Charge Momentum Research Articles

Hopfion-like solutions in de Sitter spacetime

Abstract We construct electromagnetic field with non-trivial topological properties on de Sitter background. The field is closely related with Hopf fibration. We analyze energy, angular momentum and topological charges for this solution. The paper is a generalization of Smołka and Jezierski (2018 Class. Quantum Grav. 35 245010) to de Sitter spacetime.

Vector superstrata. Part II

Microstate geometries are proposed microstates of black holes which can be described within supergravity. Even though their number may not reproduce the full entropy of black holes with finite-sized horizons, they still offer a glimpse into the microscopic structure of black holes. In this paper we construct a new set of microstate geometries of the supersymmetric D1-D5-P black hole, where the momentum charge is carried by a vector field, as seen from the perspective of six-dimensional supergravity. To aid our construction, we develop an algorithm which solves a complicated partial differential equation using the regularity of the geometries. The new solutions are asymptotically AdS3 × S3, and have a long, but finite AdS2 throat that caps off without ever developing a horizon. These microstate geometries have a holographic interpretation as coherent superpositions of heavy states in the boundary D1-D5 CFT. We identify the states which are dual to our newly constructed solutions and carry out some basic consistency checks to support our identification.

Direct determination of topological charge of structured light via phase-shift interference

We present a straightforward theoretical approach for the direct observation of the orbital angular momentum (OAM) charge inherent in structured light. Our method involves utilizing phase-shift interference of beams to discern the sign and magnitude of the topological charge associated with Laguerre–Gaussian (LG) beams. Specifically, we demonstrate that the topological charge of an LG beam can be ascertained through the interference with a corresponding helical wavefront beam possessing an opposite charge due to the reflection in Mach–Zehnder-like interferometer. The determination of the topological charge magnitude is facilitated by examining the interference pattern’s half number of petals. Additionally, our study reveals that the petal-like interference pattern undergoes azimuthal shift, with the direction of rotation being contingent upon the sign of the topological charge of the beam. Notably, for a negative phase shift, a anti-clockwise azimuthal shift corresponds to a positive topological charge, while an clockwise rotation is associated with a negative topological charge. This work contributes to the advancement of methods for characterizing structured light based on OAM charge, with potential applications in diverse fields such as optics, telecommunications and topological photonics.

Inscribing geodesic circles on the face of the superstratum

We use families of circular null geodesics as probes of a family of microstate geometries, known as (1, 0, n) superstrata. These geometries carry a left-moving momentum wave and the behavior of some of the geodesic probes is very sensitive to this background wave. The left-moving geodesics behave like BPS particles and so can be placed in circular orbits anywhere in the geometry and actually “float” at fixed radius and angle in the three-dimensional “capped BTZ” geometry. The right-moving geodesics behave like non-BPS particles. We show that they provide a simple geometric characterization of the black-hole bound: when the momentum charge of the geometry is below this bound, such geodesics can be placed anywhere, but exceeding the bound, even by a small amount, means these geodesics are restricted to the deep interior of the geometry. We also show that for left-moving string probes, the tidal forces remain comparable with those of global AdS3. Nevertheless, for some of these probes, the “bumps” in the geometry induce an oscillatory mass term and we discuss how this can lead to chaotic scrambling of the state of the string.

Coherent γ*-nucleus scattering and coherent nuclear states

In the context of a McLerran-Venugopalan (MV) model for a large nucleus, coherent scattering of a virtual photon on that nucleus is evaluated in the A− = 0 gauge, the gauge appropriate for the target nucleus. The evaluation of the scattering in A− = 0 gauge is very intricate compared to the usual A+ = 0 gauge evaluation natural for the scattering process, but has the advantage of directly giving the scattering in terms of a partonic description of the nucleus. In the limit where a tagged forward jet puts the dipole-nucleus scattering in the saturation regime the coherent reactions are equal to the inelastic reactions. In terms of the nuclear wave function the coherent reactions come from color singlet and zero total transverse momentum quark-antiquark pairs in the wave function and in the saturation regime the nuclear wave function is a coherent state for these pairs. In the saturation region half of all quarks (or antiquarks) come from zero momentum and color charge pairs.

Computational investigation of the effect of geometry and fuel composition on the performance of a solid oxide fuel cell

The need to reduce the consumption of fossil fuels due to their negative impact on the quality of the air and on the greenhouse effect is causing major changes in the energy sector, with a progressively greater contribution of renewable energy sources to satisfy the global energy demand. Fuel cell technology is emerging as a key player in the energy transition since fuel cells convert directly chemical energy to electricity and heat without pollutant emissions. Among the different types available, solid oxide fuel cells (SOFC) can operate at high temperatures (up to 1000ºC), leading to high efficiency and stability. This work is concerned with the computational investigation of a planar solid oxide fuel cell. The governing conservation equations for mass, momentum, energy, species transport and electric charge are solved for a three-dimensional planar fuel cell. Different fuel and oxidizer compositions are considered and their influence on the performance of the fuel cell is investigated. The results show that when the hydrogen molar fraction in the fuel decreases, the maximum power and temperature decrease. The power, the efficiency and the maximum temperature are greater when the oxidizer is oxygen rather than air. The influence of the geometry of the air and fuel channels is also assessed, namely the dimensions of the channels and the effect of steps and obstacles in those channels.

Three Puzzles with Covariance and Supertranslation Invariance of Angular Momentum Flux and Their Solutions.

We describe and solve three puzzles arising in covariant and supertranslation-invariant formulas for the flux of angular momentum and other Lorentz charges in asymptotically flat spacetimes: (i)Supertranslation invariance and covariance imply invariance under spacetime translations; (ii)the flux depends on redundant auxiliary degrees of freedom that cannot be set to zero in all Lorentz frames without breaking Lorentz covariance; (iii)supertranslation-invariant Lorentz charges do not generate the transformations of the Bondi mass aspect implied by the isometries of the asymptotic metric. In this Letter, we solve the first two puzzles by presenting covariant formulas that unambiguously determine the auxiliary degrees of freedom and clarify the last puzzle by explaining the different roles played by covariant and canonical charges. Our construction makes explicit the choice of reference frame underpinning seemingly unambiguous results presented in the current literature.

Relaxation terms for anomalous hydrodynamic transport in Weyl semimetals from kinetic theory

We consider as a model of Weyl semimetal thermoelectric transport a (3 + 1)-dimensional charged, relativistic and relaxed fluid with a U(1)V × U(1)A chiral anomaly. We take into account all possible mixed energy, momentum, electric and chiral charge relaxations, and discover which are compatible with electric charge conservation, Onsager reciprocity and a finite DC conductivity. We find that all relaxations respecting these constraints necessarily render the system open and violate the second law of thermodynamics. We then demonstrate how the relaxations we have found arise from kinetic theory and a modified relaxation time approximation. Our results lead to DC conductivities that differ from those found in the literature opening the path to experimental verification.

Excess heat production of the pair annihilation of ionic vacancies in a copper redox reaction using a double bipolar MHD electrode.

Through a copper double bipolar magnetohydrodynamic (MHD) electrode (MHDE) producing twice the amounts of ionic vacancies than a conventional single MHDE, the molar excess heat of the pair annihilation of ionic vacancies, 702kJmol-1 at 10T on average was obtained in a copper redox reaction. It was about twice as large as that of a single MHDE, 387kJmol-1 at the same magnetic field. This result strongly suggests that a multi-channel bipolar MHDE will produce much greater excess heat. To conserve the linear momentum and electric charge during electron transfer in an electrode reaction, ionic vacancies are created, storing the solvation energy in the polarized core of the order of 0.1nm, and the pair annihilation of the vacancies with opposite charges liberates the energy as excess heat. The promoted excess heat by the double bipolar MHDE with a diffuser at 10T was 710 ± 144kJmol-1, whereas as mentioned above, 702 ± 426kJmol-1 was obtained by the same electrode without such a diffuser. From the theoretical excess heat of 1140kJmol-1, the collision efficiencies in pair annihilation were 0.623 ± 0.126 and 0.616 ± 0.374, respectively. From these results, the reproducibility of the thermal measurement was experimentally validated. At the same time, it was concluded that at magnetic fields beyond 10T, the concentration of ionic vacancy and the collision efficiency take constant uppermost values.

Classical and Quantum Descriptions of the Geometrodynamics of Black Holes

Analytical aspects of the classical and quantum geometrodynamics of charged black hole are considered. We start with a reduced action for a spherically symmetric of Maxwell-Einstein system written in characteristic variables. The feature of these configurations is that they admit two motion integrals, the total mass and charge. Momenta and constraint are introduced. Using the conservation laws and the Hamiltonian constraint, the momenta as functions of configuration variables are found. It turns out that the system of equations relating momenta and functional derivatives of an action on a configuration space (CS) is integrable. This allows us to obtain the action functional, as a solution of the Einstein-Hamilton-Jacobi equation in functional derivatives. Variations of the action functional with respect to mass and charge of the configuration lead to the motion trajectories in the CS. Further, the space-temporal action is transformed into an action in the configuration space similar to the Jacobi action of classical mechanics. This induces a metric in the CS. Thus, the metric on the CS is introduced and its geometry is studied. The field variables transformation is obtained which brings the CS metric to the "quasi-Lorentzian" form. On this basis, quantization is considered. Taking into account the structure of the CS, the momentum operators, DeWitt equations, mass and charge operators are constructed. Further, for comparison, consider the reduced CBH model defined in the T-region. In this simplified formulation, the T-model equations are integrated and lead to CBH with a continuous spectrum of mass and charge.

Analytic study of the Maxwell electromagnetic invariant in spinning and charged Kerr-Newman black-hole spacetimes

The Maxwell invariant plays a fundamental role in the mathematical description of electromagnetic fields in charged spacetimes. In particular, it has recently been proved that spatially regular scalar fields which are non-minimally coupled to the Maxwell electromagnetic invariant can be supported by spinning and charged Kerr-Newman black holes. Motivated by this physically intriguing property of asymptotically flat black holes in composed Einstein-Maxwell-scalar field theories, we present a detailed analytical study of the physical and mathematical properties of the Maxwell electromagnetic invariant FKNrθMaQ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\mathcal{F}}_{\ extrm{KN}}\\left(r,\ heta; M,a,Q\\right) $$\\end{document} which characterizes the Kerr-Newman black-hole spacetime [here {r, θ} are respectively the radial and polar coordinates of the curved spacetime and {M, J = M a, Q} are respectively the mass, angular momentum, and electric charge parameters of the black hole]. It is proved that, for all Kerr-Newman black-hole spacetimes, the spin and charge dependent minimum value of the Maxwell electromagnetic invariant is attained on the equator of the black-hole surface. Interestingly, we reveal the physically important fact that Kerr-Newman spacetimes are characterized by two critical values of the dimensionless rotation parameter â≡a/r+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\hat{a}\\equiv a/{r}_{+} $$\\end{document} [here r+ (M, a, Q) is the black-hole horizon radius], âcrit−=3−22\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\hat{a}}_{\ extrm{crit}}^{-}=\\sqrt{3-2\\sqrt{2}} $$\\end{document} and âcrit+=5−25\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\hat{a}}_{\ extrm{crit}}^{+}=\\sqrt{5-2\\sqrt{5}} $$\\end{document}, which mark the boundaries between three qualitatively different spatial functional behaviors of the Maxwell electromagnetic invariant: (i) Kerr-Newman black holes in the slow-rotation â<âcrit−\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\hat{a}<{\\hat{a}}_{\ extrm{crit}}^{-} $$\\end{document} regime are characterized by negative definite Maxwell electromagnetic invariants that increase monotonically towards spatial infinity, (ii) for black holes in the intermediate spin regime âcrit−≤â≤âcrit+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\hat{a}}_{\ extrm{crit}}^{-}\\le \\hat{a}\\le {\\hat{a}}_{\ extrm{crit}}^{+} $$\\end{document}, the positive global maximum of the Kerr-Newman Maxwell electromagnetic invariant is located at the black-hole poles, and (iii) Kerr-Newman black holes in the super-critical regime â<âcrit+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\hat{a}<{\\hat{a}}_{\ extrm{crit}}^{+} $$\\end{document} are characterized by a non-monotonic spatial behavior of the Maxwell electromagnetic invariant FKNr=r+θMaQ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\mathcal{F}}_{\ extrm{KN}}\\left(r={r}_{+},\ heta; M,a,Q\\right) $$\\end{document} along the black-hole horizon with a spin and charge dependent global maximum whose polar angular location is characterized by the dimensionless functional relation â2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\hat{a}}^2 $$\\end{document} · (cos2θ)max = 5 – 25\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ 2\\sqrt{5} $$\\end{document}.

Holographic CFT phase transitions and criticality for rotating AdS black holes

Employing the novel exact dictionary between the laws of extended black hole thermodynamics and the laws of the dual CFT, we study the extended thermodynamics for CFT states that are dual to neutral singly-spinning asymptotically AdS black holes in d bulk spacetime dimensions. On the field theory side we include two independent pairs of thermodynamic conjugate variables: the central charge-chemical potential term and the pressure-volume term. In this setting we uncover various phase transitions and critical behaviour in the CFT, focusing on three different thermodynamic ensembles. Namely, for fixed angular momentum and central charge, we show there is a Van der Waals-like criticality for d = 4, 5 and reentrant phase transitions for d ≥ 6. At fixed angular velocity and central charge, there is a first-order (de)confinement phase transition in all dimensions d ≥ 3. Finally, at fixed angular momentum and chemical potential we find a plethora of zero-order phase transitions and unstable phases in both d = 4 and d = 6.

Vector Superstrata

We present the construction of several microstate geometries of the supersymmetric D1-D5-P black hole in which, within six-dimensional supergravity, the momentum charge is carried by a vector field. The fully backreacted geometries are smooth and horizonless: they are asymptotically AdS3 × S3 with an AdS2 throat that smoothly caps off. We propose a holographic dual for these bulk solutions and discuss their extension to asymptotically flat space. In addition, we present several uplifts of the full six-dimensional supersymmetric ansatz to ten-dimensions. In particular, we show that there exists a frame in which geometries based on vector field momentum carriers are entirely in the NS-NS sector, making them possible starting points for the exploration of stringy black-hole microstates.

Boundary terms and conserved charges in higher-derivative gauged supergravity

We address some issues in higher-derivative gauged supergravity with Chern-Simons terms, focusing on the five-dimensional case. We discuss the variational problem with Dirichlet boundary conditions as well as holographic renormalization in asymptotically locally AdS spacetimes, and derive the corresponding boundary terms. We then employ Wald’s formalism in order to define conserved charges associated to local symmetries (diffeomorphisms and U(1) gauge transformations), taking into account the effect of generic gauge Chern-Simons terms. We prove that the first law of black hole mechanics and the quantum statistical relation hold in this setup. Chern-Simons terms also lead us to distinguish between Noether charges and Page (or Komar) charges which satisfy the Gauss law. We make use of the latter to compute corrections to the angular momentum and electric charge of the supersymmetric black hole in AdS5 from its corrected near-horizon geometry. This also allows us to derive the microcanonical form of the entropy as a function of the conserved charges relying entirely on the near-horizon geometry. Finally, we comment on four-derivative gauged supergravity in four dimensions, showing that field redefinitions permit to simplify the action at linear order in the corrections, so that the equations of motion are those of the two-derivative theory.

Holographic thermodynamics of rotating black holes

We provide mass/energy formulas for the extended thermodynamics, mixed thermodynamics, and holographic conformal field theory (CFT) thermodynamics for the charged and rotating Kerr-Newman Anti-de Sitter black holes. Then for the CFT thermal states dual to the black hole, we find the first-order phase transitions and criticality phenomena in the canonical ensemble with fixed angular momentum, volume, and central charge. We observe that the CFT states cannot be analogous to the Van der Waals fluids, despite the critical exponents falling into the universality class predicted by the mean field theory. Additionally, we examine the (de)confinement phase transitions within the grand canonical ensemble with fixed angular velocity, volume, and central charge of the CFT. Our findings suggest that the near zero temperature (de)confinement phase transitions can occur with the angular velocity of the CFT that solely depends on the CFT volume.

Optimization of flow field structure for proton exchange membrane fuel cell stack by multi-physics coupling simulation

In this paper, the three demission multi-physics model for the proton exchange membrane fuel cell (PEMFC), which carefully considers the mass, momentum, energy, species and electric charges conserving and liquid water managing processes, has been completed. The grid independence verification and good agreements between the calculated results and the reported experimental results well illustrate the validation of the developed model. Then, it is further used to investigate the potential application of the novel compensation flow field by comparing the PEMFCs with the parallel flow channel and the parallel-serpentine-parallel flow channel. The research result show that although there is low pressure difference throughout the PEMFC, there is a big oxygen depleting zone over the electrolyte surface, while the parallel flow channel is adopted. Choosing the parallel-serpentine-parallel flow channel will have more uniform oxygen and electrochemical reacting distributions over the electrolyte surface and higher water management ability than that of the PEMFC with parallel flow channel.

Local continuity of angular momentum and noether charge for matter in general relativity

Conservation laws have many applications in numerical relativity. However, it is not straightforward to define local conservation laws for general dynamic spacetimes due the lack of coordinate translation symmetries. In flat space, the rate of change of energy-momentum within a finite spacelike volume is equivalent to the flux integrated over the surface of this volume; for general spacetimes it is necessary to include a volume integral of a source term arising from spacetime curvature. In this work a study of continuity of matter in general relativity is extended to include angular momentum of matter and Noether currents associated with gauge symmetries. Expressions for the Noether charge and flux of complex scalar fields and complex Proca fields are found using this formalism. Expressions for the angular momentum density, flux and source are also derived which are then applied to a numerical relativity collision of boson stars in 3D with non-zero impact parameter as an illustration of the methods.

Worldsheet computation of heavy-light correlators

We compute a large collection of string worldsheet correlators describing light probes interacting with heavy black hole microstates. The heavy states consist of NS5 branes carrying momentum and/or fundamental string charge. In the fivebrane decoupling limit, worldsheet string theory on a family of such backgrounds is given by exactly solvable null-gauged WZW models. We construct physical vertex operators in these cosets, including all massless fluctuations. We compute a large class of novel heavy-light-light-heavy correlators in the AdS3 limit, where the light operators include those dual to chiral primaries of the holographically dual CFT. We compare a subset of these correlators to the holographic CFT at the symmetric product orbifold point, and find precise agreement in all cases, including for light operators in twisted sectors of the orbifold CFT. The agreement is highly non-trivial, and includes amplitudes that describe the analogue of Hawking radiation for these microstates. We further derive a formula for worldsheet correlators consisting of n light insertions on these backgrounds, and discuss which subset of these correlators are likely to be protected. As a test, we compute a heavy-light five-point function, obtaining precisely the same result both from the worldsheet and the symmetric orbifold CFT. This paper is a companion to and extension of [1].

On the black hole/string transition

We discuss aspects of the possible transition between small black holes and highly excited fundamental strings. We focus on the connection between black holes and the self gravitating string solution of Horowitz and Polchinski. This solution is interesting because it has non-zero entropy at the classical level and it is natural to suspect that it might be continuously connected to the black hole. Surprisingly, we find a different behavior for heterotic and type II cases. For the type II case we find an obstruction to the idea that the two are connected as classical solutions of string theory, while no such obstruction exists for the heterotic case. We further provide a linear sigma model analysis that suggests a continuous connection for the heterotic case. We also describe a solution generating transformation that produces a charged version of the self gravitating string. This provides a fuzzball-like construction of near extremal configurations carrying fundamental string momentum and winding charges. We provide formulas which are exact in α′ relating the thermodynamic properties of the charged and the uncharged solutions.

Differential Frequency Exploration of Vortex Light in Lithium Niobate Crystals

In recent years, Orbital Angular Momentum (OAM) beams have been applied in optical communications to improve channel capacity and spectral efficiency. However, in practical applications, OAM information is often imprinted on short-wavelength light beams. How to completely transfer this information to the O-band to achieve long-distance transmission has not been conveniently achieved through most traditional methods. We studied the differential frequency experiment of OAM-carrying beams from both theoretical and experimental facets. In the periodic polarization 0 class matched lithium niobate crystal, the difference in frequency between the incident 1950 nm strong pump light and the 780 nm weak input light is achieved, resulting in output light in the O band. The polarization period of the crystal is 20 μm, and the best phase matching is achieved when the temperature is maintained at 41.2 °C. At this time, 780 nm vortex light produces 1300 nm vortex light, and the nonlinear conversion efficiency reaches 0.1387% (topological charge number l = 5). During the experiment, momentum, energy, and topological charge are all conserved. Our experiment successfully converted vortex light at 780 nm into vortex light at 1300 nm, paving the way for the subsequent conversion of 780 nm single photons generated by quantum dots carrying OAM into OAM photons in the communication band.