Novinky: Fyzikální ústav

Love numbers describe the induced conservative response of an object subject to the action of an external gravitational field. They offer insight into the body's internal structure, and can be used to test gravity in the strong-field regime. In particular, Linear Love numbers are known to be zero for Schwarzschild black holes in four dimensions. In this talk I show how to extend this result to include nonlinear effects. I define these coefficients as Wilson couplings in the context of the point-particle effective field theory (EFT). After finding an explicit solution for the (static) response of a perturbed Schwarzschild black hole, I perform a matching with the aforementioned EFT, showing that: (i) the vanishing of the linear Love numbers is robust against nonlinear corrections and (ii) the quadratic Love number couplings also vanish.

Scientific Research has recently evolved by performing data-driven modeling via machine learning (ML) techniques. ML is used to make machines "intelligent" by allowing them to learn from data (i.e. experience). Integrating ML in astrophysics can open new frontiers, revolutionize data analysis, and improve our understanding. However, challenges persist in deploying ML in Astrophysics research, including the need for robust algorithms, data limitations, and the interpretability of AI-driven decisions in critical scenarios. As advancements continue, ML and astrophysics exploration synergy promises groundbreaking discoveries and enhanced capabilities for humanity's endeavors beyond Earth's boundaries. This talk will explore the multifaceted potential applications of ML in multiple domains of astrophysics, for example, gravitational wave detection, exoplanet studies, astrochemistry.

Abstract:  NA62 is a fixed-target experiment at the CERN Super Proton Synchrotron studying rare decays of kaons and pions. Its primary objective is to measure the branching ratio of the ultra-rare decay of a charged kaon into a charged pion and two neutrinos. Additionally, the NA62 undertakes a diverse physics program that includes searches for new physics and precision measurements of other kaon and pion decays. In this seminar, I will present the recent results of the experiment, with a focus on contributions from our research group.    The seminar will be held in the main conference hall, Institute of Physics, Na Slovance 2, Prague 8. Location: https://goo.gl/maps/wEf7PsiLimSXMZhE9 For more info, see : https://indico.fzu.cz/event/245/ 

V úterý 8. dubna zemřel ve věku 95 let Peter Ware Higgs, britský teoretický fyzik, jehož jméno je neodmyslitelně spojeno s Higgsovým bosonem a Higgsovým mechanismem.

When primordial inhomogeneities are produced with sufficiently large amplitude in the early universe, they may subsequently collapse into primordial black holes. I will explain why the effect of quantum diffusion during inflation needs to be taken into account in such a case, and how the statistics of cosmological fluctuations can be predicted within the formalism of stochastic inflation. Quantum diffusion leads to a peculiar type of non-Gaussianity that cannot be captured by perturbative parametrisations. This leaves specific imprints on the statistics of collapsed structures that I will discuss. In particular, I will present recent results on the clustering of primordial black holes, which conditions the rate at which they merge and emit gravitational waves.

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

Domain wall networks arise in several new physics models and lead to many observable cosmological signatures: gravitational waves, primordial black holes among others. A proper calculation of these signals is an interesting but challenging problem. I will present recent progress on the topic and some phenomenological applications.

In the fully nonlinear regime, gravitational waves can reveal drastic new phenomenology absent in the linearized theory. In this talk, I will review the role of disformal field redefinition to explore both the theories space and the solution space of modified gravity theories (focusing on scalar-tensor gravity). I shall first comment on the effect of disformal transformations on the Petrov type of a given geometry and use this opportunity to discuss how this can guide us in the construction of new exact solutions in scalar-tensor theories. Then, I will show how disformal field redefinition can the properties of a congruence of geodesics and in particular how they can generate disformal gravitational waves at the fully nonlinear level. I will illustrate this by presenting a new exact radiative solution in Horndeski gravity describing a scalar pulse. Analyzing this new radiative solution will show that in such higher order scalar-tensor theory, shear can be generated by a purely (time-dependent) scalar monopole, a feature which only emerge at the fully non-perturbative level and descends from the scalar-tensor mixing inbuilt in Horndeski gravity

V uměleckém světě inspirovaném fyzikou elementárních částic se ocitnou návštěvníci výstavy prací vytvořených během úvodního lednového workshopu projektu BeInspired, určeného pro studenty základních a středních škol, který má za cíl propojovat svět vědy a svět umění. Vernisáž výstavy se konala v budově SOLIDu ve čtvrtek 14. března a dokazuje, že propojování vědců, učitelů fyziky a studentů napomáhá lepšímu porozumění oboru, ale i odkrývání často skryté vizuální krásy fyziky.

Abstract:  Ultra-high-energy cosmic rays have puzzled scientists for over six decades since their discovery. While their sources remain unknown, observational evidence suggests they are of extragalactic origin. The arrival directions of cosmic rays do not point back to their sources as they are charged particles and their trajectories are deflected in magnetic fields in the universe. However, the presence of anisotropic patterns in their arrival directions can help us in understanding their origins. In this talk, I will report on the observations of cosmic ray anisotropies, with a particular focus on the dipole anisotropy observed above 8 EeV and discuss the possible origins of this anisotropic pattern.     The seminar will be held in the main conference hall, Institute of Physics, Na Slovance 2, Prague 8. Location: https://goo.gl/maps/wEf7PsiLimSXMZhE9   The seminar will be also available via ZOOM video conference system: Meeting ID: 674 9629 6646 Passcode: 575511 or join meeting via direct ZOOM link  

Tajemství kosmického záření a způsoby jeho měření v argentinské Observatoři Pierra Augera přibližovali v pátek 8. března téměř třicítce středoškolských studentů vědci z Fyzikálního ústavu.

Letošní prestižní zlatou medaili SASP Erwina Schrödingera obdržel profesor Karl-Heinz Ernst za průkopnický příspěvek k základním a aplikovaným aspektům povrchových věd, stereochemie, chirality a nanomateriálů. Cena byla udělena v únoru na XXIV. sympoziu o atomové, klastrové a povrchové fyzice (SAPS) v italském Andalu.

First, I will present a novel approach to the flat-sky angular power spectrum approximation, highlighting its comparison to the full-sky formalism and presenting fast and efficient computational methods paramount for the data analysis of upcoming galaxy surveys. I will then construct the 3D galaxy observables like the power spectrum, systematically exploring the projection effects and relations of these observables to the theoretically computed quantities. These are becoming increasingly important in times of large-volume surveys that have an opportunity to detect GR effects related to the Hubble scale.

V pátek 19. dubna proběhne závěrečný souboj Turnaje mladých fyziků, fyzikální soutěže určené týmům středoškolských studentů. Na akci rádi uvítáme budoucí zájemce o soutěž z řad studentů i učitelů, bývalé účastníky i další diváky! Více informací o soutěži se dozvíte na webové stránce Turnaje mladých fyziků.

Vážení kolegové, dovolujeme si Vás pozvat na seminář Sekce fyziky elementárních částic, který přednese Ing. Jiří Hošek, DrSc. Více informací naleznete v pozvánce.