Hakuaika päättyy 31.1.2020.

**QCD matter at high density**

We are searching for a summer student to work on the theoretical description of ultradense quark matter expected to be found inside the cores of neutron stars. The student to be chosen is expected to be a 2nd, 3rd, or 4th year theoretical physics major, have a strong background in mathematical methods, and possess a working knowledge of basic quantum mechanics and thermal or statistical physics. Depending on the background and profile of the student, possible topics of study include the perturbative thermodynamics of quark matter, the holographic description of dense strongly interacting matter, and implementing gravitational wave and other astrophysical constraints on the neutron star matter equation of state.

The project is expected to lead either to a BSc or MSc thesis for the student, and if possible also to a publication.

For more information, see https://www.mv.helsinki.fi/home/arjvuori/ or contact Aleksi Vuorinen, aleksi.vuorinen@helsinki.fi

### Computational field theory

The computational field theory research group is searching for summer trainees interested in particle physics and cosmology, and preferably also in computational methods. The positions are for 3 months, with exact dates to be agreed upon.

We are studying gravitational wave production in exotic particle physics processes in the very early Universe. The produced gravitational waves may be observable with the European Space Agency's LISA gravitational wave mission, scheduled for launch in 2032. This yields a unique window to the early Universe and to the particle physics processes which can produce gravitational waves.

The summer trainee research projects are chosen according to the experience and preference of the trainees. The research projects can form the basis for either a Bachelor or a Master thesis.

Visualisations of past research, including some by previous summer trainees, can be seen at:

https://vimeo.com/user65863371

For more information:

Mark Hindmarsh mark.hindmarsh@helsinki.fi

Kari Rummukainen kari.rummukainen@helsinki.fi

David Weir david.weir@helsinki.fi

Or visit our website:

https://blogs.helsinki.fi/computational-field-theory/

### Space physics

The Space Physics Group at the Department of Physics at the University of Helsinki (UH) is looking for several summer trainees. Summer trainees will work with space weather simulation Vlasiator and with the projects investigating solar eruptions in the corona and interplanetary space. Both projects dealing with modelling and data analysis are possible. Experience with Python and knowledge of plasma physics are a plus, but not required. Summer trainee positions offer an excellent chance also for BSc and MSc theses!

The topics are listed below. You may indicate what project/which projects you would in particular be interested in and whether you have any preference between modelling, observations/data analysis or theory. Also, please indicate if you would like to do your BSc or MSc work based on your summer trainee work.

- Exploring Properties of Solar Storms Using Radio Observations and Modelling of Magnetic Fields (data analysis and modelling)
- Energy transfer at the Magnetopause (data analysis and modelling)
- Turbulence driven by coronal mass ejections (data analysis, theory)
- Magnetic Structures at the Earth’s Bow Shock (data analysis and modelling)
- Space weather modelling with EUHFORIA (modeling)
- Numerical analysis of Precipitation of particles from the Earth's magnetosphere (data analysis and modelling)
- Interplanetary shock database (database development, data analysis.)
- Programming a new energetic particle acceleration model (modelling)
- Magnetospheric wave activity driven by interplanetary shocks (data analysis)
- Shock ion reflection in Vlasiator (modelling)
- Hamiltonian approach to wave-particle interactions of relativistic electrons.
- Flux Transfer Events and their interaction with Earth's polar cusps

More detailed descriptions of these projects can be found at

https://blogs.helsinki.fi/spacephysics/2019/12/17/looking-for-summer-trainees/

https://blogs.helsinki.fi/spacephysics/msc-thesis-topics/

For possible questions about summer trainee positions, please contact Minna.Palmroth@helsinki.fi, Emilia.Kilpua@helsinki.fi, or the person listed under each topic.

The University of Helsinki Space Physics Group is a leading European space physics team specialised both in observations and modelling of space plasmas. For example, we develop the novel global hybrid-Vlasov simulation Vlasiator and have a strong focus on solar eruptions. We have a dynamic and international research group with currently about 20 members including three professors and several post-docs and PhD students. The recently established Centre of Excellence in Research of Sustainable Space is led by the UH Space Physics Group. For more information, please visit:

https://blogs.helsinki.fi/spacephysics/

https://www.helsinki.fi/sustainable-space

https://www.physics.helsinki.fi/vlasiator

### Euclid

Finland participates in the European Space Agency cosmology satellite mission Euclid. Euclid will be launched in 2022, and during the next six years it will map the distribution of galaxies and dark matter in the Universe, with the aim of solving the question of the nature of dark energy. The Euclid project has open one or two paid summer trainee positions for physics, theoretical physics, and astronomy students. The position is for three months in May-August (the exact dates to be agreed). The work is related to the Finnish Euclid Science Data Center (simulating and analyzing Euclid data) and/or the physics of the expanding universe and dark energy. The work involves study of some of these topics, and related tasks suitable for the student's level. Working on a Bachelor's or Master's thesis can be included. A good study record and computer skills (e.g., Unix, C, C++, python) are important. It would be good if the student has taken at least some of the courses FYS2081 Cosmology I, PAP326 Cosmology II, PAP335 General Relativity, PAP341 Galaxy Survey Cosmology, and/or PAP342 Cosmological Perturbation Theory.

More information: Hannu Kurki-Suonio (hannu.kurki-suonio (at) helsinki.fi, office hour Mo 10:30-11:30 Physicum C328).

### Holographic duality and its applications

The goal of this project is to learn about and perform calculations in holographic duality. This duality is a discovery in theoretical physics (more specifically in string theory) that relates two very different types of theories; a gravitational theory and a quantum field theory. Results in one theory can be translated to results in the other.

This duality can be used as a tool to explore many different areas of physics. Researchers including several here in Helsinki are using it to study nuclear physics, condensed matter physics, and more.

We are searching for one summer trainee interested in learning about holographic duality as well as other areas of theoretical physics and in gaining some experience in performing related calculations. The details of the project are quite flexible and will be chosen considering the experience and interests of the trainee.

For more information, contact Oscar Henriksson, oscar.henriksson@helsinki.fi.

### Planetary-System Research

Planetary-system research (PSR) at the University of Helsinki comprises theoretical, computational, experimental, and observational research of Solar System objects (planets and their moons, asteroids and comets). The research has close connections to geophysics, geology, as well as meteorology. The research of the Planetary System research group at the University of Helsinki is focused on asteroids (e.g., ESA Gaia mission, ESA Euclid mission, ESA Hera mission in planetary defense), comets (ESA Comet Interceptor mission), Mercury (ESA/JAXA BepiColombo and NASA MESSENGER missions), and other atmosphereless bodies, as well as the planet Earth (notably NASA DSCOVR mission). Astronomical observations are carried out, for example, at the Nordic Optical Telescope (NOT) and, in the future, with the Large Synoptic Survey Telescope (LSST). The PSR group runs the Astrophysical Scattering Laboratory consisting of a state-of-the-art levitator-driven scatterometer, UV-Vis-NIR spectrometer, and a polarimetric spectrogoniometer. The development of hyperspectral imaging based backscatterometer is ongoing. Laboratory collaboration in X-ray fluorescence spectroscopy progresses with the University of Leicester. In more detail, the research involves forward and inverse light scattering, X-ray fluorescence, and celestial mechanics methods for accrueing knowledge on individual planetary-system objects as well as entire populations of asteroids and comets.

Within PSR, four summer trainee positions are opened in the following topics:

**1)** Real-time online monitoring system for the spherical albedo (or Bond albedo) of the planet Earth, crucial for the estimation of the radiation budget of the planet.

**2)** Experimental light-scattering and X-ray fluorescence measurements and laboratory development at the University of Helsinki and at the University of Leicester.

**3)** Inverse methods for the combined UV-Vis-NIR and X-ray data on planet Mercury collected by the NASA MESSENGER mission, in view of applying the methods in the ongoing ESA/JAXA BepiColombo mission.

In all three cases, the training will take place in synergy with the forecoming ESA Hera and Comet Interceptor missions.

Contact person: Karri Muinonen (karri.muinonen at helsinki.fi)

**4)** Development of an efficient Hamiltonian Monte Carlo method for the simultaneous global inversion of astrometric observations by ESA's Gaia mission to self-consistently solve for the orbits and masses of up to hundreds of thousands of known asteroids.

Contact person: Mikael Granvik (mikael.granvik@helsinki.fi)

### Theoretical Extragalactic Research Group

We are looking for summer trainees with an interest in theoretical astrophysics and/or theoretical physics. In addition to theoretical work, our projects include a significant computational aspect. We encourage students interested in theory and computation to join the Theoretical Extragalactic astrophysics research group for a three-month period over the summer.

This year, the research projects we offer are divided into three larger themes.

The first set of projects on offer are related to the KETJU-project, which was recently funded by the European Research Council. In this project the aim is to use the newly developed simulation code KETJU to model the dynamics of supermassive black holes in galaxy mergers. Using KETJU the large-scale structure of galaxies can be studied, while simultaneously resolving accurately, the small-scale dynamics close to the supermassive black holes.

The research topics for the KETJU-project include:

#### 1) Modelling the formation of cored early-type galaxies:

In this project the goal is to use numerical simulations to study the effect of binary supermassive black holes (SMBHs) on the central structure of massive elliptical galaxies. The interaction between the SMBH and the surrounding stars tend to eject stars from the centre of the galaxy and using KETJU this process can be studied in detail. Good computing skills and knowledge of galaxy formation theory and galactic dynamics are advantageous for this project.

#### 2) Gravitational waves from merging supermassive black holes:

In the final stages of the merger of a supermassive black hole (SMBH) binary copious amounts of gravitational waves will be emitted. Using the Post-Newtonian formalism in KETJU the gravitational wave energy spectrum as a function of frequency can be calculated based on the relative orbital motion of the SMBH binary. Good computing skills and prior knowledge of general relativity and galactic dynamics are advantageous for this project.

The second set of projects concerns radiative transfer in the curved spacetimes of general relativity. The Theoretical Extragalactic group has developed a multipurpose tensor calculus and radiative transfer code Arcmancer, which can, for example, create scientifically accurate images of black holes and neutron stars. All the Arcmancer projects require familiarity with general relativity and a working knowledge of C++ and Python. General experience with numerical algorithms will be helpful.

The research topics for the Arcmancer-project include:

#### 3) Monte Carlo radiative transfer in general relativity:

The goal of this summer project is to investigate radiative transfer in relativistic matter near black holes and neutron stars using the Monte Carlo approach. The project will consist of using the Arcmancer code to construct simple Monte Carlo solvers and evaluating their performance.

#### 4) Reflection spectra from thick accretion disks:

The goal of this project is to study the properties of reflected X-ray spectra from thick accretion disks around black holes using the Arcmancer code. The project will consist of applying the existing ray-tracing code to different accretion disk models in combination with models of X-ray reflection.

#### 5) Improved methods for mock observations of compact objects:

The goal of this project is to investigate new methods for generating mock observations of compact objects in general relativity that produce improved performance or accuracy. The project will involve implementing and evaluating methods such as adaptive image sampling and modified formulations of the radiative transfer equation in the Arcmancer code.

The third set of summer research projects is related to mathematical and statistical aspects of astrophysics. We offer the following two summer projects:

#### 6) Bayesian statistics and machine learning in theoretical astrophysics:

This project involves applying the methods of Bayesian statistics and machine learning in general to both observational and simulated astrophysical data. For example, this can consist of investigating the fundamental relations of elliptical galaxies and the relations between galaxies and their central supermassive black holes, both in observed and simulated data. Experience with (Bayesian) statistics and machine learning would be beneficial for this project.

#### 7) The geometric properties of the logarithmic Hamiltonian integrator:

The logarithmic Hamiltonian integrator is a numerical solver of Hamiltonian ordinary differential equations, known for exactly preserving the gravitational two-body orbit even in the rectilinear case. This summer project focuses on understanding how this phenomenon arises from the geometry of Newtonian gravity and the properties of conic sections. The project requires working knowledge of Hamiltonian mechanics and applied geometry, in addition to some mathematical aptitude.

When applying please indicate your preference for the research topic. All research topics could also form the basis for either a Bachelor or a Master thesis in Astrophysics, Theoretical physics or a related field. For advanced students there is also a possibility to continue with a PhD thesis project after the successful completion of the Master thesis.

For more information see:

http://www.helsinki.fi/~phjohans/Site/Group.html

Contact persons: Prof. Peter Johansson peter.johansson[at]helsinki.fi

Dr. Pauli Pihajoki pauli.pihajoki[at]Helsinki.fi