News: Institute of Physics

Do you sometimes find an error in the largest internet encyclopedia? Are you missing Wikipedia articles about eminent scientists? We can change that together! In March, we’re going to start with the topic of Women in Science and join this year’s "Měsíc žen na Wikipedii" (Women's month on Wikipedia). Newbies need not worry; experienced editors will be at their disposal to help them with the articles. All you need is to bring your laptop. We will arrange refreshments for you in the beautiful building of the Academy of Sciences. We are looking forward to welcoming you at the edit-a-thon! P.S.: Some of us organizers are newbies too. We are going to learn best practices in editing together!

The Institute of Physics of the Czech Academy of Sciences organizes the Physics Photography 2024 competition, which this year is thematically dedicated to "transformation".  The main goal of the competition is to popularize the beauty of physics and to break the stereotypes of the perception of this field of science. The photography competition ends with the announcement of winners and an exhibition of the awarded and selected photos during the Night of Scientists, which is organized by the institute in the Na Slovance facility on Friday, September 27, 2024.

In this talk I will discuss the potentialities of future ground-based millimeter-wavelength line intensity mapping for constraining the properties of gravity at cosmological scales. I shall first introduce line intensity mapping experiments, focusing on their key properties and differences with respect to galaxy surveys. I will describe the main reasons to consider alternative theories of gravity. I will concentrate on the properties of the theories that have been tested in arXiv:2304.08471. Finally, I will present and discuss the results obtained.

Part1: The Scalar Field Dark Matter (SFDM) model assumes an ultralight scalar particle (m~1e-22 eV) as a candidate to explain the Dark Matter nature. This model obeys the Schrodinger-Poisson (SP) system of equations coupled to gravity in the non-relativistic approximation. While on a large scale, it behaves as a non-relativistic and pressureless fluid, equivalent to CDM, on a galactic scale, it leads to effective "quantum pressure" and the formation of Bose-Einstein condensates (BEC). This implies an interesting phenomenology which is different from CDM. In fact, the SFDM model shows a cut-off on small-scale structures and predicts cored halos. In this presentation, I will show how to construct the initial conditions for the SP system and the evolution for both small-scale and cosmological simulations. Additionally, I will show some examples of mergers of different halos assembly and the final states of such systems. Finally, I will discuss some perspectives that include Zoom-in cosmological simulations for this model. Since these efforts are expected to be compared with observations, we will use the rotation curves derived from the MaNGA galaxy catalogue to constrain the SFDM-free parameters of the model. Part2: Given that the nature of dark matter is currently unknown, exploring alternative theories to the Standard Model and their implications on galactic scales is both feasible and compelling, partly because of the continuous development of computational resources. In this talk, we will review the implementation of numerical methods to study the properties and evolution of some astrophysical systems in dark matter models. First, we will study the impact of the Generalized Dark Matter (GDM) model on the formation and distribution of Hickson Compact Groups (HCGs) using the merger trees method and mock catalogues. Studying these systems is interesting for understanding the effects of dark matter on galactic scales in dynamically active structures. Additionally, we will explore the evolution at small scales of halos within the Cold Dark Matter (CDM) and Scalar Field Dark Matter (SFDM) models, using initial conditions from cosmological N-body simulations to compare the final state of the halos, including the shape of the density profile and the process of virialization. In both cases, the properties of astrophysical systems can be compared to observations of nearby galaxies through their rotational curves, as well as distant galaxies, by studying the hierarchy of each model. This allows us to describe the weaknesses and strengths of the dark matter candidates.

We invite you to a seminar by Professor Kenichi L. Ishikawa of The University of Tokyo at the HiLASE Centre on the topic of Building artificial intelligence and science-and-theory-based simulations toward cyber-physical-system (CPS) laser manufacturing.

Calculation of the mass-transfer rate of a Roche lobe overflowing star is a fundamental task in binary star evolution theory. First, we introduce existing mass-transfer prescriptions that are based on a common set of assumptions that combine optically-thick and optically-thin regimes with different flow geometries. Next, we present our new model of mass transfer based on the assumption that the Roche potential sets up a nozzle converging on the inner Lagrangian point and that the gas flows mostly along the axis connecting both stars. We derive a set of 1D hydrodynamic equations governing the gas flow with the value of the mass-transfer rate being determined as the eigenvalue of the system. The inner boundary condition directly relates our model to the structure of the donor obtained from 1D stellar evolution codes. For the polytropic equation of state we obtain an algebraic solution that gives the mass-transfer rate within a factor of 0.9 to 1.0 of existing optically-thick prescriptions and reduces to the existing optically-thin prescription for isothermal gas. For a realistic EOS, we find that the mass-transfer rate differs by up to a factor of 4 from existing prescriptions. We illustrate the effects of our new model on a realistic binary star system. Finally, we explain how additional physics such as radiation or magnetic fields can be implemented into our new model.