Publications

2021

• Symmetry restoration and the gluon mass in the Landau gauge
  
  • Reinosa Urko
  • Serreau Julien
  • Terin Rodrigo Carmo
  • Tissier Matthieu
  SciPost Physics, SciPost Foundation, 2021, 10 (2), pp.035. We investigate the generation of a gluon screening mass in Yang-Mills theory in the Landau gauge. We propose a gauge-fixing procedure where the Gribov ambiguity is overcome by summing over all Gribov copies with some weight function. This can be formulated in terms of a local field theory involving constrained, nonlinear sigma model fields. We show that a phenomenon of radiative symmetry restoration occurs in this theory, similar to what happens in the standard nonlinear sigma model in two dimensions. This results in a nonzero gluon screening mass, as seen in lattice simulations. (10.21468/SciPostPhys.10.2.035)
  DOI : 10.21468/SciPostPhys.10.2.035
• One-loop masses of Neumann-Dirichlet open strings and boundary-changing vertex operators
  
  • Coudarchet Thibaut
  • Partouche Hervé
  Journal of High Energy Physics, Springer, 2021, 12, pp.022. We derive the masses acquired at one loop by massless scalars in the Neumann-Dirichlet sector of open strings, when supersymmetry is spontaneously broken. It is done by computing two-point functions of “boundary-changing vertex operators” inserted on the boundaries of the annulus and Möbius strip. This requires the evaluation of correlators of “excited boundary-changing fields,” which are analogous to excited twist fields for closed strings. We work in the type IIB orientifold theory compactified on T$^{2}$× T$^{4}$/ℤ$_{2}$, where $ \mathcal{N} $ = 2 supersymmetry is broken to $ \mathcal{N} $ = 0 by the Scherk-Schwarz mechanism implemented along T$^{2}$. Even though the full expression of the squared masses is complicated, it reduces to a very simple form when the lowest scale of the background is the supersymmetry breaking scale M$_{3/2}$. We use our results to analyze in this regime the stability at the quantum level of the moduli fields arising in the Neumann-Dirichlet sector. This completes the study of ref. [32], where the quantum masses of all other types of moduli arising in the open- or closed-string sectors are derived. Ultimately, we identify all brane configurations that produce backgrounds without tachyons at one loop and yield an effective potential exponentially suppressed, or strictly positive with runaway behavior of M$_{3/2}$. (10.1007/JHEP12(2021)022)
  DOI : 10.1007/JHEP12(2021)022
• Nuclear scattering configurations of onia in different frames
  
  • Le Anh Dung
  • Mueller Alfred H.
  • Munier Stéphane
  Physical Review D, American Physical Society, 2021, 103 (5), pp.054031. In the scattering of a small onium off a large nucleus at high center-of-mass energies, when the parameters are set in such a way that the cross section at a fixed impact parameter is small, events are triggered by rare partonic fluctuations of the onium, which are very deformed with respect to typical configurations. Using the color dipole picture of high-energy interactions in quantum chromodynamics, in which the quantum states of the onium are represented by sets of dipoles generated by a branching process, we describe the typical scattering configurations as seen from different reference frames, from the rest frame of the nucleus to frames in which the rapidity is shared between the projectile onium and the nucleus. We show that taking advantage of the freedom to select a frame in the latter class makes it possible to derive complete asymptotic expressions for some boost-invariant quantities, beyond the total cross section, from a procedure which leverages the limited available knowledge on the properties of the solutions to the Balitsky-Kovchegov equation that governs the rapidity dependence of total cross sections. We obtain, in this way, an analytic expression for the rapidity distribution of the first branching of the slowest parent dipole of the set of those which scatter. This distribution provides an estimator of the correlations of the interacting dipoles and is also known to be related to the rapidity-gap distribution in diffractive dissociation, an observable measurable at a future electron-ion collider. Furthermore, our result may be formulated as a more general conjecture that we expect to hold true for any one-dimensional branching random walk model, on the branching time of the most recent common ancestor of all the particles that end up to the right of a given position. (10.1103/PhysRevD.103.054031)
  DOI : 10.1103/PhysRevD.103.054031
• Skewed non-Fermi liquids and the Seebeck effect
  
  • Georges Antoine
  • Mravlje Jernej
  Physical Review Research, American Physical Society, 2021, 3 (4), pp.043132. We consider non-Fermi liquids in which the inelastic scattering rate has an intrinsic particle-hole asymmetry and obeys <math><mrow><mi>ω</mi><mo>/</mo><mi>T</mi></mrow></math> scaling. We show that, in contrast to Fermi liquids, this asymmetry influences the low-temperature behavior of the thermopower even when the impurity scattering dominates. Implications for the unconventional sign and temperature dependence of the thermopower in cuprates in the strange metal (Planckian) regime are emphasized. (10.1103/PhysRevResearch.3.043132)
  DOI : 10.1103/PhysRevResearch.3.043132
• Phenomenological assessment of proton mechanical properties from deeply virtual Compton scattering
  
  • Dutrieux H.
  • Lorcé C.
  • Moutarde H.
  • Sznajder P.
  • Trawiński A.
  • Wagner J.
  European Physical Journal C: Particles and Fields, Springer Verlag (Germany), 2021, 81 (4), pp.300. A unique feature of generalised parton distributions is their relation to the QCD energy–momentum tensor. In particular, they provide access to the mechanical properties of the proton i.e. the distributions of pressure and shear stress induced by its quark and gluon structure. In principle the pressure distribution can be experimentally determined in a model-independent way from a dispersive analysis of deeply virtual Compton scattering data through the measurement of the subtraction constant. In practice the kinematic coverage and accuracy of existing experimental data make this endeavour a challenge. Elaborating on recent global fits of deeply virtual Compton scattering measurements using artificial neural networks, our analysis presents the current knowledge on this subtraction constant and assesses the impact of the most frequent systematic assumptions made in this field of research. This study will pave the way for future works when more precise data will become available, e.g. obtained in the foreseen electron-ion colliders EIC and EIcC. (10.1140/epjc/s10052-021-09069-w)
  DOI : 10.1140/epjc/s10052-021-09069-w
• Interacting Stochastic Topology and Mott Transition from Light Response
  
  • Klein Philipp W.
  • Grushin Adolfo G.
  • Le Hur Karyn
  Physical Review B, American Physical Society, 2021, 103 (3), pp.035114. We develop a stochastic description of the topological properties in an interacting Chern insulator. We confirm the Mott transition's first-order nature in the interacting Haldane model on the honeycomb geometry from a mean-field variational approach supported by density matrix renormalization group results and Ginzburg-Landau arguments. From the Bloch sphere, we make predictions for circular dichroism of light related to the quantum Hall conductivity on the lattice and in the presence of interactions. This analysis shows that the topological number can be measured from the light response at the Dirac points. Electron-electron interactions can also produce a substantial number of particle-hole pairs above the band gap, which leads us to propose a stochastic Chern number as an interacting measure of the topology. The stochastic Chern number can describe disordered situations with a fluctuating staggered potential, and we build an analogy between interaction-induced particle-hole pairs and temperature effects. Our stochastic approach is physically intuitive, easy to implement, and leads the way to further studies of interaction effects. (10.1103/PhysRevB.103.035114)
  DOI : 10.1103/PhysRevB.103.035114
• Instability of complex CFTs with operators in the principal series
  
  • Benedetti Dario
  Journal of High Energy Physics, Springer, 2021, 05, pp.004. We prove the instability of d-dimensional conformal field theories (CFTs) having in the operator-product expansion of two fundamental fields a primary operator of scaling dimension h = $ \frac{d}{2} $ + i r, with non-vanishing r ∈ ℝ. From an AdS/CFT point of view, this corresponds to a well-known tachyonic instability, associated to a violation of the Breitenlohner-Freedman bound in AdS$_{d+1}$; we derive it here directly for generic d-dimensional CFTs that can be obtained as limits of multiscalar quantum field theories, by applying the harmonic analysis for the Euclidean conformal group to perturbations of the conformal solution in the two-particle irreducible (2PI) effective action. Some explicit examples are discussed, such as melonic tensor models and the biscalar fishnet model. (10.1007/JHEP05(2021)004)
  DOI : 10.1007/JHEP05(2021)004
• Energy-momentum tensor in QCD: nucleon mass decomposition and mechanical equilibrium
  
  • Lorcé Cédric
  • Metz Andreas
  • Pasquini Barbara
  • Rodini Simone
  Journal of High Energy Physics, Springer, 2021, 11, pp.121. We review and examine in detail recent developments regarding the question of the nucleon mass decomposition. We discuss in particular the virial theorem in quantum field theory and its implications for the nucleon mass decomposition and mechanical equilibrium. We reconsider the renormalization of the QCD energy-momentum tensor in minimal-subtraction-type schemes and the physical interpretation of its components, as well as the role played by the trace anomaly and Poincaré symmetry. We also study the concept of “quantum anomalous energy” proposed in some works as a new contribution to the nucleon mass. Examining the various arguments, we conclude that the quantum anomalous energy is not a genuine contribution to the mass sum rule, as a consequence of translation symmetry. (10.1007/JHEP11(2021)121)
  DOI : 10.1007/JHEP11(2021)121
• Line and surface defects for the free scalar field
  
  • Lauria Edoardo
  • Liendo Pedro
  • van Rees Balt C.
  • Zhao Xiang
  Journal of High Energy Physics, Springer, 2021, 01, pp.060. For a single free scalar field in d ≥ 2 dimensions, almost all the unitary conformal defects must be ‘trivial’ in the sense that they cannot hold interesting dynamics. The only possible exceptions are monodromy defects in d ≥ 4 and co-dimension three defects in d ≥ 5. As an intermediate result we show that the n-point correlation functions of a conformal theory with a generalized free spectrum must be those of the generalized free theory. (10.1007/JHEP01(2021)060)
  DOI : 10.1007/JHEP01(2021)060
• Shifting spin on the celestial sphere
  
  • Pasterski Sabrina
  • Puhm Andrea
  Physical Review D, American Physical Society, 2021, 104 (8), pp.086020. We explore conformal primary wave functions for all half integer spins up to the graviton. Half steps are related by supersymmetry, integer steps by the classical double copy. The main results are as follows: we 1) introduce a convenient spin frame and null tetrad to organize all radiative modes of varying spin; 2) identify the massless spin-<math display="inline"><mfrac><mn>3</mn><mn>2</mn></mfrac></math> conformal primary wave function as well as the conformally soft Goldstone mode corresponding to large supersymmetry transformations; 3) indicate how to express a conformal primary of arbitrary spin in terms of differential operators acting on a scalar primary; 4) demonstrate that conformal primary metrics satisfy the double copy in a variety of forms—operator, Weyl, and Kerr-Schild—and are exact, albeit complex, solutions to the fully nonlinear Einstein equations of Petrov type <math display="inline"><mrow><mi mathvariant="bold">N</mi></mrow></math>; 5) propose a novel generalization of conformal primary wave functions; and 6) show that this generalization includes a large class of physically interesting metrics corresponding to ultra-boosted black holes, shockwaves and more. (10.1103/PhysRevD.104.086020)
  DOI : 10.1103/PhysRevD.104.086020
• Analytical approach for the Mott transition in the Kane-Mele-Hubbard model
  
  • Hutchinson Joel
  • Klein Philipp W.
  • Le Hur Karyn
  Physical Review B, American Physical Society, 2021, 104 (7), pp.075120. The description of interactions in strongly correlated topological phases of matter remains a challenge. Here, we develop a stochastic functional approach for interacting topological insulators including both charge and spin channels. We find that the Mott transition of the Kane-Mele-Hubbard model may be described by the variational principle with one equation. We present different views of this equation from the electron Green's function, the free-energy, and the Hellmann-Feynman theorem. In particular, we show the stability of the transition line towards fluctuations, in good agreement with numerical results. The band gap remains finite at the transition and the Mott phase is characterized by antiferromagnetism in the <math><mrow><mi>x</mi><mtext>-</mtext><mi>y</mi></mrow></math> plane. The interacting topological phase is described through a <math><msub><mi mathvariant="double-struck">Z</mi><mn>2</mn></msub></math> number related to helical edge modes. Our results then show that improving stochastic approaches can give further insight on the understanding of interacting phases of matter. (10.1103/PhysRevB.104.075120)
  DOI : 10.1103/PhysRevB.104.075120
• Light-control of materials via nonlinear phononics
  
  • Subedi Alaska
  Comptes Rendus. Physique, Académie des sciences (Paris), 2021, 22 (S2), pp.1-24. (10.5802/crphys.44)
  DOI : 10.5802/crphys.44
• Tracing Evolution of Angle-Wavelength Spectrum along the 40-m Postfilament in Corridor Air
  
  • Mokrouso Daria V
  • Pushkarev Dmitrii V
  • Panov Nikolay A
  • Nikolaeva Irina A
  • Shipilo Daniil E
  • Zhidovtsev Nikita A
  • Rizaev Georgy E
  • Uryupina Daria S
  • Couairon Arnaud
  • Houard Aurélien
  • Skryabin Dmitry V
  • Savel'Ev Andrey B
  • Kosareva Olga G
  • Seleznev Leonid V
  • Ionin Andrey A
  Photonics, MDPI, 2021, 8 (10), pp.446. Postfilamentation channel resulting from filamentation of freely propagating 744-nm, 5-mJ, 110-fs pulse in the corridor air is examined experimentally and in simulations. The longitudinal extension of postfilament was determined to be 55–95 m from the compressor output. Using single-shot angle-wavelength spectra measurements, we observed a series of red-shifted maxima in the spectrum, localized on the beam axis with the divergence below 0.5 mrad. In the range 55–70 m, the number of maxima and their red-shift increase with the distance reaching 1 μm, while the pulse duration measured by the autocorrelation technique is approximately constant. Further on, for distances larger than 70 m and up to 95 m, the propagation is characterized by the suppressed beam divergence and unchanged pulse spectrum. The pulse duration increases due to the normal air dispersion. (10.3390/photonics8100446)
  DOI : 10.3390/photonics8100446
• Schrodinger's original quantum-mechanical solution for hydrogen
  
  • Galler Anna
  • Canfield Jeremy
  • Freericks James K.
  Eur.J.Phys., 2021, 42 (3), pp.035405. In 1926, Erwin Schrodinger wrote a series of papers that invented wave mechanics and set the foundation for much of the single-particle quantum mechanics that we teach today. In his first paper, he solved the Schrodinger equation using the Laplace method, which is a technique that is quite powerful, but rarely taught. This is unfortunate, because it opens the door to examining quantum mechanics from a complex-analysis perspective. Gaining this experience with complex analysis is a useful notion to consider when teaching quantum mechanics, as these techniques can be widely used outside of quantum mechanics, unlike the standard Frobenius summation method, which is normally taught, but rarely used elsewhere. The Laplace method strategy is subtle and no one has carefully gone through the arguments that Schrodinger did in this first paper, instead it is often just stated that the solution was adopted from Schlesinger's famous differential equation textbook. In this work, we show how the Laplace method can be used to solve for the quantum-mechanical energy eigenfunctions of the hydrogen atom, following Schrodinger's original solution, with all the necessary details, and illustrate how it can be taught in advanced instruction; it does require familiarity with intermediate-level complex analysis, which we also briefly review. (10.1088/1361-6404/abb9ff)
  DOI : 10.1088/1361-6404/abb9ff
• Coulomb gluons will generally destroy coherence
  
  • Forshaw Jeffrey R.
  • Holguin Jack
  Journal of High Energy Physics, Springer, 2021, 12, pp.084. Coherence violation is an interesting and counter-intuitive phenomenon in QCD. We discuss the circumstances under which violation occurs in observables sensitive to soft radiation and arrive at the conclusion that almost all such observables at hadron colliders will violate coherence to some degree. We illustrate our discussion by considering the gaps-between-jets observable, where coherence violation is super-leading, then we generalise to other observables, including precise statements on the logarithmic order of coherence violation. (10.1007/JHEP12(2021)084)
  DOI : 10.1007/JHEP12(2021)084
• Topological Bifurcations and Reconstruction of Travelling Waves
  
  • Oblak Blagoje
  Phys.Fluids, 2021, 33, pp.027107. This paper is devoted to periodic travelling waves solving Lie-Poisson equations based on the Virasoro group. We show that the reconstruction of any such solution can be carried out exactly, regardless of the underlying Hamiltonian (which need not be quadratic), provided the wave belongs to the coadjoint orbit of a uniform profile. Equivalently, the corresponding "fluid particle motion" is integrable. Applying this result to the Camassa-Holm equation, we express the drift of particles in terms of parameters labelling periodic peakons and exhibit orbital bifurcations: points in parameter space where the drift velocity varies discontinuously, reflecting a sudden change in the topology of Virasoro orbits. (10.1063/5.0041269)
  DOI : 10.1063/5.0041269
• Plasmas créés par laser: Généralités et applications choisies
  
  • Mora Patrick
  , 2021.
• Comparing light-front quantization with instant-time quantization
  
  • Mannheim Philip D.
  • Lowdon Peter
  • Brodsky Stanley J.
  Physics Reports, Elsevier, 2021, 891, pp.1-65. In this paper we compare light-front quantization and instant-time quantization both at the level of operators and at the level of their Feynman diagram matrix elements. At the level of operators light-front quantization and instant-time quantization lead to equal light-front time commutation (or anticommutation) relations that appear to be quite different from equal instant-time commutation (or anticommutation) relations. Despite this we show that at unequal times instant-time and light-front commutation (or anticommutation) relations actually can be transformed into each other, with it only being the restriction to equal times that makes the commutation (or anticommutation) relations appear to be so different. While our results are valid for both bosons and fermions, for fermions there are subtleties associated with tip of the light cone contributions that need to be taken care of. At the level of Feynman diagrams we show for non-vacuum Feynman diagrams that the pole terms in four-dimensional light-front Feynman diagrams reproduce the widely used three-dimensional light-front on-shell Hamiltonian Fock space formulation in which the light-front energy and light-front momentum are on shell. Moreover, we show that the contributions of pole terms in non-vacuum instant-time and non-vacuum light-front Feynman diagrams are equal. However, because of circle at infinity contributions we show that this equivalence of pole terms fails for four-dimensional light-front vacuum tadpole diagrams. Then, and precisely because of these circle at infinity contributions, we show that light-front vacuum tadpole diagrams are not only nonzero, they quite remarkably are actually equal to the pure pole term instant-time vacuum tadpole diagrams. Light-front vacuum diagrams are not correctly describable by the on-shell Hamiltonian formalism, and thus not by the closely related infinite momentum frame prescription either. Thus for the light-front vacuum sector we must use the off-shell Feynman formalism as it contains information that is not accessible in the on-shell Hamiltonian Fock space approach. We show that light-front quantization is intrinsically nonlocal, and that for fermions this nonlocality is present in Ward identities. One can project fermion spinors into so-called good and bad components, and both of these components contribute in Ward identities. Central to our analysis is that the transformation from instant-time coordinates and fields to light-front coordinates and fields is a unitary, spacetime-dependent translation. Consequently, not only are instant-time quantization and light-front quantization equivalent, because of general coordinate invariance they are unitarily equivalent. (10.1016/j.physrep.2020.09.001)
  DOI : 10.1016/j.physrep.2020.09.001
• Extracting color octet NRQCD matrix elements from $J/\psi$ production at the EIC
  
  • Boer Daniël
  • Pisano Cristian
  • Taels Pieter
  Physical Review D, American Physical Society, 2021, 103 (7), pp.074012. Recently unpolarized and polarized J/ψ(ϒ) production at the Electron-Ion Collider (EIC) has been proposed as a new way to extract two poorly known color-octet NRQCD long-distance matrix elements: ⟨0|O8J/ψ(S01)|0⟩ and ⟨0|O8J/ψ(P03)|0⟩. The proposed method is based on a comparison to open heavy-quark pair production ideally performed at the same kinematics. In this paper we analyze this proposal in more detail and provide predictions for the EIC based on the available determinations of the color-octet matrix elements. We also propose two additional methods that do not require comparison to open heavy-quark pair production. (10.1103/PhysRevD.103.074012)
  DOI : 10.1103/PhysRevD.103.074012
• Double Copy for Celestial Amplitudes
  
  • Casali Eduardo
  • Puhm Andrea
  Physical Review Letters, American Physical Society, 2021, 126 (10), pp.101602. Celestial amplitudes which use conformal primary wave functions rather than plane waves as external states offer a novel opportunity to study properties of amplitudes with manifest conformal covariance and give insight into a potential holographic celestial conformal field theory at the null boundary of asymptotically flat space. Since translation invariance is obscured in the conformal basis, features of amplitudes that heavily rely on it appear to be lost. Among these are the remarkable relations between gauge theory and gravity amplitudes known as the double copy. Nevertheless, properties of amplitudes reflecting fundamental aspects of the perturbative regime of quantum field theory are expected to survive a change of basis. Here we show that there exists a well-defined procedure for a celestial double copy. This requires a generalization of the usual squaring of numerators which entails first promoting them to generalized differential operators acting on external wave functions and then squaring them. We demonstrate this procedure for three- and four-point celestial amplitudes and give an argument for its validity to all multiplicities. (10.1103/PhysRevLett.126.101602)
  DOI : 10.1103/PhysRevLett.126.101602
• Celestial diamonds: conformal multiplets in celestial CFT
  
  • Pasterski Sabrina
  • Puhm Andrea
  • Trevisani Emilio
  Journal of High Energy Physics, Springer, 2021, 11, pp.072. We examine the structure of global conformal multiplets in 2D celestial CFT. For a 4D bulk theory containing massless particles of spin s = $ \left\{0,\frac{1}{2},1,\frac{3}{2},2\right\} $ we classify and construct all SL(2,ℂ) primary descendants which are organized into ‘celestial diamonds’. This explicit construction is achieved using a wavefunction-based approach that allows us to map 4D scattering amplitudes to celestial CFT correlators of operators with SL(2,ℂ) conformal dimension ∆ and spin J. Radiative conformal primary wavefunctions have J = ±s and give rise to conformally soft theorems for special values of ∆ ∈ $ \frac{1}{2}\mathbb{Z} $. They are located either at the top of celestial diamonds, where they descend to trivial null primaries, or at the left and right corners, where they descend both to and from generalized conformal primary wavefunctions which have |J| ≤ s. Celestial diamonds naturally incorporate degeneracies of opposite helicity particles via the 2D shadow transform relating radiative primaries and account for the global and asymptotic symmetries in gauge theory and gravity. (10.1007/JHEP11(2021)072)
  DOI : 10.1007/JHEP11(2021)072
• Revisiting the conformally soft sector with celestial diamonds
  
  • Pasterski Sabrina
  • Puhm Andrea
  • Trevisani Emilio
  Journal of High Energy Physics, Springer, 2021, 11, pp.143. Celestial diamonds encode the structure of global conformal multiplets in 2D celestial CFT and offer a natural language for describing the conformally soft sector. The operators appearing at their left and right corners give rise to conformally soft factorization theorems, the bottom corners correspond to conserved charges, and the top corners to conformal dressings. We show that conformally soft charges can be expressed in terms of light ray integrals that select modes of the appropriate conformal weights. They reside at the bottom corners of memory diamonds, and ascend to generalized currents. We then identify the top corners of the associated Goldstone diamonds with conformal Faddeev-Kulish dressings and compute the sub-leading conformally soft dressings in gauge theory and gravity which are important for finding nontrivial central extensions. Finally, we combine these ingredients to speculate on 2D effective descriptions for the conformally soft sector of celestial CFT. (10.1007/JHEP11(2021)143)
  DOI : 10.1007/JHEP11(2021)143
• Functional renormalization group and 2PI effective action formalism
  
  • Blaizot Jean-Paul
  • Pawlowski Jan M.
  • Reinosa Urko
  Annals of Physics, Elsevier Masson, 2021, 431, pp.168549. We combine two non-perturbative approaches, one based on the two-particle-irreducible (2PI) action, the other on the functional renormalization group (fRG), in an effort to develop new non-perturbative approximations for the field theoretical description of strongly coupled systems. In particular, we exploit the exact 2PI relations between the two-point and four-point functions in order to truncate the infinite hierarchy of equations of the functional renormalization group. The truncation is ”exact” in two ways. First, the solution of the resulting flow equation is independent of the choice of the regulator. Second, this solution coincides with that of the 2PI equations for the two-point and the four-point functions, for any selection of two-skeleton diagrams characterizing a so-called <math display="inline" id="d1e1205" altimg="si322.svg"><mi>Φ</mi></math>-derivable approximation. The transformation of the equations of the 2PI formalism into flow equations offers new ways to solve these equations in practice, and provides new insight on certain aspects of their renormalization. It also opens the possibility to develop approximation schemes going beyond the strict <math display="inline" id="d1e1210" altimg="si322.svg"><mi>Φ</mi></math>-derivable ones, as well as new truncation schemes for the fRG hierarchy. (10.1016/j.aop.2021.168549)
  DOI : 10.1016/j.aop.2021.168549
• Quantum Entangled Fractional Topology and Curvatures
  
  • Hutchinson Joel
  • Hur Karyn Le
  Commun.Phys., 2021, 4 (1), pp.144. We propose a two-spin quantum-mechanical model with applied magnetic fields acting on the Poincaré-Bloch sphere, to reveal a new class of topological energy bands with Chern number one half for each spin-1/2. The mechanism behind this fractional topology is a two-spin product state at the north pole and a maximally entangled state close to the south pole. The fractional Chern number of each spin can be measured through the magnetizations at the poles. We study a precise protocol where the spin dynamics in time reflects the Landau-Zener physics associated with energy band crossing effects. We show a correspondence between the two-spin system and topological bilayer models on a honeycomb lattice. These models describe semimetals with a nodal ring surrounding the region of entanglement. (10.1038/s42005-021-00641-0)
  DOI : 10.1038/s42005-021-00641-0
• Incoherent hydrodynamics of density waves in magnetic fields
  
  • Donos Aristomenis
  • Pantelidou Christiana
  • Ziogas Vaios
  Journal of High Energy Physics, Springer, 2021, 05, pp.270. We use holography to derive effective theories of fluctuations in spontaneously broken phases of systems with finite temperature, chemical potential, magnetic field and momentum relaxation in which the order parameters break translations. We analytically construct the hydrodynamic modes corresponding to the coupled thermoelectric and density wave fluctuations and all of them turn out to be purely diffusive for our system. Upon introducing pinning for the density waves, some of these modes acquire not only a gap, but also a finite resonance due to the magnetic field. Finally, we study the optical properties and perform numerical checks of our analytical results. A crucial byproduct of our analysis is the identification of the correct current which describes the transport of heat in our system. (10.1007/JHEP05(2021)270)
  DOI : 10.1007/JHEP05(2021)270