Publications

2024

• Interaction-enhanced nesting in Spin-Fermion and Fermi-Hubbard models
  
  • Rossi R.
  • Iv F. Šimkovic
  • Ferrero Michel
  • Georges A.
  • Tsvelik A. M.
  • Prokof'Ev N. V.
  • Tupitsyn I. S.
  Physical Review Research, American Physical Society, 2024, 6 (3), pp.L032058. The spin-fermion (SF) model postulates that the dominant coupling between low-energy fermions in near critical metals is mediated by collective spin fluctuations (paramagnons) peaked at the N\'{e}el wave vector, ${\bf Q}_N$, connecting hot spots on opposite sides of the Fermi surface. It has been argued that strong correlations at hot spots lead to a Fermi surface deformation (FSD) featuring flat regions and increased nesting. This conjecture was confirmed in the perturbative self-consistent calculations when the paramagnon propagator dependence on momentum deviation from ${\bf Q}_N$ is given by $\chi^{-1} \propto |\Delta q|$. Using diagrammatic Monte Carlo (diagMC) technique we show that such a dependence holds only at temperatures orders of magnitude smaller than any other energy scale in the problem, indicating that a different mechanism may be at play. Instead, we find that a $\chi^{-1} \propto |\Delta q|^{2}$ dependence yields a robust finite-$T$ scenario for achieving FSD. To link phenomenological and microscopic descriptions, we applied the connected determinant diagMC method to the $(t-t')$ Hubbard model and found that in this case: (i) the FSD is not very pronounced, and, instead, it is the lines of zeros of the renormalized dispersion relation that deform towards nesting; (ii) this phenomenon appears at large $U/t>5.5$ before the formation of electron and hole pockets; (iii) the static spin susceptibility is well described by $\chi^{-1} \propto |\Delta q|^{2}$. Flat FS regions yield a non-trivial scenario for realizing a non-Fermi liquid state. (10.1103/PhysRevResearch.6.L032058)
  DOI : 10.1103/PhysRevResearch.6.L032058
• Exclusive leptoproduction of a light vector meson at the twist-3 in a GTMD framework
  
  • Boussarie Renaud
  • Fucilla Michael
  • Szymanowski Lech
  • Wallon Samuel
  , 2025, 18 (1), pp.1-A25. We provide the most general description of the exclusive leptoproduction of a light vector meson, at high center-of-mass energy, within the CGC/shockwave formalism. We keep a twist-3 accuracy in $s$ channel, thus being able to describe all possible helicity amplitudes, including the ones for the production of a transversally polarized meson. In this latter case, we overcome the well-known issue of endpoint singularities by promoting the GPD to a GTMD given by matrix elements of dipole and double dipole operators. The all-twists treatment of the proton (nucleon) target allow to safely twist-expand the general vacuum-to-meson matrix elements. Therefore, unlike previous attempts in the modified perturbative approach, our final results are expressed in terms of the twist-3 collinear distribution amplitudes, introduced in the context of the higher-twist collinear formalism. (10.5506/APhysPolBSupp.18.1-A25)
  DOI : 10.5506/APhysPolBSupp.18.1-A25
• Quantum Hall and Light Responses in a 2D Topological Semimetal
  
  • Hur Karyn Le
  • Saati Sariah Al
  Comptes Rendus. Physique, Académie des sciences (Paris), 2024. We have recently identified a protected topological semimetal in graphene which presents a zero-energy edge mode robust to disorder and interactions. Here, we address the characteristics of this semimetal and show that the $\mathbb{Z}$ topological invariant of the Hall conductivity associated to the lowest energy band can be equivalently measured from the resonant response to circularly polarized light resolved at the Dirac points. The (non-quantized) conductivity responses of the intermediate energy bands, including the Fermi surface, also give rise to a $\mathbb{Z}_2$ invariant. We emphasize on the bulk-edge correspondence as a protected topological half metal, i.e. one spin-population polarized in the plane is in the insulating phase related to the robust edge mode while the other is in the metallic regime. The quantized transport at the edges is equivalent to a $\frac{1}{2}-\frac{1}{2}$ conductance for spin polarizations along $z$ direction. We also build a parallel between the topological Hall response and a pair of half numbers (half Skyrmions) through the light response locally resolved in momentum space and on the sphere.
• Holography beyond AdS
  
  • Georgescu Silvia
  , 2024. The motivation for this thesis is to understand how the holographic principle is realized in spacetimes that are not asymptotically AdS. The main focus is on the holographic duality between type IIB string theory with pure NS-NS flux in asymptotically linear dilaton background and the 6d non-local theory living on the NS5 worldvolume, which is called Little string theory (LST). Recently, LST compactified to 2d was related to a tractable dimension (2,2) irrelevant deformation of 2d CFTs called TTbar, or more precisely, "single-trace TTbar", which preserves (4,4) supersymmetry. A similar relation was proposed between the null-warped AdS background, which encodes the near horizon geometry of extremal black holes, and another tractable irrelevant deformation called JTbar. The thesis is divided into three parts, which explore these deformations and the related backgrounds, as well as possible generalizations.The first part of the thesis is purely field-theoretical and is dedicated to the TTbar and JTbar deformations and their single-trace versions. We show that the method of computing the spectrum of a symmetric product orbifold CFT from a sum over covering spaces can also be applied when the seed theory is a TTbar or JTbar deformed CFT, due to the modular properties of these theories. We establish the existence of infinite dimensional symmetry algebras in single-trace TTbar and JTbar, which are non-linear modifications of the symmetry algebras of the undeformed theories. A particular feature of the symmetry transformations is that they are parametrized by functions of field-dependent coordinates. Following a proposal for JTbar deformed CFTs, we use these symmetries to define a set of operators in single-trace JTbar that obey certain Ward identities. We studied the correlation functions of these operators and showed that they can be expressed in terms of correlation functions in the undeformed symmetric orbifold, with modified momentum and charge-dependent conformal dimensions.The second part of the thesis is devoted to the asymptotic symmetries of two backgrounds: asymptotically AdS3 with mixed boundary conditions, which is the holographic dual of a TTbar deformed CFT, and the asymptotically linear dilaton background which arises in the near horizon region of NS5 branes. Regardless of the different asymptotics, we obtain in both cases the same non-linear asymptotic symmetry algebra, which matches perfectly the field theory results for (single-trace) TTbar. In either case, the asymptotic Killing vectors preserving the boundary conditions of the corresponding phase space are expressed in terms of field-dependent coordinates, the same which arise in field theory. A key point in the analysis is the inclusion of charge-dependent rescalings of space and time that are required for the well-definiteness of the symmetry transformations in finite size and which are the origin of the non-linearity.The third part of the thesis studies deformations of the D1-D5 or NS5-F1 system which are similar to single-trace TTbar, in the sense that they start as (2,2) deformations of the D1-D5 CFT that preserve supersymmetry and lead to UV complete theories. We choose to compactify on K3, which yields 6d N=(2,0) supergravity. The structure of the solutions to the supergravity equations of motion which correspond to finite deformations reveals a codimension 1 subspace where the asymptotics is no longer flat, but linear dilaton-like. We show that the condition defining this subspace corresponds to known decoupling limits in string theory. This ensures holographic dualities between the linear dilaton-like decoupled backgrounds and UV-complete non-gravitational theories which are deformations of LST. We compute the entropy of black holes in the decoupled backgrounds and obtain that it interpolates between Cardy at low energies and Hagedorn at high energies, just like in single-trace TTbar. (10.70675/cdc2c44ezbb6ez428ez8844z443bff1ed99a)
  DOI : 10.70675/cdc2c44ezbb6ez428ez8844z443bff1ed99a
• Center-symmetric Landau gauge, the deconfinement transition and the gluon propagator as seen in lattice QCD
  
  • van Egmond Duifje Maria
  • Oliveira Orlando
  • Reinosa Urko
  • Serreau Julien
  • Silva Paulo J
  • Tissier Matthieu
  , 2025, QCHSC24, pp.169. We address the lattice computation of the gluon propagator in the center-symmetric Landau gauge. After discussing a proper lattice implementation of the center-symmetric Landau gauge, we compare the lattice data with analytical results, and we identify various signatures of center symmetry breaking. (10.22323/1.483.0169)
  DOI : 10.22323/1.483.0169
• Gravitational form factors of the nucleon and their mechanical structure: Twist-2 case
  
  • Kim Hyun-Chul
  • Kim June-Young
  • Won Ho-Yeon
  , 2025, QCHSC24, pp.074. We present a series of recent works on the gravitational form factors (GFFs) of the nucleon within a pion mean-field approach, which is also called the chiral quark-soliton model. We investigate the flavor structure of the mass, angular momentum, and $D$-term form factors of the nucleon. The main findings of the present work are given as follows: the contribution of the strange quark is rather small for the mass and angular momentum form factors, it plays an essential role in the $D$-term form factors. It indicates that the $D$-term form factor is sensitive to the outer part of the nucleon. The flavor blindness, i.e, $D^{u-d}\simeq 0$, is valid only if the strange quark is considered. We also discuss the effects of twist-4 operators. Though the gluonic contributions are suppressed by the packing fraction of the instanton vacuum in the twist-2 case, contributions from twist-4 operators are significant. (10.22323/1.483.0074)
  DOI : 10.22323/1.483.0074
• Detector-tuned overlap catastrophe in quantum dots
  
  • Sankar Sarath
  • Bertrand Corentin
  • Georges Antoine
  • Sela Eran
  • Meir Yigal
  Physical Review B, American Physical Society, 2024, 110 (8), pp.085133. The Anderson overlap catastrophe (AOC) is a many-body effect arising as a result of a shakeup of a Fermi sea due to an abrupt change of a local potential, leading to a power-law dependence of the density of states on energy. Here we demonstrate that a standard quantum-dot detector can be employed as a highly tunable probe of the AOC, where the power law can be continuously modified by a gate voltage. We show that signatures of the AOC have already appeared in previous experiments, and give explicit predictions allowing to tune and pinpoint their nonperturbative aspects. (10.1103/PhysRevB.110.085133)
  DOI : 10.1103/PhysRevB.110.085133
• Frequency-dependent superconducting states from the two-time linear response theory: Application to Sr2RuO4
  
  • Gingras Olivier
  • Georges Antoine
  • Parcollet Olivier
  Physical Review B, American Physical Society, 2024, 110 (5), pp.054509. We investigate the possible superconducting instabilities of strongly correlated electron materials using a generalization of linear response theory to external pairing fields depending on frequency. We compute a pairing susceptibility depending on two times, allowing us to capture dynamical pairing and in particular odd-frequency solutions. We first benchmark this method on the attractive one-band Hubbard model and then consider the superconductivity of strontium ruthenate Sr2RuO4 within single-site dynamical mean-field theory, hence restricting ourselves to pairing states which are momentum independent in the orbital basis. The symmetry of the superconducting order parameter of this material is still debated, and local odd-frequency states have been proposed to explain some experimental discrepancies. In the temperature range studied, we find that the leading eigenvectors are odd-frequency intraorbital spin-triplet states, while the eigenvectors with the highest predicted transition temperature correspond to even-frequency intraorbital spin-singlet states. The latter include a state with d-wave symmetry when expressed in the band basis. (10.1103/PhysRevB.110.054509)
  DOI : 10.1103/PhysRevB.110.054509
• Displaced Drude peak from π -ton vertex corrections
  
  • Krsnik J.
  • Simard O.
  • Werner P.
  • Kauch A.
  • Held K.
  Physical Review B, American Physical Society, 2024, 110 (7), pp.075118. Correlated electron systems often show strong bosonic fluctuations, e.g., of antiferromagnetic nature, around a large wave vector such as q = (π, π . . .). These fluctuations can give rise to vertex corrections to the optical conductivity through the (transversal) particle-hole channel, coined π -ton contributions. Previous numerical results differed qualitatively on how such vertex corrections alter the optical conductivity. Here we clarify that π -ton vertex corrections lead to a displaced Drude peak, by studying the weakly correlated regime of a onedimensional single-orbital Hubbard model. The proximity and enhancement of the effect when approaching a phase transition of, e.g., antiferromagnetic nature can be utilized for discriminating π -tons in experiments from other physics leading to a displaced Drude peak. (10.1103/PhysRevB.110.075118)
  DOI : 10.1103/PhysRevB.110.075118
• Two convergent NPA-like hierarchies for the quantum bilocal scenario
  
  • Renou Marc-Olivier
  • Xu Xiangling
  • Ligthart Laurens
  , 2022. Characterising the correlations that arise from locally measuring a single part of a joint quantum system is one of the main problems of quantum information theory. The seminal work [M. Navascués et al, NJP 10,7,073013 (2008)], known as the NPA hierarchy, reformulated this question as a polynomial optimisation problem over noncommutative variables and proposed a convergent hierarchy of necessary conditions, each testable using semidefinite programming. More recently, the problem of characterising the quantum network correlations, which arise when locally measuring several independent quantum systems distributed in a network, has received considerable interest. Several generalisations of the NPA hierarchy, such as the Scalar Extension [Pozas-Kerstjens et al, Phys. Rev. Lett. 123, 140503 (2019)], were introduced while their converging sets remain unknown. In this work, we introduce a new hierarchy, prove its equivalence to the Scalar Extension, and characterise its convergence in the case of the simplest network, the bilocal scenario, and explore its relations with the known generalisations. (10.48550/arXiv.2210.09065)
  DOI : 10.48550/arXiv.2210.09065
• Linear dynamical stability and the laws of thermodynamics
  
  • Goutéraux Blaise
  • Mefford Eric
  , 2024. We show that the dynamical stability under linear perturbations of interacting systems in the hydrodynamic regime follows from the first and the second laws of thermodynamics. Our argument extends to systems with spontaneously or softly broken symmetries and in the presence of magnetic fields.
• One-dimensional Carrollian fluids II: $C^1$ blow-up criteria
  
  • Athanasiou Nikolaos
  • Petropoulos P. Marios
  • Schulz Simon
  • Taujanskas Grigalius
  , 2024. The Carrollian fluid equations arise from the equations for relativistic fluids in the limit as the speed of light vanishes, and have recently experienced a surge of interest in the theoretical physics community in the context of asymptotic symmetries and flat-space holography. In this paper we initiate the rigorous systematic analysis of these equations by studying them in one space dimension in the $C^1$ setting. We begin by proposing a notion of isentropic Carrollian equations, and use this to reduce the Carrollian equations to a $2 \times 2$ system of conservation laws. Using the scheme of Lax, we then classify when $C^1$ solutions to the isentropic Carrollian equations exist globally, or blow up in finite time. Our analysis assumes a Carrollian analogue of a constitutive relation for the Carrollian energy density, with exponent in the range $\gamma \in (1,3]$.
• Competition between d-wave superconductivity and magnetism in uniaxially strained Sr2RuO4
  
  • Profe Jonas
  • Beck Sophie
  • Kennes Dante
  • Georges Antoine
  • Gingras Olivier
  Npj Quantum Materials, Nature publishing, 2024, 9 (1), pp.53. The pairing symmetry of Sr2RuO4 is a long-standing fundamental question in the physics of superconducting materials with strong electronic correlations. We use the functional renormalization group to investigate the behavior of superconductivity under uniaxial strain in a two-dimensional realistic model of Sr2RuO4 obtained with density functional theory and incorporating the effect of spinorbit coupling. We find a dominant d(x2) -(y2) superconductor mostly hosted by the dxy-orbital, with no other closely competing superconducting state. Within this framework, we reproduce the experimentally observed enhancement of the critical temperature under strain and propose a simple mechanism driven by the density of states to explain our findings. We also investigate the competition between superconductivity and spin-density wave ordering as a function of interaction strength. By comparing theory and experiment, we discuss constraints on a possible degenerate partner of the d(x2) -(y2) superconducting state. (10.1038/s41535-024-00661-3)
  DOI : 10.1038/s41535-024-00661-3
• Power efficiency of Hall-like devices: Comparison between reciprocal and antireciprocal Onsager relations
  
  • Wegrowe Jean-Eric
  • Zhou Luqian
  • Al Saati Sariah
  Physical Review B, American Physical Society, 2024, 110 (2), pp.024412. Two well-known Hall-like effects occur in ferromagnets: the anomalous Hall effect (AHE) and the planar Hall effect (PHE). AHE is analogous to the classical Hall effect and is characterized by the antireciprocal Onsager relation (antisymmetric conductivity matrix), whereas PHE is defined by the reciprocal Onsager relation (symmetric conductivity matrix). The distinction is fundamental, as it stems from time-reversal symmetry breaking at the microscopic scale. We examine theoretically the Hall current generated in both AHE and PHE, along with the electric power that can be transferred from the edges of the Hall bar into a load circuit. Using a variational method based on the second law of thermodynamics, we derive expressions for the distribution of the electric currents, the distribution of electric carriers, and the power efficiencies. Our results show that the distribution of the transverse Hall current is identical for both AHE and PHE (with all other parameters being equals) but the longitudinal current and the power dissipated differ at the second order in the Hall angle. (10.1103/PhysRevB.110.024412)
  DOI : 10.1103/PhysRevB.110.024412
• Celestial amplitudes and holography
  
  • Pano Yorgo
  , 2024. The holographic principle puts forward a duality between a theory of quantum gravity in the bulk of spacetime and a conformal field theory at its boundary. The most fruitful realization of this conjecture is the AdS/CFT correspondence where observables in the bulk of a negatively curved spacetime can be recast in a codimension-one CFT. This provides new insight into quantum gravity using the powerful tools of conformal symmetry. However we have motive to explore the possible holographic nature of asymptotically flat spacetimes since they serve as a good approximation for physical phenomena such as particle scattering.We therefore explore holographic properties of the S-matrix in asymptotically flat spacetimes in this thesis. For massless particles, performing a Mellin transform on the energies of the external particles expresses the scattering process in a basis of Lorentz eigenstates. The resulting celestial amplitude transforms as a conformal correlator in a codimension-two celestial CFT. However the scattering amplitude in momentum space is divergent and should be treated as a tempered distribution, i.e. by smearing it against rapidly decreasing test functions (wave packets). We therefore provide a well-defined setting for constructing celestial amplitudes by considering the Mellin transform of tempered distributions. We do so by characterizing the Mellin transform dollartilde{mathcal M}^+(dollar) of the Schwartz space. The smearing in momentum space can then be expressed in the new conformal space and the two brackets are shown to be completely equivalent using a Parseval-type relation.After that, we study the symmetries of the putative celestial CFT in an arbitrary number of dimensions using soft theorems. We use tools from conformal representation theory to classify the symmetries associated to conformallysoft operators in celestial CFT (CCFT) in general dimensions d. The conformal multiplets in d>2 take the form of celestial necklaces whose structure is much richer than the celestial diamonds in d=2, it depends on whether (dollar)d(dollar) is even or odd and involves mixed-symmetric tensor representations of SO(d). The existence of primary descendants in CCFT multiplets corresponds to (higher derivative) conservation equations for conformally soft operators. We lay out a unified method for constructing the conserved charges associated to operators with primary descendants. In contrast to the infinite local symmetry enhancement in CCFT2, we find the soft symmetries in d>2 to be finite-dimensional.The conserved charges that follow directly from soft theorems are trivial in d>2, while non trivial charges associated to (generalized) currents and stress tensor are obtained from the shadow transform of soft operators which we relate to (an analytic continuation of) a specific type of primary descendants. The symmetry group generated by these charges constitutes a subset of the asymptotic symmetry group. The charges in the complement are not symmetries of the celestial CFT but map one celestial CFT to another. This is analogous to having a conformal manifold.Finally we study fermionic symmetries in N=1 supersymmetric QED and supergravity in four spacetime dimensions. We construct boundary fermionic operators and build the appropriate conformal primary wavefunctions using adequate spinors/vectors. Large supersymmetry transformations are equivalent to the leading soft gravitino theorem and we cast its generator on the celestial sphere. We then provide a spacetime interpretation to the leading soft photino theorem and subleading soft gravitino theorem by building the associated soft charges using the covariant phase space formalism. We also elucidate the role played by global SUSY generators in conformal representation theory: they relate fermionic celestial diamonds to bosonic ones and the conformal multiplets stack into a celestial pyramid. (10.70675/621c4a34z6dd5z4846za6bezca716c9aee82)
  DOI : 10.70675/621c4a34z6dd5z4846za6bezca716c9aee82
• The low energy effective action in superstring theory
  
  • Bossard Guillaume
  , 2024.
• No distributed quantum advantage for approximate graph coloring
  
  • Coiteux-Roy Xavier
  • d'Amore Francesco
  • Gajjala Rishikesh
  • Kuhn Fabian
  • Le Gall François
  • Lievonen Henrik
  • Modanese Augusto
  • Renou Marc-Olivier
  • Schmid Gustav
  • Suomela Jukka
  , 2024, pp.1901-1910. We give an almost complete characterization of the hardness of $c$-coloring $\chi$-chromatic graphs with distributed algorithms, for a wide range of models of distributed computing. In particular, we show that these problems do not admit any distributed quantum advantage. To do that: 1. We give a new distributed algorithm that finds a $c$-coloring in $\chi$-chromatic graphs in $\tilde{\mathcal{O}}(n^{\frac{1}{\alpha}})$ rounds, with $\alpha = \bigl\lfloor\frac{c-1}{\chi - 1}\bigr\rfloor$. 2. We prove that any distributed algorithm for this problem requires $\Omega(n^{\frac{1}{\alpha}})$ rounds. Our upper bound holds in the classical, deterministic LOCAL model, while the near-matching lower bound holds in the non-signaling model. This model, introduced by Arfaoui and Fraigniaud in 2014, captures all models of distributed graph algorithms that obey physical causality; this includes not only classical deterministic LOCAL and randomized LOCAL but also quantum-LOCAL, even with a pre-shared quantum state. We also show that similar arguments can be used to prove that, e.g., 3-coloring 2-dimensional grids or $c$-coloring trees remain hard problems even for the non-signaling model, and in particular do not admit any quantum advantage. Our lower-bound arguments are purely graph-theoretic at heart; no background on quantum information theory is needed to establish the proofs. (10.1145/3618260.3649679)
  DOI : 10.1145/3618260.3649679
• Compact fermionic quantum state preparation with a natural-orbitalizing variational quantum eigensolving scheme
  
  • Besserve Pauline
  • Ferrero Michel
  • Ayral Thomas
  , 2024. Assemblies of strongly interacting fermions, whether in a condensed-matter or a quantum chemistry context, range amongst the most promising candidate systems for which quantum computing platforms could provide an advantage. Near-term quantum state preparation is typically realized by means of the variational quantum eigensolver (VQE) algorithm. One of the main challenges to a successful implementation of VQE lies in the sensitivity to noise exhibited by deep variational circuits. On the other hand, sufficient depth must be allowed to be able to reach a good approximation to the target state. In this work, we present a refined VQE scheme that consists in topping VQE with state-informed updates of the elementary fermionic modes (spin-orbitals). These updates consist in moving to the natural-orbital basis of the current, converged variational state, a basis we argue eases the task of state preparation. We test the method on the Hubbard model in the presence of experimentally relevant noise levels. For a fixed circuit structure, the method is shown to enhance the capabilities of the circuit to reach a state close to the target state without incurring too much overhead from shot noise. Moreover, coupled with an adaptive VQE scheme that constructs the circuit on the fly, we evidence reduced requirements on the depth of the circuit as the orbitals get updated. (10.48550/arXiv.2406.14170)
  DOI : 10.48550/arXiv.2406.14170
• Laguerre–Gaussian laser filamentation for the control of electric discharges in air
  
  • Fu Silin
  • Arantchouk Leonid
  • Lozano Magali
  • Mysyrowicz André
  • Couairon Arnaud
  • Houard Aurelien
  Optics Letters, Optical Society of America - OSA Publishing, 2024, 49 (13), pp.3540. We study the use of Laguerre–Gaussian (LG) femtosecond laser filament with multi GW peak power to guide electric sparks in the atmosphere. We demonstrate that an LG beam with a vortex phase or with 6 azimuthal phase steps generates a filamentation regime, where a longer and more uniform energy deposition is produced compared to a normal beam with a flat phase. Such filaments can guide electric discharges over much longer distances. This technique could significantly extend the guiding range of laser filaments for lightning control and other long-range atmospheric experiments involving filamentation. (10.1364/OL.522594)
  DOI : 10.1364/OL.522594
• Symmetry-broken perturbation theory to large orders in antiferromagnetic phases
  
  • Garioud Renaud
  • Šimkovic Fedor
  • Rossi Riccardo
  • Spada Gabriele
  • Schäfer Thomas
  • Werner Félix
  • Ferrero Michel
  Physical Review Letters, American Physical Society, 2024, 132 (24), pp.246505. We introduce a spin-symmetry-broken extension of the connected determinant algorithm [Phys.Rev. Lett. 119, 045701 (2017)]. The resulting systematic perturbative expansions around an antiferromagnetic state allow for numerically exact calculations directly inside a magnetically ordered phase. We show new precise results for the magnetic phase diagram and thermodynamics of the three-dimensional cubic Hubbard model at half-filling. With detailed computations of the order parameter in the low to intermediate-coupling regime, we establish the N\'eel phase boundary. The critical behavior in its vicinity is shown to be compatible with the $O(3)$ Heisenberg universality class. By determining the evolution of the entropy with decreasing temperature through the phase transition we identify the different physical regimes at $U/t\!=\!4$. We provide quantitative results for several thermodynamic quantities deep inside the antiferromagnetic dome up to large interaction strengths and investigate the crossover between the Slater and Heisenberg regimes. (10.1103/PhysRevLett.132.246505)
  DOI : 10.1103/PhysRevLett.132.246505
• Leakage detection applied to the Da Hedong Reservoir dam (China) based on the flow-field fitting method
  
  • Zhao Xiang
  • Zhang Hongbing
  • Revil André
  • Liu Yandong
  • Zeng Fanxin
  • Wang Ping
  • Ren Quan
  Geophysics, Society of Exploration Geophysicists, 2024, 89 (4), pp.KS105 - KS118. <div><p>Detecting leakage in concrete gravity dams presents a formidable challenge. The flow-field fitting (FFF) method is used to identify leaks in China's Da Hedong Reservoir dam. We develop vertical-and horizontal-gradient approaches based on the transmitted signal electrical field. A plastic frame is developed to allow the probe to measure horizontal gradients. We determine the exact location of leaks at the reservoir's bottom and upstream face, respectively, assuming that current leakages are located in hydraulic leakage zones. Numerical experiments and water pressure tests reveal that the conductive silt layer beneath the reservoir can lower the response of the potential values at the leakage inlet, and the effect of the silt layer should be considered and not ignored when interpreting measured data. In addition, with regard to the principle of superposition, the contribution associated with metal pipes in the dam body can be roughly determined by subtracting it from the original potential field data, thereby aiding in locating leaks around the metal pipes. In addition, the FFF measurements from the reservoir's bottom also confirm the position of existing faults in the substratum at the reservoir site. Last, the results of the FFF method are tested against supporting evidence, such as ground penetrating radar and water pressure tests. In conclusion, these independent data confirm the effectiveness of the FFF method for leakage localization in the concrete gravity dam.</p></div> (10.1190/geo2023-0288.1)
  DOI : 10.1190/geo2023-0288.1
• Local and Nonlocal Electronic Correlations at the Metal-Insulator Transition in the Two-Dimensional Hubbard Model
  
  • Chatzieleftheriou Maria
  • Biermann Silke
  • Stepanov Evgeny
  Physical Review Letters, American Physical Society, 2024, 132 (23), pp.236504. Elucidating the physics of the single-orbital Hubbard model in its intermediate coupling regime is a key missing ingredient to our understanding of metal-insulator transitions in real materials. Using recent non-perturbative many-body techniques that are able to interpolate between the spin-fluctuation-dominated Slater regime at weak coupling and the Mott insulator at strong-coupling, we obtain the momentum-resolved spectral function in the intermediate regime and disentangle the effects of antiferromagnetic fluctuations and local electronic correlations in the formation of an insulating state. This allows us to identify the Slater and Heisenberg regimes in the phase diagram, which are separated by a crossover region of competing spatial and local electronic correlations. We identify the crossover regime by investigating the behavior of the local magnetic moment, shedding light on the formation of the insulating state at intermediate couplings. (10.1103/PhysRevLett.132.236504)
  DOI : 10.1103/PhysRevLett.132.236504
• On energy and particle production in cosmology: the particular case of the gravitino
  
  • Casagrande Gabriele
  • Dudas Emilian
  • Peloso Marco
  Journal of High Energy Physics, Springer, 2024, 2024 (6), pp.3. It is well-known that the number of particles produced in cosmology, commonly defined in the literature from the Fock space of the instantaneous hamiltonian of the canonically normalized fields, is ambiguous. On the other hand, the energy computed from the energy-momentum tensor should be physical. We compare the corresponding Fock spaces and relate them through a Bogolyubov transformation. We find that for particles of spin 0, 1 and 3/2 the two Fock spaces are different, whereas they are the same for spin 1/2 fermions. For spin 0 and 1, for particles of high momenta the two Fock spaces align, as intuitively expected. For the spin 3/2, one finds two puzzles. The first one is that the two corresponding Fock spaces do not match even in the limit of high momenta. The second is that whereas we provide evidence for the equivalence theorem between longitudinal gravitinos and the goldstino in terms of an exact matching between the lagrangians and the instantaneous hamiltonians for the canonically normalized fields, the energy operator computed from the Rarita-Schwinger action does not seem to be captured in a simple way by the goldstino action. Our results suggest a re-analysis of non-thermal gravitino production in cosmology. (10.1007/JHEP06(2024)003)
  DOI : 10.1007/JHEP06(2024)003
• Many-body physics in the era of quantum simulation III
  
  • Sanchez-Palencia Laurent
  , 2024.
• Many-body physics in the era of quantum simulation II
  
  • Sanchez-Palencia Laurent
  , 2024.