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Journal Club

Journal Club

The Journal Club (JC) sessions aim to provide a safe space for early-career researchers working in the field of cosmology to freely interact, present their work and exchange ideas.

The friendly environment of the sessions provides a medium for participants to ask the questions they want. The JC sessions are designed to foster a culture of communication, collaboration and learning, empowering early-career researchers to advance their knowledge and skills in cosmology interactively.

The sessions will be held on a monthly basis and will feature 2 talks, each lasting for 20 minutes,
followed by 10 minutes of discussion and Q&A.

Upcoming Sessions

Coming soon...

Past Sessions

Miguel Pinto
University of Lisbon
Tuesday - May 7, 2024 @ 10:00am CET
Title: Cosmology, matter creation, and regular black holes in non-minimal geometry-matter coupling theories

Although General Relativity remains an impressive description of gravitational phenomena, it suffers from specific issues, such as the incapacity of producing an accelerated expansion without introducing a cosmological constant, non-renormalizability, and lack of uniqueness. These problems could hint that new physics is needed, and one possible avenue is to assume that a more general action describes gravity, which is the core idea behind Modified Gravity Theories (MTGs). In this talk, I provide an overview of a particular class of MTGs, the non-minimal geometry-matter coupling theories. More specifically, I offer my perspective on why this class of theories remains a valid option to put our knowledge of gravity to the test. Moreover, I highlight some projects I have been working on in this line of research, such as gravitationally induced particle production, late-time cosmic evolution, and regular black hole solutions. Finally, I plan to briefly mention a work-in-progress Hubble tension research program involving a theory of this type.

arXiv:2205.12545, 2309.15497, 2310.15018

Masoume Reyhani
K.N. Toosi University of Technology, Tehran
Tuesday - May 7, 2024 @ 10:00am CET
Title: Structure Formation in Various Dynamical Dark Energy Scenarios

In modern cosmology, cosmological tensions are a leading topic in the field. One of the most controversial subjects in the wake of these discrepancies is the difference between the direct and indirect measurements of the Hubble constant. This has led to alternative scenarios becoming the subject of study in modern cosmology, with dynamical dark energy being one of the most promising. Studies have shown that the key to distinguishing between different dynamical dark energy models lies in their effects on large scales. Therefore, the Integrated Sachs-Wolfe (ISW) effect could be a hint for finding the most convincing scenarios for dark energy. In this work, we have investigated the effect of dynamical dark energy models (CPL, JBP and BA) in comparison with constant dark energy models (LCDM and wCDM) on structure formation in late time by evaluating the matter power spectrum and ISW effect. Our study confirms that the matter power spectrum and the ISW effect are suitable probes for studying dark energy.


Marcin Postolak
University of Wroclaw | WROC · Instytut Fizyki Teoretycznej
Monday - March 18, 2024 @ 10:30am CET
Title: Is it possible to separate baryonic from dark matter within the Λ-CDM formalism?

We found general solutions of matter stress-energy (non-)conservation in scalar-tensor FLRW-type cosmological models by extending the logotropic formalism to the case of non-minimal coupling between the scalar field and new dark fluid candidates. The energy conditions expressed by the generating function are introduced. Next, we investigate the possibility of separating baryonic from dark matter and explain their ratio as a chameleon effect in the presence of non-minimal coupling. To answer the question affirmatively we analyze simple extensions of the Λ-CDM model by adding a non-minimally coupled scalar field in the Einstein frame. Two scenarios involving either a scalaron (quintessence) or a phantom (ghost) are numerically solved and compared. As a result, it is shown that in both cases LCDM model can be reproduced with a high accuracy in the region covered by observations. As expected, in the case of the phantom (ghost) field the Big-Bang scenario is replaced by the (matter) Bounce.

Yashi Tiwari
Indian Institute of Science
Monday - March 18, 2024 @ 10:30am CET
Title: Towards a possible solution to the Hubble tension with Horndeski gravity

The Hubble tension refers to the discrepancy in the value of the Hubble constant H0 inferred from the cosmic microwave background observations, assuming the concordance ΛCDM model of the Universe, and that from the distance ladder and other direct measurements. In order to alleviate this tension, we construct a plausible dark energy scenario, within the framework of Horndeski gravity which is one of the most general scalar-tensor theories yielding second-order equations. In our set-up, we include the self-interactions and nonminimal coupling of the dynamical dark energy scalar field which enable very interesting dynamics leading to a phantom behaviour at low redshifts along with negative dark energy densities at high redshifts. These two features together make this model a promising scenario to alleviate the Hubble tension for appropriate choices of the model parameters. Towards a consistent model building, we show that this set-up is also free from both the gradient and ghost instabilities. Finally, we confront the predictions of the model with low redshift observations from Pantheon, SH0ES, cosmic chronometers and BAO, to obtain best fit constraints on model parameters.

Future Talks