المؤلفون: Roussille, Hugo, Langlois, David, Noui, Karim

المصدر: Journal of Cosmology and Astroparticle Physics ; volume 2024, issue 01, page 054 ; ISSN 1475-7516

الوصف: We present a novel approach to the numerical computation of quasi-normal modes, based on the first-order (in radial derivative) formulation of the equations of motion and using a matrix version of the continued fraction method. This numerical method is particularly suited to the study of static black holes in modified gravity, where the traditional second-order, Schrödinger-like, form of the equations of motion is not always available. Our approach relies on the knowledge of the asymptotic behaviours of the perturbations near the black hole horizon and at spatial infinity, which can be obtained via the systematic algorithm that we have proposed recently. In this work, we first present our method for the perturbations of a Schwarzschild black hole and show that we recover the well-know frequencies of the QNMs to a very high precision. We then apply our method to the axial perturbations of an exact black hole solution in a particular scalar-tensor theory of gravity. We also cross-check the obtained QNM frequencies with other numerical methods.

الإتاحة: https://doi.org/10.1088/1475-7516/2024/01/054Test

المؤلفون: Noui, Karim, Roussille, Hugo, Langlois, David

المصدر: Journal of Cosmology & Astroparticle Physics; Nov2023, Vol. 2023 Issue 11, p1-27, 27p

المؤلفون: Ganz, Alexander, Noui, Karim

المساهمون: Università degli Studi di Padova = University of Padua (Unipd), Istituto Nazionale di Fisica Nucleare, Sezione di Padova (INFN, Sezione di Padova), Istituto Nazionale di Fisica Nucleare (INFN), Institut Denis Poisson (IDP), Université d'Orléans (UO)-Université de Tours (UT)-Centre National de la Recherche Scientifique (CNRS), AstroParticule et Cosmologie (APC (UMR_7164)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Laboratoire de physique de l'ENS - ENS Paris (LPENS), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Département de Physique de l'ENS-PSL, École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)

المصدر: ISSN: 0264-9381.

مصطلحات موضوعية: derivative: high, mechanics: classical, stability, ghost, higher-order, Hamiltonian, propagation, covariance, [PHYS.HTHE]Physics [physics]/High Energy Physics - Theory [hep-th], [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc]

الوصف: International audience ; We review the fate of the Ostrogradsky ghost in higher-order theories. We start by recalling the original Ostrogradsky theorem and illustrate, in the context of classical mechanics, how higher-derivatives Lagrangians lead to unbounded Hamiltonians and then lead to (classical and quantum) instabilities. Then, we extend the Ostrogradsky theorem to higher-derivatives theories of several dynamical variables and show the possibility to evade the Ostrogradsky instability when the Lagrangian is ‘degenerate’, still in the context of classical mechanics. In particular, we explain why higher-derivatives Lagrangians and/or higher-derivatives Euler–Lagrange equations do not necessarily lead to the propagation of an Ostrogradsky ghost. We also study some quantum aspects and illustrate how the Ostrogradsky instability shows up at the quantum level. Finally, we generalize our analysis to the case of higher order covariant theories where, as the Hamiltonian is vanishing and thus bounded, the question of Ostrogradsky instabilities is subtler.

العلاقة: info:eu-repo/semantics/altIdentifier/arxiv/2007.01063; hal-02905282; https://hal.science/hal-02905282Test; https://hal.science/hal-02905282/documentTest; https://hal.science/hal-02905282/file/2007.01063.pdfTest; ARXIV: 2007.01063; INSPIRE: 1804793

الإتاحة: https://doi.org/10.1088/1361-6382/abe31dTest
https://hal.science/hal-02905282Test
https://hal.science/hal-02905282/documentTest
https://hal.science/hal-02905282/file/2007.01063.pdfTest

المؤلفون: Charmousis, Christos, Crisostomi, Marco, Langlois, David, Noui, Karim

المساهمون: Laboratoire de Physique Théorique d'Orsay Orsay (LPT), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique Théorique - UMR CNRS 3681 (IPHT), Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), AstroParticule et Cosmologie (APC (UMR_7164)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Institut Denis Poisson (IDP), Université d'Orléans (UO)-Université de Tours (UT)-Centre National de la Recherche Scientifique (CNRS), CC and KN acknowledge support from the CNRS project 80PRIME. MC is supported by the Labex P2IO.

المصدر: ISSN: 0264-9381.

مصطلحات موضوعية: black hole: rotation, perturbation: scalar, perturbation: linear, perturbation: tensor, black hole: spin, black hole: hair, gravitational radiation: emission, Teukolsky equation, general relativity, parametrization, scalar tensor, gravitation: higher-order, geometry, [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc], [PHYS.HTHE]Physics [physics]/High Energy Physics - Theory [hep-th]

الوصف: International audience ; We study linear perturbations of a rotating black hole solution that has been recently discovered in the subset of degenerate higher-order scalar–tensor (DHOST) theories where gravity and light propagate with the same speed. We find a parametrization which permits the explicit resolution of the scalar perturbation while the tensor perturbation is obtained as a Teukolsky equation supplemented by an effective source term. The effective source term is related to the black hole hair and can be computed exactly for any value of the black hole spin. We discuss how the perturbations of the geometry and thus the emitted gravitational waves could be modified in comparison with general relativity.

العلاقة: info:eu-repo/semantics/altIdentifier/arxiv/1907.02924; hal-02188141; https://hal.science/hal-02188141Test; https://hal.science/hal-02188141/documentTest; https://hal.science/hal-02188141/file/1907.02924.pdfTest; ARXIV: 1907.02924; INSPIRE: 1742724

الإتاحة: https://doi.org/10.1088/1361-6382/ab4fb1Test
https://hal.science/hal-02188141Test
https://hal.science/hal-02188141/documentTest
https://hal.science/hal-02188141/file/1907.02924.pdfTest

المؤلفون: Liu, Hongguang, Noui, Karim

المساهمون: Centre de Physique Théorique - UMR 7332 (CPT), Aix Marseille Université (AMU)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Mathématiques et Physique Théorique (LMPT), Université de Tours (UT)-Centre National de la Recherche Scientifique (CNRS), AstroParticule et Cosmologie (APC (UMR_7164)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)

المصدر: ISSN: 0264-9381.

مصطلحات موضوعية: kinematics: Hilbert space, spectrum: discrete, phase space: parametrization, representation: unitarity, symmetry: gauge, dimension: 4, quantum gravity, gravitation, Hamiltonian formalism, gauge field theory, electric field, quantization, gauge fixing, space-time, holography, black hole, splitting, signature, SU(1, 1), [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc], [PHYS.HTHE]Physics [physics]/High Energy Physics - Theory [hep-th]

الوصف: International audience ; We start with the Hamiltonian formulation of the first order action of pure gravity with a full $\mathfrak{sl}(2, \mathbb C)$ internal gauge symmetry. We make a partial gauge-fixing which reduces $\mathfrak{sl}(2, \mathbb C)$ to its sub-algebra $\mathfrak{su}(1, 1)$ . This case corresponds to a splitting of the space-time ${\mathcal M}=\Sigma \times \mathbb R$ where $\Sigma$ inherits an arbitrary Lorentzian metric of signature (−, +, +). Then, we find a parametrization of the phase space in terms of an $\mathfrak{su}(1, 1)$ commutative connection and its associated conjugate electric field. Following the techniques of loop quantum gravity, we start the quantization of the theory and we consider the kinematical Hilbert space on a given fixed graph $\Gamma$ whose edges are colored with unitary representations of $\mathfrak{su}(1, 1)$ . We compute the spectrum of area operators acting on the kinematical Hilbert space: we show that space-like areas have discrete spectra, in agreement with usual $\mathfrak{su}(2)$ loop quantum gravity, whereas time-like areas have continuous spectra. We conclude on the possibility to make use of this formulation of gravity to construct a holographic description of black holes in the framework of loop quantum gravity.

العلاقة: info:eu-repo/semantics/altIdentifier/arxiv/1702.06793; hal-01582725; https://hal.science/hal-01582725Test; https://hal.science/hal-01582725/documentTest; https://hal.science/hal-01582725/file/1702.06793.pdfTest; ARXIV: 1702.06793; INSPIRE: 1514714

الإتاحة: https://doi.org/10.1088/1361-6382/aa7348Test
https://hal.science/hal-01582725Test
https://hal.science/hal-01582725/documentTest
https://hal.science/hal-01582725/file/1702.06793.pdfTest

المؤلفون: Langlois, David, Liu, Hongguang, Noui, Karim, Wilson-Ewing, Edward

المساهمون: AstroParticule et Cosmologie (APC (UMR_7164)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Centre de Physique Théorique - UMR 7332 (CPT), Aix Marseille Université (AMU)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Mathématiques et Physique Théorique (LMPT), Université de Tours (UT)-Centre National de la Recherche Scientifique (CNRS)

المصدر: ISSN: 0264-9381.

مصطلحات موضوعية: loop gravity, mimetic gravity, loop cosmology, quantum cosmology: loop space, derivative: high, Friedman model, space-time, gravitation: scalar tensor, family, cosmological model, bounce, [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc], [PHYS.HTHE]Physics [physics]/High Energy Physics - Theory [hep-th]

الوصف: International audience ; Recently, Chamseddine and Mukhanov introduced a higher-derivative scalar-tensor theory which leads to a modified Friedmann equation allowing for bouncing solutions. As we note in the present work, this Friedmann equation turns out to reproduce exactly the loop quantum cosmology effective dynamics for a flat isotropic and homogeneous space-time. We generalize this result to obtain a class of scalar-tensor theories, belonging to the family of mimetic gravity, which all reproduce the loop quantum cosmology effective dynamics for flat, closed and open isotropic and homogeneous space-times.

العلاقة: info:eu-repo/semantics/altIdentifier/arxiv/1703.10812; hal-01645529; https://hal.science/hal-01645529Test; https://hal.science/hal-01645529/documentTest; https://hal.science/hal-01645529/file/1703.10812.pdfTest; ARXIV: 1703.10812; INSPIRE: 1520856

الإتاحة: https://doi.org/10.1088/1361-6382/aa8f2fTest
https://hal.science/hal-01645529Test
https://hal.science/hal-01645529/documentTest
https://hal.science/hal-01645529/file/1703.10812.pdfTest

المؤلفون: Langlois, David, Noui, Karim, Roussille, Hugo

المصدر: Journal of Cosmology and Astroparticle Physics ; volume 2022, issue 08, page 040 ; ISSN 1475-7516

الوصف: We study axial (or odd-parity) perturbations about static and spherically symmetric hairy black hole (BH) solutions in shift-symmetric DHOST (Degenerate Higher-Order Scalar-Tensor) theories. We first extend to the family of DHOST theories the first-order formulation that we recently developed for Horndeski theories. Remarkably, we find that the dynamics of DHOST axial perturbations is equivalent to that of axial perturbations in general relativity (GR) evolving in a, distinct, effective metric. In the particular case of quadratic DHOST theories, this effective metric is derived from the background BH metric via a disformal transformation. We illustrate our general study with three examples of BH solutions. In some so-called stealth solutions, the effective metric is Schwarzschild with a shifted horizon. We also give an example of BH solution for which the effective metric is associated with a naked singularity.

الإتاحة: https://doi.org/10.1088/1475-7516/2022/08/040Test

المؤلفون: Langlois, David, Noui, Karim, Roussille, Hugo

المصدر: Journal of Cosmology and Astroparticle Physics ; volume 2022, issue 09, page 019 ; ISSN 1475-7516

الوصف: We study linear perturbations about non rotating black hole solutions in scalar-tensor theories, more specifically Horndeski theories. We consider two particular theories that admit known hairy black hole solutions. The first one, Einstein-scalar-Gauss-Bonnet theory, contains a Gauss-Bonnet term coupled to a scalar field, and its black hole solution is given as a perturbative expansion in a small parameter that measures the deviation from general relativity. The second one, known as 4-dimensional-Einstein-Gauss-Bonnet theory, can be seen as a compactification of higher-dimensional Lovelock theories and admits an exact black hole solution. We study both axial and polar perturbations about these solutions and write their equations of motion as a first-order (radial) system of differential equations, which enables us to study the asymptotic behaviours of the perturbations at infinity and at the horizon following an algorithm we developed recently. For the axial perturbations, we also obtain effective Schrödinger-like equations with explicit expressions for the potentials and the propagation speeds. We see that while the Einstein-scalar-Gauss-Bonnet solution has well-behaved perturbations, the solution of the 4-dimensional-Einstein-Gauss-Bonnet theory exhibits unusual asymptotic behaviour of its perturbations near its horizon and at infinity, which makes the definition of ingoing and outgoing modes impossible. This indicates that the dynamics of these perturbations strongly differs from the general relativity case and seems pathological.

الإتاحة: https://doi.org/10.1088/1475-7516/2022/09/019Test

المؤلفون: Motohashi, Hayato, Noui, Karim, Suyama, Teruaki, Yamaguchi, Masahide, Langlois, David

المصدر: Journal of Cosmology and Astroparticle Physics ; volume 2016, issue 07, page 033-033 ; ISSN 1475-7516

الإتاحة: https://doi.org/10.1088/1475-7516/2016/07/033Test
http://stacks.iop.org/1475-7516/2016/i=07/a=033/pdfTest
http://stacks.iop.org/1475-7516/2016/i=07/a=033?key=crossref.af6709c2d412c8612c7de442b7762725Test

المؤلفون: Ben Achour, Jibril, Grain, Julien, Noui, Karim

المساهمون: AstroParticule et Cosmologie (APC (UMR_7164)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Institut d'astrophysique spatiale (IAS), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales Paris (CNES), Laboratoire de Mathématiques et Physique Théorique (LMPT), Université de Tours (UT)-Centre National de la Recherche Scientifique (CNRS)

المصدر: ISSN: 0264-9381.

مصطلحات موضوعية: Loop quantum gravity, Loop quantum cosmology, [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc], [PHYS.HTHE]Physics [physics]/High Energy Physics - Theory [hep-th]

الوصف: 22 pages ; International audience ; We construct and study Loop Quantum Cosmology (LQC) when the Barbero-Immirzi parameter takes the complex value $\gamma=\pm i$. We refer to this new quantum cosmology as complex Loop Quantum Cosmology. We proceed in making an analytic continuation of the Hamiltonian constraint (with no inverse volume corrections) from real $\gamma$ to $\gamma=\pm i$ in the simple case of a flat FLRW Universe coupled to a massless scalar field with no cosmological constant. For that purpose, we first compute the non-local curvature operator (defined by the trace of the holonomy of the connection around a fundamental plaquette) evaluated in any spin $j$ representation and we find a new close formula for it. This allows to define explicitly a one parameter family of regularizations of the Hamiltonian constraint in LQC, parametrized by the spin $j$. It is immediate to see that any spin $j$ regularization leads to a bounce scenario. Then, motivated particularly by previous results on black hole thermodynamics, we perform the analytic continuation of the Hamiltonian constraint defined by $\gamma=\pm i$ and $j=-1/2+is$ where $s$ is real. Even if the area spectrum is now continuous, we show that the so-defined complex LQC removes also the original singularity which is replaced by a quantum bounce. In addition, the maximal density and the minimal volume of the Universe are obviously independent of $\gamma$. Furthermore, the dynamics before and after the bounce are no more symmetric, which makes a clear distinction between these two phases of the evolution of the Universe.

العلاقة: info:eu-repo/semantics/altIdentifier/arxiv/1407.3768; hal-01023613; https://hal.science/hal-01023613Test; https://hal.science/hal-01023613/documentTest; https://hal.science/hal-01023613/file/complexcosmo8.pdfTest; ARXIV: 1407.3768

الإتاحة: https://doi.org/10.1088/0264-9381/32/2/025011Test
https://hal.science/hal-01023613Test
https://hal.science/hal-01023613/documentTest
https://hal.science/hal-01023613/file/complexcosmo8.pdfTest