News from FZU

In this talk, I will discuss our recent analyses of the BOSS galaxy-clustering power spectrum and bispectrum data using the one-loop predictions from the Effective Field Theory of Large-Scale Structure (EFTofLSS), where we find impressive constraints on cosmological parameters, including primordial non-Gaussianity. After reviewing the theoretical underpinnings of the EFTofLSS, which allows for a controlled and consistent perturbative expansion of cosmological observables on large scales, I will describe our results. Overall, we find that including higher-order predictions, which allows us to analyze the data to smaller length scales and access more physical modes, significantly reduces the error bars of cosmological parameters. Even with this existing BOSS data, some of our results are competitive with CMB constraints. This points to exciting, even stronger constraints from future surveys such as DESI, Euclid, and MegaMapper. I will also discuss some new theoretical developments, including signals that allow us to directly measure the formation time of galaxies.

I will review recent progress in understanding the connection between positivity bounds and scattering time delays in effective field theories.

In a ground-breaking discovery, the Telescope Array Collaboration has detected an extremely energetic particle, named "Amaterasu" after the Japanese celestial sun goddess. This cosmic rays event surpasses the energy achieved by artificial particle accelerators by more than a million times. The origins of such high-energy particle remain mysterious, as tracing back the arrival direction does not reveal an obvious source, for example a galaxy.

With the upcoming generation of galaxy surveys such as Euclid, LSST (Vera Rubin Observatory) DESI and SKAO, among others, the cosmological community will have groundbreaking measurements of the Large Scale Structure of the Universe. These measurements will provide very precise information about the expansion rate, the growth of non-linear structures as a function of scale and the impact of baryonic feedback. These measurements have to be confronted against theoretical models that aim to explain the nature of Dark Matter, Dark Energy and possibly resolve the ongoing tensions we face in cosmology, such as the H0 and the S8 discrepancies. In this talk I will recall some of the competing and alternative models to the standard LCDM paradigm that have been proposed in the literature in the last decades, focusing on scalar-tensor theories with and without screening and generalized parametrizations of Modified Gravity. I will discuss how, with the combined observations from Euclid (especially with the complementarity of Weak Lensing and Galaxy Clustering) and the advent of Radio-cosmology, we expect to be able to constrain that vast theoretical parameter space. By doing so, we will also hopefully measure the neutrino mass and learn about the fundamental physics of baryons and non-linear structure formation. Towards the end I will discuss also the challenges we face in computational complexity and how this is being resolved with emulators and the emerging field of differentiable programming.

Dear colleagues, we would like to invite you to the seminar of Division of Elementary Particle Physics of Institute of Physics, presented by Dr. Petr Závada. For more info, please see invitation.

Dr. Eva Maria Martins dos Santos of the FZU received the Auger Impact Award 2023 on November 17 in recognition of the outstanding efforts on Monte-Carlo simulation coordination, which has a tremendous impact on the results published by the Pierre Auger Observatory but is not necessarily visible, and for her extremely responsive and service oriented attitude.  

Black holes contain, deep in their interior, theoretical evidence of the failure of general relativity. A series of fundamental results, starting from the 1965 Penrose singularity theorem, proved that physically realistic initial conditions will unavoidably produce a singular black hole spacetime. It is generally expected that a full theory of quantum gravity should remove the singularities that appear in general relativity. However, the lack of proper understanding of the dynamical laws dictating the evolution of spacetime and matter in these extreme situations hinders the extraction of predictions in specific models. I will discuss, in a model-independent manner, the different possibilities that singularity regularization may open, focus on fundamental open issues that need to be addressed to obtain viable nonsingular black hole candidates, and finally discuss observational signatures.

The program is composed of four sessions. Each session starts with a lecture and continues with practical exercises. For practical exercises, the users will be provided with a cookbook, installation files and necessary data. Preliminary experience with Jana2006/Jana2020 is not required. The workshop is OFF LINE. For registration please send e-mail to Michal Dusek, dusek [at] fzu [dot] cz

Courtyard at Cukrovarnická, morning, around 2015. I was heading to work, and Ondra was approaching me, just leaving the institute. We looked at each other briefly, and Ondra blurted out, "What are you staring at? I've already earned my keep!" That was typical Ondra’s humor, snappy and unexpected, with a sense of the moment. (MD)

Light particles are very attractive candidates for new physics beyond the Standard Model. Several theories introduce them and, in some portion of the parameter space, they can act as good dark matter candidates. Their phenomenology is very diverse and specific signatures can be tackled using astroparticle experiments. I will provide an overview on the techniques and recent results used to constrain light particles with gamma rays and celestial objects.

Globular clusters (GCs) have the potential to bring light in the missing mass problem. It has been argued earlier that dark matter halos of dwarf galaxies must have central cores, to prevent their GCs to quickly settle into their galaxy nuclei: the time necessary for dynamical friction to remove their GC's energy and angular momentum would come out less than the age of the clusters if the halos were cuspy. The sunk GCs would form nuclear star clusters. It was found analytically that the problem of fast GC sinking is even more severe for MOND, a leading alternative to dark matter that otherwise well reproduces galaxy dynamics. The problem was anticipated for low-mass low-surface-brightness galaxies. We inspected the issue using high-resolution simulations. We initially investigated GCs of gas-free ultra-diffuse galaxies. We found that first GCs indeed approach the center of their host galaxy quickly, but then, once the GC moves within the central half effective radius of the galaxy, the sinking almost stops, opposing the analytic predictions. This comes from simplifying assumptions made when deriving analytically the dynamical friction effect. Actually, the phenomenon called core stalling occurs, that had previously been described in Newtonian gravity and is the reason why GCs can survive for a long time in cored dark matter halos. Next, we explored the consistency of MOND with the existence of GCs in isolated dwarf galaxies. These disky galaxies hold a large fraction of their baryons in the form of gas. We found that a GC can indeed spiral quickly into the center. However, if the supernova explosion rate is sufficient, then the GC has no problem to survive for a Hubble time, since the supernova explosions cause strong fluctuations in the gravitational potential of the galaxy, such that they give the GC random pushes.

On October 28, 2023, President Petr Pavel awarded astrophysicist Jiří Grygar of the Institute of Physics, Czech Academy of Sciences, the Medal of Merit 1st class for services to the state in the field of science.

As gravitational-wave detectors become more sensitive to lower frequencies, they will increasingly detect binaries with smaller mass ratios, larger spins, and higher eccentricities. In this talk I describe how gravitational self-force theory, when combined with a method of multiscale expansions, provides an ideal framework for modelling these systems. The framework proceeds from first principles while simultaneously enabling rapid generation of waveforms on a timescale of milliseconds. I discuss the state of the art in this method: nonspinning, quasicircular waveforms at second perturbative order in the mass ratio. I present progress toward extending this second-order model to include spins and to include the final merger and ringdown. I also discuss the domain of validity of these models, focusing on their accuracy for mass ratios in the intermediate regime ~1:10 to 1:100.

In the webinar, we will describe what considerations should be taken during the design of high energy and average power laser like Bivoj.