Publications

2023

• Microstates of a 2d Black Hole in string theory
  
  • Betzios Panos
  • Papadoulaki Olga
  Journal of High Energy Physics, Springer, 2023, 2023 (1), pp.28. A bstract We analyse models of Matrix Quantum Mechanics in the double scaling limit that contain non-singlet states. The finite temperature partition function of such systems contains non-trivial winding modes (vortices) and is expressed in terms of a group theoretic sum over representations. We then focus in the case when the first winding mode is dominant (model of Kazakov-Kostov-Kutasov). In the limit of large representations (continuous Young diagrams), and depending on the values of the parameters of the model such as the compactification radius and the string coupling, the dual geometric background corresponds to that of a long string (winding mode) condensate or a 2 d (non-supersymmetric) Black Hole. In the matrix model we can tune these parameters and explore various phases and regimes. Our construction allows us to identify the origin of the microstates of these backgrounds, arising from non trivial representations, and paves the way for computing various observables on them. (10.1007/JHEP01(2023)028)
  DOI : 10.1007/JHEP01(2023)028
• Thermodynamic origin of the Landau instability of superfluids
  
  • Goutéraux Blaise
  • Mefford Eric
  • Sottovia Filippo
  , 2023. In this work, we revisit the question of the linear stability of superfluid phases of matter. Famously, Landau predicted superfluid Helium would become unstable for large enough superfluid velocities. We demonstrate that this instability simply follows from a thermodynamic argument, by showing that its onset corresponds to a change of sign of one of the eigenvalues of the matrix of second derivatives of the free energy. Turning on dissipation and without any particular assumption on invariance under boosts, we show that a linear dynamical instability also develops, leading to exponential growth in time of perturbations around equilibrium. Specializing to Galilean superfluids and assuming the existence of quasiparticles, our criterion matches Landau's critical velocity. We also verify that it correctly reproduces the onset of the instability in relativistic superfluids constructed using gauge/gravity duality. Our work provides a simple, comprehensive and unified description of the Landau instability for superfluids independently of the microscopic details of the system.
• AdS$_2$ Holography and Effective QFT
  
  • Choi Sangmin
  • Larsen Finn
  Journal of High Energy Physics, Springer, 2023, 11, pp.151. We discuss AdS$_2$ quantum gravity from an unconventional perspective that emphasizes bulk geometry. In our approach, AdS$_2$ has no boundary, there are no divergences that require renormalization, and the dilaton of JT-gravity can be omitted altogether. The result is the standard Schwarzian theory. However, it may be advantageous that our derivation just relies on conventional AdS/CFT correspondence and effective quantum field theory. For example, it clarifies the symmetry breaking pattern. It also puts the non-compact AdS$_2$ topology on the same footing as compact Riemann surfaces. (10.1007/JHEP11(2023)151)
  DOI : 10.1007/JHEP11(2023)151
• Restoring time-reversal covariance in relaxed hydrodynamics
  
  • Amoretti Andrea
  • Brattan Daniel K
  • Martinoia Luca
  • Matthaiakakis Ioannis
  Physical Review D, American Physical Society, 2023, 108 (5), pp.056003. In hydrodynamics, for generic relaxations, the stress tensor and $U(1)$ charge current two-point functions are not time-reversal covariant. This remains true even if the Martin-Kadanoff procedure happens to yield Onsager reciprocal correlators. We consider linearised relativistic hydrodynamics on Minkowski space in the presence of energy, $U(1)$ charge and momentum relaxation. We then show how one can find the minimal relaxed hydrodynamic framework that does yield two-point functions consistent with time-reversal covariance. We claim the same approach naturally applies to boost agnostic hydrodynamics and its limits (e.g. Carrollian, Galilean and Lifshitz fluids). (10.1103/PhysRevD.108.056003)
  DOI : 10.1103/PhysRevD.108.056003
• Ehlers, Carroll, Charges and Dual Charges
  
  • Mittal Nehal
  • Petropoulos P. Marios
  • Rivera-Betancour David
  • Vilatte Matthieu
  Journal of High Energy Physics, Springer, 2023, 07, pp.065. We unravel the boundary manifestation of Ehlers' hidden Möbius symmetry present in four-dimensional Ricci-flat spacetimes that enjoy a time-like isometry and are Petrov-algebraic. This is achieved in a designated gauge, shaped in the spirit of flat holography, where the Carrollian three-dimensional nature of the null conformal boundary is manifest and covariantly implemented. The action of the Möbius group is local on the space of Carrollian boundary data, among which the Carrollian Cotton tensor plays a predominent role. The Carrollian and Weyl geometric tools introduced for shaping an appropriate gauge, as well as the boundary conformal group, which is $\text{BMS}_4$, allow to define electric/magnetic, leading/subleading towers of charges directly from the boundary Carrollian dynamics and explore their behaviour under the action of the Möbius duality group. (10.1007/JHEP07(2023)065)
  DOI : 10.1007/JHEP07(2023)065
• Bridging the static patches: de Sitter holography and entanglement
  
  • Franken Victor
  • Partouche Hervé
  • Rondeau François
  • Toumbas Nicolaos
  Journal of High Energy Physics, Springer, 2023, 08, pp.074. In the context of de Sitter static-patch holography, two prescriptions have been put forward for holographic entanglement entropy computations, the monolayer and bilayer proposals. In this paper, we reformulate both prescriptions in a covariant way and extend them to include quantum corrections. We argue that the bilayer proposal is self-consistent, while the monolayer proposal exhibits contradictory behavior. In fact, the bilayer proposal leads to a stronger holographic description, in which the full spacetime is encoded on two screens at the cosmological horizons. At the classical level, we find large degeneracies of minimal extremal homologous surfaces, localized at the horizons, which can be lifted by quantum corrections. The entanglement wedges of subregions of the screens exhibit non-trivial behaviors, hinting at the existence of interesting phase transitions and non-locality in the holographic theory. In particular, while each screen encodes its corresponding static patch, we show that the entanglement wedge of the screen with the larger quantum area extends and covers the causal diamond between the screens, with a phase transition occurring when the quantum areas of the screens become equal. We argue that the capacity of the screens to encode the region between them is lost, when these are pushed further in the static patches of the observers and placed on stretched horizons. (10.1007/JHEP08(2023)074)
  DOI : 10.1007/JHEP08(2023)074
• Metal–insulator transition in composition-tuned nickel oxide films
  
  • Fowlie Jennifer
  • Georgescu Alexandru
  • Suter Andreas
  • Mundet Bernat
  • Toulouse Constance
  • Jaouen Nicolas
  • Viret Michel
  • Domínguez Claribel
  • Gibert Marta
  • Salman Zaher
  • Prokscha Thomas
  • Alexander Duncan
  • Kreisel Jens
  • Georges Antoine
  • Millis Andrew
  • Triscone Jean-Marc
  Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2023, 35 (30), pp.304001. Thin films of the solid solution Nd_1-xLa_xNiO₃ are grown in order to study the expected 0 K phase transitions at a specific composition. We experimentally map out the structural, electronic and magnetic properties as a function of x and a discontinuous, possibly first order, insulator–metal transition is observed at low temperature when x = 0.2. Raman spectroscopy and scanning transmission electron microscopy show that this is not associated with a correspondingly discontinuous global structural change. On the other hand, results from density functional theory (DFT) and combined DFT and dynamical mean field theory calculations produce a 0 K first order transition at around this composition. We further estimate the temperature-dependence of the transition from thermodynamic considerations and find that a discontinuous insulator–metal transition can be reproduced theoretically and implies a narrow insulator–metal phase coexistence with x . Finally, muon spin rotation (µSR) measurements suggest that there are non-static magnetic moments in the system that may be understood in the context of the first order nature of the 0 K transition and its associated phase coexistence regime. (10.1088/1361-648X/accd38)
  DOI : 10.1088/1361-648X/accd38
• Gravitational transverse-momentum distributions
  
  • Lorcé Cédric
  • Song Qin-Tao
  Physics Letters B, Elsevier, 2023, 843, pp.138016. We study the energy-momentum tensor of spin-$0$ and spin-$\frac{1}{2}$ hadrons in momentum space. We parametrize this object in terms of so-called gravitational transverse-momentum distributions, and we identify in the quark sector the relations between the latter and the usual transverse-momentum distributions. Focusing on particular components of the energy-momentum tensor, we study momentum densities, flux of inertia and stress distribution in momentum space, revealing part of the wealth of physical information that can be gained from higher-twist transverse-momentum distributions. (10.1016/j.physletb.2023.138016)
  DOI : 10.1016/j.physletb.2023.138016
• Fractional Topology in interacting 1D Superconductors
  
  • del Pozo Frederick
  • Herviou Loïc
  • Le Hur Karyn
  Physical Review B, American Physical Society, 2023, 107 (15), pp.155134. We investigate the topological phases of two one-dimensional (1D) interacting superconducting wires, and propose topological invariants directly measurable from ground state correlation functions. These numbers remain powerful tools in the presence of couplings and interactions. We show with the density matrix renormalization group that the double critical Ising (DCI) phase discovered in [1] is a fractional topological phase with gapless Majorana modes in the bulk and a one-half topological invariant per wire. Using both numerics and quantum field theoretical methods we show that the phase diagram remains stable in the presence of an inter-wire hopping amplitude $t_{\bot}$ at length scales below $\sim 1/t_{\bot}$. A large inter-wire hopping amplitude results in the emergence of two integer topological phases hosting one edge mode per boundary, shared between both wires. At large interactions the two wires are described by Mott physics, with the $t_{\bot}$ hopping amplitude resulting in a paramagnetic order. (10.1103/PhysRevB.107.155134)
  DOI : 10.1103/PhysRevB.107.155134
• AdS Witten Diagrams to Carrollian Correlators
  
  • Bagchi Arjun
  • Dhivakar Prateksh
  • Dutta Sudipta
  Journal of High Energy Physics, Springer, 2023, 04, pp.135. Carrollian Conformal Field Theories (CFTs) have been proposed as co-dimension one holographic duals to asymptotically flat spacetimes as opposed to Celestial CFTs which are co-dimension two. In this paper, drawing inspiration from Celestial holography, we show by a suitable generalisation of the flat space limit of AdS that keeps track of the previously disregarded null direction, one can reproduce Carrollian CFT correlation functions from AdS Witten diagrams. In particular, considering Witten diagrams in AdS4, we reproduce two and three-point correlation functions for three dimensional Carrollian CFTs in the so-called delta-function branch. Along the way, we construct non-trivial Carrollian three-point functions in the delta-branch by considering a collinear limit. We also obtain a generalised anti-podal matching condition that now depends on the retarded time direction. (10.1007/JHEP04(2023)135)
  DOI : 10.1007/JHEP04(2023)135
• Accessing GPDs through the exclusive photoproduction of a gamma-meson pair
  
  • Duplančić Goran
  • Nabeebaccus Saad
  • Passek-Kumerički Kornelija
  • Pire Bernard
  • Szymanowski Lech
  • Wallon Samuel
  , 2023. We consider the exclusive photo-production of a photon-meson pair with a large invariant mass, working in the QCD factorisation framework. Explicitly, we consider a $ \rho $-meson or a charged $ \pi $ in the final state. This process gives access both to chiral-even GPDs and chiral-odd GPDs, which are not well-known experimentally, especially the latter ones. The computation is performed at leading order and leading twist. We discuss the prospects of measuring them in experiments, focusing on the kinematics at the JLab 12-GeV experiment, and pPb ultra-peripheral collisions at LHC. In particular, the latter gives access to the small $ \xi $ regime of GPDs.
• Resolving the Scales of the Quark-Gluon Plasma with Energy Correlators
  
  • Andres Carlota
  • Dominguez Fabio
  • Kunnawalkam Elayavalli Raghav
  • Holguin Jack
  • Marquet Cyrille
  • Moult Ian
  Physical Review Letters, American Physical Society, 2023, 130 (26), pp.262301. Jets provide us with ideal probes of the quark-gluon plasma (QGP) produced in heavy-ion collisions, since its dynamics at its different scales is imprinted into the multi-scale substructure of the final state jets. We present a new approach to jet substructure in heavy-ion collisions based on the study of correlation functions of energy flow operators. By analysing the two-point correlator of an in-medium quark jet, we demonstrate that the spectra of correlation functions robustly identify the scales defined by the properties of the QGP, particularly those associated with the onset of colour coherence. (10.1103/PhysRevLett.130.262301)
  DOI : 10.1103/PhysRevLett.130.262301
• Accessing GPDs through the exclusive photoproduction of a photon-meson pair with a large invariant mass
  
  • Duplančić Goran
  • Nabeebaccus Saad
  • Passek-Kumerički Kornelija
  • Pire Bernard
  • Szymanowski Lech
  • Wallon Samuel
  Acta Physica Polonica B Proceedings Supplement, Jagiellonian University, 2023, 16 (5), pp.16. We study the exclusive photoproduction of a photon-meson pair with a large invariant mass, working in the QCD factorisation framework. Explicitly, we consider a $ \rho $-meson or a charged $ \pi $ in the final state. This process gives access to chiral-even GPDs as well as chiral-odd GPDs. We focus here on the chiral-even sector. The computation is performed at leading order and leading twist. We discuss the prospects of measuring them in various experiments such as JLab 12-GeV, COMPASS, future EIC and LHC (in ultraperipheral collisions). In particular, the high centre of mass energies available at collider experiments can be used to probe GPDs at small skewness $ \xi $. We also compute the polarisation asymmetries with respect to the incoming photon. The results for an alternative distribution amplitude (`holographic' form) are also compared with the predictions obtained with an asymptotic distribution amplitude. (10.5506/APhysPolBSupp.16.5-A16)
  DOI : 10.5506/APhysPolBSupp.16.5-A16
• A topologically protected quantum dynamo effect in a driven spin-boson model
  
  • Bernhardt Ephraim
  • Elouard Cyril
  • Le Hur Karyn
  Physical Review A, American Physical Society, 2023, 107 (2), pp.022219. We describe a quantum dynamo effect in a driven system coupled to a harmonic oscillator describing a cavity mode or to a collection of modes forming an Ohmic bosonic bath. When the system Hamiltonian changes in time, this induces a dynamical field in the bosonic modes having resonant frequencies with the driving velocity. This field opposes the change of the external driving field in a way reminiscent of the Faraday effect in electrodynamics, justifying the term `quantum dynamo effect'. For the specific situation of a periodically driven spin-$\frac{1}{2}$ on the Bloch sphere, we show that the work done by rolling the spin from north to south pole can efficiently be converted into a coherent displacement of the resonant bosonic modes, the effect thus corresponds to a work-to-work conversion and allows to interpret this transmitted energy into the bath as work. We study this effect, its performance and limitations in detail for a driven spin-$\frac{1}{2}$ in the presence of a radial magnetic field addressing a relation with topological systems through the formation of an effective charge in the core of the sphere. We show that the dynamo effect is directly related to the dynamically measured topology of this spin-$\frac{1}{2}$ and thus in the adiabatic limit provides a topologically protected method to convert driving work into a coherent field in the reservoir. The quantum dynamo model is realizable in mesoscopic and atomic systems. (10.1103/PhysRevA.107.022219)
  DOI : 10.1103/PhysRevA.107.022219
• Minority-spin conducting states in Fe substituted pyrite CoS$_2$
  
  • Mukherjee Anustup
  • Subedi Alaska
  Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2023, 36 (2), pp.025501. There has been a longstanding debate whether the pyrite CoS$_2$ or its alloys with FeS$_2$ are half metallic. We argue using first principles calculations that there is a finite occupation of minority-spin states at the Fermi level throughout the series Co$_{1-x}$Fe$_x$S$_2$. Although the exchange-correlation functional influences the specifics of the electronic structure, we observe a similar trend with increasing Fe concentration in both LDA and GGA calculations. Specifically, even as band filling is decreased through Fe substitution, the lowest-lying conduction band in the minority-spin channel broadens such that these states keep getting lowered relative to the Fermi level, which is contrary to the expectations from a rigid band picture. Furthermore, the exchange splitting decreases as more Co atoms are replaced by Fe, and this again brings the minority-spin states closer to the Fermi level. These two mechanisms, in conjunction with the experimental observation that minority-spin bands cross the Fermi level in stoichiometric CoS$_2$, indicate that minority-spin charge carriers will always be present in Co$_{1-x}$Fe$_x$S$_2$. (10.1088/1361-648X/acfde9)
  DOI : 10.1088/1361-648X/acfde9
• Extended geometry of magical supergravities
  
  • Bossard Guillaume
  • Cederwall Martin
  • Kleinschmidt Axel
  • Palmkvist Jakob
  • Sezgin Ergin
  • Sundberg Linus
  Journal of High Energy Physics, Springer, 2023, 05, pp.162. We provide, through the framework of extended geometry, a geometrisation of the duality symmetries appearing in magical supergravities. A new ingredient is the general formulation of extended geometry with structure group of non-split real form. A simple diagrammatic rule for solving the section constraint by inspection of the Satake diagram is derived. (10.1007/JHEP05(2023)162)
  DOI : 10.1007/JHEP05(2023)162
• Physique de la matière condensée
  
  • Georges Antoine
  L'Annuaire du Collège de France. Résumés des cours et travaux, Collège de France, 2023 (120), pp.73-76. (10.4000/annuaire-cdf.18154)
  DOI : 10.4000/annuaire-cdf.18154
• Colloquium: Hydrodynamics and holography of charge density wave phases
  
  • Baggioli Matteo
  • Goutéraux Blaise
  Rev.Mod.Phys., 2023, 95 (1), pp.011001. In this Colloquium, we review recent progress in the effective description of strongly-correlated phases of matter with spontaneously broken translations, such as charge density waves or Wigner crystals. In real materials, disorder is inevitable and pins the Goldstones of broken translations. We describe how pinning can be incorporated in the effective field theory at low energies, without making any assumption on the presence of boost symmetry. We review the essential role played by gauge-gravity duality models in establishing these effective field theories with only approximate symmetries. We close with a discussion on the relevance of these models for the phenomenology of dc and ac transport in strongly-correlated strange and bad metals, such as high temperature superconductors. (10.1103/RevModPhys.95.011001)
  DOI : 10.1103/RevModPhys.95.011001
• Singularities in 2D and 3D quantum black holes
  
  • Kolanowski Maciej
  • Tomašević Marija
  Journal of High Energy Physics, Springer, 2023, 12, pp.102. We study black holes in two and three dimensions that have spacelike curvature singularities behind horizons. The 2D solutions are obtained by dimensionally reducing certain 3D black holes, known as quantum BTZ solutions. Furthermore, we identify the corresponding dilaton potential and show how it can arise from a higher-dimensional theory. Finally, we show that the rotating BTZ black hole develops a singular inner horizon once quantum effects are properly accounted for, thereby solidifying strong cosmic censorship for all known cases. (10.1007/JHEP12(2023)102)
  DOI : 10.1007/JHEP12(2023)102
• Equilibrium Quantum Impurity Problems via Matrix Product State Encoding of the Retarded Action
  
  • Kloss Benedikt
  • Thoenniss Julian
  • Sonner Michael
  • Lerose Alessio
  • Fishman Matthew T
  • Stoudenmire E.M
  • Parcollet Olivier
  • Georges Antoine
  • Abanin Dmitry A
  Physical Review B, American Physical Society, 2023, 108 (20), pp.205110. In the $0+1$ dimensional imaginary-time path integral formulation of quantum impurity problems, the retarded action encodes the hybridization of the impurity with the bath. In this Article, we explore the computational power of representing the retarded action as matrix product state (RAMPS). We focus on the challenging Kondo regime of the single-impurity Anderson model, where non-perturbative strong-correlation effects arise at very low energy scales. We demonstrate that the RAMPS approach reliably reaches the Kondo regime for a range of interaction strengths $U$, with a numerical error scaling as a weak power law with inverse temperature. We investigate the convergence behavior of the method with respect to bond dimension and time discretization by analyzing the error of local observables in the full interacting problem and find polynomial scaling in both parameters. Our results show that the RAMPS approach offers promise as an alternative tool for studying quantum impurity problems in regimes that challenge established methods, such as multi-orbital systems. Overall, our study contributes to the development of efficient and accurate non-wavefunction-based tensor-network methods for quantum impurity problems. (10.1103/PhysRevB.108.205110)
  DOI : 10.1103/PhysRevB.108.205110
• $\overline{\textrm{D}3}$-branes and gaugino condensation
  
  • Bena Iosif
  • Dudas Emilian
  • Graña Mariana
  • Lo Monaco Gabriele
  • Toulikas Dimitrios
  Journal of High Energy Physics, Springer, 2023, 2023 (12), pp.19. Anti-D3 branes at the bottom of warped throats, commonly used to uplift the cosmological constant in String-Theory de Sitter proposals, source a plethora of supersymmetry-breaking fluxes, that can interact nontrivially with other ingredients of the flux compactification. In this paper we perform a complex-structure decomposition of these fluxes, and compute the effect of the (0,3) flux component on the stabilization of Kähler moduli via D7-branes gaugino condensation. This allows us to obtain a new constraint on the validity of this stabilization mechanism. This effect does not appear hard to satisfy in de Sitter construction proposals that use long warped throats, but may be problematic in proposals where the warping is small. (10.1007/JHEP12(2023)019)
  DOI : 10.1007/JHEP12(2023)019
• A Coherent View of the Quark-Gluon Plasma from Energy Correlators
  
  • Andres Carlota
  • Dominguez Fabio
  • Holguin Jack
  • Marquet Cyrille
  • Moult Ian
  Journal of High Energy Physics, Springer, 2023, 09, pp.088. The ability to measure detailed aspects of the substructure of high-energy jets traversing the quark-gluon plasma (QGP) has provided a new window into its internal dynamics. However, drawing robust conclusions from traditional jet substructure observables has been difficult. In this manuscript we expand on a new approach to jet substructure in heavy-ion collisions based on the study of correlation functions of energy flow operators (energy correlators). We compute the two-point energy correlator of an in-medium massless quark jet and perform a detailed numerical analysis of the produced spectra. Our calculation incorporates vacuum radiation resummed at next-to-leading log accuracy together with the leading order contribution in medium-induced splittings evaluated through the BDMPS-Z multiple scattering and GLV single scattering formalisms. Our analysis demonstrates how particular features of the modifications of in-medium splittings are imprinted in the correlator spectra, particularly showing how energy correlators may be used to extract the onset of colour coherence. We further present a comprehensive discussion on the accuracy and limitations of our study emphasizing how it can be systematically improved. This work sets the foundations for a rich program studying energy correlators in heavy-ion collisions. (10.1007/JHEP09(2023)088)
  DOI : 10.1007/JHEP09(2023)088
• Non-dissipative electrically driven fluids
  
  • Amoretti Andrea
  • Brattan Daniel K.
  • Martinoia Luca
  • Matthaiakakis Ioannis
  Journal of High Energy Physics, Springer, 2023, 05, pp.218. Existing hydrodynamic models of charged fluids consider any external electric field acting on the fluid as either first order in the hydrodynamic derivative expansion and completely arbitrary or zeroth order but constrained by the fluid's chemical potential. This is in tension with experiments on charged fluids, where the electric field is both zeroth order and completely arbitrary. In this work, we take the first step at resolving this conundrum by introducing a new class of hydrodynamic stationary states, including an arbitrary zeroth order electric field, upon which hydrodynamics can be built. We achieve this by first writing down the hydrostatic constitutive relations for a boost-agnostic charged fluid up to first order in derivatives. Then we introduce suitable energy and momentum relaxation terms to balance the influence of the electric field on the fluid. This analysis leads to a new hydrostatic constraint on the spatial fluid velocity, which can be used to define our class of states. This constraint generalizes to the realm of hydrodynamics a similar constraint on the velocity found in the Drude model of electronic transport. Our class of states exhibits non-trivial thermo-electric transport even at ideal order, since it hosts non-zero DC electric and heat currents. We derive the explicit form of the corresponding conductivities and show they depend non-linearly on the electric field. (10.1007/JHEP05(2023)218)
  DOI : 10.1007/JHEP05(2023)218
• Supergravity Scattering Amplitudes
  
  • Dudas Emilian
  • Gherghetta Tony
  • Olive Keith A.
  • Verner Sarunas
  Physical Review D, American Physical Society, 2023, 108 (7), pp.076024. Supergravity theories with non-minimal Kähler potentials are characterized by a non-trivial field space manifold with corresponding non-trivial kinetic terms. The scattering amplitudes in these theories can be calculated at fixed background field values by making a field redefinition to Riemann normal coordinates. Because of the Kähler structure of supergravity, a more compact method for calculating amplitudes is obtained by a redefinition to Kähler normal coordinates. We compare both methods and calculate the explicit transformations and amplitudes for several examples in the context of no-scale supergravity with one and two chiral superfields. We show that in all cases the equivalence of the scattering amplitudes using either Riemann normal or Kähler normal coordinates is possible only at extremal points of the scalar potential. (10.1103/PhysRevD.108.076024)
  DOI : 10.1103/PhysRevD.108.076024
• Flat from anti-de Sitter
  
  • Campoleoni Andrea
  • Delfante Arnaud
  • Pekar Simon
  • Petropoulos P. Marios
  • Rivera-Betancour David
  • Vilatte Matthieu
  Journal of High Energy Physics, Springer, 2023, 12, pp.078. Ricci-flat solutions to Einstein's equations in four dimensions are obtained as the flat limit of Einstein spacetimes with negative cosmological constant. In the limiting process, the anti-de Sitter energy--momentum tensor is expanded in Laurent series in powers of the cosmological constant, endowing the system with the infinite number of boundary data, characteristic of the asymptotically flat solution space. The governing flat Einstein dynamics is recovered as the limit of the original energy--momentum conservation law and from the additional requirement of the line-element finiteness, providing at each order the necessary set of flux-balance equations for the boundary data. This analysis is conducted using a covariant version of the Newman--Unti gauge designed for taking advantage of the boundary Carrollian structure emerging at vanishing cosmological constant and its Carrollian attributes such as the Cotton tensor. (10.1007/JHEP12(2023)078)
  DOI : 10.1007/JHEP12(2023)078