News: Institute of Physics

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Looking for inflationary features – the Bayesian way

Mon, 15/01/2024 - 09:52
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.
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New Year’s speech: a billion from OP JAK, 70th anniversary celebration and higher energy costs

Thu, 11/01/2024 - 06:37
At the beginning of his New Year's speech, Director Michael Prouza thanked the employees at all three facilities for coping with the difficult situation in 2023, when owing to their joint efforts FZU managed to overcome all the difficulties.
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Filip Matějka has succeeded with his lecture at the Materials Research Society meeting

Fri, 15/12/2023 - 11:22
The award for the best student lecture at one of the world's most important materials conferences was awarded to Filip Matějka, a PhD student working at the Institute of Physics. At the Fall Meeting of the Materials Research Society in Boston as part of a symposium on plasma technologies, he presented a lecture entitled "Unlocking the Limits of Plasma-Activated Liquids and Plasma Synthesis of Silicon Nanoparticles".
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The BOSS bispectrum analysis at one loop from the Effective Field Theory of Large-Scale Structure

Mon, 11/12/2023 - 09:25
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.
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Delta phosphorus doped diamond

Tue, 05/12/2023 - 12:54
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Causality and Effective Field Theories

Mon, 04/12/2023 - 10:32
I will review recent progress in understanding the connection between positivity bounds and scattering time delays in effective field theories.
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The Telescope Array Collaboration Detects an extreme-energy Cosmic Particle Named 'Amaterasu'

Fri, 01/12/2023 - 10:36
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.
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What will Large Scale Structure tell us about Dark Energy in the next decade?

Wed, 29/11/2023 - 10:28
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.
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Binary and multiple stellar systems from data analysis of the space observatory GAIA

Fri, 24/11/2023 - 10:11
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.
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Eva Maria Martins dos Santos of the FZU received the Auger Impact Award 2023

Thu, 23/11/2023 - 10:34
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.  
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Hearts of Darkness: Nonsingular Black Holes Beyond General Relativity

Mon, 20/11/2023 - 09:48
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.
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The 45th Ad Hoc Workshop on Jana2020. Standard, modulated and magnetic structures

Wed, 15/11/2023 - 12:56
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
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Remembering RNDr. Ondřej Šipr, CSc.

Mon, 13/11/2023 - 11:13
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)
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Probing light particles with high-energy astrophysics

Mon, 13/11/2023 - 10:52
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.
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