Graduate School in Particle and Nuclear Physics

Here you can find the list of supervisors and research projects in Graduate School in Particle and Nuclear Physics. If you're interested in applying for a position in the thematic field of the pilot, you should contact a possible supervisor from the list as soon as possible.

Dr. Henning Kirschenmann - Vector boson scattering in the all-hadronic final state 
Prof. Oleg Lebedev - Dark matter freeze-in at stronger coupling 
Prof. Kari Rummukainen - Phase transitions in gauge field theories with high-performance lattice simulations 
Dr. Matti Heikinheimo - Dark matter direct detection and constraints on non-relativistic effective operators 
Prof. Aleksi Vuorinen - Transport properties of cold and dense quark matter 
Prof. David Weir - Stochastic backgrounds and the LISA global fit 
Prof. Kenneth Österberg - Study of glueball candidates using central exclusive processes at the LHC 

Graduate School in Particle and Nuclear Physics research projects

The PhD research will be conducted within the “ForVVard” project funded by the Research
Council of Finland (PI Henning Kirschenmann), running in parallel to the doctoral pilot and
ending in August 2027.

The goal of the ForVVard project is to analyze the all-hadronic final state of Vector Boson
Scattering (VBS), a powerful probe into the mechanism of electroweak symmetry breaking
and highly sensitive to new physics contributions: Small deviations from Standard Model
predictions can signal the presence of anomalous electroweak couplings and of new physics
at energy scales beyond the reach of direct resonance production.

The research is conducted as part of the CMS collaboration at the LHC (CERN). It is also
tightly embedded into the CMS research group at the Helsinki Institute of Physics, well
known for its leading expertise in hadronic jets.

The candidate selected for this project will join the effort of performing the all-hadronic VBS
analysis on the combination of Run 2 and Run 3 data recorded by the CMS experiment,
within the time frame of the ForVVard project.

Depending on the profile of the candidate, two of the following areas would be the main
focus of the candidate’s research:

  • improving the understanding of jets in the challenging forward region, contributing to
    • the further development and validation of quark-gluon discrimination
      techniques in this region
    • or to improve jet calibrations in this region in synergy with the parallel ERC
      project “JEC4HL-LHC”
  • applying cutting-edge machine learning techniques to enable
    • particle-level jet energy calibrations, reducing flavour-related uncertainties
    • and/or to gain access to the polarization of wide jets from hadronic W/Z boson
  • analysis design for effective suppression of the QCD multijet background and
    improved signal sensitivity.

The candidate is expected to have a solid understanding of particle physics, which can be
complemented by previously attended high-energy physics-related schools or programs and
thesis work. To perform their studies, the student is required to have at least good skills in
Python or C/C++. Previous experience with big data tools such as Spark or Dask and CERN's
ROOT is considered an advantage, but not necessary for the application.


Supervisor: Prof. Henning Kirschenmann.
The position will start in the fall of 2024 and is expected to be carried out within three years.

The Standard Model particles account for about 5% of the energy density of the Universe, while
the rest of it is ``dark’’. One of the outstanding questions of modern physics is the nature of dark
matter. It is likely that dark matter corresponds to a new stable particle with weak enough
interactions. There are two leading mechanisms that can generate such particles in the Early
Universe. The first one is known as ``freeze-out’’ and assumes that dark matter was in thermal
equilibrium with the Standard Model plasma at some early stage in the evolution of the
Universe. The drawback of this idea is that no expected signatures of such dark matter have
been observed in various experiments. The second common option is known as ``freeze-in’’, in
which case dark matter was always out of equilibrium. The required coupling to other fields is
then tiny, making dark matter detection almost impossible.

It has recently been proposed (by the PI) that there could be a third option, which in a way
interpolates between freeze-in and freeze-out. In this case, dark matter is non-thermal, yet its
couplings are large enough to be observable. Such a possibility is realized if the dark matter
mass is above the maximal temperature of the Standard Model sector, making its production
Boltzmann-suppressed. The aim of the project is to study this novel idea in detail, focussing
both on the Early Universe dynamics and observational signatures. In particular, this type of
dark matter can be observed in direct detection experiments such as XENONnT. It can also be
probed at the LHC via ``invisible’’ Higgs decay, which will be measured precisely in the high
luminosity runs. The project will study correlations among the signals, which could answer
some of the important questions about the thermal history of the Universe.

Prof. Oleg Lebedev (Department of Physics)
The position will start in the fall of 2024 and is expected to be carried out within three years.

Non-Abelian gauge field theories are an essential building block in the Standard Model of particle
physics and feature also in several beyond-the-Standard-Model scenarios, including models with
strongly coupled Higgs sector and dark sector models. These models may have first order phase
transitions in the early Universe, which, in turn, may lead to gravitational wave generation, creation
of topological defects and may have influence on baryon number generation.

Phase transitions in non-Abelian gauge field theories are non-perturbative, and in order to obtain
reliable results numerical lattice Monte Carlo simulations are required. In this project the following
aspects of phase transitions are studied:

  • Surface tension between the confined-deconfined and deconfined-deconfined phases in
    SU(N) gauge field theory. This has been studied only for SU(3), and for larger N there are
    several different classes of surfaces. The results at larger N are also of theoretical interest in
    quantifying the accuracy of analytical large-N expansions.
  • Phase transition in model with adjoint representation fermions. These fermions preserve
    the center symmetry of SU(N), and thus confinement remains an exact symmetry.

The numerical simulations will be done using the high-performance hila lattice simulation
framework developed at the University of Helsinki. The project includes:

  • optimizing the GPU implementation in hila, using cuda and hip programming tools,
    especially using streams for asynchronous execution.

CSC provides support for program development, in the form of expert advice, benchmarking and
computational resources. The hila framework is published as open source, and includes easy-touse
tools for different lattice simulation projects.

Supervisor: Kari Rummmukainen (Department of Physics).
co-supervisor: Jussi Heikonen (CSC – IT Center for Science).
The position will start in the fall of 2024 and is expected to be carried out within three years.

The search for dark matter is one of the main interests of contemporary particle physics. Direct detection
experiments aim to observe the scattering events between dark matter particles and atoms in the target.
This is a rapidly advancing field, driven by developments in detector technology and by progress in
theoretical understanding of dark matter scattering events. This two-fold advance requires active
interaction between experts in experimental and theoretical methods and connects fields such as particle
physics and materials science. Our theoretical particle cosmology group has strong connections with
computational material physics research groups and with the research groups developing detectors for
dark matter direct detection experiments [1]. These lead to fruitful and innovative collaborations and this
PhD project will be carried out within this network. Depending on the candidate’s interests there is a
possibility to do part of the work as a member of a dark matter direct detection experiment.

The project contains three parts:

  1. Using existing results from direct detection experiments, constraints will be implemented on
    operators of the non-relativistic dark matter effective theory. The set of operators to be
    considered depends on the type of the dark matter candidate and on the target material of each
    experiment [1]. The results will be important in the interpretation of current and future results.
  2. Recent developments suggest that the time dependence of a possible signal may provide
    important new observables in dark matter direct detection experiments [2]. Several ongoing and
    planned experiments will utilize these features. In the project, analysis methods will be developed
    and strategies for their application will be outlined for this purpose.
  3. Recent development towards low-threshold detectors have raised the need to understand the
    precise response of the target materials to low energy scattering events [3]. In addition to the
    materials used in current experiments, there is potential for discovery and characterization of
    new suitable targets. In this part of the project, the materials science simulations will be combined
    with the results in parts 1 and 2.

The PhD project will be supervised by Doc. Matti Heikinheimo and Prof. Kimmo Tuominen.
The position will start in the beginning of 2025 and is expected to be carried out within three years.

[1] M. Heikinheimo, N. Mirabolfathi, K. Nordlund and K. Tuominen, Velocity Dependent Dark Matter
Interactions in Single-Electron Resolution Semiconductor Detectors with Directional Sensitivity, Phys. Rev. D 99 10 103018, 2019.
[2] M. Heikinheimo, K. Nordlund, S. Sassi and K. Tuominen, Probing the dark matter velocity distribution via daily modulation, ArXiv 2312.17550, accepted in Phys. Rev. D.
[3] S. Sassi et al, Energy loss in low energy nuclear recoils in dark matter detector materials, Phys. Rev. D 106 6, 063012, 2022.

Description of project: While the macroscopic properties of quiescent neutron stars (NSs) are mostly determined by the bulk thermodynamic properties of dense Quantum Chromo-dynamics (QCD) matter, their binary mergers – observable via both electromagnetic and gravitational waves – are highly sensitive to the transport properties of the system as well. Although higher-order corrections to the transport coefficients of cold and dense quark matter (QM) are in principle more straightforwardly available than those of high-temperature quark-gluon plasma (QGP), the weak-coupling expansions for the former are currently limited to the leading order. This greatly limits their use in relativistic hydrodynamic simulations of NS mergers and poses an obvious and well-motivated challenge for perturbative thermal field theory.

In the proposed project, we aim to evaluate the most important transport coefficients of unpaired quark matter to the next-to-leading order (NLO) in perturbation theory. This is facilitated in part by our existing preliminary results for the NLO gluon self-energy and our planned collaboration with Prof. Aleksi Kurkela, who is an expert of NLO transport calculations for high-temperature QGP. Quantities of interest include at least the shear and bulk viscosities of unpaired QM as well as its electrical and thermal conductivities that may all play an important role in the merger process. Due to the well-developed plans for the project, achieving the doctorate in the required three years is anticipated to be perfectly feasible with active engagement from the candidate’s side.

Supervisors: Academy research fellow Risto Paatelainen and prof. Aleksi Vuorinen.
The position will start in the fall of 2024 and is expected to be carried out within three years.

The LISA gravitational wave mission was adopted in January 2024, and will launch in the
mid-2030s. With a peak frequency of a few milliHertz, it will be sensitive to a wide range of
sources including supermassive black hole binary mergers and – potentially – a stochastic
background of gravitational waves from the early universe. However, the loudest source is
likely to be the many millions of compact binaries in the Milky Way and nearby galaxies,
some of which will be resolvable, but the majority will form a stochastic foreground to any
cosmological source. Their presence makes resolving other sources, such as a cosmological
background, a real challenge. Parameter estimation codes and ‘global fit’ approaches to
interpreting the LISA data area being developed (see e.g. Ref. [1]).

However, at the same time, modelling of the gravitational wave source from primordial
physics is improving [2]. This is particularly so for the strongest cases which could be most
easily constrained despite the bright foreground. In this project, you will investigate the
implications of improved stochastic background modelling on the ability to recover sources in
a global fit to LISA data. You will evaluate different approaches of generating mock data
(ranging from injection of a cosmological background into existing data, to a full ab initio
LISA simulation) and compare methods of recovering the phase transition signal.

The project benefits from and builds upon our group’s expertise in simulating and modelling
stochastic backgrounds of gravitational waves from primordial physics such as phase
transitions, as well as parameter estimation for stochastic backgrounds [3,4]. You will be
affiliated with the new Cosmology Data Centre Finland (CDC-FI), responsible for Finland’s
contribution to the Euclid and LISA ground segments. You will be expected to contribute to
CDC-FI’s operational work and commitments.

Anticipated results:
  • Realistic estimation of the ‘reach’ of the LISA mission to detect or constrain
    gravitational waves from primordial phase transitions, and potentially other stochastic
    backgrounds, based on combination of the effectiveness of global fit methods and
    state-of-the art modelling of gravitational wave backgrounds.
  • Contributions to the LISA global fit, focussed on improved predictions for the
    brightest potential cosmological backgrounds.

1. Tyson B. Littenberg and Neil J. Cornish. Prototype global analysis of LISA data with
multiple source types, Phys. Rev. D 107 (2023) 6, 063004
2. Chiara Caprini et al. (incl. Hindmarsh, Rummukainen, Weir). Detecting gravitational
waves from cosmological phase transitions with LISA: an update, JCAP 03 (2020)
024 [10.1088/1475-7516/2020/03/024].
3. Chloe Gowling, Mark Hindmarsh, Deanna C. Hooper and Jesús Torrado.
Reconstructing physical parameters from template gravitational wave spectra at
LISA: first order phase transitions, JCAP 04 (2023) 061 [10.1088/1475-
4. Mark Hindmarsh, Deanna C. Hooper, Tiina Minkkinen and David J. Weir. Recovering
a phase transition signal in simulated LISA data, in preparation.

Computational Field Theory Group
(David J. Weir and Mark Hindmarsh).
The position will start in the beginning of 2025 and is expected to be carried out within three years.

The existence of glueballs, particles made up exclusively of the mediators of the strong force,
gluons, are predicted by Quantum Chromodynamics (QCD), the theory describing the strong
interaction, however convincing experimental evidence of glueballs has not yet been found
despite large e?orts. Central exclusive processes at low invariant masses (2-6 GeV) with intact
protons in the final state are a promising gluon-enriched environment to produce glueballs,
especially tensor and pseudoscalar glueballs. These are predicted to be predominantly pure
gluon states without any mixing with quark-antiquark states and hence characterized by a
narrow width and flavour symmetric decay to all light (u, d and s) quark states. To be able to
identify that a particle is a glueball, its mass, decay width and spin as well as its decays to
mesons containing di?erent combinations of light quarks should to be determined.

You will study particle resonances that are glueball candidates in detail during the project using
the unprecedented large sample of ultra-pure low mass central exclusive events (ca 100 million)
collected by the CMS and TOTEM experiments at LHC during a dedicated LHC run with special
beam optics in 2018. The exclusivity of the events will be ensured by the matching of the
kinematics of the final state protons measured by TOTEM and the centrally produced hadronic
system decaying to charged particles measured by the CMS tracker. In addition, the CMS
tracker allows at these particle momenta to separate charged pions, kaons and protons, and,
hence provide a powerful tool to enhanced identification of the decay products of the glueball
candidates. You will determine the properties (mass, width and spin) and decays of candidates
for the tensor and pseudoscalar glueballs, especially vector-vector decays like 𝜌!𝜌!,𝐾∗!𝐾∗!
and 𝜙𝜙, in the mass ranges predicted by lattice QCD. You will work within the combined CMS
and TOTEM analysis working group for glueball analyses under the supervision of Prof. Kenneth
Österberg (University of Helsinki, Finland) and Prof. Christophe Royon (University of Kansas,
USA) together with other CMS and TOTEM colleagues.

Supervisor: Prof. Kenneth Österberg.
The position will start in the fall of 2024 and is expected to be carried out within three years.