Current Group Members
Aleksander Kozak
Aleksander Kozak's research focuses on the theoretical and observational aspects of modified gravity theories, exploring their implications for both fundamental physics and astrophysical phenomena. His expertise lies primarily in scalar-tensor theories of gravity, studied through both the metric and Palatini formalisms. A key area of his work examines how these theories behave under Weyl transformations of the metric tensor and independent transformations of the linear connection. Aleksander has delved into the mathematical and physical equivalence of different conformal frames within the Palatini approach and is currently extending Horndeski’s theories into the metric-affine framework to analyze their properties under conformal changes.
Another significant aspect of Aleksander’s research involves the minisuperspace formulation of scalar-tensor gravity in cosmology. He has investigated scenarios where a dynamic scalar field drives the accelerated expansion of the Universe at late times. Together with Andrzej Borowiec, he demonstrated how observables in such theories can be expressed in terms of conformal invariants, simplifying the framework and enabling more efficient identification of integrals of motion. Their ongoing research focuses on spherically symmetric metrics within this formalism.
Aleksander has also studied the effects of modified gravity on terrestrial planets, including Earth. Collaborating with Aneta Wojnar, he showed that seismic data can constrain modified gravity models by revealing how these theories alter the internal structure of massive objects through modifications to the Newtonian limit. Their future research will extend this work to denser astrophysical objects, such as neutron stars.
Additionally, Aleksander has explored the implications of modified gravity for Big Bang nucleosynthesis (BBN). Since many modified gravity models affect the primordial abundances of elements, they offer a means to constrain alternatives to general relativity, which aligns well with observations but struggles with the lithium-7 problem, where observed lithium abundances are lower than theoretical predictions. Modifying the Universe’s expansion rate during BBN offers a potential resolution to this discrepancy, an avenue of ongoing investigation in Aleksander's research.
For more information on his publications, visit his INSPIRE profile.
Débora Aguiar Gomes
PhD Thesis: Theoretical and Astrophysical Aspects of Extended General Relativity
Débora Aguiar Gomes is a PhD student at the University of Tartu, Estonia, working under the supervision of Tomi Koivisto and Aneta Wojnar. Her research focuses on the theoretical foundations and applications of gravity, particularly in the context of extended general relativity. Her work explores the intersection of gravity theories, cosmology, and stellar physics.
For more information on her publications, visit her INSPIRE profile.
Sofía Vidal
PhD Thesis: Compact Objects and Gravitational Waves in Modified Gravity
Sofía Vidal is a PhD student at the University of Tartu, Estonia, working under the supervision of Laur Järv and Aneta Wojnar. Her work focuses on the astrophysical implications of modified gravity theories, in particular scalar-tensor theories, on compact objects as well as gravitational wave physics. Her research interests include the physics of white dwarfs and neutron stars.
For more information on her publications, visit her INSPIRE profile.
Grzegorz Dziewisz
MSc Thesis: Concept of Mass in Extensions of General Relativity
Grzegorz Dziewisz is a Master's student at the University of Wrocław, Poland, currently working under the supervision of Aneta Wojnar. His research focuses on the concept of mass in General Relativity and its extensions.
For his bachelor thesis, titled “Uncertainty of photon emission in Deformed Special Relativity”, Grzegorz worked under the supervision of Jerzy Kowalski-Glikman.
Niko Klag
BSc Thesis: Searching for the Dark Sector of the Universe in Stars
Dominika Klag is a Bachelor's student at the University of Wrocław, Poland, currently working under the supervision of Aneta Wojnar. She is researching the Dark Sector of the Universe in Stars.
She attempts to become a modern-day bard and considers options to achieve vampirism.
Marcin Klinkosz
BSc Thesis: Exoplanets as a Tool for Probing New Physics
Marcin Klinkosz is a Bachelor's student at the University of Wrocław, Poland, currently working under the supervision of Aneta Wojnar. His scientific interests are related to the physics of the Solar System planets and exoplanets.
In his free time....
Sebastian Marczyński
BSc Thesis: Light Elements Burning in Low-Mass Stars
Sebastian Marczyński is a Bachelor's student at the University of Wrocław, Poland, currently working under the supervision of Aneta Wojnar. His research focuses on the light elements burning in low-mass stars.
In his free time, Sebastian enjoys reading and practicing the guitar.
Dhrubajyoti Rakshit
Scientific project: Neutron stars in modified gravity
Dhrubajyoti Rakshit is a Master's student at the University of Wrocław, Poland. In his scientific project, supervised by Aneta Wojnar and Aleksander Kozak, he focuses on the astroparticle physics of neutron stars.
For his bachelor thesis, titled “...”, Dhrubajyoti worked under the supervision of ....
Andrzej Szczęśniak
Scientific project: White stars in modified gravity
Andrzej Szczęśniak is a Master's student at the University of Wrocław, Poland. In his scientific project, supervised by Aneta Wojnar, Andrzej focuses on the white dwarf stars data.
For his bachelor thesis, titled “...”, he worked under the supervision of ....
Collaborators from Other Institutions
Rebecca Briffa
Rebecca Briffa is a Researcher at Institute of Space Sciences and Astronomy, University of Malta. Her passion for the origins and evolution of the Universe has driven her research journey in this field. She collaborates with our group on topics related to the lithium problem and cosmic tensions in modified gravity. Additionally, she is skilled in using LaTeX as a tool for producing professional and scientific documents. Rebecca was supervised by Jackson Levi Said.
Outside of her academic career, she finds joy in staying active, particularly in rediscovering her love for running. It helps her maintain balance between her research and personal life.
For more information on her publications, visit her GoogleScholar profile.
Jackson Levi Said
Jackson Levi Said is a Professor at Institute of Space Sciences and Astronomy, University of Malta. He works mainly on the interface of fundamental physics with cosmological observational data. This involves both local distance ladder and early Universe cosmic microwave background data sets. He also works on developing new machine learning-driven data analysis toolkits that use the emerging suite of artificial intelligence techniques to explore the model space of new physics using these more sophisticated numerical techniques. He collaborates with our group on the project related to the problems of the Big Bang Nucleosynthesis.
Jackson is also a Chairperson of the COST Action CosmoVerse.
For more information on his publications, visit his INSPIRE profile.
Eva Lope-Oter
Eva holds a Ph.D. in Theoretical Physics from the Complutense University of Madrid, where her research focused on neutron star equations of state. She is currently contributing to the project “Effective Theories, Particle Physics, and Cosmology” within the same department. Her research interests include Nuclear Theory, High-Energy Astrophysical Phenomena, High-Energy Physics Phenomenology, General Relativity, and Quantum Cosmology.
In her free time, Eva enjoys reading, hiking, and dancing.
For more information on her publications, visit her INSPIRE profile.
Christian Pfeifer
Christian Pfeifer is a Postdoctoral Researcher at the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen, leading the research project "Momentum and velocity-dependent spacetime geometries: Traces of quantum gravity, fields in media and the gravitational field of kinetic gases".
His research is primarily focused on theoretical mathematical physics, particularly in the areas of general relativity, Finsler and Hamiltonian spacetimes, and quantum gravity phenomenology. He explores the mathematical foundations and physical implications of extending classical metric geometry to more generalized geometrical frameworks, such as Finsler and Hamiltonian spacetimes as well as metric affine gravity.
His work includes the gravitational field of kinetic gases, modified dispersion relations, radar length in non-metric geometries, and the implications of Finslerian structures on gravity and electrodynamics. These areas are significant in understanding potential deviations from standard relativistic physics and exploring physics beyond the standard model.
In addition, he is very active in organizing conferences like the yearly Tartu Gravity Conference, schools such as Searching for Quantum Gravity in the Sky, and community networks like the COST actions Quantum Gravity Phenomenology in the Multi Messenger Approach (QGMM) or Bridging High and Low Energies in Search of Quantum Gravity (BridgeQG).
Visit Christian's website to learn more about him and his research!
For more information on his publications, visit his INSPIRE profile.
Anna Horváth
Anna Horváth is a PhD student at HUN-REN Wigner Research Centre for Physics and Eötvös Loránd University, Budapest, Hungary. She collaborates with our group on topics related to theoretical and astrophysical aspects of Kaluza-Klein theory. Her research interests include the physics of neutron stars, with the PhD topic of "Modelling of compact stars using modern scientific methods". Anna is currently supervised by Gergely Gábor Barnaföldi.
In her free time, she likes to spend time on literature, music, and slightly weird sports.
For more information on her publications, visit her INSPIRE profile.
Former Students
Thesis Supervisions
- Pablo Navarro Moreno (U. Complutense of Madrid, Spain), supervised a master thesis titled “Modified Gravity in Neutron Stars”, co-supervised by Prof. Felipe J. Llanes-Estrada. Defended in June 2024. See the paper.
- Kärt Soieva (University of Tartu, Estonia), supervised a bachelor thesis titled “The cooling process of brown dwarfs in Horndeski theory of gravity.” Defended in June 2022. See the paper.
Project Supervision
- Anna Horváth (Wigner Research Centre for Physics, Budapest Hungary), supervised under the Hungarian programme Mobilitas at Complutense University of Madrid. February–March 2024 and September 2024. Paper in preparation.
- Aleksander Kozak (University of Wrocław, Poland), supervised under the Erasmus+ Traineeship at Complutense University of Madrid. February 2023. See the paper.
- Sreekanth Harikumar (National Centre for Nuclear Research, Warsaw, Poland), co-supervised together with Dr. Laur Jarv under the Dora Plus grant for visiting doctoral students at Tartu University. January–October 2022. See the paper.
- Débora Aguiar Gomes (Universidade Federal do Ceará, Brazil), co-supervised together with Dr. Tomi Koivisto under the Dora Plus grant for visiting doctoral students at Tartu University. February–December 2022. See the paper.
- Mercé Guerrero (Complutense University of Madrid, Spain), supervised under the Dora Plus grant for visiting doctoral students at Tartu University. April–July 2021 and October 2021 (under a Spanish grant). See the paper.