms one problem of homogeneity into another one, since a very homogeneous initial state is required. To draw this conclusion, relativistic simulations of the pre-inflation era have been conducted by solving the full Einstein equations in 1+1 or 3+1 dimensions. However, most of these works were realised in the 1990's with limited computational facilities compared to the large numerical resources available today. This allows us to improve the size and the accuracy of such simulations and to study a broader variety of single field and multi-field potentials. For this purpose, an existing code working for pressureless matter will have to be adapted to this problem. A collaboration with C. Ringeval (UCLouvain, Belgium) and J. Martin (IAP, Paris) could be envisaged.

Project 6: What may have happened between nucleosynthesis and photon decoupling?

**Field:** cosmology (particle cosmology)

**Main supervisor:** Julien Lesgourgues

**Other supervisors:** Maria Archidiacono

**Abstract:**

Primordial element abundances give us a clue of some properties of the universe at temperature of order T~0.01-1MeV, and CMB observations of its composition at T~0.1-100eV. Usually, these observations are compared with each other under the assumption that the particle content did not change between nucleosynthesis and decoupling. We will use the combination of both observables to study whether there could have been instead some particle decay, entropy release, or any non-trivial mechanism occurring between these two stages. This idea is not new but bounds have not been updated recently, since CMB data from the Planck satellite is available.

Project 7: Interactions in the dark sector: constraints on dark energy - dark matter coupling

**Field:** cosmology (dark matter - dark energy)

**Main supervisor:** Maria Archidiacono

**Other supervisor:** Julien Lesgourgues

**Abstract:**

In the last few years cosmic microwave background and large scale structure measurements have provided a precise answer about the composition of the Universe, validating the standard Lambda cold dark matter model. Nevertheless only 5% of the present Universe is made of ordinary baryonic matter. The remaining is non-baryonic dark matter (27%) and dark energy (68%), whose nature is still an unanswered question. Given the lack of any conclusive explanation of their phenomenology, coupled dark energy - dark matter models may constitute a viable alternative to the minimal Lambda cold dark matter model. Indeed dark energy - dark matter interactions would affect the evolution of the Universe, rebuilding our interpretation of cosmological measurements. This project is aimed at searching for the imprint of dark interactions in the early Universe, as well as in the local Universe. Using up-to-date cosmological data, we will derive current constraints on time-evolving dark coupling at different epochs of the cosmic evolution. Finally simulated data of new galaxy surveys, such as the European Space Agency Euclid mission, will allow us to predict the future sensitivity to dark matter - dark energy coupled models.

Project 8: SKA forecasts for dark energy and/or modified gravity

**Field:** Cosmology (21cm signal, dark energy and/or modified gravity)

**Main supervisor:** Sebastien Clesse

**Other supervisors:** Maria Archidiacono, Julien Lesgourgues

**Abstract:**

One aim of the Square Kilometre Array (SKA) radiotelescope will be to map the distribution of neutral hydrogen at high redshifts, during the reionozation era, by measuring its 21cm hyperfine line. Under some hypothesis, the large scale distribution of neutral hydrogen is related to the matter power spectrum, and thus 21cm observations can be used (at least in principle) to probe cosmology. Compared to the CMB, the 21-cm tomography is particularly promising given that a very broad range of redshifts (from the dark ages down to the end of the reionisation) and a much wider range of perturbation wavelengths are potentially accessible. The objective of this project is to calculate SKA forecasts on the standard cosmological parameters, as well as for some typical models of dark energy (such as early and stressed dark energy) and modified gravity (such as f(R), chameleons, symmetrons), by using either Fisher matrix or Monte-Carlo-Markov-Chain statistical methods.