The Fifth Zeldovich Meeting

Invited speakers

Gennady Bisnovatyi-Kogan Space Research Institute (IKI), Russia	Hubble Tension challenge in the modern cosmology: possible solutions One of the problems in the modern cosmology is a so-called Hubble tension (HT), which is the difference between values of the present Hubble constant H0, measured by observation of the universe at redshift z ≤ 1, and the same value measured by observations of a distant universe by observations of CMB fluctuations corresponding to z ≌1100. We suggest that this Tension may be explained by deviation of the cosmological expansion from a standard 𝜦CDM model of a flat universe, due to the action of an additional variable component DEV during the post-recombination stage. In order to maintain the almost constant DEV/DM energy density ratio during the whole time interval at z < 1100z<1100, it is necessary to allow the existence of a wide mass DM particle distribution.
Maria Giovanna Dainotti National Astronomical Observatory of Japan, Japan	TBD
Massimo Della Valle Capodimonte Astronomical Observatory and INAF, Italy (TBC)	TBD
Evgeny Derishev Institute of Applied Physics, Russia	Pair-balance model for relativistic shocks and its application to astrophysical sources Among astrophysical objects whose emission originates from relativistic shocks are active galactic nuclei, gamma-ray bursts, and pulsar winds. Their exceptionally broad spectra are due to synchrotron and inverse Compton emission of accelerated leptons. Although these radiation processes are common in space, the relativistic shocks and shear flows possess an efficient feedback mechanism that sets them apart from other particle acceleration sites. The feedback operates through inelastic collisions of high-energy inverse Compton photons with low-energy synchrotron photons, that create electron-positron pairs in a region where the flow's velocity is relativistic with respect to the photons' source. The pairs gain energy from the difference in flow's velocity. This constitutes the converter acceleration mechanism. Whenever it is efficient, the converter acceleration reaches nonlinear saturation regime, where momentum transfer by high-energy photons keeps flow's velocity gradient at minimum necessary for converter acceleration to operate. The balance occurs when photons from the inverse Compton peak in the spectrum have barely enough energy to produce pairs with photons from the synchrotron peak. This balance condition predicts the positions of both synchrotron and inverse Compton peaks, and the ratio of their heights. The predictions are in line with recent observations of TeV emission from gamma-ray burst afterglows.
Zhan-Arys Dzhilkibaev Institute for Nuclear Research of the Russian Academy of Sciences, Russia	Neutrino Telescope Baikal-GVD: Status and Nearest Future The progress in the construction and operation of the Baikal Gigaton Volume Detector in Lake Baikal is reported. The detector is designed for search for high energy neutrinos whose sources are not yet reliably identified. It currently includes over 3500 optical modules arranged on 98 strings, providing an effective volume of 0.6 km3 for cascades with energy above 1 PeV. We review the scientific case for Baikal-GVD, the construction plan, and first results from the partially built experiment, which is currently the largest neutrino telescope in the Northern Hemisphere and still growing up.
Marat Gilfanov Max-Planck Institute for Astrophysics, Germany and IKI, Russia	SRG/eROSITA all-sky survey: from solar flares and neutrino sources to cosmology After more than two years of scanning the sky the eROSITA X-ray telescope aboard SRG orbital observatory produced the best ever X-ray maps of the sky and discovered more than three million X-ray sources, of which about 20% are stars with active coronas in the Milky Way, and most of the rest are galaxies with active nuclei, quasars and clusters of galaxies. eROSITA detected over 103 sources that changed their luminosity by more than an order of magnitude, including about a hundred tidal disruption events. Two tidal disruption events are associated with IceCube neutrinos. SRG/eROSITA samples of quasars and galaxy clusters will make it possible to study the large-scale structure of the Universe at z~1 and measure its cosmological parameters. I will review some of the SRG/eROSITA results in the Eastern Galactic hemisphere.	Spektr-RG, a Russian–German high-energy astrophysics space observatory, to be reported by Rashid Sunyaev and Marat Gilfanov, Max-Planck Institute for Astrophysics, Germany and Space Research Institute (IKI) of Russian Academy of Sciences, Russia
Paolo Giommi Italian Space Agency, Italy	TBD
Luca Izzo Niels Bohr Institute, Denmark (TBC)	TBD
Sang Pyo Kim Kunsan National University, South Korea	TBD
Michael Kramer Max-Planck-Institut fuer Radioastronomie, Germany (TBC)	TBD
Jutta Kunz University of Oldenburg, Germany (TBC)	TBD
Claus Laemmerzahl University Bremen, Germany	New quantum technologies and gravity As has been emphasized in the talk of Hansjoerg Dittus, the second quantum revolution enables new technologies which are not accessible through classical physics. These technologies are characterized by the engineering and manipulating of quantum states. In this talk the interface between these new technologies and the gravitational interaction is highlighted by considering a few topics: (i) a metrological triangle for gravity, (ii) two gravitational constants, (iii) Hong-Ou-Mandel interferometry in gravitational fields, and (iv) quantum imaging of the gravitational field.
Di Li National Astronomical Observatories of China, China	Discoveries from FAST The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has been in operation since early 2020. Largely motivated by the great Arecibo observatory, FAST now perches on the apex of sensitivity among centimeter-band radio instruments and will stay there until the advent of SKA. In a little three years, FAST data has facilitated more than 150 journal papers, including at least 7 on Nature, 2 on Science, 1 on Science Bulletin, and a few more on high-impact astronomy journals, such as Nature Astronomy. I will present a brief overview of FAST's discoveries so far, with particular emphasis on those that better reflects the unique advantages of this observatory. For example, the precise Zeeman measurement based on our novel HI Narrow Self-Absorption (HINSA) technique, the high quality HI images (~1% flux uncertainty), the world's first persistently active fast radio bursts (FRBs), etc. With these discoveries, I will also ponder upon the potential progresses to be made in terms of the better understanding the fundamental physical principles of the cosmos.	FAST (Five-hundred-meter Aperture Spherical radio Telescope), the world's largest filled-aperture radio telescope, observing pulsars and fast radio bursts, to be reported by Di Li, National Astronomical Observatories, Chinese Academy of Sciences, China
Massimiliano Lincetto Ruhr-Universität Bochum, Germany	TBD	ICECube, neutrino observatory located at the South Pole, measuring neutrinos in the energy range 100 GeV to several PeV, with the volume 1 km3, to be reported by Massimiliano Lincetto, Ruhr-Universität Bochum, Germany
Vladimir Lipunov SAI, Moscow, Russia	TBD	MASTER (Mobile Astronomical System of the TElescope-Robots), a global robotic network of optical telescopes, observing transients such as gamma-ray bursts, to be reported by Vladimir Lipunov, Moscow State University, Russia
Ruoyu Liu Nanjing University, China	TBD	LHAASO (Large High Altitude Air Shower Observatory), a gamma-ray (200 GeV to 1 PeV) and cosmic-ray (from 1 TeV to 1 EeV) observatory in Tibet, China, to be reported by Ruoyu Liu, Nanjing University, China
Andrea Merloni Max Planck Institute for extraterrestrial Physics, Germany (TBC)	TBD
Felix Mirabel CEA Saclay, France	Black hole induced star formation in the early universe In the local universe have been observed enhancements of star formation due to relativistic jets from accreting black holes (BHs). These BH “positive feedbacks” take place by the interaction of BH-jets with high-density molecular clouds, which leads to compression of the gas and subsequent enhancement of star formation. This BH-jet triggering mechanism of star formation must have been more important in the early universe, for two reasons. First, the global gas density in the universe evolves with redshift z as (1+z)3, and at z = 30 the global gas density would be more than 104 times the global gas density in the local universe. Second, revently have been increasing indications that in the galaxies of the early universe massive BHs came first and grow faster than the stellar populations. In this context, I propose that the rapidly growing BH seeds of the SMBHs of 109 M⊙ in quasars at z = 7 may have induced the formation of the first massive stars of Pop III.
Razmik Mirzoyan Max-Planck-Institute for Physics, Germany	Selected Studies of Cosmic and Gamma Rays with the MAGIC telescopes MAGIC is a ground-based Imaging Atmospheric Cherenkov Telescope (IACT) for very high energy gamma-ray measurements that has pioneered high-sensitivity measurements down to a few tens of GeV. It includes a system of double telescopes with a diameter of 17 m, separated by a distance of 85 m, operating in coincidence mode (stereo). The telescopes are located at an altitude of 2200 m above sea level in the European Northern Observatory El Roque de los Muchachos on the Canary Island of La Palma. In recent years, the MAGIC collaboration has developed innovative techniques that have increased the dynamic range and sensitivity of the telescopes to around 20 GeV and up to 100 TeV. These have expanded and greatly improved the capabilities of the instrument. In this report we want to focus on some selected observations of cosmic and gamma rays of galactic and extragalactic origin.	MAGIC (Major Atmospheric Gamma Imaging Cherenkov Telescope), operating in the energy range from 30 GeV to 100 TeV, to be reported by Razmik Mirzoyan, Max-Planck-Institute for Physics, Germany
Volker Perlick ZARM, University Bremen, Germany   Personal website	Influence of a plasma on the shadow of black holes If a black hole is seen against a backdrop of bright light sources, it forms as dark disc on the observer's sky, known as the "shadow" of the black hole. If one assumes that light rays are not influenced by a medium, i.e., if one assumes that they are lightlike geodesics of the spacetime metric, the boundary curve of the shadow can be analytically determined, provided that the spacetime is stationary and axisymmetric and that the Hamilton-Jacobi equation for lightlike geodesics separates. In this talk it is discussed under which conditions such an analytical determination of the shadow is possible if the light rays are influenced by a non-magnetised pressure-less electron-ion plasma. Several examples are worked out, not only for black holes but also, for the sake of comparison, for some "black-hole impostors" such as wormholes. In particular, it is discussed if the boundary curve of the shadow can form "fishtails".  The talk is partly based on joined papers with Oleg Tsupko, Gennady Bisnovatyi-Kogan, Barbora Bezděková and Jiří Bičák.	Shadow curve with fishtails, in a plasma on Kerr spacetime.
Tsvi Piran The Hebrew University, Israel	TBD
Konstantin Postnov Sternberg Astronomical Institute, Moscow State University, Russia	TBD
Paolo Soffitta IAPS, INAF, Rome, Italy	The Imaging X-ray Polarimetry Explorer (IXPE) results from the first 1.5 years of observation The Imaging X-ray Polarimetry Explorer (IXPE) is a NASA-ASI Small Explorer mission selected on January 2017 and launched on 9th December 2021. Three X-ray mirrors are coupled to three Detector Units clocked at 120° each one hosting a Gas Pixel Detector, sensitive to X-ray polarization designed, built tested, and calibrated by INAF and INFN institutes. Some dozens of celestial X-ray sources, from almost all the classes, were observed so far, and for more than a half IXPE detected significant polarization. Some unexpected results were found by IXPE and in this talk after an introduction to the mission I will describe the main Astrophysical achievements reached so far.	IXPE (Imaging X-ray Polarimetry Explorer), space-based observatory for measuring the polarization of X-rays launched by NASA, to be reported by Paolo Soffitta, Istituto Nazionale di Astrofisica, Italy
Rashid Sunyaev Max-Planck Institute for Astrophysics, Germany and Space Research Institute (IKI), Russia (TBC)	TBD	Spektr-RG, a Russian–German high-energy astrophysics space observatory, to be reported by Rashid Sunyaev and Marat Gilfanov, Max-Planck Institute for Astrophysics, Germany and Space Research Institute (IKI) of Russian Academy of Sciences, Russia
Alexei Starobinsky Landau Institute for Theoretical Physics, Russia	New developments in the inflationary scenario
Lev Titarchuk University di Ferrara, Italy and Astro Space Center, Lebedev Physical Institute, Russia	The spectral signatures of BHs versus NSs In 2017 the work on the Comptonization (Sunyaev-Titarchuk) seen in the X-ray spectra of astrophysical sources was a candidate for the Nobel Prize in Physics. In this talk I provide all the details of the exciting prehistory of this topic and precise details of this discovery. The solution of this problem and its subsequent development and application to the spectra of accreting neutron star (NS) and black hole (BH) binaries reveals a lot of information on these objects. In particular, now we can unambiguously distinguish between a NS and a BH (Galactic or extragalactic) using correlations of their spectral indices vs mass accretion rate (or QPO frequency). I further demonstrate how we can determine a BH mass using this correlation.
Shuang Nan Zhang Institute of High Energy Physics, China	Pair-balance model for relativistic shocks and its application to astrophysical sources Among astrophysical objects whose emission originates from relativistic shocks are active galactic nuclei, gamma-ray bursts, and pulsar winds. Their exceptionally broad spectra are due to synchrotron and inverse Compton emission of accelerated leptons. Although these radiation processes are common in space, the relativistic shocks and shear flows possess an efficient feedback mechanism that sets them apart from other particle acceleration sites. The feedback operates through inelastic collisions of high-energy inverse Compton photons with low-energy synchrotron photons, that create electron-positron pairs in a region where the flow's velocity is relativistic with respect to the photons' source. The pairs gain energy from the difference in flow's velocity. This constitutes the converter acceleration mechanism. Whenever it is efficient, the converter acceleration reaches nonlinear saturation regime, where momentum transfer by high-energy photons keeps flow's velocity gradient at minimum necessary for converter acceleration to operate. The balance occurs when photons from the inverse Compton peak in the spectrum have barely enough energy to produce pairs with photons from the synchrotron peak. This balance condition predicts the positions of both synchrotron and inverse Compton peaks, and the ratio of their heights. The predictions are in line with recent observations of TeV emission from gamma-ray burst afterglows.	Insight-HXMT (Hard X-ray Modulation Telescope), a Chinese X-ray space telescope observing black holes, neutron stars and active galactic nuclei, to be reported by Shuang-Nan Zhang, Institute of High Energy Physics, Chinese Academy of Sciences, China