Seminar of Theory of Relativity and Gravitation
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2024-12-13 (Friday)
join us at 11:15 
Koushiki Bhattacharyya (Ahmedabad University, India)Gravitational Collapse of Real Scalar Fields: Fundamentals and Applications
Gravitational collapse is a physical process that begins when an object's outward pressure—whether that of a star, galaxy, or a dust cloud—fails to counteract its own self-gravity. Without gravitational collapse in an ever-expanding Universe, there would be no stable dense objects in the sky: no stars, nebulas, galaxies, or black holes. Among the various collapse scenarios studied, the gravitational collapse of real scalar fields holds particular interest due to its dual appeal: its mathematical simplicity and its ability to model realistic matter fields in Cosmological and Astrophysical phenomena. This talk will provide a comprehensive overview of the possible end-states, both singular and regular, arising from such collapses. In the first part, I will discuss the unhindered collapse of scalar fields, exploring the nature of the resulting singularities and their physical viability, including whether they are visible or hidden from external observers. In the second part, I will explain how introducing specific non-zero potentials can halt the collapse, leading to the formation of regular end-states. Finally, I will highlight the relevance of these regular end-states in a Cosmological context.
2024-11-29 (Friday)
room 1.40, Pasteura 5 at 11:15
Sebastian Szybka (UJ)Linearized Halilsoy and Chandrasekhar standing gravitational waves
The Halilsoy and Chandrasekhar cylindrical gravitational waves are two different classes of exact solutions to the vacuum Einstein equations that describe standing gravitational waves. Both families satisfy the definition of standing gravitational waves proposed by Stephani, but only the latter class satisfies Chandrasekhar's stricter definition. The aim of our research is to compare both classes of solutions in the linearized regime.
2024-11-22 (Friday)
room 1.40, Pasteura 5 at 11:15
Wojciech Kaminski (IFT UW)Extreme isolated horizons
Based on joint work with Jurek Lewandowski arxiv:2406.20068
2024-11-15 (Friday)
room 1.40, Pasteura 5 at 11:15
Alice Boldrin (NCBJ)Time problem in perturbation theory
I will discuss the time problem in the framework of quantum fields on quantum spacetimes, considering the specific example of primordial gravitational waves propagating through a bouncing quantum Friedman universe. We will see that the dynamical variables, such as the scale factor or the amplitude of a gravitational wave, obtained from different internal clocks, evolve differently. These expectation values (background evolution) and mode functions of operators (perturbations), irrespective of the clock chosen, converge to a unique evolution for large classically-behaving universes. This is the phase space domain in which unambiguous predictions can be made.
2024-11-08 (Friday)
room 1.40, Pasteura 5 at 11:15
Prof. Jerzy Lewandowski memorial seminar
This seminar will be devoted to the life and scientific achievements of professor Jerzy (Jurek) Lewandowski, who passed away on October 8-th. Speakers: Abhay Ashtekar, Hanno Sahlmann, Paweł Nurowski, Yongge Ma, Wojciech Kamiński and Denis Dobkowski-Ryłko.
2024-10-11 (Friday)
room 1.40, Pasteura 5 at 11:15
Alex Colling (University of Cambridge, UK)Rigidity of the extremal Kerr-Newman horizon
The Einstein equations for a spacetime containing an extremal horizon induce a set of equations determined completely by quantities intrinsic to a compact cross-section of the horizon. Significant progress on classifying solutions to these equations was recently made by Dunajski and Lucietti, who showed that any non-static vacuum solution must admit a Killing vector field.I will present joint work with David Katona and James Lucietti extending the Dunajski-Lucietti proof to four-dimensional Einstein-Maxwell theory. It follows that any non-trivial cross-section in this theory is given by the extremal Kerr-Newman family. I will also discuss rigidity results for the quasi-Einstein equation and a more general extremal horizon equation introduced by Kaminski and Lewandowski.
2024-10-04 (Friday)
room 1.40, Pasteura 5 at 11:15
Shubhagata Bhaumik and Tanmaya Mishra (University of Florida)Expanding the Gravitational Wave Frontier: Detecting Exceptional Binary Black Hole Mergers with a Model-Independent Search
The advanced LIGO-Virgo detectors have identified over 90 binary black hole (BBH) mergers so far, providing valuable insights into the environments where these systems form and merge. In the ongoing fourth observing run of LIGO-Virgo-KAGRA (LVK), binary black hole candidates are being detected every 3 days, owing to the increased sensitivity of the detectors. With the substantial increase in the number of BBH observations, there is growing interest in detecting gravitational waves from uncommon BBH systems, particularly those with orbital eccentricity or high masses which point to dynamical origin for these binaries. Moreover, detecting elusive intermediate-mass black hole (IMBH) mergers can have far-reaching astrophysical implications and help in understanding the formation of supermassive black holes. Template-based searches, which rely on accurate simulated waveforms can miss such events, especially in the presence of non-Gaussian noise. This highlights the importance of model-independent searches like Coherent WaveBurst (cWB) which play a crucial role in detecting gravitational waves from unusual sources like IMBH and eccentric binary black hole (eBBH) mergers. The cWB search was recently upgraded and demonstrates an improvement in the detection efficiency by approximately 40% for simulated BBH events at a false alarm rate of less than one per year. The search uncovers three candidates in LIGO-Virgo-KAGRA’s (LVK) third observing run (O3), not found by LVK’s matched-filtering searches. Notably, the most significant detection involves a black hole merger with an upper mass gap component with low mass ratio, suggesting a possible dynamical origin. Lastly, we will also discuss cWB’s sensitivity to eBBH mergers and its potential for astrophysical interpretations.