Novinky z FZÚ AV ČR

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.

Zveme vás na seminář profesora Kenichi L. Ishikawy z Univerzity Tokyo v Centru HiLASE na téma Building artificial intelligence and science-and-theory-based simulations toward cyber-physical-system (CPS) laser manufacturing.

Tématem fotografické soutěže roku 2023 byla fyzika v našem každodenním životě, zadání pro pracovníky Fyzikálního ústavu snadno uchopitelné. Ale ačkoli by se mohlo zdát, že se v soutěži utkají především snímky vzniklé během pracovní doby, vítězná trojice snímků tento předpoklad nepotvrzuje. Stejný trend kopírují i fotografie zaslané do studentské soutěže.

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.

Vážení kolegové, dovolujeme si Vás pozvat na seminář Sekce fyziky elementárních částic, který přednese Dr. Roman Lysák. Více informací naleznete v pozvánce.

Ve čtvrtek 11. ledna předala předsedkyně Akademie věd ČR Eva Zažímalová čtyřem předním vědcům statut emeritního vědeckého pracovníka AV ČR. Slavnostní udílení se uskutečnilo v sále Fyzikálního ústavu na Slovance za účasti zástupců Akademické rady AV ČR a vedení Fyzikálního ústavu.

The all-sky diffuse astrophysical neutrino spectrum is measured by IceCube with increasing statistical significance, since more than 10 years. In addition, recent observational findings manifest some connections with astrophysical sources, and for the first time a non-electromagnetic image of our galaxy has been delivered by IceCube. In this seminar I will present the most recent experimental results on high-energy neutrinos, and I will deeply discuss the connections with other astrophysical messengers. In particular, I will show how the study of interactions of cosmic rays, in the extragalactic propagation and in the candidate sources, might help in unveiling the origin of high-energy neutrinos and ultra-high-energy cosmic rays. Prospects from future experimental upgrades will be also highlighted, as well as the importance of a multimessenger approach in the modelling of astrophysical sources.

The seeds of the Universe’s large scale structure are widely thought to have been generated during a period of cosmic inflation. Simple, generic models of inflation lead to a smooth, almost scale-invariant spectrum of primordial curvature perturbations. However, this prediction relies on a set of physical assumptions, which, if broken, could lead to a power spectrum with strong scale dependence in the form of, e.g., cutoffs spikes or modulations – commonly referred to as inflationary “features”. The search for features is complicated by increased numerical precision requirements and typically non-trivial shapes of the likelihood function – taking conventional random sampling-based analysis methods to their limits. I will introduce a new, efficient machine-learning approach based on Gaussian Process Regression and Bayesian Optimisation. Applying it to search for inflationary features in Planck data, I will demonstrate its effectiveness and discuss further applications, such as the calculation of Bayesian evidences for model selection.

Baví vás popularizovat vědu a rádi se zapojujete do popularizačních akcí FZU, teprve o tom uvažujete, nebo s tím třeba začínáte díky novému grantu zahrnujícímu i body vzdělávání a popularizace vědy? Ať už máte jakékoli zkušenosti a cíle, je právě vám určeno novoroční setkání popularizátorů a popularizátorek vědy na FZU konající se v pondělí 29. ledna v sále a předsálí SOLIDu.