BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Alberto Salvio (U. Rome and INFN) DTSTART:20200521T133000Z DTEND:20200521T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/1 DESCRIPTION:Title: I nflation and Ultracompact Objects in Quadratic Gravity\nby Alberto Sal vio (U. Rome and INFN) as part of CENTRA Seminar\n\n\nAbstract\nAn extensi on of general relativity obtained by adding quadratic terms to the action will be considered. Such theory is a UV completion of GR: the additional t erms soften gravity above a certain scale and render gravity renormalizabl e. The presence of 4 derivatives implies via the Ostrogradsky theorem that the classical Hamiltonian is unbounded from below. Nevertheless\, I will argue that the relevant solutions are not unstable\, but metastable: when the energies are much below a threshold (that is high enough to describe t he whole cosmology) runaways are avoided. Remarkably\, the chaotic inflati on theory of initial conditions ensures that such bound is satisfied and t estable implications for the early universe will be discussed. I will also argue that the basic unitarity condition is satisfied. Moreover\, thanks to the UV softening of gravity in this theory\, sufficiently light objects must be horizonless and explicit analytic examples of horizonless ultraco mpact objects (UCOs) will be discussed. These UCOs are more compact than S chwarzschild black holes and their spacetime is regular everywhere. Due to the lack of a horizon\, light UCOs do not evaporate and\, therefore\, the y may play the role of dark matter.\n LOCATION:https://researchseminars.org/talk/CENTRA/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Hans Bantilan (Queen Mary\, U. of London) DTSTART:20200528T133000Z DTEND:20200528T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/2 DESCRIPTION:Title: R eal-time Dynamics of Plasma Balls\nby Hans Bantilan (Queen Mary\, U. o f London) as part of CENTRA Seminar\n\n\nAbstract\nIn this talk\, I will d escribe the first simulations of finite-sized black holes that are dual to droplets of deconfined plasma surrounded by a confining vacuum known as p lasma balls. These solutions are obtained by solving the Einstein field eq uations with a negative cosmological constant in four spatial dimensions\, where one of the spatial coordinates is compactified to form a circle who se size shrinks to zero size at the IR bottom of the geometry. The dual ga uge theory is four-dimensional\, $\\mathcal{N}=4$ super Yang-Mills compact ified on a circle with supersymmetry-breaking boundary conditions. I will show simulations where prompt scalar field collapse produces an excited bl ack hole at the IR bottom together with gravitational and scalar radiation \, in a process that corresponds to particle production in the dual gauge theory.\n LOCATION:https://researchseminars.org/talk/CENTRA/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Bruno Ribeiro (Leiden Observatory\, Leiden U.) DTSTART:20200604T133000Z DTEND:20200604T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/3 DESCRIPTION:Title: T he evolving shapes of star-forming galaxies in the young Universe\nby Bruno Ribeiro (Leiden Observatory\, Leiden U.) as part of CENTRA Seminar\n \n\nAbstract\nThe global properties of galaxies show a strong evolution of the star formation rate and stellar mass density at the epoch of galaxy a ssembly\, driven by several competing physical processes (merging\, accret ion\, feedback\, environment\,...). The morphological properties of galaxi es are also strongly evolving over the same timescales. In such early stag e evolution\, galaxy evolution is believed to be a turbulent process where gas inflows\, strong winds and galaxy-galaxy interactions give rise to th e intricate shapes that we encounter in HST photometric observations of hi gh redshift galaxies. The shape of galaxies is a simple\, yet fundamental\ , property of galaxies. In this talk\, I would like to highlight two main results on the evolution of rest-frame UV galaxy morphology at 2E arly-type galaxies: climbing to the top of the mass ladder\nby Eric Em sellem (ESO) as part of CENTRA Seminar\n\n\nAbstract\nNearby galaxies disp lay a range of morphologies\, sizes\, masses\, which are the results of a complex set of formation and evolution processes. In this talk\, I will fo cus on early-type galaxies which contain about half of all the stars in ou r local Universe. I will review our current knowledge of how they form\, w hat are the most important mechanisms which shaped them\, and illustrate h ow our understanding of these objects changed over the last decade via the use of simulations and integral-field spectroscopy. I will then focus on the most massive galaxies\, and report on results from numerical simulatio ns and an observational campaign conducted with the MUSE spectrograph\, wh ich led to some interesting surprises.\n LOCATION:https://researchseminars.org/talk/CENTRA/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Sumanta Chakraborty (IACS\, Kolkata) DTSTART:20200625T133000Z DTEND:20200625T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/5 DESCRIPTION:Title: S earching for theories beyond General Relativity through various observatio nal avenues\nby Sumanta Chakraborty (IACS\, Kolkata) as part of CENTRA Seminar\n\n\nAbstract\nIn this talk I will discuss about various observat ional avenues that have been available recently and can be used to test th e structure of gravitational theories at large curvature regime. This will include gravitational wave observations\, black hole echo as well as meas urement of black hole shadow from the supermassive black hole M87*. Implic ations will also be discussed.\n LOCATION:https://researchseminars.org/talk/CENTRA/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Lorenzo Annulli (CENTRA\, Instituto Superior Tecnico) DTSTART:20200709T133000Z DTEND:20200709T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/6 DESCRIPTION:Title: S tirred and shaken: dynamical behavior of boson stars and dark matter cores \nby Lorenzo Annulli (CENTRA\, Instituto Superior Tecnico) as part of CENTRA Seminar\n\n\nAbstract\nThe nature and properties of dark matter are arguably among the most important open issues in science. Interesting can didates for dark matter include light bosonic \nfields. Such scalar fields can give rise to confined structures\, as boson stars or Q-balls. Boson s tars are interesting hypothetical new "dark matter stars"\, but also good descriptions of dark matter haloes when the fields are ultralight. In this talk\, I'm going to focus on the the dynamical response of Newtonian boso nic structures when excited by external matter (stars\, planets or black h oles) in their vicinities. The study of the dynamics of such bodies is imp ortant for a number of reasons\, ranging from stability to the way they in teract with surrounding objects (stars\, planets or black holes etc.). Amo ng others issues\, I am going to describe the local changes in the density of a dark matter halo triggered by the presence of a massive black hole o r a star\, the drag exerted by the bosonic clump on stars moving within it \, the flux of energy and momentum induced by coalescing binaries\, etc. I will provide a complete picture of the interaction between black holes or stars and the ultralight dark matter environment they live in.\n LOCATION:https://researchseminars.org/talk/CENTRA/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Sarp Akcay (University Coll.\, Dublin) DTSTART:20200716T133000Z DTEND:20200716T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/8 DESCRIPTION:Title: P recession in Stellar-mass Compact Binary Inspirals\nby Sarp Akcay (Uni versity Coll.\, Dublin) as part of CENTRA Seminar\n\n\nAbstract\nI first d iscuss how precessing waveform approximants are generated for LIGO-Virgo p arameter estimation. I then introduce a new such approximant called TEOBRe sumSP that my collaborators and I have been developing. TEOBResumSP is an efficient hybrid scheme for generating precessing gravitational waveforms that combines post-Newtonian precession equations with effective-one-body aligned-spin dynamics. The approach Euler-rotates aligned-spin TEOBResumS waveforms from a precessing frame to an inertial frame via Wigner's D matr ices. The scheme is compared to current state-of-the-art precessing approx imants NRSurd74q and SEOBNRv4PHM in terms of frequency-domain matches of t he $\\el=2$ gravitational-wave strain for approximately 1300 compact binar y inspirals with the initial gravitational-wave frequencies between 20 and 50 Hz and the precessing spin parameter $\\chi_p$ ranging up to one. The matches are better than 0.965 for 85% of the NRSurd74q comparisons and 75% of the SEOBNRv4PHM set. The largest disagreements occur for large mass ra tios and for large spin components along the orbital plane quantified in t erms of a new parameter\, $\\Sperp$\, that I introduce. The disagreements stem from Euler-rotating non-precessing waveforms with constant spins\, wh ich can be replaced by time-varying z-components of spins. TEOBResumSP pro vides a robust alternative precessing approximant to be employed in the pa rameter estimation of generic-spin compact binaries.\n LOCATION:https://researchseminars.org/talk/CENTRA/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Alejandro Torres-Orjuela (Peking U.\, Beijing and Peking U.\, Beij ing\, KIAA) DTSTART:20200722T100000Z DTEND:20200722T110000Z DTSTAMP:20260422T225756Z UID:CENTRA/9 DESCRIPTION:Title: P hase Shift of Gravitational Waves induced by Aberration\nby Alejandro Torres-Orjuela (Peking U.\, Beijing and Peking U.\, Beijing\, KIAA) as par t of CENTRA Seminar\n\n\nAbstract\nThe velocity of a gravitational wave (G W) source provides crucial information about its formation and evolution p rocesses. Previous studies considered the Doppler effect on the phase of G Ws as a potential signature of a time-dependent velocity of the source. Ho wever\, the Doppler shift only accounts for the time component of the wave vector\, and in principle motion also affects the spatial components. In my talk I discuss the latter effect\, known as “aberration” for light\ , for GWs and how it affects the waveform modelling of an accelerating sou rce. I show that the additional aberrational phase shift could be detectab le in two astrophysical scenarios\, namely\, a recoiling binary black hole (BBH) due to GW radiation and a BBH in a triple system. Further\, I discu ss how adding the aberrational phase shift in the waveform templates could significantly enhance the detectability of moving sources.\n LOCATION:https://researchseminars.org/talk/CENTRA/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Erik Lentz (Inst. Astrophys. Gottingen) DTSTART:20200723T133000Z DTEND:20200723T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/10 DESCRIPTION:Title: Breaking the Warp Barrier: Hyper-fast Solitons in Einstein-Maxwell-Plasma Theory\nby Erik Lentz (Inst. Astrophys. Gottingen) as part of CENTRA S eminar\n\n\nAbstract\nSolitons in space--time capable of transporting time -like observers at superluminal speeds have long been tied to violations o f the weak\, strong\, and dominant energy conditions of general relativity . The negative-energy sources required for these solitons must be created through energy-intensive uncertainty principle processes as no such classi cal source is known in particle physics. This talk presents an approach fo r overcoming this barrier\, explicitly constructing a class of soliton sol utions that are capable of superluminal motion and sourced by purely posit ive energy densities. The solitons are also shown to be capable of being s ourced from the stress-energy of a conducting plasma and classical electro magnetic fields. This is the first example of hyper-fast solitons resultin g from known and familiar sources\, reopening the discussion of superlumin al mechanisms rooted in conventional physics.\n LOCATION:https://researchseminars.org/talk/CENTRA/10/ END:VEVENT BEGIN:VEVENT SUMMARY:Taishi Ikeda (CENTRA\, Instituto Superior Tecnico) DTSTART:20200702T133000Z DTEND:20200702T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/11 DESCRIPTION:Title: Massive scalar field around black hole binary and gravitational molecules< /a>\nby Taishi Ikeda (CENTRA\, Instituto Superior Tecnico) as part of CENT RA Seminar\n\n\nAbstract\nBlack hole binaries are one of the main sources of gravitational waves. In the age of gravitational wave astronomy\, we mu st understand many properties about black hole binaries.\nIn this talk\, I will talk about new bound states of massive fields around the binaries. W e numerically construct the bound states and discuss the fundamental prope rties. The bound state can be understood as an analogy of quantum mechanic s of molecules which is a solvable model.\n LOCATION:https://researchseminars.org/talk/CENTRA/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Sante Carloni (U. of Genova) DTSTART:20200903T133000Z DTEND:20200903T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/12 DESCRIPTION:Title: Discrete Relativistic Positioning Systems\nby Sante Carloni (U. of Gen ova) as part of CENTRA Seminar\n\n\nAbstract\nI will discuss the design fo r a discrete\, immediate\, simple relativistic positioning system (rPS) wh ich is potentially able of self-positioning (up to isometries) and operati ng without calibration or ground control assistance. The design is discuss ed in 1 + 1 spacetimes\, in Minkowski and Schwarzschild solutions\, as wel l as in 2 + 1 spacetimes in Minkowski. I will sho in particular that the s ystem is self-calibrating and robust under perturbations. The rPS can be a dapted as detectors for the gravitational field and we shall briefly discu ss their role in testing different theoretical settings for gravity. In fa ct\, rPS is a natural candidate for a canonical method to extract observab les out of a gravitational theory\, and therefore to design experiments to test gravity.\n LOCATION:https://researchseminars.org/talk/CENTRA/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Tessa Carver (Cardiff U.) DTSTART:20200910T133000Z DTEND:20200910T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/13 DESCRIPTION:Title: Fully-Coherent Gravitational Wave Searches for Binary Neutron Star Mergers and Inferring Astrophysical Signal Probabilities\nby Tessa Carver (Ca rdiff U.) as part of CENTRA Seminar\n\n\nAbstract\nBinary Neutron Star (BN S) Mergers are some of the most violent events in the universe which emit a range of astrophysical messengers and are expected to occur frequently\, currently detectable via Gamma-Ray Bursts (GRBs) on a weekly basis. These systems are an ideal target for multi-messenger astronomy due the combina tion of Gravitational Wave (GW) emission and a powerful jet formed upon co alescence\, demonstrated by the observation of a BNS via GW 170817 and GRB 170817A\, then followed up by a range of lower energy electromagnetic obs ervations. Where these jets accelerate hadrons above TeV energies there sh ould also be an observable astrophysical neutrino flux\, presenting an opp ortunity for the first GW-neutrino correlations. I will discuss work to im prove the efficiency of software pipeline searching for modelled GW signal s from BNS mergers. In addition we apply methods to infer astrophysical pr obabilities for a catalog of triggered event times and for individual pote ntial GW candidates. These probabilities could be crucial in focusing our energy to the most interest candidates for follow up and evaluating the pr esence of a population of BNS signals.\n LOCATION:https://researchseminars.org/talk/CENTRA/13/ END:VEVENT BEGIN:VEVENT SUMMARY:Edgar Gasperin (CENTRA\, IST) DTSTART:20200917T133000Z DTEND:20200917T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/14 DESCRIPTION:Title: Zero rest-mass fields in Minkowski spacetime close to spatial infinity \nby Edgar Gasperin (CENTRA\, IST) as part of CENTRA Seminar\n\n\nAbstract \nZero rest-mass fields of spin 1 (the electromagnetic field) and spin 2 p ropagating on flat space and their corresponding Newman-Penrose (NP) const ants are studied near spatial infinity. The aim of this analysis is to cla rify the correspondence between data for these fields on a spacelike hyper surface and the value of their corresponding NP constants at future and pa st null infinity. To do so\, the framework of the cylinder at spatial infi nity is employed to show that\, expanding the initial data in terms spheri cal harmonics and powers of the geodesic spatial distance ρ to spatial in finity\, the NP constants correspond to the data for the second highest po ssible spherical harmonic at fixed order in ρ. In addition\, it is shown that for generic initial data within the class considered in this article\ , the NP constants at future and past null infinity\, for both the Maxwell and spin-2 field\, do not correspond to each other. However\, if the init ial data is time-symmetric\, then\, a correspondence between the NP consta nts at future and past null infinity is established.\n LOCATION:https://researchseminars.org/talk/CENTRA/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Marcus Reitz (Radboud U.\, IMAPP) DTSTART:20200924T133000Z DTEND:20200924T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/15 DESCRIPTION:Title: Approximate Killing symmetries in non-perturbative quantum gravity\nby Marcus Reitz (Radboud U.\, IMAPP) as part of CENTRA Seminar\n\n\nAbstract \nAn open question in quantum gravity is if and how small scale fluctuatio ns and inhomogeneities behave in such a way that at some larger scale they can be well approximated by a geometry with some number of exact symmetri es. Causal Dynamical Triangulation (CDT) is a non-perturbative approach to quantum gravity\, based on a lattice regularisation of space-time\, in wh ich these kind of questions possibly can be addressed. After a short intro duction of the framework\, I will present a specific notion of approximate Killing vectors that can be generalised tosimplicial manifolds using the framework of discrete exterior calculus. These discrete approximate Killin g vectors show promise as an observable to study effective symmetries in q uantum gravity. I will present a comparison between three different two-di mensional toy-models of quantum gravity\, CDT\, Dynamical Triangulations a nd small perturbations around flat space.\n LOCATION:https://researchseminars.org/talk/CENTRA/15/ END:VEVENT BEGIN:VEVENT SUMMARY:María José Bustamante Rosell (Texas U.) DTSTART:20201210T143000Z DTEND:20201210T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/16 DESCRIPTION:Title: Self-torque and frame nutation in binary black hole simulations\nby Ma ría José Bustamante Rosell (Texas U.) as part of CENTRA Seminar\n\n\nAbs tract\nWe investigate the precession of the spin of the smaller black hole in binary black hole simulations. By considering a sequence of binaries a t higher mass ratios\, we approach the limit of geodetic precession of a t est spin. This precession is corrected by the ``self-torque'' due to the s maller black hole's own spacetime curvature. We find that the spins underg o spin nutations which are not described in conventional descriptions of s pin precession\, an effect that has been noticed previously in simulations . These nutations arise because the spins are not measured in a frame wher e the smaller hole is stationary. We develop a simple model for these fram e nutations\, extract the instantaneous spin precession rate\, and compare our results to PN and extreme-mass-ratio approximations for the self-torq ue.\n LOCATION:https://researchseminars.org/talk/CENTRA/16/ END:VEVENT BEGIN:VEVENT SUMMARY:Alexey Bobrick (Lund Observatory) DTSTART:20201015T133000Z DTEND:20201015T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/17 DESCRIPTION:Title: Binary White Dwarfs and Neutron Stars in the Transient Sky\nby Alexey Bobrick (Lund Observatory) as part of CENTRA Seminar\n\n\nAbstract\nRecent advances in all-sky synoptic surveys\, their rapid spectroscopic follow-u p and spectropolarimetry have uncovered a wealth of data about known trans ients\, such as type 1a supernovae\, as well as a variety of new classes o f transient events. In this talk\, I will review the key recent advances i n our understanding of type 1a supernovae\, both from the observational an d modelling side. Additionally\, by using white dwarf-neutron star binarie s as a show-case\, I will demonstrate how we gradually uncover the nature of new types of transients. Vera Rubin observatory\, coming operational in the next two years\, will dramatically advance this already active field of transient research.\n LOCATION:https://researchseminars.org/talk/CENTRA/17/ END:VEVENT BEGIN:VEVENT SUMMARY:Hirotada Okawa (Waseda Institute for Advanced Study) DTSTART:20201029T143000Z DTEND:20201029T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/18 DESCRIPTION:Title: Post-Newtonian Kozai-Lidov mechanism and Gravitational waves from hierarch ical triple systems\nby Hirotada Okawa (Waseda Institute for Advanced Study) as part of CENTRA Seminar\n\n\nAbstract\nWe have recently studied g ravitational waves from a hierarchical three-body system up to first-order postNewtonian approximation. One of the key players is the so-called Koza i-Lidov oscillation\, which causes periodic exchange between eccentricity of inner bindary and relative inclination. In our recent papers\, we analy zed dynamics of three-body system which consists of pulsars or black holes \, and gravitational waves from such systems. In my talk\, I will first ex plain the results obtained so far by perturbation and/or double-averaging method in the literature and will next discuss our direct simulation for t hree-body problems and those results.\n LOCATION:https://researchseminars.org/talk/CENTRA/18/ END:VEVENT BEGIN:VEVENT SUMMARY:Jorge H. C. Martins (Porto U.\, IA) DTSTART:20201001T133000Z DTEND:20201001T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/19 DESCRIPTION:Title: A Nobel Prize for the discovery of other worlds\nby Jorge H. C. Martin s (Porto U.\, IA) as part of CENTRA Seminar\n\n\nAbstract\nIn 2019\, the N obel Prize of Physics was awarded "for contributions to our understanding of the evolution of the universe and Earth's place in the cosmos". The pri ze was actually shared between two subjects that could not be more distinc t: cosmology and exoplanetary science. \n\nIn this presentation\, I will s peak about the exoplanetary science half of the prize\, the discovery of a n exoplanet orbiting a solar-type star by Michel Mayor and Didier Queloz. In particular\, I will focus on how this discovery opened the window to a whole new field of astrophysics and drove (and still drives) the developme nt of the new generations of ground based instruments and space missions d edicated to the discovery and characterization of the planets around stars other than the Sun.\n LOCATION:https://researchseminars.org/talk/CENTRA/19/ END:VEVENT BEGIN:VEVENT SUMMARY:Alejandro Torres-Forne (Potsdam\, Max Planck Inst.) DTSTART:20201022T133000Z DTEND:20201022T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/20 DESCRIPTION:Title: Understanding GWs from core-collapse supernovae\nby Alejandro Torres-F orne (Potsdam\, Max Planck Inst.) as part of CENTRA Seminar\n\n\nAbstract\ nCore collapse supernovae is among the most exciting events that we expect to observe in the future by gravitational-wave interferometers. They prov ide a unique multi-messenger opportunity with the combined emission of gra vitational waves\, neutrinos and electromagnetic waves. In this talk\, I w ill focus in the current understanding of core-collapse GW signals and how they can be modelled in terms of normal oscillations modes of proto-neutr on stars excited during the post-bounce phase before the onset of the SN e xplosion. The observation of such modes in the future by gravitational wav e observatories (Virgo\, LIGO) may allow to infer the properties of proto- neutron stars and learn about the engine powering supernova explosions.\n LOCATION:https://researchseminars.org/talk/CENTRA/20/ END:VEVENT BEGIN:VEVENT SUMMARY:Ippei Obata (Garching\, Max Planck Inst.) DTSTART:20201105T143000Z DTEND:20201105T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/21 DESCRIPTION:Title: Axion Dark Matter Search with Optical Interferometer\nby Ippei Obata ( Garching\, Max Planck Inst.) as part of CENTRA Seminar\n\n\nAbstract\nAxio n dark matter differentiates the phase velocities of the circular-polarize d photons. In this talk\, we present a scheme to measure its phase differe nce by using a linear optical cavity. We applied this scheme to the Fabry- Perot arm of gravitational wave detectors such as DECIGO\, CE\, and aLIGO. We found that their potential sensitivities to the axion-photon coupling constant\, g_{aγ}\, can reach beyond the current limit of CAST with sever al orders of magnitude\, at a wide axion mass range 10^{-16}eV < m < 10^{- 9} eV. Our sensitivity can be achieved without losing any sensitivity to g ravitational waves. This talk is based on our recent paper Phys. Rev. Lett . 123 (2019) 111301 [arXiv:1903.02017].\n LOCATION:https://researchseminars.org/talk/CENTRA/21/ END:VEVENT BEGIN:VEVENT SUMMARY:Antoine Lehebel (CENTRA\, IST) DTSTART:20201112T143000Z DTEND:20201112T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/22 DESCRIPTION:Title: Onset of spontaneous scalarization in generalized scalar-tensor theories\nby Antoine Lehebel (CENTRA\, IST) as part of CENTRA Seminar\n\n\nAbstr act\nSpontaneous scalarization is a mechanism that endows relativistic sta rs and black holes with a nontrivial configuration only when their spaceti me curvature exceeds some threshold. Beyond this threshold\, they acquire a nontrivial scalar configuration\, which also affects their structure. Th e onset of scalarization is controlled only by terms that contribute to li near perturbation around solutions of general relativity. I will present t he complete set of these terms in generalized scalar-tensor theories\, and determine the relevant thresholds in terms of the contributing coupling c onstants and the properties of the compact object.\n LOCATION:https://researchseminars.org/talk/CENTRA/22/ END:VEVENT BEGIN:VEVENT SUMMARY:Juan Diego Soler (Heidelberg\, Max Planck Inst. Astron.) DTSTART:20201119T143000Z DTEND:20201119T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/23 DESCRIPTION:Title: The cycle of matter in the magnetized interstellar medium as revealed by m achine vision\nby Juan Diego Soler (Heidelberg\, Max Planck Inst. Astr on.) as part of CENTRA Seminar\n\n\nAbstract\nMachine vision (MV) is the g eneral name given to the methods for automatic inspection and analysis of images\, from pattern recognition to object classification. I will present the results of MV techniques applied to the study of the formation and ev olution of star-forming clouds in the Milky Way\, both in observations and numerical simulations. First\, the characterization of filamentary struct ures in the observations of the atomic hydrogen (HI) emission at 21 cm in The HI/OH/Recombination-line (THOR) survey of the Galactic plane. Second\, the evaluation of the correlation between the HI emission and the emissio n from molecular species in star-forming clouds. Finally\, in the study of the anisotropy introduced by the interstellar magnetic fields in the velo city field in and around star-forming clouds.\n LOCATION:https://researchseminars.org/talk/CENTRA/23/ END:VEVENT BEGIN:VEVENT SUMMARY:Clémence Fontanive (Center for Space and Habitability\, Universit y of Bern) DTSTART:20201203T143000Z DTEND:20201203T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/24 DESCRIPTION:Title: Brown dwarfs binaries: from statistics to formation and evolution\nby Clémence Fontanive (Center for Space and Habitability\, University of Ber n) as part of CENTRA Seminar\n\n\nAbstract\nThe binary properties of brown dwarfs in the field form a continuum with the trends observed in the stel lar regime\, with fewer binary systems\, smaller separations and higher ma ss ratios seen around lower-mass objects. However\, the binary statistics of the latest-type T and Y brown dwarfs are sparse and it is unclear wheth er the trends seen for their more massive counterparts hold for the very c oolest brown dwarfs. On the other hand\, young brown dwarfs appear to have different multiplicity properties than those observed in the older field population. Measuring and understanding these discrepancies is necessary t o allow more realistic modelling for formation theories and be able to pre dict the evolution and fate of binaries. In this talk\, I will present res ults from a campaign compiled to investigate the binary statistics as a fu nction of age for the extreme low-mass end of the Initial Mass Function. B ased on constraints from Bayesian statistical analyses\, I will discuss th e implications of the observed disparities for brown dwarf formation and e volution models.\n LOCATION:https://researchseminars.org/talk/CENTRA/24/ END:VEVENT BEGIN:VEVENT SUMMARY:Hector O. Silva (Illinois U.\, Urbana) DTSTART:20201126T143000Z DTEND:20201126T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/25 DESCRIPTION:Title: Probing fundamental physics with neutron stars\nby Hector O. Silva (Il linois U.\, Urbana) as part of CENTRA Seminar\n\n\nAbstract\nNeutron stars are some of the most extreme objects in Nature. Their large masses (typic ally around 1.4 times that of the mass) combined with their small radii (t ypically around 12 km) result in interior densities that can exceed nuclea r saturation density\, above which exotic states of matter can arise. Mor eover\, neutron stars are\, next to black holes\, the strongest gravitatio nal field sources known. These properties make neutron stars outstanding l aboratories to study both matter and gravity in situations out of reach in terrestrial and Solar System experiments. In this presentation\, I will d iscuss how recent of neutron star observations\, through both electromagne tic and gravitational waves\, are allowing us to improve our understanding of the internal composition of these stars and to even test Einstein's th eory of general relativity.\n LOCATION:https://researchseminars.org/talk/CENTRA/25/ END:VEVENT BEGIN:VEVENT SUMMARY:RESCHEDULED DTSTART:20201008T133000Z DTEND:20201008T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/26 DESCRIPTION:by RESCHEDULED as part of CENTRA Seminar\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/CENTRA/26/ END:VEVENT BEGIN:VEVENT SUMMARY:Antonio Mario Magalhães (IAG\, São Paulo U.) DTSTART:20210121T143000Z DTEND:20210121T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/27 DESCRIPTION:Title: Optical Polarimetry and the Galactic Magnetic Field\nby Antonio Mario Magalhães (IAG\, São Paulo U.) as part of CENTRA Seminar\n\n\nAbstract\n Interstellar optical polarization is produced by dust grains aligned by a magnetic field and can be used as a tracer of the latter. We discuss the r esults of our Interstellar Polarization Survey and what we have learned ab out the magnetic field structure of the Galaxy at small and large scales a nd at high Galactic latitudes. The data include the Local Interstellar Med ium (ISM) and the nature of the SMC dust and its magnetic field structure. We also look into intriguing data concerning the relationship between the ambient magnetic field direction and that of disks around young stars in the Galaxy. \n\nWe describe the numerical tools we are currently developin g towards a Galactic Magnetic field model. It combines radio (synchrotron) and optical data and a dust model that may explain the observations. Appl ications of this model include the interpretation of our optical polarizat ion data towards cosmological fields.\n\nFinally\, we describe our plans f or SOUTH POL\, a forthcoming survey of the whole Southern sky in optical p olarized light. SOUTH POL will impact several areas\, from Cosmology to So lar System studies.\n LOCATION:https://researchseminars.org/talk/CENTRA/27/ END:VEVENT BEGIN:VEVENT SUMMARY:Mikhail Solon (UCLA) DTSTART:20210128T150000Z DTEND:20210128T160000Z DTSTAMP:20260422T225756Z UID:CENTRA/28 DESCRIPTION:Title: Binary Black Holes and Scattering Amplitudes\nby Mikhail Solon (UCLA) as part of CENTRA Seminar\n\n\nAbstract\nFuture gravitational wave detecto rs will map out and characterize every binary merger in the history of the universe. The possibilities for new and unexpected scientific discoveries from this wealth of data is staggering\, but hinges crucially on compleme ntary advances in our theoretical understanding of the nature of gravitati onal wave sources. However\, the path from Einstein’s equation to precis ion binary dynamics is notoriously difficult\, and conventional methods do not scale to the demands of future detectors. I will describe our recent efforts in solving the relativistic two body problem using modern tools fr om quantum field theory.\n LOCATION:https://researchseminars.org/talk/CENTRA/28/ END:VEVENT BEGIN:VEVENT SUMMARY:Branislav Nikolic (Cologne U.) DTSTART:20210204T143000Z DTEND:20210204T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/29 DESCRIPTION:Title: Classical\, semiclassical\, and quantum aspects of higher derivative gravi tational actions\nby Branislav Nikolic (Cologne U.) as part of CENTRA Seminar\n\n\nAbstract\nWhat is the motivation for introducing gravitationa l actions containing quadratic curvature or other higher derivative terms in investigations of gravity? What is the classical and quantum interpreta tion of such actions and what are the prospects for their observational te sts?\nIn this talk we address these questions from one approach to quantum gravity: quantum geometrodynamics and its semiclassical limit. We shall d raw attention to some conceptual and mathematical inconsistencies that qua ntum geometrodynamics and exact classical quadratic curvature gravity suff er from. We emphasize how one must be very cautious with classical and qua ntum interpretation of higher-derivative actions\, if one wants to maintai n a semiclassical limit to quantum geometrodynamics that is consistent wit h quantum field theory in curved spacetime. \nWe hope to inspire the resea rchers to critically pursue this line of inquiry in other approaches to qu antum gravity and their semiclassical limit\, and especially to revisit th e classical interpretation of higher-derivative gravitational actions.\n LOCATION:https://researchseminars.org/talk/CENTRA/29/ END:VEVENT BEGIN:VEVENT SUMMARY:Patrick Antolin (Northumbria U.) DTSTART:20210211T143000Z DTEND:20210211T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/30 DESCRIPTION:Title: Nanojets of coronal heating\nby Patrick Antolin (Northumbria U.) as pa rt of CENTRA Seminar\n\n\nAbstract\nThe solar corona is shaped and mysteri ously heated to millions of degrees by the Sun’s magnetic field. It has long been hypothesized that the heating results from a myriad of tiny magn etic energy outbursts called nanoflares\, driven by the fundamental proces s of magnetic reconnection. Misaligned magnetic field lines can break and reconnect\, producing nanoflares in avalanche-like processes. However\, no direct and unique observations of such nanoflares exist to date\, and the lack of a smoking gun has cast doubt on the possibility of solving the co ronal heating problem. From coordinated multi-band high-resolution observa tions\, we report on the discovery of very fast and bursty nanojets\, the telltale signature of reconnection-based nanoflares resulting in coronal h eating. The nanojet is uniquely characterised by being transverse to the l oop and appears as a unidirectional jet from the reconnection point. Isola ted and clustered nanojets are detected\, and a myriad are observed in an avalanche-like progression\, leading to the formation of a coronal loop. U sing state-of-the-art numerical simulations\, we demonstrate that the nano jet is a consequence of the slingshot effect from the magnetically tensed\ , curved magnetic field lines reconnecting at small angles. Nanojets are t herefore the key signature of reconnection-based coronal heating in action .\n LOCATION:https://researchseminars.org/talk/CENTRA/30/ END:VEVENT BEGIN:VEVENT SUMMARY:Boris Safonov (Sternberg Astronomical Institute\, MSU\, Moscow) DTSTART:20210218T143000Z DTEND:20210218T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/31 DESCRIPTION:Title: Differential Speckle Polarimetry of evolved stars\, including Betelgeuse\nby Boris Safonov (Sternberg Astronomical Institute\, MSU\, Moscow) as part of CENTRA Seminar\n\n\nAbstract\nDifferential speckle polarimetry (DS P) is a method aimed at study of distribution of polarized flux in astroph ysical objects at diffraction limited resolution. Using DSP at SAI 2.5 m\, telescope we detected in visual wavelength range dusty envelopes with an angular size of 0.05-0.15 arcsec around a number of evolved stars\, e.g. m u Cep (Safonov et al\, MNRAS\, 484\, 5129). Quite frequently these envelop es exhibit variability of morphology associated with the photometric varia bility. For example\, in the circumstellar envelope of semiregular variabl e star V CVn we detected two regions changing their brightness with the sa me period as the star\, but with significant phase delays\, up to a half o f the period. On the basis of these data we suggest that the pulsations of V CVn are non-radial (Safonov et al\, AstL\, 45\, 453). In case of Betelg euse we confirm that the brightness minimum of 2019-2020 is due to the for mation of a dust cloud at the line of sight. Apart from this\, during reco very from minimum the amount of scattering dust in the envelope increased (arXiv:2005.05215). DSP provides new interesting opportunities to study th e mass loss of evolved stars.\n LOCATION:https://researchseminars.org/talk/CENTRA/31/ END:VEVENT BEGIN:VEVENT SUMMARY:Yossef Zenati (Johns Hopkins U.) DTSTART:20210311T143000Z DTEND:20210311T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/32 DESCRIPTION:Title: The physical mechanism behind normal and peculiar SN Ia\nby Yossef Zen ati (Johns Hopkins U.) as part of CENTRA Seminar\n\n\nAbstract\nType Ia su pernovae (SNe) are thought to originate from the thermonuclear explosions of carbon-oxygen (CO) white dwarfs (WDs). The proposed progenitors of stan dard type Ia SNe have been studied for decades and can be\, generally\, di vided into explosions of CO WDs accreting material from stellar non-degene rate companions (single-degenerate\; SD models)\, and those arising from t he explosive interaction of two CO WDs (double-degenerate\; DD models). Ho wever\, current models for the progenitors of such SNe fail to reproduce t he diverse properties of the observed explosions\, nor do they explain the inferred rates and the characteristics of the observed populations of typ e Ia SNe and their expected progenitors. Here we show that the little-stud ied mergers of CO-WDs with hybrid Helium-CO (He-CO) WDs can provide for a significant fraction of the normal type Ia SNe. Here we use detailed therm onuclear-hydrodynamical and radiative-transfer models to show that a wide range of mergers of CO WDs with hybrid He-CO WDs can give rise to normal t ype Ia SNe. We find that such He-enriched mergers give rise to explosions for which the synthetic light-curves and spectra resemble those of observe d type Ia SNe\, and in particular\, they can produce a wide range of peak- luminosities\, MB(MR)~ 18.4 to 19.2 (~ 18.5 to 19:45)\, consistent with th ose observed for normal type Ia SNe. Moreover\, our population synthesis m odels show that\, together with the contribution from mergers of massive d ouble CO-WDs (producing the more luminous SNe)\, they can potentially repr oduce the full range of type Ia SNe\, their rate and delay-time distributi on.\n LOCATION:https://researchseminars.org/talk/CENTRA/32/ END:VEVENT BEGIN:VEVENT SUMMARY:Valerio Faraoni (Bishop’s University\, Sherbrooke\, Canada) DTSTART:20210225T143000Z DTEND:20210225T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/33 DESCRIPTION:Title: Imperfect fluid description of scalar-tensor gravity and an application to the GR limit\nby Valerio Faraoni (Bishop’s University\, Sherbrooke\ , Canada) as part of CENTRA Seminar\n\n\nAbstract\nScalar-tensor gravity c an be described as general relativity plus an effective imperfect fluid co rresponding to the scalar field degree of freedom of this class of theorie s. A symmetry of electrovacuum Brans-Dicke gravity translates into a symme try of the corresponding effective fluid. We present the formalism and an application to an anomaly in the limit of Brans-Dicke to Einstein gravity\ , and outline a possible application to the thermodynamics of spacetime.\n LOCATION:https://researchseminars.org/talk/CENTRA/33/ END:VEVENT BEGIN:VEVENT SUMMARY:Poojan Agrawal (Swinburne U.\, Ctr. Astrophys. Supercomput.) DTSTART:20210408T100000Z DTEND:20210408T110000Z DTSTAMP:20260422T225756Z UID:CENTRA/34 DESCRIPTION:Title: Can uncertainties in the evolution of massive stars explain properties of gravitational wave progenitors?\nby Poojan Agrawal (Swinburne U.\, Ctr . Astrophys. Supercomput.) as part of CENTRA Seminar\n\n\nAbstract\nMassiv e stars play a critical role in the evolution of galaxies and star cluster s. Recent observations of the latter have highlighted the need for systema tic studies dedicated to probing the impact of massive stellar evolution o n the properties of stellar populations. While the use of fitting formulae to stellar tracks remains a popular choice for modelling stellar evolutio n in population synthesis codes\, these formulae are not adaptable to chan ges. In this talk\, I will discuss and present results from an alternative approach\, one that is more adaptable: Method of Interpolation for Single Star Evolution (METISSE). It can readily make use of stellar models compu ted with different stellar evolution codes and compare their predictions f or populations of stars. Using METISSE with the data from different stella r evolution codes\, I will show how various physical ingredients used in t he evolution of massive stars\, such as the treatment of their radiation d ominated envelopes\, can lead to differences in their evolutionary propert ies. I will discuss the implications of these differences on the evolution and interaction of stars in binaries\, and how it can impact compact bina ry mergers and the properties of gravitational wave events.\n LOCATION:https://researchseminars.org/talk/CENTRA/34/ END:VEVENT BEGIN:VEVENT SUMMARY:Milton Ruiz (Illinois U.\, Urbana) DTSTART:20210304T143000Z DTEND:20210304T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/35 DESCRIPTION:Title: Full GR simulations of stellar compact binary mergers: from GW170817 to GW 190814.\nby Milton Ruiz (Illinois U.\, Urbana) as part of CENTRA Semin ar\n\n\nAbstract\nStellar Compact object mergers are not only important so urces of gravitational waves but also central engines that power electroma gnetic transients and r-processes\, if matter is involved. I will revie w recent progress modeling the merger of black hole-neutron star and neutr on stars binaries highlighting state-of-the-art general relativistic magne tohydrodynamic simulations. In particular\, I focus on the effort to esta blish these systems as viable progenitors of short-hard gamma ray bursts a nd understanding their role in triggering the r-process. We use the predic tions of these numerical simulations to impose constraints on the nature o f GW170817 and GW190814.\n LOCATION:https://researchseminars.org/talk/CENTRA/35/ END:VEVENT BEGIN:VEVENT SUMMARY:Francisco Duque (CENTRA\, Instituto Superior Técnico) DTSTART:20210318T143000Z DTEND:20210318T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/36 DESCRIPTION:Title: Gravitational tuning forks and hierarchical triple systems\nby Francis co Duque (CENTRA\, Instituto Superior Técnico) as part of CENTRA Seminar\ n\n\nAbstract\nThe LIGO-Virgo collaboration recently reported evidence for coalescences involving hierarchical triples composed by a stellar-mass bi nary system in the vicinity of a supermassive black hole (SMBH). We study gravitational wave emission in the strong-field regime of these systems an d find that the binary system can resonantly excite the quasinormal modes of the SMBH\, as in the resonant excitation of two tuning forks with match ing frequencies. Moreover\, the flux of energy crossing the SMBH horizon can be much more significant than in the standard extreme-mass-ratio inspi rals. Consequently\, these systems have a natural mechanism to probe stron g-field physics. This can lead to distinctive signatures in their waveform such as Doppler shifts\, aberration\, lensing and strong amplitude modula tions Finally\, we address the impact of our results for the space-based L ISA mission\, which is particularly designed to detect gravitiational wave s originated in galactic centers\, where hierarchical triple systems are k nown to be abundant.\n LOCATION:https://researchseminars.org/talk/CENTRA/36/ END:VEVENT BEGIN:VEVENT SUMMARY:Sabyasachi Goswami (SISSA\, Trieste\, Italy) DTSTART:20210325T143000Z DTEND:20210325T153000Z DTSTAMP:20260422T225756Z UID:CENTRA/37 DESCRIPTION:Title: On the effects of Initial Mass function on the galactic chemical enrichmen t\nby Sabyasachi Goswami (SISSA\, Trieste\, Italy) as part of CENTRA S eminar\n\n\nAbstract\nContext: There is mounting evidence that the stellar initial mass function (IMF) could extend much beyond the canonical Mi ~10 0\, Msun limit\, but the impact of such hypothesis on the chemical enrichm ent of galaxies still remains to be clarified.\n\nAim: We aim to address t his question by analysing the observed abundances of thin- and thick-disc stars in the Milky Way with chemical evolution models that account for the contribution of very massive stars dying as pair-instability supernovae.\ n\nMethod: We built new sets of chemical yields from massive and very mass ive stars up to Mi ~ 350 Msun\, by combining the wind ejecta extracted fr om our hydrostatic stellar evolution models with explosion ejecta from the literature. Using a simple chemical evolution code we analyse the effects of adopting different yield tables by comparing predictions against obser vations of stars in the solar vicinity.\n\nResults: After several tests\, we focus on the [O/Fe] ratio which best separates the chemical patterns of the two Milky Way components. We find that with a standard IMF\, truncate d at Mi ~ 100 Msun\, we can reproduce various observational constraints fo r thin-disc stars\, but the same IMF fails to account for the [O/Fe] rat ios of thick-disc stars. The best results are obtained by extending the IM F up to Mi = 350 Msun and including the chemical ejecta of very massive s tars\, in the form of winds and pair-instability supernova explosions.\n\n Conclusions: Our study indicates that PISN played a significant role in sh aping the chemical evolution of the Milky Way thick disc. By including the ir chemical yields it is easier to reproduce not only the level of the alp ha-enhancement but also the observed slope of thick-disc stars in the [O/F e] vs [Fe/H] diagram. The bottom line is that the contribution of very mas sive stars to the chemical enrichment of galaxies is potentially quite imp ortant and should not be neglected in chemical evolution models.\n LOCATION:https://researchseminars.org/talk/CENTRA/37/ END:VEVENT BEGIN:VEVENT SUMMARY:Abbas Askar (Lund U.) DTSTART:20210422T133000Z DTEND:20210422T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/38 DESCRIPTION:Title: Black Hole Dynamics in Star Clusters: Evolution and Growth from Stellar to Supermassive Scales\nby Abbas Askar (Lund U.) as part of CENTRA Semin ar\n\n\nAbstract\nOver the past five years\, nearly fifty merging binary b lack holes have been discovered through the direct detection of gravitatio nal waves by the LIGO/Virgo collaboration. While these observations provid e unprecedented insights into the demographics of black holes\, they also raise important questions about the astrophysical origin and formation of these elusive binary systems. One of the formation channels for these obse rved gravitational wave sources are dynamical interactions in dense star c luster. In this talk\, I will describe how star clusters evolve and discus s the various processes by which merging binary black holes can form in th em based on results from state-of-the-art simulations of nearly two thousa nd stellar clusters. I will also give an overview of the main processes in volved in the retention and long-term evolution of black holes in star clu sters and explain how they shape the properties and merger rates for binar y black holes that originate in these dense stellar environments. Addition ally\, it has also been suggested that massive and dense star clusters cou ld be potential sites for forming black holes with masses between ~ 100 to 10\,000 solar masses. I will discuss the key processes and caveats involv ed in the formation\, retention and growth of these intermediate-mass blac k holes in the densest of star clusters. Finally\, I will discuss how star clusters that host intermediate-mass black holes can potentially end up i n the center of the galaxy where they may play a role in seeding the forma tion of supermassive black holes.\n LOCATION:https://researchseminars.org/talk/CENTRA/38/ END:VEVENT BEGIN:VEVENT SUMMARY:Miren Radia (DAMTP\, Cambridge U.) DTSTART:20210429T133000Z DTEND:20210429T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/39 DESCRIPTION:Title: Anomalies in the gravitational recoil of eccentric black-hole mergers with unequal mass ratios\nby Miren Radia (DAMTP\, Cambridge U.) as part of CENTRA Seminar\n\n\nAbstract\nThe radiation of linear momentum imparts a recoil (or "kick") to the center of mass of a merging black hole binary sy stem. In 2019\, numerical relativity calculations showed that the addition of orbital eccentricity can lead to an approximate 25% increase in recoil velocities for equal-mass\, spinning binaries with spins lying in the orb ital plane ("superkick" configurations) [arXiv:1910.01598]. I will present recent results [arXiv:2101.11015] obtained from numerical simulations inv estigating the impact of nonzero eccentricity on the kick magnitude and gr avitational-wave emission of nonspinning\, unequal-mass black hole binarie s. Like the spinning case\, nonzero eccentricities at merger can lead to k icks which are larger by up to ~25% relative to the quasicircular case. Ho wever\, we also find that the kick velocity has an oscillatory dependence on the eccentricity. I will discuss our interpretation of this phenomenon and our observations.\n LOCATION:https://researchseminars.org/talk/CENTRA/39/ END:VEVENT BEGIN:VEVENT SUMMARY:Fábio Cruz (GoLP\, Instituto Superior Técnico) DTSTART:20210506T133000Z DTEND:20210506T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/40 DESCRIPTION:Title: First-principles kinetic simulations of pulsar magnetospheres\nby Fáb io Cruz (GoLP\, Instituto Superior Técnico) as part of CENTRA Seminar\n\n \nAbstract\nPulsars gather a wealth of extreme physical conditions\, makin g them unique environments where general relativity\, quantum electrodynam ics\, and plasma physics meet. The electron-positron plasma that partially fills the pulsar magnetosphere is thought to be created via strong Quantu m Electrodynamics (QED) cascades. In each step of this positive feedback p rocess\, electrons and positrons accelerated to TeV energies emit gamma-ra ys that\, in the presence of 10^12 Gauss magnetic fields\, decay into new electron-positron pairs. In this talk\, I will present two classes of full y kinetic particle-in-cell simulations of pulsar magnetospheres. First\, I will show local simulations including the QED processes relevant in pulsa rs from first principles\, and show that plasma waves triggered by QED cas cades can produce coherent electromagnetic waves\, that are strong candida tes for the longstanding problem of pulsar radio emission. Second\, I will present global simulations\, that demonstrate that QED cascades operating up to only a few stellar radii above the central neutron star can provide enough plasma to fill the whole pulsar magnetosphere and trigger dissipat ion at large radii\, consistently with observations. Preliminary results o f simulations of pulsars where general relativity is taken into account wi ll be presented\, and its role in the global dynamics of the magnetosphere will be discussed.\n LOCATION:https://researchseminars.org/talk/CENTRA/40/ END:VEVENT BEGIN:VEVENT SUMMARY:Jonathan Thompson (Cardiff U.) DTSTART:20210415T133000Z DTEND:20210415T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/41 DESCRIPTION:Title: Modelling precession in gravitational waves through inspiral\, merger and ringdown\nby Jonathan Thompson (Cardiff U.) as part of CENTRA Seminar\ n\n\nAbstract\nAs gravitational wave detectors increase in sensitivity\, p reviously unmodelled physical effects will play an important role in advan cing the accuracy of future gravitational wave models. For signals arising from precessing compact binaries\, current models map non-precessing wave forms onto the precessing parameter space through a non-inertial rotation using Euler angles derived from the post-Newtonian dynamics of the inspira ling system. While these angles approximate well the motion of the orbital plane relative to the direction of total (fixed) angular momentum at earl y times or low frequencies of the signal\, the morphology of these angles disagrees strongly with numerical relativity results through merger and ri ngdown\, where the post-Newtonian approximation breaks down. We present th e first model of these precession angles that has been tuned to precessing numerical relativity simulations through merger and ringdown\, and discus s additional changes to the underlying non-precessing waveform needed to e nsure accuracy for more challenging precessing binaries with higher mass r atios and spin magnitudes.\n LOCATION:https://researchseminars.org/talk/CENTRA/41/ END:VEVENT BEGIN:VEVENT SUMMARY:Andreas Mantziris (Imperial College) DTSTART:20210513T133000Z DTEND:20210513T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/42 DESCRIPTION:Title: Cosmological implications of electroweak vacuum instability: constraints o n the Higgs curvature coupling from inflation\nby Andreas Mantziris (I mperial College) as part of CENTRA Seminar\n\n\nAbstract\nSpeaker: Andreas Mantziris (Imperial College)\n\nTitle: Cosmological implications of elect roweak vacuum instability: constraints on the Higgs curvature coupling fro m inflation \n\nAbstract: \nThe current experimentally measured parameters of the Standard Model (SM) suggest that our universe lies in a metastable electroweak vacuum\, where the Higgs field could decay to a lower vacuum state with catastrophic consequences. Our measurements dictate that such a n event has not happened yet\, despite the many different mechanisms that could have triggered it during our past light-cone. Via this observation\, we can establish a promising link between cosmology and particle physics and thus constrain important parameters of our theories. The focus of our work has been to explore this possibility by calculating the probability o f the false vacuum to decay during the period of inflation and using it to constrain the last unknown renormalisable SM parameter $\\xi$\, which cou ples the Higgs field with space-time curvature. In our latest study\, we d erived lower bounds for the Higgs-curvature coupling from vacuum stability in three inflationary models: quadratic and quartic chaotic inflation\, a nd Starobinsky-like power-law inflation. In contrast to most previous stud ies\, we took the time-dependence of the Hubble rate into account both in the geometry of our past light-cone and in the Higgs effective potential\, which is approximated with three-loop renormalisation group improvement s upplemented with one-loop curvature corrections. We find that in all three models\, the lower bound is $\\xi \\gtrsim 0.051 ... 0.066$ depending on the top quark mass. We also demonstrated that vacuum decay is most likely to happen a few e-foldings before the end of inflation. \n\nRoom: ZOOM vid eoconference (contact justin.feng@tecnico.ulisboa.pt for URL)\n LOCATION:https://researchseminars.org/talk/CENTRA/42/ END:VEVENT BEGIN:VEVENT SUMMARY:Donato Bini (IAC\, Rome and INFN\, Naples) DTSTART:20210520T133000Z DTEND:20210520T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/43 DESCRIPTION:Title: Recent results in the relativistic two-body problem: the scattering angle< /a>\nby Donato Bini (IAC\, Rome and INFN\, Naples) as part of CENTRA Semin ar\n\n\nAbstract\nThe recent progress in understanding the features of the relativistic two-body problem has been possible by combining information taken from various different contexts\, namely Post-Newtonian\, Post-Min kowskian\, Self-Force\, and Effective one-body formalisms. A novel approac h (termed "Tutti Frutti") has allowed us to reach the 6PN level of accurac y in the discussion of the problem (modulo some unknown parameter). Other results have already been obtained (and much is currently expected) from E ffective Field Theories. The status of the art and the current research tr ends will be reviewed here.\n LOCATION:https://researchseminars.org/talk/CENTRA/43/ END:VEVENT BEGIN:VEVENT SUMMARY:Chen Yuan (ITP\, Chinese Academy of Sciences) DTSTART:20210527T133000Z DTEND:20210527T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/44 DESCRIPTION:Title: Non-tensorial Gravitational Wave Background in NANOGrav 12.5-Year Data Set \nby Chen Yuan (ITP\, Chinese Academy of Sciences) as part of CENTRA Seminar\n\n\nAbstract\nThe North American Nanohertz Observatory for Gravit ational Waves (NANOGrav) collaboration has reported a strong evidence of a stochastic process\, modeled as a power-law\, with common amplitude and s pectral index among all pulsars. However\, there is no statistically signi ficant evidence for quadrupolar spatial correlations and hence this proces s can not be explained by a gravitational-wave background (GWB) detection. We perform a search for an isotropic non-tensorial GWB allowed in general metric theories of gravity in the NANOGrav 12.5-year data set. By modelin g the GWB as a power-law spectrum\, we find strong Bayesian evidence for a spatially correlated process with scalar transverse (ST) correlations.\n LOCATION:https://researchseminars.org/talk/CENTRA/44/ END:VEVENT BEGIN:VEVENT SUMMARY:Patrick Bourg (Southampton U.) DTSTART:20210617T133000Z DTEND:20210617T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/45 DESCRIPTION:Title: Critical collapse of a spherically symmetric ultrarelativistic fluid in 2 + 1 dimensions\nby Patrick Bourg (Southampton U.) as part of CENTRA Se minar\n\n\nAbstract\nWe present new numerical simulations of the gravitati onal collapse of a perfect fluid with the ultrarelativistic equation of st ate P = κρ\, in spherical symmetry in 2 + 1 spacetime dimensions with Λ < 0. At the threshold of prompt collapse\, we find type I (lifetime scale s as logarithm of distance from the threshold) and type II critical phenom ena (apparent horizon mass and maximum curvature scale as powers of distan ce from the threshold) depending on κ. Moreover\, the type II critical so lution is not self-similar (as in higher dimensions) but contracting quasi -statically.\n LOCATION:https://researchseminars.org/talk/CENTRA/45/ END:VEVENT BEGIN:VEVENT SUMMARY:Ali Seraj (Brussels U. and Intl. Solvay Inst.\, Brussels) DTSTART:20210701T133000Z DTEND:20210701T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/46 DESCRIPTION:Title: Gravitational breathing memory and dual symmetries\nby Ali Seraj (Brus sels U. and Intl. Solvay Inst.\, Brussels) as part of CENTRA Seminar\n\n\n Abstract\nBrans-Dicke theory contains an additional propagating mode which causes homogeneous expansion and contraction of test bodies in transverse directions. This "breathing" mode is associated with novel memory effects in addition to those of general relativity. Standard tensor mode memories are related to a symmetry principle: they are determined by the balance e quations corresponding to the BMS symmetries. In this paper\, we show that the leading and subleading breathing memory effects are determined by the balance equations associated with the leading and "overleading" asymptoti c symmetries of a dual formulation of the scalar field in terms of a two-f orm gauge field. The memory effect causes a transition in the vacuum of th e dual gauge theory. These results highlight the significance of dual char ges and the physical role of overleading asymptotic symmetries.\n LOCATION:https://researchseminars.org/talk/CENTRA/46/ END:VEVENT BEGIN:VEVENT SUMMARY:Rodrigo Panosso Macedo (Queen Mary University of London) DTSTART:20210715T133000Z DTEND:20210715T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/47 DESCRIPTION:Title: Pseudospectrum and black hole quasi-normal mode (in)stability\nby Rodr igo Panosso Macedo (Queen Mary University of London) as part of CENTRA Sem inar\n\n\nAbstract\nWe study the stability of quasi-normal modes (QNM) in asymptotically flat black hole spacetimes by means of a pseudospectrum ana lysis. The construction of the Schwarzschild QNM pseudospectrum reveals: i ) the stability of the slowest decaying QNM under perturbations respecting the asymptotic structure\, reassessing the instability of the fundamental QNM discussed by Nollert (1996)\; ii) the instability of all overtones un der small scale perturbations of sufficiently high frequency\, that migrat e to a universal class of QNM branches along pseudospectra boundaries\, sh edding light on Nollert & Price's analysis (1996).\n LOCATION:https://researchseminars.org/talk/CENTRA/47/ END:VEVENT BEGIN:VEVENT SUMMARY:Kyriakos Destounis (Tubingen U.) DTSTART:20210608T133000Z DTEND:20210608T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/48 DESCRIPTION:Title: Gravitational-wave imprints of non-integrable extreme-mass-ratio inspirals \nby Kyriakos Destounis (Tubingen U.) as part of CENTRA Seminar\n\n\nA bstract\nThe detection of gravitational waves from extreme-mass-ratio insp irals (EMRIs) with upcoming space-borne detectors will allow for unprecede nted tests of general relativity in the strong-field regime. Aside from as sessing whether black holes are unequivocally described by the Kerr metric \, they may place constraints on the degree of spacetime symmetry. Dependi ng on exactly how a hypothetical departure from the Kerr metric manifests\ , the Carter symmetry\, which implies the integrability of the geodesic eq uations\, may be broken. In this talk\, I will discuss the impact of non-i ntegrability in EMRIs which involve a supermassive compact object with ano malous multipolar structure. After reviewing the features of chaotic pheno mena in EMRIs\, I will argue that non-integrability is precisely imprinted in the gravitational waveform. Explicit examples of non-integrable EMRIs will be discussed\, as well as their role in LISA data analysis.\n\nThis t alk will be based on the following articles:\n\nPhys.Rev.D 102 (2020) 6\, 064041\nPhys.Rev.Lett. 126 (2021) 14\, 141102\n LOCATION:https://researchseminars.org/talk/CENTRA/48/ END:VEVENT BEGIN:VEVENT SUMMARY:Sjoert van Velzen (Leiden Observ.\, New York U.\, CCPP\, Maryland U.) DTSTART:20210624T133000Z DTEND:20210624T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/49 DESCRIPTION:Title: Stellar tidal disruption events: a new probe for black hole astrophysics\nby Sjoert van Velzen (Leiden Observ.\, New York U.\, CCPP\, Maryland U .) as part of CENTRA Seminar\n\n\nAbstract\nThe tidal disruption of a star by a massive black hole is a rare event that results in a spectacular fla re of electromagnetic radiation. Visible from radio to X-ray wavelengths\, tidal disruption flares are a unique probe to study massive black holes a nd the nucleus of their host galaxies. The advent of optical transient sur veys has accelerated this field\, resulting in a large number of (often un expected) discoveries. I will review this recent progress\, demonstrating the application of tidal disruption events as tools to measure black hole spin and the launch mechanism of relativistic jets.\n LOCATION:https://researchseminars.org/talk/CENTRA/49/ END:VEVENT BEGIN:VEVENT SUMMARY:David Pereñiguez (Madrid\, IFT) DTSTART:20210708T133000Z DTEND:20210708T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/50 DESCRIPTION:Title: Quasinormal modes of NUT-charged black branes in AdS/CFT\nby David Per eñiguez (Madrid\, IFT) as part of CENTRA Seminar\n\n\nAbstract\nIn the co ntext of AdS/CFT\, the quasinormal modes (QNM) of black holes in the bulk correspond to the poles of the Green’s functions of the dual finite-temp erature QFT. In this talk I will show how 4d black hole perturbation theor y in the Newman—Penrose formalism extends to planar black holes in AdS w ith NUT charge. Scalar\, electromagnetic and gravitational modes come orga nised precisely as Landau levels\, the NUT charge playing the role of a co nstant magnetic field. I will derive the boundary conditions at infinity t hat are relevant for holography\, and conclude by presenting the associate d QNM spectrum and discussing its main features.\n LOCATION:https://researchseminars.org/talk/CENTRA/50/ END:VEVENT BEGIN:VEVENT SUMMARY:Justin Feng (CENTRA\, IST) DTSTART:20210722T133000Z DTEND:20210722T143000Z DTSTAMP:20260422T225756Z UID:CENTRA/51 DESCRIPTION:Title: Self-collision of a portal wormhole\nby Justin Feng (CENTRA\, IST) as part of CENTRA Seminar\n\n\nAbstract\nPortals (also known as loop based th in shell wormholes or gates in the literature) are wormholes supported by a single loop of negative mass\, negative tension cosmic string and have t he property that the geometry is everywhere flat except at the cosmic stri ng. In this talk\, I describe the construction\, topology\, and smoothing of portals\, and consider what happens if one attempts to collide the mout hs of a portal\, which naively resembles a topology changing process. For a simple anisotropic fluid\, it is found that in general relativity\, port al mouths do not experience an acceleration as they are brought together\, and a curvature singularity forms in the limit that the separation distan ce vanishes.\n LOCATION:https://researchseminars.org/talk/CENTRA/51/ END:VEVENT END:VCALENDAR