infinity. Lastly, we obtain the quantum corrections to the Regge action because of the O(1/j) contribution to the spinfoam amplitude.}, author = {Han, Muxin and Huang, Zichang and Liu, Hongguang and Qu, Dongxue}, doi = {10.1103/PhysRevD.102.124010}, faupublication = {yes}, journal = {Physical Review D}, note = {CRIS-Team WoS Importer:2021-01-01}, peerreviewed = {Yes}, title = {{Numerical} computations of next-to-leading order corrections in spinfoam large-j asymptotics}, volume = {102}, year = {2020} } @article{faucris.246373745, abstract = {Using the disformal solution-generating method, we construct new axisymmetric solutions in Degenerate Higher Order Scalar Tensor (DHOST) theories. The method consists in first considering a "seed"known solution in DHOST theories and then performing a disformal transformation of the metric to obtain a new solution. In vacuum, the two solutions are equivalent but they become physically inequivalent when one considers coupling to matter. In that way, we "disform"the stealth Kerr black hole solution and we obtain a first analytic rotating non-stealth solution in DHOST theories, while the associated scalar field is time-dependent with a constant kinetic density. The new solution is characterized by three parameters: the mass, the spin and the disformal parameter which encodes the deviation with respect to the Kerr geometry. We explore some geometrical properties of the novel disformed Kerr geometry which is no more Ricci flat but has the same singularity as the Kerr metric, admits an ergoregion, and is asymptotically flat. Moreover, the hidden symmetry of the Kerr solution is broken, providing an example of a non-circular geometry in a higher order theory of gravity. We also discuss geodesic motions and compute its (disformed) null directions which are interesting tools to understand the causal structure of the geometry. In addition, to illustrate again the potentiality of the disformal solution-generating method, we present another axisymmetric solution for DHOST theories obtained from a disformal transformation of the generalized Kerr solution of Einstein-Scalar gravity. }, author = {Ben Achour, Jibril and Liu, Hongguang and Motohashi, Hayato and Mukohyama, Shinji and Noui, Karim}, doi = {10.1088/1475-7516/2020/11/001}, faupublication = {yes}, journal = {Journal of Cosmology and Astroparticle Physics}, keywords = {astrophysical black holes; GR black holes; modified gravity}, note = {CRIS-Team Scopus Importer:2020-12-04}, peerreviewed = {Yes}, title = {{On} rotating black holes in {DHOST} theories}, volume = {2020}, year = {2020} } @article{faucris.261330080, abstract = {A coarse graining technique akin to block spin transformations that groups together fiducial cells in a homogeneous and isotropic universe has been recently developed in the context of loop quantum cosmology. The key technical ingredient was an SU(1,1) group and Lie algebra structure of the physical observables as well as the use of Perelomov coherent states for SU(1,1). It was shown that the coarse graining operation is completely captured by changing group representations. Based on this result, it was subsequently shown that one can extract an explicit renormalization group flow of the loop quantum cosmology Hamiltonian operator in a simple model with dust-clock. In this paper, we continue this line of investigation and derive a coherent state path integral formulation of this quantum theory and extract an explicit expression for the renormalization-scale dependent classical Hamiltonian entering the path integral for a coarse grained description at that scale. We find corrections to the nonrenormalized Hamiltonian that are qualitatively similar to those previously investigated via canonical quantization. In particular, they are again most sensitive to small quantum numbers, showing that the large quantum number (spin) description captured by so called "effective equations"in loop quantum cosmology does not reproduce the physics of many small quantum numbers (spins). Our results have direct impact on path integral quantization in loop quantum gravity, showing that the usually taken large spin limit should be expected not to capture (without renormalization, as mostly done) the physics of many small spins that is usually assumed to be present in physically reasonable quantum states. }, author = {Bodendorfer, Norbert and Han, Muxin and Haneder, Fabian and Liu, Hongguang}, doi = {10.1103/PhysRevD.103.126021}, faupublication = {yes}, journal = {Physical Review D}, note = {CRIS-Team Scopus Importer:2021-07-09}, peerreviewed = {Yes}, title = {{Path} integral renormalization in loop quantum cosmology}, volume = {103}, year = {2021} } @article{faucris.296249388, abstract = {Based on the effective dynamics in the μ¯ scheme of the spherical symmetry reduced model in the reduced phase space formulation of loop quantum gravity (LQG), we investigate the gravitational collapse of a homogeneous dust cloud, with Gaussian dust serving as both the reference field and the source of the gravitational collapse. The effective dynamics from the considered model for a homogeneous dust cloud reduces precisely to the effective dynamics of loop quantum cosmology (LQC) with extrinsic curvature based K-quantization, indicating that the LQC effective dynamics lives as a subsector of the model presented here. In both the marginally bound and the bound cases of the collapse in effective dynamics, the singularity is resolved and replaced by a bounce. Though quantum geometric modification from spatial curvature is not directly included in the K-quantization it does affect the qualitative dynamics of the collapsing dust cloud in the sense that on the one hand for the marginally bound case, the dust cloud bounces once at fixed maximum energy density and on the other hand for the bound case, the dust cloud undergoes infinite cycles of contraction and expansion at energy densities dependent on the dust mass. Finally, the mass threshold for the formation of a trapped surface in each case is found and the matching conditions between the interior collapsing spacetime and an effective exterior static solution are discussed. }, author = {Giesel, Kristina and Han, Muxin and Li, Bao Fei and Liu, Hongguang and Singh, Parampreet}, doi = {10.1103/PhysRevD.107.044047}, faupublication = {yes}, journal = {Physical Review D}, note = {Created from Fastlane, Scopus look-up}, peerreviewed = {Yes}, title = {{Spherical} symmetric gravitational collapse of a dust cloud: {Polymerized} dynamics in reduced phase space}, volume = {107}, year = {2023} } @article{faucris.257694219, abstract = {We compute numerically the Lorentzian Engle-Pereira-Rovelli-Livine spinfoam propagator on a 4-simplex, by adapting the Lefschetz thimble and Markov chain Monte-Carlo methods to oscillatory spinfoam integrals. Our method can compute any spinfoam observables at relatively large spins. We obtain the numerical results of the propagators at different spins and demonstrate their consistency with the expected spinfoam semiclassical behavior in the large spin limit. Our results exhibit significant quantum corrections at smaller spins. Our method is reliable and thus can be employed to discover the semiclassical and quantum behaviors of the spinfoam model.}, author = {Han, Muxin and Huang, Zichang and Liu, Hongguang and Qu, Dongxue and Wan, Yidun}, doi = {10.1103/PhysRevD.103.084026}, faupublication = {yes}, journal = {Physical Review D}, note = {CRIS-Team Scopus Importer:2021-05-07}, peerreviewed = {Yes}, title = {{Spinfoam} on a {Lefschetz} thimble: {Markov} chain {Monte} {Carlo} computation of a {Lorentzian} spinfoam propagator}, volume = {103}, year = {2021} }