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Thermodynamics of dynamical black holes beyond perturbation theory
Abhay Ashtekar, Daniel E. Paraizo, Jonathan Shu
The close similarities of the three laws of black hole mechanics, discovered by Bardeen, Carter and Hawking, with the laws of thermodynamics led to the identification of a multiple…
Thermodynamics of Black Holes, far from Equilibrium
Abhay Ashtekar, Daniel E. Paraizo, Jonathan Shu
As in thermodynamics, the celebrated first law of black hole mechanics relates infinitesimal changes in the properties of nearby equilibrium states of black holes (without referenc…
Dynamical Horizon Segments and Spacetime Isometries
Abhay Ashtekar, Badri Krishnan
Given a space-time admitting a dynamical horizon segment (DHS) , we show that there are stringent constraints on the Killing fields that…
Black Hole Evaporation in Loop Quantum Gravity
Abhay Ashtekar
The conference \emph{Black Holes Inside and Out} marked the 50th anniversary of Hawking's seminal paper on black hole radiance. It was clear already from Hawking's analysis that a…
Quasi-Local Black Hole Horizons: Recent Advances
Abhay Ashtekar, Badri Krishnan
While the early literature on black holes focused on event horizons, subsequently it was realized that their teleological nature makes them unsuitable for many physical application…
Black Holes Inside and Out 2024: visions for the future of black hole physics
Niayesh Afshordi, Abhay Ashtekar, Enrico Barausse +27
The gravitational physics landscape is evolving rapidly, driven by our ability to study strong-field regions, in particular black holes. Black Holes Inside and Out gathered world e…
The Operational Meaning of Total Energy of Isolated Systems in General Relativity
Abhay Ashtekar, Simone Speziale
We present thought experiments to measure the Arnowitt-Deser-Misner and Bondi-Sachs energy of isolated systems in general relativity. The expression of the Bondi-Sachs energy used…
Horizons and Null Infinity: A Fugue in 4 voices
Abhay Ashtekar, Simone Speziale
Black hole horizons in equilibrium and null infinity of asymptotically flat space-times are null 3-manifolds but have very different physical connotations. We first show that they…
Unified Treatment of null and Spatial Infinity IV: Angular Momentum at Null and Spatial Infinity
Abhay Ashtekar, Neev Khera
In a companion paper we introduced the notion of asymptotically Minkowski spacetimes. These space-times are asymptotically flat at both null and spatial infinity, and furthermore t…
Unified Treatment of Null and Spatial Infinity III: Asymptotically Minkowski Space-times
Abhay Ashtekar, Neev Khera
The Spi framework provides a 4-dimensional approach to investigate the asymptotic properties of gravitational fields as one recedes from isolated systems in any space-like directio…
Black Hole Horizons and their Mechanics
Abhay Ashtekar
Black holes are often characterized by event horizons, following the literature that laid the mathematical foundations of the subject in the 1970s. However black hole event horizon…
Regular black holes from Loop Quantum Gravity
Abhay Ashtekar, Javier Olmedo, Parampreet Singh
There is rich literature on regular black holes from loop quantum gravity (LQG), where quantum geometry effects resolve the singularity, leading to a quantum extension of the class…
Exploring quantum geometry created by quantum matter
Abhay Ashtekar
Exactly soluble models can serve as excellent tools to explore conceptual issues in non-perturbative quantum gravity. In perturbative approaches, it is only the two radiative modes…
Probing cosmological singularities with quantum fields: Open and closed FLRW universes
Abhay Ashtekar, Adrián del Río
It was recently pointed out that linear quantum fields can be meaningfully propagated across the big bang (and the big crunch) singularities of spatially flat Friedmann…
Space-like Singularities of General Relativity: A Phantom menace?
Abhay Ashtekar, Adrián del Río, Marc Schneider
The big bang and the Schwarzschild singularities are space-like. They are generally regarded as the "final frontiers" at which space-time ends and general relativity breaks down. W…
Charges and Fluxes on (Perturbed) Non-expanding Horizons
Abhay Ashtekar, Neev Khera, Maciej Kolanowski +1
In a companion paper we showed that the symmetry group of non-expanding horizons (NEHs) is a 1-dimensional extension of the Bondi-Metzner-Sachs group …
Non-Expanding horizons: Multipoles and the Symmetry Group
Abhay Ashtekar, Neev Khera, Maciej Kolanowski +1
It is well-known that blackhole and cosmological horizons in equilibrium situations are well-modeled by non-expanding horizons (NEHs). In the first part of the paper we introduce m…
Testing gravitational waveform models using angular momentum
Neev Khera, Abhay Ashtekar, Badri Krishnan
The anticipated enhancements in detector sensitivity and the corresponding increase in the number of gravitational wave detections will make it possible to estimate parameters of c…
Probing the Big Bang with quantum fields
Abhay Ashtekar, Tommaso De Lorenzo, Marc Schneider
By carrying out a systematic investigation of linear, test quantum fields in cosmological space-times, we show that remain well-defined across the big bang as…
A Short Review of Loop Quantum Gravity
Abhay Ashtekar, Eugenio Bianchi
An outstanding open issue in our quest for physics beyond Einstein is the unification of general relativity (GR) and quantum physics. Loop quantum gravity (LQG) is a leading approa…
Cosmic tango between the very small and the very large: Addressing CMB anomalies through Loop Quantum Cosmology
Abhay Ashtekar, Brajesh Gupt, V. Sreenath
While the standard, six-parameter, spatially flat CDM model has been highly successful, certain anomalies in the cosmic microwave background bring out a tension between this mod…
Gravitational dynamics: A novel shift in the Hamiltonian paradigm
Abhay Ashtekar, Madhavan Varadarajan
It is well known that Einstein's equations assume a simple polynomial form in the Hamiltonian framework based on a Yang-Mills phase space. We re-examine the gravitational dynamics…
Inferring the gravitational wave memory for binary coalescence events
Neev Khera, Badri Krishnan, Abhay Ashtekar +1
Full, non-linear general relativity predicts a memory effect for gravitational waves. For compact binary coalescence, the total gravitational memory serves as an inferred observabl…
Properties of a recent quantum extension of the Kruskal geometry
Abhay Ashtekar, Javier Olmedo
Recently it was shown that, in an effective description motivated by loop quantum gravity, singularities of the Kruskal space-time are naturally resolved [1,2]. In this note we exp…