BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:The effect of tidal deformations on the gravitational wave signal during neutron star mergers DTSTART;VALUE=DATE-TIME:20241023T144500Z DTEND;VALUE=DATE-TIME:20241023T150000Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4151@cern.ch DESCRIPTION:Speakers: Irina KlopovaSaporovskaia ()\nThis work is devoted t o the analysis of the influence of tidal effects on the shape of the gravi tational signal from the fusion of neutron stars. The main part of the wo rk is divided into theoretical information\, analytical and numerical mode ls\, and practical implementation.\n\nThe theoretical section includes a d escription of the basic model for black holes and neutron stars\, as well as the methods used to add tidal effects. The basic model is based on the post-Newtonian approach\, which allows us to take into account the effects of interaction of compact objects without solving the Einstein equations. Within the framework of this model\, a differential equation arises descr ibing the evolution of the post-Newtonian parameter\, and it is further so lved in two different ways.\n\nThe practical part includes calculating the parameters of the model and solving the differential equation using maxim a code.\n\nThe discussion section of the results presents a comparison of numerical and analytical solutions. It turns out that the analytical solut ion allows you to look a little further in time and evaluate the behavior of the system at closer distances.\n\nThe conclusion summarizes the work p erformed\, indicating the fulfillment of the tasks set\, such as the analy sis of modern models\, calculation of coefficients for differential equati ons\, and comparison of the results obtained by different methods. In the future\, it is planned to continue work on calculating the shape of the gr avitational wave signal from merging black holes and adding tidal effects to the model for calculating the shape of gravitational waves.\n\nhttps:// indico.particle.mephi.ru/event/436/contributions/4151/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4151/ END:VEVENT BEGIN:VEVENT SUMMARY:Quartet-metric gravity and scalar graviton dark holes DTSTART;VALUE=DATE-TIME:20241025T151500Z DTEND;VALUE=DATE-TIME:20241025T153000Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4166@cern.ch DESCRIPTION:Speakers: Oleg Zenin (NRC KI -- IHEP)\nIn the framework of the quartet-metric gravity [1] the so called ``dark holes'' combining a centr al black hole and a peripheral scalar graviton dark halo are considered. I t is shown that the dark holes can quite naturally explain asymptotically flat rotation curves\, otherwise explained by presence of dark matter in g alaxies. Possibilities of further modification of basic dark hole solution s are discussed\, in order to apply them to modeling of realistic cosmic s tructures.\n\n[1] Yu.F. Pirogov\, ``Multiscalar-Metric Gravity: Cosmologic al Constant Screening and Emergence of Massive-Graviton Dark Components of the Universe''\, Grav. Cosmol. 28\, 263 (2022)\; arXiv:2105.09897 [gr-qc ].\n\nhttps://indico.particle.mephi.ru/event/436/contributions/4166/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4166/ END:VEVENT BEGIN:VEVENT SUMMARY:Viscosity in an accelerated relativistic medium from the Unruh eff ect vs string theory bound DTSTART;VALUE=DATE-TIME:20241025T143000Z DTEND;VALUE=DATE-TIME:20241025T144500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4164@cern.ch DESCRIPTION:Speakers: Dmitriy Lapygin (Southern federal university)\nThis project investigates the dissipative properties of an accelerated relativi stic medium and their connection to the Unruh effect and effective black h ole radiation. The thermodynamic properties in spaces with a horizon is on e of the most discussed in modern fundamental physics. A notable 2005 stri ng theory limit sets a minimum shear viscosity. We calculated viscosity in an accelerated frame for a photon medium\, where no holographic descripti on exists\, treating the black hole horizon as a membrane of finite thickn ess. While the average viscosity\nmeets the string theory limit\, local va lues are described by a universal function that is independent of particle spin. Specifically\, on the membrane surface\, the ratio of local viscosi ty to local entropy is half the string theory limit. Importantly\, this re sult is gauge-independent\, with the positive contribution from gauge fixi ng exactly canceling the negative contribution from Faddeev-Popov ghosts.\ n\nhttps://indico.particle.mephi.ru/event/436/contributions/4164/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4164/ END:VEVENT BEGIN:VEVENT SUMMARY:Schwarzschild self-consistent modeling of the Fornax dSph galaxy u sing line-of-sight velocity distribution. DTSTART;VALUE=DATE-TIME:20241025T154500Z DTEND;VALUE=DATE-TIME:20241025T160000Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4138@cern.ch DESCRIPTION:Speakers: Galina Shchelkanova (Kurchatov Institute)\nDwarf sph eroidal (dSph) satellites of the Milky Way (MW) are the\nmostly dark matte r (DM) dominated systems. Their dynamical parameters\nsuch as line-of-sigh t (LOS) velocities are measured very accurately\, so they\nare very good p robes of DM properties. We have constructed nearly\nself-consistent stars- halo model of the dSph Fornax galaxy using \nSchwarzschild orbit-superposi tion code of the AGAMA software library. \nThis is a step forward after pr evious studies\nof this object based on more approximate Jeans equation ap proach.\nThe code fits Gauss–Hermite (GH) expansion coefficients of the LOS velocity\ndistribution for each apperture of the galaxy to their obser vational estimates. \nWe use the latest data on the stellar velocities and their probability \nmembership to estimate the GH coefficients of the obs ervational data\nby the AGAMA code.\n\nhttps://indico.particle.mephi.ru/ev ent/436/contributions/4138/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4138/ END:VEVENT BEGIN:VEVENT SUMMARY:Tidal force in Newtonian gravity DTSTART;VALUE=DATE-TIME:20241025T153000Z DTEND;VALUE=DATE-TIME:20241025T154500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4158@cern.ch DESCRIPTION:Speakers: Sameer Malik (Indian Institute of Technology Kharagp ur)\nIn this presentation\, I will delve into the behavior and impact of t idal forces within the realm of Newtonian gravity. I will provide concrete examples that illustrate solutions and outcomes by analyzing the Newtonia n deviation equation. Furthermore\, I will extensively explore the conditi ons under which tidal forces can exhibit compressive or disruptive effects by leveraging different model density profiles. Lastly\, I will rigorousl y analyze the stability criteria for two density profiles\, namely the Pow er Law and Sersic\, using the Jog mass and length conditions in the presen ce of tidal forces\, and draw comparisons to the Jeans mass and length in their absence.\n\nhttps://indico.particle.mephi.ru/event/436/contributions /4158/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4158/ END:VEVENT BEGIN:VEVENT SUMMARY:Non-Gaussianities in the bouncing Universe model DTSTART;VALUE=DATE-TIME:20241025T150000Z DTEND;VALUE=DATE-TIME:20241025T151500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4146@cern.ch DESCRIPTION:Speakers: Maxim Kotenko ()\nWe acquired and analyzed the primo rdial bispectrum and the corresponding non-gaussianity in the particular m odel of the bouncing universe within the framework of the Horndeski theory . The analytical shape function of the bispectrum did not correspond to th e widely used local\, equilateral of orthogonal shapes. The non-gaussianit y parameter is compatible with the current observational bounds even unde r the restrictions of the regime where the background evolution and pertu rbations are legitimately described within classical field theory and wea kly coupled quantum theory at all times.\n\nhttps://indico.particle.mephi. ru/event/436/contributions/4146/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4146/ END:VEVENT BEGIN:VEVENT SUMMARY:Cosmological Constant Suppression in Non-Stationary Scalar Covaria nt State DTSTART;VALUE=DATE-TIME:20241025T144500Z DTEND;VALUE=DATE-TIME:20241025T150000Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4154@cern.ch DESCRIPTION:Speakers: Asya Aynbund (MIPT)\nWe study spatial-temporal struc ture of quantum fluctuations in stress-energy tensor of zero-point modes o f scalar field in order to formulate relativistically covariant model. The model describes a vacuum contribution to cosmological constant in non-sta tionary state of finite volume. Bare and effective mean values of vacuum e nergy are compared.\n\nhttps://indico.particle.mephi.ru/event/436/contribu tions/4154/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4154/ END:VEVENT BEGIN:VEVENT SUMMARY:Superfluid Stars and the Dawn of Quantum Astrophysics DTSTART;VALUE=DATE-TIME:20241025T141500Z DTEND;VALUE=DATE-TIME:20241025T143000Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4162@cern.ch DESCRIPTION:Speakers: Konstantin Zloshchastiev (Durban University of Techn ology)\nAstrophysics traditionally deals with phenomena and objects in whi ch quantum effects are not expected to be important or even significant – too large\, too massive\, too hot. Therefore\, does it make sense to s peak about “quantum astrophysics” as a separate discipline\, and what would its key features and ideology be?\n\nWe consider a general relativis tic model of a self-interacting complex scalar field with logarithmic nonl inearity motivated by studies of laboratory superfluids and Bose-Einstein condensates. Spherically-symmetric gravitational equilibria are shown in t his model\, which do not have event horizons but which are regular\, singu larity-free and asymptotically flat. They can be thus interpreted as compa ct stars whose stability against gravitational collapse is enhanced not on ly by the Heisenberg uncertainty principle but also by the property of sup erfluidity itself\, their ``darkness'' comes naturally as a result of supp ressed dissipative excitations. Such objects do not obey any absolute uppe r mass limit of a Tolman-Oppenheimer-Volkoff type\, while their relativist icity and effective compactness values are comparable to those of black ho les. Their spatial density distribution drops abruptly (at the Gaussian-li ke rate)\, which can be mistaken in realistic astronomical observations fo r the presence of an exact material surface.\n\nWe therefore present logar ithmic superfluid stars as dark compact objects and black hole mimickers. Their existence would be a serious argument towards accepting quantum astr ophysics as a next step in understanding phenomena occurring in supermassi ve objects and high-energy phenomena observed in astronomy.\n\nhttps://ind ico.particle.mephi.ru/event/436/contributions/4162/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4162/ END:VEVENT BEGIN:VEVENT SUMMARY:Formation and evolution of complex soliton structures in the early Universe DTSTART;VALUE=DATE-TIME:20241025T140000Z DTEND;VALUE=DATE-TIME:20241025T141500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4147@cern.ch DESCRIPTION:Speakers: Boris Murygin ()\nThe formation of composite soliton s produced by scalar fields without thermal phase transitions in the early Universe is considered. We present numerical simulations of the formation and evolution of soliton structures at the post-inflationary stage. The r ealistic initial conditions are obtained through the simulation of multipl e quantum fluctuations during the inflation epoch. The initial field distr ibutions allow to form local soliton clusters in the early Universe withou t the need for the thermal production of a soliton network throughout the Universe. We find that in three-dimensional space\, the nontrivial composi te field structures are formed in the form of soliton foam\, consisting of closed domain walls\, domain walls bounded by cosmic strings\, and scalar field radiation. The possible cosmological implications of the soliton fo am are discussed.\n\nhttps://indico.particle.mephi.ru/event/436/contributi ons/4147/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4147/ END:VEVENT BEGIN:VEVENT SUMMARY:Formation of dark atoms DTSTART;VALUE=DATE-TIME:20241025T134500Z DTEND;VALUE=DATE-TIME:20241025T140000Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4161@cern.ch DESCRIPTION:Speakers: Danila Sopin ()\nNew stable heavy particles with eve n negative charge $X^{-2n}$ arise in several extensions of the Standard Mo del. The Thomson-like neutral bound states $XHe$ called dark atoms are the dark matter candidates. However\, at present there is no comprehensive de scription of their formation at early stages of the cosmological evolution . The process of the $X^{-2n}$ excess generation depends significantly on a model\, pending on the electroweak properties of $X$-particles. If these particles have nontrivial $SU(2)$ electroweak charges\, such excess shoul d be balanced with baryon asymmetry by sphaleron transitions.The successiv e development of the nucleosynthesis\, modified by the presence of dark at oms\, is determined by their nuclear interaction with the baryonic matter. We approach these open questions of dark atom cosmology in the present wo rk.\n\nhttps://indico.particle.mephi.ru/event/436/contributions/4161/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4161/ END:VEVENT BEGIN:VEVENT SUMMARY:Ultralight ALP dark matter and 21 cm absorption signals in new phy sics DTSTART;VALUE=DATE-TIME:20241025T133000Z DTEND;VALUE=DATE-TIME:20241025T134500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4149@cern.ch DESCRIPTION:Speakers: Chitta Ranjan Das (BLTP\, JINR)\nA hypothetical part icle known as the axion holds the potential to resolve both the cosmic dar k matter riddle and particle physics' long-standing\, strong CP dilemma. U nusual strong 21 cm absorption feature associated with the initial star fo rmation era\, maybe due to ultralight axion dark matter ($\\sim 10^{-22}$ eV) at this time. The radio wave observation's 21 cm absorption signal can be explained as either anomalous baryon cooling or anomalous cosmic micro wave background photon heating. Shortly after the axions and axion like pa rticles (ALPs) thermalize among themselves and form a Bose-Einstein conden sate\, the cold dark matter ALPs make thermal contact with baryons\, cooli ng them. ALPs are thought to be the source of some new evidence for dark m atter\, as the baryon temperature at cosmic dawn was lower than predicted based on presumptions. The detection of baryon acoustic oscillations is fo und to be consistent with baryon cooling by dark matter ALPs. Simultaneous ly\, under the influence of the primordial black hole or intergalactic mag netic fields\, the dark radiation composed of ALPs can resonantly transfor m into photons\, significantly heating up the radiation in the frequency r ange relevant for the 21 cm tests. The two scenarios were considered. An i nteresting chance to investigate novel physics dynamics in the early cosmo s is presented by the 21 cm cosmology.\n\nhttps://indico.particle.mephi.ru /event/436/contributions/4149/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4149/ END:VEVENT BEGIN:VEVENT SUMMARY:Primordial black holes mergers DTSTART;VALUE=DATE-TIME:20241023T143000Z DTEND;VALUE=DATE-TIME:20241023T144500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4163@cern.ch DESCRIPTION:Speakers: Viktor Stasenko ()\nWe consider the formation and dy namics of primordial black holes (PBHs) binaries in both the early and lat e Universe\, taking into account clustering effects. The evolution of the PBH merger rate with redshift is obtained and shown to depend on the clust ering efficiency. The observation of gravitational waves by the LIGO-Virgo -KAGRA collaboration imposes the constraint that PBHs constitute no more t han 10% of the dark matter.\n\nhttps://indico.particle.mephi.ru/event/436/ contributions/4163/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4163/ END:VEVENT BEGIN:VEVENT SUMMARY:Black Hole Singularity with Quantum Geometric Approach DTSTART;VALUE=DATE-TIME:20241023T140000Z DTEND;VALUE=DATE-TIME:20241023T141500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4086@cern.ch DESCRIPTION:Speakers: Abdel Nasser Tawfik (Future Univrsity of Egypt)\nThe emergence of relativistic quantum gravitational effects is well anticipat ed when the Planck density ($m_p/\\ell_p^3$\, where $m_p$ is the Planck ma ss and $\\ell_p$ is the Planck length)\, regardless of whether the predict ion of an infinite-density singularity is viewed as a flaw in general rela tivity. Over the past century\, the orthogonality between quantum mechanic s and general relativity has been a persistent issue\, prompting the dedic ated efforts of brilliant scholars. Our focus is on a quantum geometric ap proach that expands the four-dimensional Riemann geometry (spacetime) to i ncorporate quantum-mechanical principles. This approach enables a comprehe nsive exploration of the fundamental nature of the Universe\, offering a m ore profound understanding of the underlying relativity and quantum princi ples governing its structure and evolution. The quantum geometric approach facilitates the derivation of the fundamental tensor\, upon which quantum -mechanically induced revisions are imposed. This\, in turn\, allows for t he construction of the general theory of relativity and the verification o f various black hole metrics\, while also enabling the examination of init ial and space singularities through timelike geodesic congruence.\n\nhttps ://indico.particle.mephi.ru/event/436/contributions/4086/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4086/ END:VEVENT BEGIN:VEVENT SUMMARY:Evolution of the mass spectrum of primordial black holes in the Fr iedmann Universe DTSTART;VALUE=DATE-TIME:20241023T153000Z DTEND;VALUE=DATE-TIME:20241023T154500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4155@cern.ch DESCRIPTION:Speakers: Lidiia Solnyshko (MIPT)\nWe investigated the evoluti on of the mass spectrum of primordial black holes (PBHs) in the expanding Universe under the action of Bondi-Hoyle-Lyttleton accretion and Hawking r adiation. The initial mass spectrum of primordial black holes was assumed to be flat (independent of mass). It was shown that accretion of matter su rrounding a black hole does not significantly affect the growth of the mas s of black holes. Using modeling\, it was found that by the end of the rad iation-dominated era\, all primordial black holes with masses up to $M=2\\ times10^{9}$ g had evaporated. We also confirmed the critical mass value f or primordial black holes\, at which they evaporate in our time. It is $M_ {cr}=2\\times10^{14}$ g.\n\nhttps://indico.particle.mephi.ru/event/436/con tributions/4155/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4155/ END:VEVENT BEGIN:VEVENT SUMMARY:Limits on the properties of primordial black holes clusters from m icrolensing analysis DTSTART;VALUE=DATE-TIME:20241023T151500Z DTEND;VALUE=DATE-TIME:20241023T153000Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4144@cern.ch DESCRIPTION:Speakers: Konstantin Toshchenko ()\nMicrolensing experiments s earching for MACHOs (massive astrophysical compact halo object\, MACHO) ha ve limited the possibility of the existence of dark matter in the form of MACHOs. These constraints on the fraction of dark matter are made for sing le MACHOs. The microlensing light curve for single MACHOs agrees well with the standard microlensing model. However\, the mutual influence of cluste red MACHOs can significantly change the light curves and therefore change the constraints on the MACHO fraction. \n\nWe have simulated microlensing events for models of the class of clustered primordial black holes (PBH). The analysis of microlensing events for these cluster models showed that t he fraction of MACHO mass that is not detected as single ones can reach up to 40%. Therefore\, observations of experiments such as MCHO\, EROS\, OGL E\, POINT-AGAPE\, HSC can impose tighter constraints on the fraction of MA CHOs. Although the models of PBH clusters that we consider reduce the lim itations due to clustering\, it is not possible to completely remove the l imitations on MACHO.\n\nhttps://indico.particle.mephi.ru/event/436/contrib utions/4144/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4144/ END:VEVENT BEGIN:VEVENT SUMMARY:Relic gravitational waves in cosmological models based on Einstein -Gauss-Bonnet gravity DTSTART;VALUE=DATE-TIME:20241023T150000Z DTEND;VALUE=DATE-TIME:20241023T151500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4141@cern.ch DESCRIPTION:Speakers: Gevorg Manucharyan (BMSTU\, SAI MSU)\nThe influence of non-minimal coupling between the scalar field and the Gauss-Bonnet term on the background parameters of cosmological models and the parameters of cosmological perturbations is considered by comparison with the case of t he Einstein gravity. The possibility of parametrization of this influence is shown.\nA procedure for reconstructing solutions of the cosmological dy namic equations obtained within the framework of General Relativity for th e case of the Einstein-Gauss-Bonnet gravity is presented.\nAs an example\, some models of cosmological inflation are considered. It is shown that th ese cosmological models can be verified by observational constraints on th e parameters of cosmological perturbations by taking into account the infl uence of the Gauss-Bonnet term.\nAlso\, proposed cosmological models satis fy modern observational constraints on the propagation speed of the gravit ational waves.\n\nThe specificity of the spectrum of relic gravitational w aves for inflationary models based on Einstein-Gauss-Bonnet gravity in com parison with the case of General Relativity is considered.\nThe effect of increasing energy density of the high-frequency relic gravitational waves in the proposed inflationary models is analyzed.\nThe possibility of regis tering relic gravitational waves predicted in these inflationary models is considered as well.\nTo assess the possibility of detection of relic grav itational waves\, the application of classical and modified Herzenstein ef fects and the high-frequency gravitational-optical resonance in multi-beam interferometers are analysed.\n\nhttps://indico.particle.mephi.ru/event/4 36/contributions/4141/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4141/ END:VEVENT BEGIN:VEVENT SUMMARY:Dark matter around primordial black holes DTSTART;VALUE=DATE-TIME:20241023T141500Z DTEND;VALUE=DATE-TIME:20241023T143000Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4148@cern.ch DESCRIPTION:Speakers: Yury Eroshenko (INR RAS)\nMassive primordial black h oles may have formed in the early universe\, accounting for a small fracti on of dark matter. Most of dark matter\, however\, may be composed of elem entary particles or black holes with smaller masses. These objects could f orm dense spikes around the large black holes during the radiation-dominat ed phase of the universe's evolution. Dark matter particles can annihilate in the spikes. In this study\, we discuss the structure and properties of the spikes\, considering their transformation due to annihilation. In the hybrid scenario involving black holes of various masses\, small black hol es can scatter and merge in the central regions around larger black holes. \n\nhttps://indico.particle.mephi.ru/event/436/contributions/4148/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4148/ END:VEVENT BEGIN:VEVENT SUMMARY:Multidimensional gravity\, black holes and mirror stars DTSTART;VALUE=DATE-TIME:20241023T154500Z DTEND;VALUE=DATE-TIME:20241023T160500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4139@cern.ch DESCRIPTION:Speakers: Kirill Bronnikov (VNIIMS)\nWe discuss a class of sol utions of multidimensional gravity which are formally related to black-hol e solutions but can observationally look like stars whose surface reflects back particles or signals getting there. Some particular examples of such solutions are presented and studied.\n\nhttps://indico.particle.mephi.ru/ event/436/contributions/4139/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4139/ END:VEVENT BEGIN:VEVENT SUMMARY:Cosmological models in the scalar-tensor theories of gravity\, con sistent with observational constraints DTSTART;VALUE=DATE-TIME:20241023T080000Z DTEND;VALUE=DATE-TIME:20241023T081500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4137@cern.ch DESCRIPTION:Speakers: Nickolay Koshelev (Ulyanovsk State Pedagogical Unive rsity)\nThis work considers two classes of cosmological models based on sc alar-tensor theories of gravity. The models are obtained using certain fun ctional relationships between the dynamics of the expansion of the Univers e and the type of scalar-tensor theories of gravity. The consistency of th e models with observational constraints according to Planck-2018 data is c onsidered.\n\nhttps://indico.particle.mephi.ru/event/436/contributions/413 7/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4137/ END:VEVENT BEGIN:VEVENT SUMMARY:Reconstruction the scalar-torsion gravity version from the frame o f exact cosmological solutions DTSTART;VALUE=DATE-TIME:20241023T074500Z DTEND;VALUE=DATE-TIME:20241023T080000Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4142@cern.ch DESCRIPTION:Speakers: Evgenii Dentsel (Assistant professor)\nCosmological models based on scalar-torsion gravity with non-minimal coupling between t he scalar field and torsion are considered. These models were obtained as a consequence of the generalized exact solutions of cosmological dynamic e quations for an arbitrary Hubble parameter and an arbitrary scalar field e volution.\n\nAn inflation models classification according to the expansion order of the tensor-to-scalar ratio dependence on spectral index of the scalar perturbations $r=r(1-n_{S})$ was also proposed. On the basis of thi s classification\, the method for constructing inflationary models based o n scalar-torsion gravity verified by observational constraints was consid ered\, implying a linear dependence $r\\sim(1-n_{S})$ for arbitrary model 's parameters.\nFor the gravity theory under consideration the type of sca lar field potential or other background parameters doesn't affect the poss ibility of verifying the inflationary models.\n\nAlso\, proposed inflation ary models can predict different types of tensor perturbation spectrum (re d\, blue or flat) depending on the tensor-to-scalar ratio value and how cl ose the early universe cosmological dynamics is to the purely exponential (de Sitter) expansion regime.\nThe proposed type of the scalar-torsion gra vity implying the wide class of verified cosmological models with arbitrar y parameters is of interest for the further deviations research in the rel ict gravitational waves spectrum and in the compact astrophysical objects evolution from teleparallel equivalent of general relativity or from the other modified gravity theories.\n\nhttps://indico.particle.mephi.ru/event /436/contributions/4142/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4142/ END:VEVENT BEGIN:VEVENT SUMMARY:On reconstruction procedure for special spherically-symmetric metr ics in scalar-Einstein-Gauss-Bonnet model: the Schwarzschild metric test DTSTART;VALUE=DATE-TIME:20241023T073000Z DTEND;VALUE=DATE-TIME:20241023T074500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4143@cern.ch DESCRIPTION:Speakers: Vladimir Ivashchuk (Center for Gravitation\, VNIIMS) \nThe $4d$ gravitational model with real scalar field $\\varphi$\, Einstei n and Gauss-Bonnet terms\nis considered. The action contains potential te rm $U(\\varphi)$ and Gauss-Bonnet coupling function $f(\\varphi)$.\nFor a special (static) spherically symmetric metric\n$ds^2 = \\left(A(u)\\right) ^{-1}du^2 - A(u)dt^2 + u^2 d\\Omega^2$\nwith $A(u) > 0$ ($u > 0$ is a rad ial coordinate) \nwe verify and correct the so-called reconstruction proc edure suggested by\n Nojiri and Nashed. This procedure presents certain implicit relations \n for $U(\\varphi)$\, $f(\\varphi)$ which lead to ex act solutions \nto the equations of motion for a given metric governed b y $A(u)$.\nHere we apply the procedure to (external) Schwarzschild metri c with gravitational radius $2 \\mu $ and $u > 2 \\mu$. Using ``no-ghost' ' restriction (i.e. reality of $\\varphi(u)$) we find two family of $(U(\ \varphi)\, f(\\varphi))$. The first one gives us the Schwarzschild metri c defined for $u > 3 \\mu$ and the second one describes the Schwarzschild metric defined for $ 2 \\mu \n\nhttps://indico.particle.mephi.ru/event/436 /contributions/4143/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4143/ END:VEVENT BEGIN:VEVENT SUMMARY:Horndeski theory on a dynamical spherically-symmetric background DTSTART;VALUE=DATE-TIME:20241023T071500Z DTEND;VALUE=DATE-TIME:20241023T073000Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4153@cern.ch DESCRIPTION:Speakers: Mikhail Sharov (Institute for Nuclear Research of th e Russian Academy of Sciences)\nWe study the stability of classical soluti ons in Horndeski theory\, which is the most general scalar-tensor theory o f gravity with an additional scalar field and second-order motion equation s\, which in turn provides absence of Ostrogradski ghosts. In this work\, we address a general dynamical spherically symmetric background. We derive the set of stability conditions in the cubic subclass of Horndeski theory and formulate the no-go theorem for this subclass.\n \nFor full Horndeski theory and beyond Horndeski theory we formulate a set of linear stability conditions for high energy odd parity perturbation modes above an arbitra ry solution. In this general setting we derive speeds of propagation in bo th radial and angular directions for gravity waves and compare them with t he speed of light in the case of minimally coupled photon. In particular\, we find that the class of beyond Horndeski theories\, which satisfy the e quality of gravity waves’ speed to the speed of light over a cosmologica l background\, feature gravity waves propagating at luminal speeds above a time-dependent inhomogeneous background as well. [arXiv:2408.01480]\n\nWe revisit the models recently derived from a Kaluza-Klein compactification of higher dimensional Horndeski theory\, where the resulting electromagnet ic sector features non-trivial couplings to Horndeski scalar. In this work we prove that both gravitational wave and its electromagnetic counterpart propagate at the same\, although non-unit\, speed above an arbitrarily ti me-dependent\, spherically symmetric background within the theories in que stion. Hence\, we support the statement that several subclasses of Horndes ki theories are not necessarily ruled out after the GW170817 event provide d the photon-Galileon couplings are allowed. We also formulate the set sta bility conditions based on odd parity perturbations for an arbitraty solut ion within the discussed theoretical setting. [arXiv:2408.06329]\n\nhttps: //indico.particle.mephi.ru/event/436/contributions/4153/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4153/ END:VEVENT BEGIN:VEVENT SUMMARY:Should we take into account nontrivial spacetime topology\, change s of metric signature and similar hypothetical phenomena when quantizing g ravity? DTSTART;VALUE=DATE-TIME:20241023T070000Z DTEND;VALUE=DATE-TIME:20241023T071500Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4156@cern.ch DESCRIPTION:Speakers: Tatyana Shestakova (Department of Theoretical and Co mputational Physics\, Southern Federal University)\nThe founders of quantu m geometrodynamics assumed that spacetime may have nontrivial topology: Jo hn Wheeler suggested the idea of spacetime foam\; Stephen Hawking wrote th at one would expect that quantum gravity would allow all possible topologi es of spacetime. Later\, A. D. Sakharov put forward yet more exotic hypoth esis that metric signature may change. Then the question arises\, do we re ally need to take into account all these hypothetical phenomena when quant izing gravity? Since observational data witnesses for an open flat univers e\, it is possible\, in principle\, to construct a theory of perturbations of gravitational and matter fields. However\, it would not be a full quan tum theory of gravity. I shall argue that the assumption about nontrivial spacetime topology\, etc. leads to a new description of the Universe in wh ich periods of unitary evolution give place to non-unitary changes of the Universe state. It gives a hope that it may shed light on an origin of irr eversibility.\n\nhttps://indico.particle.mephi.ru/event/436/contributions/ 4156/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4156/ END:VEVENT BEGIN:VEVENT SUMMARY:New slow-roll approximations for inflation in Einstein-Gauss-Bonne t gravity DTSTART;VALUE=DATE-TIME:20241023T081500Z DTEND;VALUE=DATE-TIME:20241023T083000Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4159@cern.ch DESCRIPTION:Speakers: Maria Skugoreva ()\nWe propose new slow-roll approxi mations for inflationary models with the Gauss-Bonnet term. We find more a ccurate expressions of the standard slow-roll parameters as functions of t he scalar field. To check the accuracy of approximations considered we con struct inflationary models with quadratic and quartic monomial potentials and the Gauss-Bonnet term. Numerical analysis of these models indicates th at the proposed inflationary scenarios do not contradict to the observatio n data. New slow-roll approximations show that the constructed inflationar y models are in agreement with the observation data\, whereas one does not get allowed observational parameters at the same values of parameters of the constructed models in the standard slow-roll approximation.\n\nhttps:/ /indico.particle.mephi.ru/event/436/contributions/4159/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4159/ END:VEVENT BEGIN:VEVENT SUMMARY:Finding the valid gravity theory from observations of black hole s ilhouettes DTSTART;VALUE=DATE-TIME:20241023T064000Z DTEND;VALUE=DATE-TIME:20241023T070000Z DTSTAMP;VALUE=DATE-TIME:20260422T081407Z UID:indico-contribution-215-4160@cern.ch DESCRIPTION:Speakers: Vyacheslav Dokuchaev (Institute for Nuclear Research of the Russian Academy of Sciences)\nNowadays the major problem in cosmol ogy is in the choice of the valid gravity theory for interpretation of the observational data. Usually in cosmology it is used the Einstein general theory of relativity and the corresponding Friedman-Robertson-Walker equat ions in the strong field limit (when gravitational potential is of the ord er of square of the light velocity). Meanwhile\, the general theory of rel ativity is verified and confirmed only in the weak field limit in the near est cosmological environments. Observations of black hole images (silhouet tes) opens a unique possibility for the verification (or falsification) of modified gravity theories in the strong field limit when gravitation domi nates over astrophysical or cosmological factors. This is especially cruci al for physical interpretation of astrophysical and cosmological observati ons of the far regions of the Universe and for understanding the physical origin of enigmatic dark matter and dark energy. The first visual images o f supermassive black holes M87* and SgrA* have been observed recently by t he Event Horizon Telescope. These images demonstrate a qualitative agreeme nt with the general theory of relativity. In the nearest future it would be possible to quantitatively scrutinize the known modified gravity theori es after construction of the Space Millimetron Observatory with nano-arcse cond angular resolution.\n\nhttps://indico.particle.mephi.ru/event/436/con tributions/4160/ LOCATION: Moskvorechye 1 URL:https://indico.particle.mephi.ru/event/436/contributions/4160/ END:VEVENT END:VCALENDAR