Archived weekly pre-print 21-06-21

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[2106.09466] - A Rigorous Derivation of the Functional Renormalisation Group Equation - Jobst Ziebell
[2106.09037] - Conformal Rigidity from Focusing - Åsmund Folkestad, Sergio Hernández-Cuenca
[2106.09048] - Quantum Gravity Microstates from Fredholm Determinants - Clifford V. Johnson

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[2106.08739] - Cosmological particle production in quantum gravity - Yaser Tavakoli

Authors: Cong Zhang
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
Arxiv link: https://arxiv.org/abs/2106.08202
Abstract We consider the loop quantum theory of the spherically symmetric model of gravity coupled to Gaussian dusts, where the Guassian dusts provide a material reference frame of the space and time to deparameterize gravity. This theory, used to study the quantum features of the spherically symmetric BH, is constructed based on an 1-dimensional lattice $\gamma\subset\mathbb R$. Taking advantage of the path integral formulation, we investigate the quantum dynamics and obtain an effective action. With this action, we get an effective continuous description of this quantum lattice system which is not the same as the one described by the effective Hamiltonian used in arXiv:2012.05729, i.e. the classical Hamiltonian with the holonomy correction. It turns out that, the Hamiltonian derived in this paper can return to that used in arXiv:2012.05729 only for macro black holes, since the lattice $\gamma$ should be chosen sufficiently fine. Moreover, the lattice is chosen sufficiently fine so that the continuous description can describe the underlying lattice theory well.

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[2106.07650] - The FL bound and its phenomenological implications - Miguel Montero, Cumrun Vafa, Thomas Van Riet, Gerben Venken
[2106.07835] - Time-independence of gravitational Rényi entropies and unitarity in quantum gravity - Donald Marolf, Zhencheng Wang

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[2106.07128] - Black hole perturbations in DHOST theories: Master variables, gradient instability, and strong coupling - Kazufumi Takahashi, Hayato Motohashi

Authors: S. Schander, T. Thiemann
Subjects: [‘gr-qc’, ‘hep-th’, ‘math-ph’, ‘math.MP’, ‘quant-ph’]
Arxiv link: http://arxiv.org/abs/2106.06043v1
Abstract In this review, we investigate the question of backreaction in different approaches to cosmological perturbation theory, and with a special focus on quantum theoretical aspects. By backreaction we refer here to the effects of matter field or cosmological inhomogeneities on the homogeneous dynamical background degrees of freedom of cosmology. We begin with an overview of classical cosmological backreaction which is ideally suited for physical situations in the late time Universe. We then proceed backwards in time, considering semiclassical approaches such as semiclassical or stochastic (semiclassical) gravity which take quantum effects of the perturbations into account. Finally, we review approaches to backreaction in quantum cosmology that should apply to the very early Universe where classical and semiclassical approximations break down. The main focus is on a recently proposed implementation of backreaction in quantum cosmology using a Born-Oppenheimer inspired method.

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