Publications

2023

• Celestial open strings at one-loop
  
  • Donnay Laura
  • Giribet Gaston
  • González Hernán
  • Puhm Andrea
  • Rojas Francisco
  Journal of High Energy Physics, Springer, 2023, 10, pp.047. We study celestial amplitudes in string theory at one-loop. Celestial amplitudes describe scattering processes of boost eigenstates and relate to amplitudes in the more standard basis of momentum eigenstates through a Mellin transform. They are thus sensitive to both the ultraviolet and the infrared, which raises the question of how to appropriately take the field theory limit of string amplitudes in the celestial basis. We address this problem in the context of four-dimensional genus-one scattering processes of gluons in open string theory which reach the two-dimensional celestial sphere at null infinity. We show that the Mellin transform commutes with the adequate limit in the worldsheet moduli space and reproduces the celestial one-loop field theory amplitude expressed in the worldline formalism. The dependence on $\alpha'$ continues to be a simple overall factor in one-loop celestial amplitudes albeit with a power that is shifted by three units with respect to tree-level, thus making manifest that the dimensionless parameter $g_{10}^2/\alpha'^3$ organizes the loop expansion in the celestial basis. (10.1007/JHEP10(2023)047)
  DOI : 10.1007/JHEP10(2023)047
• Spectrum continuity and level repulsion: the Ising CFT from infinitesimal to finite $\boldsymbol\varepsilon$
  
  • Henriksson Johan
  • Kousvos Stefanos R.
  • Reehorst Marten
  Journal of High Energy Physics, Springer, 2023, 02, pp.218. Using numerical conformal bootstrap technology we perform a non-perturbative study of the Ising CFT and its spectrum from infinitesimal to finite values of $\varepsilon=4-d$. Exploiting the recent navigator bootstrap method in conjunction with the extremal functional method, we test various qualitative and quantitative features of the $\varepsilon$-expansion. We follow the scaling dimensions of numerous operators from the perturbatively controlled regime to finite coupling. We do this for $\mathbb Z_2$-even operators up to spin 12 and for $\mathbb Z_2$-odd operators up to spin 6 and find a good matching with perturbation theory. In the finite coupling regime we observe two operators whose dimensions approach each other and then repel, a phenomenon known as level repulsion and which can be analyzed via operator mixing. Our work improves on previous studies in both increased precision and the number of operators studied, and is the first to observe level repulsion in the conformal bootstrap. (10.1007/JHEP02(2023)218)
  DOI : 10.1007/JHEP02(2023)218
• Order-by-disorder charge density wave condensation at $\mathbf{\textit{q} =(\frac{1}{3},\frac{1}{3},\frac{1}{3})}$ in kagome metal ScV$_6$Sn$_6$
  
  • Subedi Alaska
  Physical Review Materials, American Physical Society, 2023, 8 (1), pp.014006. The recent discovery of a charge density wave order at the wave vector $P$ $(\frac{1}{3},\frac{1}{3},\frac{1}{3})$ in the kagome metal ScV$_6$Sn$_6$ has created a mystery because subsequent theoretical and experimental studies show a dominant phonon instability instead at another wave vector $H$ $(\frac{1}{3},\frac{1}{3},\frac{1}{2})$. In this paper, I use first principles total energy calculations to map out the landscape of the structural distortions due to the unstable phonon modes at $H$, $L$ $(\frac{1}{2},0,\frac{1}{2})$, and $P$ present in this material. In agreement with previous results, I find that the distortions due to the $H$ instability cause the largest gain in energy relative to the parent structure, followed in order by the $L$ and $P$ instabilities. However, only two distinct structure occur due to this instability, which are separated by 6 meV/f.u. The instability at $L$ results in three distinct structures separated in energy by 5 meV/f.u. In contrast, six different distorted structures are stabilized due to the instability at $P$, and they all lie within 2 meV/f.u.\ of each other. Hence, despite a lower energy gain, the condensation at $P$ could be favorable due to a larger entropy gain associated with the fluctuations within a manifold with larger multiplicity via the order-by-disorder mechanism. (10.1103/PhysRevMaterials.8.014006)
  DOI : 10.1103/PhysRevMaterials.8.014006
• Prospects for GPDs Extraction with Double DVCS
  
  • Deja K.
  • Martínez-Fernández V.
  • Sznajder P.
  • Pire B.
  • Wagner Jakub
  Acta Physica Polonica B Proceedings Supplement, Jagiellonian University, 2023, 16 (7), pp.1. Double deeply virtual Compton scattering (DDVCS) is the process where an electron scatters off a nucleon and produces a lepton pair. The main advantage of this process in contrast with deeply virtual and timelike Compton scatterings (DVCS and TCS) is the possibility of directly measuring GPDs for $x\neq\xi$ at leading order in $\alpha_s$ (LO). We present a new calculation of the DDVCS amplitude based on the methods developed by R. Kleiss and W. J. Stirling in the 1980s. These techniques produce expressions for amplitudes that are perfectly suited for implementation in numerical simulations. Via the PARTONS software, the correctness of this new formulation has been tested by comparing the DVCS and TCS limits of DDVCS with independent calculations of DVCS and TCS. (10.5506/APhysPolBSupp.16.7-A24)
  DOI : 10.5506/APhysPolBSupp.16.7-A24
• Vacuum stability, fixed points, and phases of QED$_3$ at large $N_f$
  
  • Di Pietro Lorenzo
  • Lauria Edoardo
  • Niro Pierluigi
  Physical Review D, American Physical Society, 2023, 108 (6), pp.L061902. We consider three-dimensional Quantum Electrodynamics in the presence of a Chern-Simons term at level $k$ and $N_f$ flavors, in the limit of large $N_f$ and $k$ with $k/N_f$ fixed. We consider either bosonic or fermionic matter fields, with and without quartic terms at criticality: the resulting theories are critical and tricritical bosonic QED$_3$, Gross-Neveu and fermionic QED$_3$. For all such theories we compute the effective potentials and the $\beta$ functions of classically marginal couplings, at the leading order in the large $N_f$ limit and to all orders in $k/N_f$ and in the couplings. We determine the RG fixed points and discuss the quantum stability of the corresponding vacua. While critical bosonic and fermionic QED$_3$ are always stable CFTs, we find that tricritical bosonic and Gross-Neveu QED$_3$ exist as stable CFTs only for specific values of $k/N_f$. Finally, we discuss the phase diagrams of these theories as a function of their relevant deformations. (10.1103/PhysRevD.108.L061902)
  DOI : 10.1103/PhysRevD.108.L061902
• Energy-momentum tensor in the scalar diquark model
  
  • Amor-Quiroz Arturo
  • Focillon William
  • Lorcé Cédric
  • Rodini Simone
  European Physical Journal C: Particles and Fields, Springer Verlag (Germany), 2023, 83 (11), pp.1012. We compute all the gravitational form factors in the scalar diquark model at the one-loop level using two different regularization methods. We check explicitly that all the Poincaré sum rules are satisfied and we discuss in detail the results for the trace of the energy-momentum tensor. Finally we discuss the spatial distributions of energy and pressure in two and three dimensions. (10.1140/epjc/s10052-023-12190-7)
  DOI : 10.1140/epjc/s10052-023-12190-7
• Critical superflows and thermodynamic instabilities in superfluids
  
  • Goutéraux Blaise
  • Sottovia Filippo
  • Mefford Eric
  Physical Review D, American Physical Society, 2023, 108 (8), pp.L081903. In this work, we study the linear stability of superfluid phases of matter irrespective of the nature of microscopic degrees of freedom and the strength of interactions between them. Famously, assuming invariance under Galilean boosts and a phonon-roton single-particle dispersion relation, Landau predicted superfluid helium 4 would become unstable for large enough superfluid velocities. Here, we demonstrate that such instabilities generically follow from a change of sign of one of the eigenvalues of the matrix of second derivatives of the free energy. Our only assumption is the existence of static thermodynamic equilibrium, irrespective of any invariance under boosts or microscopic statistics. Turning on dissipation, 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 bosonic quasiparticles, our criterion reproduces Landau’s critical velocity for Bose-Einstein condensates. Our criterion also reduces to the well-known maximal supercurrent in weakly coupled superconductors described either by Landau-Ginzburg or Bardeen-Cooper-Schrieffer theory. Further, it correctly reproduces the onset of the instability in relativistic, strongly coupled superfluids without quasiparticles at zero as well as finite temperature, which we construct using gauge/gravity duality. As a less trivial application of our criterion, we show that in dirty superfluids the instability manifests itself first in the thermal diffusion mode instead of the superfluid sound mode. Our work provides a simple, comprehensive, and unified description of the large superflow instability of superfluids and superconductors at any temperature independent of the microscopic details of the system and the strength of interactions. (10.1103/PhysRevD.108.L081903)
  DOI : 10.1103/PhysRevD.108.L081903
• Factorization for quasi-TMD distributions of sub-leading power
  
  • Rodini Simone
  • Vladimirov Alexey
  Journal of High Energy Physics, Springer, 2023, 09, pp.117. The quasi-transverse-momentum dependent (qTMD) distributions are equal-time correlators that can be computed within the lattice QCD approach. In the regime of large hadron's momentum, qTMD distributions are expressed in terms of standard TMD distributions via the factorization theorem. We derive the corresponding factorization theorem at the next-leading power (NLP), and, for the first time, we present the factorized expressions for a large class of qTMD distributions of sub-leading power. The NLP expression contains TMD distributions of twist-two, twist-three, and a new lattice-specific nonperturbative function. We point out that some of the qTMD distributions considered in this work can be employed to extract the Collins-Soper kernel using the standard techniques of different-momenta-ratio. We provide NLO expressions for all the elements of the factorization theorem. Also, for the first time, we explicitly demonstrate the restoration of boost invariance in NLP TMD factorization. (10.1007/JHEP09(2023)117)
  DOI : 10.1007/JHEP09(2023)117
• BMS modular covariance and structure constants
  
  • Bagchi Arjun
  • Mondal Saikat
  • Pal Sanchari
  • Riegler Max
  Journal of High Energy Physics, Springer, 2023, 11, pp.087. Two-dimensional (2d) field theories invariant under the Bondi-Metzner-Sachs algebra, or 2d BMSFTs in short, are putative holographic duals of Einstein gravity in 3d asymptotically flat spacetimes. When defined on a torus, these field theories come equipped with a modified modular structure. We use the modular covariance of the BMS torus two-point function to develop formulae for different three-point structure constants of the field theory. These structure constants indicate that BMSFTs follow the eigenstate thermalization hypothesis, albeit with some interesting changes to usual 2d CFTs. The singularity structures of the structure constants contain information on perturbations of cosmological horizons in 3d asymptotically flat spacetimes, which we show can also be obtained as a limit of BTZ quasinormal modes. (10.1007/JHEP11(2023)087)
  DOI : 10.1007/JHEP11(2023)087
• 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
• Singular Supertranslations and Chern-Simons Theory on the Black Hole Horizon
  
  • Akhoury Ratindranath
  • Choi Sangmin
  • Perry Malcolm J.
  Physical Review D, American Physical Society, 2023, 107 (8), pp.085019. We construct the standard and dual supertranslation charges on the future horizon of the Schwarzschild black hole, using the first-order formulation of gravity with the Holst action. The Dirac bracket algebra of standard and dual supertranslation charges is shown to exhibit a central term in the presence of singularities in the two-sphere function associated with supertranslation. We show that one can cancel this anomalous term and restore the asymptotic symmetry algebra by introducing a gravitational Chern-Simons theory on the horizon. This demonstrates that consistency of the asymptotic symmetry algebra requires a new structure on the horizon. (10.1103/PhysRevD.107.085019)
  DOI : 10.1103/PhysRevD.107.085019
• Formation of CuO$_2$ sublattices by suppression of interlattice correlations in tetragonal CuO
  
  • Bramberger Max
  • Bacq-Labreuil Benjamin
  • Grundner Martin
  • Biermann Silke
  • Schollwöck Ulrich
  • Paeckel Sebastian
  • Lenz Benjamin
  SciPost Physics, SciPost Foundation, 2023, 14 (1), pp.010. We investigate the tetragonal phase of the binary transition metal oxide CuO (t-CuO) within the context of cellular dynamical mean-field theory. Due to its strong antiferromagnetic correlations and simple structure, analysing the physics of t-CuO is of high interest as it may pave the way towards a more complete understanding of high temperature superconductivity in hole-doped antiferromagnets. In this work we give a formal justification for the weak coupling assumption that has previously been made for the interconnected sublattices within a single layer of t-CuO by studying the non-local self-energies of the system. We compute momentum-resolved spectral functions using a Matrix Product State (MPS)-based impurity solver directly on the real axis, which does not require any numerically ill-conditioned analytic continuation. The agreement with photoemission spectroscopy indicates that a single band Hubbard model is sufficient to capture the material's low energy physics. We perform calculations on a range of different temperatures, finding two magnetic regimes, for which we identify the driving mechanism behind their respective insulating state. Finally, we show that in the hole-doped regime the sublattice structure of t-CuO has interesting consequences on the symmetry of the superconducting state. (10.21468/SciPostPhys.14.1.010)
  DOI : 10.21468/SciPostPhys.14.1.010
• Reconciling scaling of the optical conductivity of cuprate superconductors with Planckian resistivity and specific heat
  
  • Michon Bastien
  • Berthod Christophe
  • Rischau Carl Willem
  • Ataei Amirreza
  • Chen Lu
  • Komiya Seiki
  • Ono Shimpei
  • Taillefer Louis
  • van der Marel Dirk
  • Georges Antoine
  Nature Communications, Nature Publishing Group, 2023, 14 (1), pp.3033. Materials tuned to a quantum critical point display universal scaling properties as a function of temperature T and frequency ω. A long-standing puzzle regarding cuprate superconductors has been the observed power-law dependence of optical conductivity with an exponent smaller than one, in contrast to T-linear dependence of the resistivity and ω-linear dependence of the optical scattering rate. Here, we present and analyze resistivity and optical conductivity of La$_{2−x}$Sr$_{x}$CuO$_{4}$ with x = 0.24. We demonstrate ℏω/k$_{B}$T scaling of the optical data over a wide range of frequency and temperature, T-linear resistivity, and optical effective mass proportional to $\sim \ln T$ corroborating previous specific heat experiments. We show that a T, ω-linear scaling Ansatz for the inelastic scattering rate leads to a unified theoretical description of the experimental data, including the power-law of the optical conductivity. This theoretical framework provides new opportunities for describing the unique properties of quantum critical matter. (10.1038/s41467-023-38762-5)
  DOI : 10.1038/s41467-023-38762-5
• Quantum Field Theory in AdS Space instead of Lehmann-Symanzik-Zimmerman Axioms
  
  • van Rees Balt C
  • Zhao Xiang
  Physical Review Letters, American Physical Society, 2023, 130 (19), pp.191601. The boundary correlation functions for a quantum field theory (QFT) in a fixed anti–de Sitter (AdS) background should reduce to <math display="inline"><mrow><mi>S</mi></mrow></math>-matrix elements in the flat-space limit. We consider this procedure in detail for four-point functions. With minimal assumptions we rigorously show that the resulting <math display="inline"><mrow><mi>S</mi></mrow></math>-matrix element obeys a dispersion relation, the nonlinear unitarity conditions, and the Froissart-Martin bound. QFT in AdS thus provides an alternative route to fundamental QFT results that normally rely on the LSZ axioms. (10.1103/PhysRevLett.130.191601)
  DOI : 10.1103/PhysRevLett.130.191601
• Magic Fermions: Carroll and Flat Bands
  
  • Bagchi Arjun
  • Banerjee Aritra
  • Basu Rudranil
  • Islam Minhajul
  • Mondal Saikat
  Journal of High Energy Physics, Springer, 2023, 03, pp.227. The Carroll algebra is constructed as the $c\to0$ limit of the Poincare algebra and is associated to symmetries on generic null surfaces. In this paper, we begin investigations of Carrollian fermions or fermions defined on generic null surfaces. Due to the availability of two different (degenerate) metrics on Carroll spacetimes, there is the possibility of two different versions of Carroll Clifford algebras. We consider both possibilities and construct explicit representations of Carrollian gamma matrices and show how to build higher spacetime dimensional representations out of lower ones. Actions for Carroll fermions are constructed with these gamma matrices and the properties of these actions are investigated. We show that in condensed matter systems where the dispersion relation becomes trivial i.e. the energy is not dependent on momentum and bands flatten out, Carroll symmetry generically appears. We give explicit examples of this including that of twisted bi-layer graphene, where superconductivity appears at so called magic angles and connect this to Carroll fermions. (10.1007/JHEP03(2023)227)
  DOI : 10.1007/JHEP03(2023)227
• A New Paradigm for Precision Top Physics: Weighing the Top with Energy Correlators
  
  • Holguin Jack
  • Moult Ian
  • Pathak Aditya
  • Procura Massimiliano
  Physical Review D, American Physical Society, 2023, 107 (11), pp.114002. Final states in collider experiments are characterized by correlation functions, $\langle \mathcal{E}(\vec n_1) \cdots \mathcal{E}(\vec n_k) \rangle$, of the energy flow operator $ \mathcal{E}(\vec n_i)$. These correlation functions typically exhibit a power-law scaling characteristic of asymptotically free Quantum Chromodynamics. In this Letter, we show that the top quark imprints itself as a peak in the three-point correlation function at an angle $\zeta \sim m_t^2/p_T^2$, with $m_t$ the top quark mass and $p_T$ its transverse momentum. This provides direct access to one of the most important parameters of the Standard Model in one of the field theoretically simplest observables. We show that the three-point correlator allows us to simultaneously achieve high sensitivity to the top mass and high insensitivity to soft physics and underlying event contamination. We find it an amusing turn of fate that correlation functions which have received the most interest in the context of conformal field theories, in fact hold the key to understanding the heaviest known particle. (10.1103/PhysRevD.107.114002)
  DOI : 10.1103/PhysRevD.107.114002