Abstract High-Q superconducting resonators have been proposed and developed as detectors of light-by-light scattering mediated by the hypothesized axion or virtual electron–positron pairs in quantum electrodynamics: the Euler–Heisenberg (EH) interaction. Photon frequency and mode conversion is central to the scheme for detecting such rare events. Superconducting resonators are nonlinear devices. The Meissner screening currents that confine the electromagnetic fields to the vacuum region of a superconducting RF cavity are nonlinear functions of the EM field at the vacuum–superconducting interface, and as a result can generate source currents and frequency conversion of microwave photons in the cavity. In this report we consider photon frequency and mode conversion in superconducting resonators with high quality factors from Meissner currents in single- and dual-cavity setups proposed for axion and QED searches based on light-by-light scattering. In a single cavity with two pump modes, photon frequency conversion by the Meissner screening current dominates photon generation by the EH interaction for cavities with . The Meissner currents also generate background photons that limit the operation of the resonator for axion detection in three-mode, single-cavity setups. We also consider the leakage of photons from pump modes into the signal mode for both axion- and EH-mediated light-by-light scattering. Photon frequency conversion by the EH interaction can compete with Meissner and leakage radiation in ultra-high-Q cavities that are beyond the current state of the art. Meissner radiation and leakage backgrounds can be suppressed in dual-cavity setups with appropriate choices for pump and spectator modes, as well as the single-cavity setup proposed for heterodyne detection of galactic axion dark matter.

United States

Hikaru Ueki

J A Sauls

Photon Frequency Conversion in High- Superconducting Resonators: Axion Electrodynamics, QED, and Nonlinear Meissner Radiation

We examine possible experimental signatures that may be exploited to search for stable supermassive particles with electric charges of  $${{\mathcal {O}}}(1)$$  <math> <mrow> <mi>O</mi> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </math>   in future underground experiments, and the upcoming JUNO experiment in particular. The telltale signal providing a unique signature of such particles, would be a correlated sequence of three or more nuclear recoils along a straight line, corresponding to the motion of a non-relativistic ( $$\beta \lesssim 10^{-2}$$  <math> <mrow> <mi>β</mi> <mo>≲</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>2</mn> </mrow> </msup> </mrow> </math>  ) particle that could enter the detector from any direction. We provide some preliminary estimates for the expected event rates.

Poland

Krzysztof Meissner

Germany

Hermann Nicolai

Searching for supermassive charged gravitinos in underground experiments

We investigate correspondence between the Melvin–Kerr–Newman–Taub–NUT spacetime, and the conformal field theory. The near horizon geometry of extremal Melvin–Kerr–Newman–Taub–NUT spacetime possesses the  $$SL\left( 2,{{\mathbb {R}}}\right) \times U\left( 1\right) $$  <math> <mrow> <mi>S</mi> <mi>L</mi> <mfenced> <mn>2</mn> <mo>,</mo> <mi>R</mi> </mfenced> <mo>×</mo> <mi>U</mi> <mfenced> <mn>1</mn> </mfenced> </mrow> </math>   isometry, which allows one to employ the asymptotic symmetry group method, in establishing the holographic correspondence for the spacetime. We also use the alternative way of the stretched horizon method, to compute the extremal entropy of the black hole. We find perfect agreement between the results of asymptotic symmetry group and the stretched horizon methods, to establish the holography for the extremal Melvin–Kerr–Newman–Taub–NUT black hole. The black hole Meissner effect for the Melvin–Kerr–Taub–NUT black hole is also discussed.

Canada

Masoud Ghezelbash

Indonesia

Haryanto Siahaan

Meissner effect and holographic dual for the Melvin–Kerr–Newman–Taub–NUT spacetimes

When approaching extremality, rotating black holes tend to expel the magnetic field in which they are immersed. This phenomenon, being reminiscent of the Meissner-Ochsenfeld effect in superconductors, is known as the black hole Meissner effect, and here we study it in the backreacting regime and from the near horizon perspective. By resorting to methods recently developed in the literature, which allow to compute conserved charges in the near horizon region, regardless the details of the asymptotia at large distance, we investigate the properties of the black hole horizon when in its Meissner state. We show that, when in such state, the horizon exhibits two sets of supertranslation symmetries as well as a symmetry generated by the local conformal group. The supertranslations are generated by two infinite sets of currents, one of which comes from local dilations of the advanced null coordinate at the horizon, and the other from local gauge transformations that preserve the electromagnetic field configuration at the horizon. We show that the evaluation of the conserved charges associated to these symmetries correctly reproduce the physical charges of the magnetized black holes and their thermodynamics. This represents a concrete application of the techniques developed in [1–3] and it extends the results of [4] to arbitrary values of the black hole charges. In addition, we elaborate on the charges computation at the horizon: we show the equivalence between the horizon charges and the evaluation of the corresponding Komar integrals. Besides, we show the validity of the Gauss phenomenon by explicitly relating near horizon charges with fluxes and charges computed by other techniques. All this provides a method to derive the thermodynamics of magnetized horizons in a quite succinct way, including the case of horizons exhibiting the Meissner effect.

Gaston Giribet

Joan Madrid

Argentina

Luciano Montecchio

Emilio Rubín de Celis

Pedro Schmied

Zooming in on the horizon when in its Meissner state

The holographic superconductor is the holographic dual of superconductivity, but there is no Meissner effect in the standard holographic superconductor. This is because the boundary Maxwell field is added as an external source and is not dynamical. We show the Meissner effect analytically by imposing the semiclassical Maxwell equation on the AdS boundary. Unlike in the Ginzburg-Landau (GL) theory, the extreme type I limit cannot be reached even in the <math><mrow><mi>e</mi><mo>→</mo><mi>∞</mi></mrow></math> limit where <math><mi>e</mi></math> is the <math><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></math> coupling of the boundary Maxwell field. This is due to the bound current which is present even in the pure bulk Maxwell theory. In the bulk 5-dimensional case, the GL parameter and the dual GL theory are obtained analytically for the order parameter of scaling dimension 2.

Japan

Makoto Natsuume

Takashi Okamura

Holographic Meissner effect

We study the quantization of the bosonic sector of supermembrane theory in double dimensional reduction, in order to extract the dependence of the resulting world-sheet action on the string dilaton (which cannot be obtained from a purely kinematic reduction). Our construction relies on a Polyakov-type approach with all six metric components on the world-volume as independent quantum fields, and shows that the correct and unique answer is only obtained if the target-space dimension of the theory is restricted to the critical value (D = 11 for the supermembrane). As a corollary, our analysis implies that there are no analogs of the non-critical string for (super-)membrane theory.

Fundamental membranes and the string dilaton

Violation of non-Abelian Bianchi identity can be regarded as <math><msup><mi>N</mi><mn>2</mn></msup><mo>−</mo><mn>1</mn></math> Abelian-like monopole currents in the continuum SU(N) QCD. Three Abelian-like monopoles, when defined in SU(2) gluodynamics on the lattice à la DeGrand–Toussaint, are shown to have the continuum limit with respect to the color-invariant monopole density and the effective monopole action. Since each Abelian-like monopole is not gauge invariant, we have introduced various partial gauge fixing for the purpose of reducing lattice artifact monopoles in the thermalized vacuum. Here we investigate Abelian and monopole dominances and the Abelian dual Meissner effects adopting the same gauges like the maximal center gauge (MCG) in comparison with the maximal Abelian gauge (MAG). Abelian and monopole contributions to the string tension in these gauges are observed to be a little smaller than the non-Abelian string tension. However, we find that the monopole dominance is improved well when use is made of the block-spin transformations with respect to Abelian-like monopoles. We find each electric field is squeezed by the corresponding colored Abelian-like monopole in such gauges and the Abelian dual Meissner effect is observed independently for each color. Moreover, we confirm the dual Ampère’s law in these new gauges as well as in MAG. The SU(2) vacuum is shown to be near the border between the type 1 and type 2 dual superconductors. The penetration length is almost equal for the four gauge fixings, and the vacuum type in MCG is almost the same value as the previous results. These results are consistent with the previous results suggesting the continuum limit and the gauge-independence of Abelian monopoles.

Atsuki Hiraguchi

Katsuya Ishiguro

Tsuneo Suzuki

New Abelian-like monopoles and the dual Meissner effect

We study the static responses of cold quark matter in the intermediate baryonic density region (characterized by a chemical potential <math><mi>μ</mi></math>) in the presence of a strong-magnetic field. We consider in particular, the so-called magnetic dual Chiral Density Wave (MDCDW) phase, which is materialized by an inhomogeneous condensate formed by a particle-hole pair. It is shown, that the MDCDW phase is more stable in the weak-coupling regime than the one considered in the magnetic catalysis of chiral symmetry braking phenomenon and even than the chiral symmetric phase that was expected to be realized at sufficiently high baryonic chemical potential. The different components of the photon polarization operator of the MDCDW phase in the one-loop approximation are calculated. We found that in the MDCDW phase there is neither Debye screening nor Meissner effect in the lowest-Landau-level approximation. The obtained Debye length depends on the amplitude <math><mi>m</mi></math> and modulation <math><mi>b</mi></math> of the inhomogeneous condensate and it is only different from zero if the relation <math><mo>|</mo><mi>μ</mi><mo>−</mo><mi>b</mi><mo>|</mo><mo>&gt;</mo><mi>m</mi></math> holds. But, we found that in the region of interest this inequality is not satisfied. Thus, no Debye screening takes place under those conditions. On the other hand, since the particle-hole condensate is electrically neutral, the U(1) electromagnetic group is not broken by the ground state and consequently there is no Meissner effect. These results can be of interest for the astrophysics of neutron stars.

China

Bo Feng

Efrain J. Ferrer

Israel Portillo

Lack of Debye and Meissner screening in strongly magnetized quark matter at intermediate densities

The full description of a superconductor requires that it has an infinite dc conductivity (or zero electrical resistivity) as well as expels the external magnetic fields. Thus, for any holographic superconductor which is dual to a real superconductor, it is necessary to examine, simultaneously, these two features based on the gauge/gravity duality. In this paper, we explore numerically these two aspects of the higher dimensional holographic superconductors, in the presence of a power-Maxwell electrodynamics as the gauge field. At first, we calculate the critical temperature, condensation, conductivity, and superconducting gap, in the absence of magnetic field and disclose the effects of both power parameter, <math><mi>s</mi></math>, as well as the spacetime dimensions, <math><mi>d</mi></math>, on this quantities. Then, we immerse the superconductor into an external magnetic field, <math><mi>B</mi></math>, and observe that with increasing the magnetic field, the starting point of condensation occurs at temperature less than the critical temperature, <math><msub><mi>T</mi><mi>c</mi></msub></math>, in the absence of magnetic field. This implies that at a fixed temperature, we can define a critical magnetic field, above which the critical temperature goes to zero which is similar to the Meissner effect in superconductor. In these indications, we also try to show the distinction of the conformal invariance of the power-Maxwell Lagrangian that occurs for <math><mi>s</mi><mo>=</mo><mi>d</mi><mo>/</mo><mn>4</mn></math>.

Iran

Doa Hashemi Asl

Ahmad Sheykhi

Meissner-like effect and conductivity of power-Maxwell holographic superconductors

The mechanism of color confinement has been studied in the framework of SU(3) color gauge theory in terms of Abelian fields and monopoles extracted by adopting magnetic symmetry. The existence of the mechanism of color confinement corresponds to the dual Meissner effect caused by monopoles. The two length scales, \ie the penetration depth and coherence length are defined to demonstrate the scaling nature of the QCD vacuum, and their ratio defines the Ginzburg--Landau parameter indicating the border of type-I and type-II dual superconductor. The existence of these two length scales describes the intrinsic shape of the confining flux tube and is a characteristic of the dual superconductor model of confinement in QCD. As a result, the quark confining potential has been computed and the resulting expression of string tension has been constructed in the infrared sector of SU(3) dual QCD formulation. Moreover, with the introduction of dynamical quarks, the flux tube breaks and leads to the creation of quark--anti-quark pairs. Finite temperature quark confining potential and the associated string tension has also been extracted which demonstrates a considerable reduction in the vicinity of critical temperature showing agreement with the recent lattice studies.

India

H.C. Chandola

Dual Meissner Effect and Quark Confinement Potential in SU(3) Dual QCD Formalism