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1. Quantization of spherically symmetric loop quantum gravity coupled to a scalar field and a clock: the asymptotic limit

   https://doi.org/10.1088/1361-6382/ad0b9d  

   Gambini, Rodolfo ; Pullin, Jorge ( November 2023 , Classical and Quantum Gravity)

   We continue our work on the study of spherically symmetric loop quantum gravity coupled to two spherically symmetric scalar fields, one which acts as a clock. As a consequence of the presence of the latter, we can define a true Hamiltonian for the theory. The spherically symmetric context allows to carry out precise detailed calculations. Here we study the theory for regions of large values of the radial coordinate. This allows us to define in detail the vacuum of the theory and study its quantum states, yielding a quantum field theory on a quantum space time that makes contact with the usual treatment on classical space times.

    

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2. Spherically symmetric random permutations

   https://doi.org/10.1002/rsa.20847  

   Gnedin, Alexander ; Gorin, Vadim ( March 2019 , Random Structures & Algorithms)

   We consider random permutations which are spherically symmetric with respect to a metric on the symmetric groupS_nand are consistent asnvaries. The extreme infinitely spherically symmetric permutation‐valued processes are identified for the Hamming, Kendall‐tau and Cayley metrics. The proofs in all three cases are based on a unified approach through stochastic monotonicity.

    

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3. Quantum geometry and black holes

   Gambini, Rodolfo ; Olmedo, Javier ; Pullin, Jorge ( January 2023 , Handbook of Quantum Gravity",)

   Bambi, Cosimo ; Modesto, Leonardo ; Shapiro, Ilya (Ed.)

   We summarize our work on spherically symmetric midi-superspaces in loop quantum gravity. Our approach is based on using inhomogeneous slicings that may penetrate the horizon in case there is one and on a redefinition of the constraints so the Hamiltonian has an Abelian algebra with itself. We discuss basic and improved quantizations as is done in loop quantum cosmology. We discuss the use of parameterized Dirac observables to define operators associated with kinematical variables in the physical space of states, as a first step to introduce an operator associated with the space-time metric. We analyze the elimination of singularities and how they are replaced by extensions of the space-times. We discuss the charged case and potential observational consequences in quasinormal modes. We also analyze the covariance of the approach. Finally, we comment on other recent approaches of quantum black holes, including mini-superspaces motivated by loop quantum gravity. 

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4. The collapse and three-dimensional explosion of three-dimensional massive-star supernova progenitor models

   https://doi.org/10.1093/mnras/stab3702  

   Vartanyan, David ; Coleman, Matthew S. B. ; Burrows, Adam ( December 2021 , Monthly Notices of the Royal Astronomical Society)

   The explosion outcome and diagnostics of core-collapse supernovae depend sensitively on the nature of the stellar progenitor, but most studies to date have focused exclusively on one-dimensional, spherically symmetric massive star progenitors. We present some of the first core-collapse supernovae simulations of three-dimensional massive star supernovae progenitors, a 12.5- and a 15-M⊙ model, evolved in three dimensions from collapse to bounce through explosion with the radiation-hydrodynamic code fornax. We compare the results using those starting from three-dimensional progenitors to three-dimensional simulations of spherically symmetric, one-dimensional progenitors of the same mass. We find that the models evolved in three dimensions during the final stages of massive star evolution are more prone to explosion. The turbulence arising in these multidimensional initial models serves as seed turbulence that promotes shock revival. Detection of gravitational waves and neutrinos signals could reveal signatures of pre-bounce turbulence.

    

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5. Ellipsars: Ring-like Explosions from Flattened Stars

   https://doi.org/10.3847/2041-8213/ac6ded  

   DuPont, Marcus ; MacFadyen, Andrew ; Zrake, Jonathan ( May 2022 , The Astrophysical Journal Letters)

   The stellar cataclysms producing astronomical transients have long been modeled as either a point-like explosion or jet-like engine ignited at the center of a spherically symmetric star. However, many stars are observed, or are expected on theoretical grounds, not to be precisely spherically symmetric, but rather to have a slightly flattened geometry similar to that of an oblate spheroid. Here we present axisymmetric two-dimensional hydrodynamical simulations of the dynamics of point-like explosions initiated at the center of an aspherical massive star with a range of oblateness. We refer to these exploding aspherical stars as “ellipsars” in reference to the elliptical shape of the isodensity contours of their progenitors in the two-dimensional axisymmetric case. We find that ellipsars are capable of accelerating expanding rings of relativistic ejecta. which may lead to the production of astronomical transients including low-luminosity gamma-ray bursts, relativistic supernovae, and fast blue optical transients

    

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