Search Results (22)

The hydrogen ions in superionic ice can move freely, playing the role of electrons in metals. Its electromagnetic behavior is the key to explaining the anomalous magnetic fields of Uranus and Neptune. Based on an ab initio evolutionary algorithm, we searched for the stable H₄O crystal structure under pressures of 500–5000 GPa and discovered a new layered-chain Pmn2₁-H₄O structure with H₃ ion clusters. Interestingly, H₃ ion clusters rotate above 900 K (with an instantaneous speed of 3000 m/s at 900 K), generating an instantaneous magnetic moment (~10⁻²⁶ A·m² ≈ 0.001 ${\mu }_{\mathrm{B}}$). Moreover, H ions diffuse in a direction perpendicular to the H-O atomic layer at 960–1000 K. This is because the hydrogen–oxygen covalent bonds within the hydrogen–oxygen plane hinder the diffusion behavior of H₃ ion clusters within the plane, resulting in the diffusion of H₃ ion clusters between the hydrogen–oxygen planes and the formation of a one-dimensional conductive superionic state. One-dimensional diffusion of ions may generate magnetic fields. We refer to these two types of magnetic moments as “thermally induced ion magnetic moments”. When the temperature exceeds 1000 K, H ions diffuse in three directions. When the temperature exceeds 6900 K, oxygen atoms diffuse and the system becomes fluid. These findings provide important references for people to re-recognize the physical and chemical properties of hydrogen and oxygen under high pressure, as well as the sources of abnormal magnetic fields in Uranus and Neptune. Full article

We investigate the phenomenological effects of the nonholomorphic (NH) higgsino mass term, ${\mu }^{\prime }$, within the minimal supersymmetric standard model (MSSM) extended by a non-abelian flavor symmetry, referred to as the sNHSSM. This flavor symmetry enables a substantial reduction in the number of free parameters inherent to the MSSM, streamlining them from a large set to just eight. Our study explores the interplay between cold dark matter (CDM) relic density (${\mathsf{\Omega }}_{\mathrm{CDM}}{h}^2$) and the anomalous magnetic moment of the muon, ${(g-2)}_{\mu }$. We study correlations among the theoretical parameters that emerge from this interplay and are further constrained by experimental data such as the Higgs boson mass, B-physics observables, and the charge and color breaking minima constraints. Moreover, our findings reveal that incorporating the NH higgsino mass term opens up new regions of parameter space that were previously inaccessible. Full article

We start with the 50-component relativistic matrix equation for a hypothetical spin-2 particle in the presence of external electromagnetic fields. This equation is hypothesized to describe a particle with an anomalous magnetic moment. The complete wave function consists of a two-rank symmetric tensor and a three-rank tensor that is symmetric in two indices. We apply the general method for performing the nonrelativistic approximation, which is based on the structure of the $50\times 50$ matrix ${\Gamma }^0$ of the main equation. Using the 7th-order minimal equation for the matrix ${\Gamma }^0$, we introduce three projective operators. These operators permit us to decompose the complete wave function into the sum of three parts: one large part and two smaller parts in the nonrelativistic approximation. We have found five independent large variables and 45 small ones. To simplify the task, by eliminating the variables related to the 3-rank tensor, we have derived a relativistic system of second-order equations for the 10 components related to the symmetric tensor. We then take into account the decomposition of these 10 variables into linear combinations of large and small ones. In accordance with the general method, we separate the rest energy in the wave function and specify the orders of smallness for different terms in the arising equations. Further, after performing the necessary calculations, we derive a system of five linked equations for the five large variables. This system is presented in matrix form, which has a nonrelativistic structure, where the term representing additional interaction with the external magnetic field through three spin projections is included. The multiplier before this interaction contains the basic magnetic moment and an additional term due to the anomalous magnetic moment. The latter characteristic is treated as a free parameter within the hypothesis. Full article

We review the hadronic light-by-light (HLbL) contribution to the muon anomalous magnetic moment. Upcoming measurements will reduce the experimental uncertainty of this observable by a factor of four; therefore, the theoretical precision must improve accordingly to fully harness such an experimental breakthrough. With regards to the HLbL contribution, this implies a study of the high-energy intermediate states that are neglected in dispersive estimates. We focus on the maximally symmetric high-energy regime and in-quark loop approximation of perturbation theory, following the method of the OPE with background fields proposed by Bijnens et al. in 2019 and 2020. We confirm their results regarding the contributions to the muon $g-2$. For this, we use an alternative computational method based on a reduction in the full quark loop amplitude, instead of projecting on a supposedly complete system of tensor structures motivated by first principles. Concerning scalar coefficients, mass corrections have been obtained by hypergeometric representations of Mellin–Barnes integrals. By our technique, the completeness of such kinematic singularity/zero-free tensor decomposition of the HLbL amplitude is explicitly checked. Full article

The anomalous magnetic moment of the electron, first calculated by Schwinger, lowers the ground state energy of the electron in a weak magnetic field. It is a function of the field and changes signs for large fields, ensuring the stability of the ground state. This has been shown in the past 50 years in numerous papers. The corresponding corrections to the mass of the electron have also been investigated in strong fields using semiclassical methods. We critically review these developments and point out that the calculation for low-lying excited states raises questions. Also, we calculate the contribution from the tadpole diagram, the relevance of which was observed only quite recently. Full article

We present the novel idea of using the atomic radiative emission of neutrino pairs to test physics beyond the Standard Model, including light vector/scalar mediators and the anomalous neutrino electromagnetic moments. With $\mathcal{O}$(eV) momentum transfer, atomic transitions are particularly sensitive to light mediators and can improve their coupling strength sensitivity by 3∼4 orders of magnitude. In particular, the massless photon belongs to this category. The projected sensitivity with respect to neutrino electromagnetic moments is competitive with dark matter experiments. Most importantly, neutrino pair emission provides the possibility of separating the electric and magnetic moments, even identifying their individual elements, which is not possible by existing observations. Full article

Permanent electric dipole moments (EDMs) are excellent probes of physics beyond the Standard Model, especially on new sources of CP violation. The muon EDM has recently attracted significant attention due to discrepancies in the magnetic anomaly of the muon, as well as potential violations of lepton-flavor universality in B-meson decays. At the Paul Scherrer Institute in Switzerland, we have proposed a muon EDM search experiment employing the frozen-spin technique, where a radial electric field is exerted within a storage solenoid to cancel the muon’s anomalous spin precession. Consequently, the EDM signal can be inferred from the upstream-downstream asymmetry of the decay positron count versus time. The experiment is planned to take place in two phases, anticipating an annual statistical sensitivity of $3\times {10}^{-21}$$e·$cm for Phase I and $6\times {10}^{-23}$$e·$cm for Phase II. Going beyond ${10}^{-21}$$e·$cm will enable us to probe various Standard Model extensions. Full article

Recent years have seen the emergence of moiré materials as an attractive platform for observing a host of novel correlated and topological phenomena. Moiré heterostructures are generated when layers of van der Waals materials are stacked such that consecutive layers are slightly mismatched in their lattice orientation or unit cell size. This slight lattice mismatch gives rise to a long-wavelength moiré pattern that modulates the electronic structure and leads to novel physics. The moiré superlattice results in flat superlattice bands, electron–electron interactions and non-trivial topology that have led to the observation of superconductivity, the quantum anomalous Hall effect and orbital magnetization, among other interesting properties. This review focuses on the experimental observation and theoretical analysis of orbital magnetism in moiré materials. These systems are novel in their ability to host magnetism that is dominated by the orbital magnetic moment of Bloch electrons. This orbital magnetic moment is easily tunable using external electric fields and carrier concentration since it originates in the quantum anomalous Hall effect. As a result, the orbital magnetism found in moiré superlattices can be highly attractive for a wide array of applications including spintronics, ultra-low-power magnetic memories, spin-based neuromorphic computing and quantum information technology. Full article

The muon anomalous magnetic moment ($g-2$) measurement at the Fermilab National Accelerator Laboratory (FNAL-E989) is consistent with a previous experiment at the Brookhaven National Laboratory (BNL-E821), and these results show a deviation of 4.2 standard deviations from the prediction of the Standard Model. This deviation may suggest the existence of unknown particles, and a completely different approach from previous experiments is needed for further verification. The J-PARC experiment’s objective is to measure the muon g-2 and the electric dipole moment (EDM) with high precision using a new method with a low-emittance muon beam generated by RF linear acceleration. In this paper, the development of an interdigital H-mode drift tube linac (IH-DTL) for the muon linear accelerator is described. Full article

Rare-earth tetraborides RB₄ are of great interest due to the occurrence of geometric magnetic frustration and corresponding unusual magnetic properties. While the Gd³⁺ spins in GdB₄ align along the ab plane, Er³⁺ spins in the isomorphic ErB₄ are confined to the c–axis. The magnetization in the latter exhibits a plateau at the midpoint of the saturation magnetization. Therefore, solid solutions of (Gd, Er)B₄ provide an excellent playground for exploring the intricate magnetic behavior in these compounds. Single crystals of Gd_1−xEr_xB₄ (x = 0, 0.2, and 0.4) were grown in aluminum flux. X-ray diffraction scans revealed single-phase materials, and a drop in the unit cell volume with increasing Er content, suggesting the partial substitution of Er at the Gd sites. Heat capacity measurements indicated a systematic decrease of the Néel temperature (T_N) with increasing Er content. The effective magnetic moment determined from the magnetization measurement agreed with the calculated free ion values for Gd³⁺ and Er³⁺, providing further evidence for the successful substitution of Er for Gd. The partial substitution resulted in an anomalous ferromagnetic phase below T_N, exhibiting significant anisotropy, predominantly along the c-axis. This intriguing behavior merits further studies of the magnetism in the Gd_1−xEr_xB₄ borides. Full article

We review instabilities that appear from the coupling of spin-one fields to a magnetic background in a non-Abelian theory. Such coupling results, due to asymptotic freedom in a negative quantum, contribute to the effective potential. In QCD, the Savvidy vacuum results. However, due to the tachyonic mode, such a state is not stable, and the question about the true ground state of QCD is still open. In the electroweak model, the corresponding instability is postponed to very large background fields and may be of relevance in the early universe, at best. We start with an introduction to the topic and display the necessary formulas and methods. Then, we consider the one-particle spectra of the fields in a magnetic background and the related Euler–Heisenberg Lagrangians. In addition, we discuss the potential instability connected with the anomalous moment of the electron. The main part is on the quantum correction to the energy in non-Abelian fields, including massive ones. Here, the focus is on so-called electroweak magnetism and the search for a classical solution of the field equations and their approximations by a lattice of flux tubes. Finally, we review approaches with non-homogeneous background fields and the background of an $A_0$-field. Full article

In this paper, we demonstrate how various external forces influence the effect of the radiation of a charged particle. As a particular example, we obtained a solution to the Dirac equation for an electron in a constant homogeneous magnetic field and by taking into account the anomalous magnetic moment and influence of possible Lorentz invariance violation in minimal CPT-odd form. Based on the solution found, we calculated the synchrotron radiation (SR) characteristics and predicted possible observable effects attributable to the Lorentz invariance violation. As another example, we calculated the stimulated synchrotron radiation in the presence of the field of an electromagnetic wave and taking into account the inhomogeneity of an external magnetic field. Moreover, the superposition of two electromagnetic waves was also considered taking into account the properties of radiated electromagnetic waves. We also point out a way to use a corresponding semiclassical solution to the Dirac equation to obtain synchrotron radiation without approximating the radiative amplitudes themselves. This last way of calculating might be of use for studying SR in real circumstances of radiation in an astrophysical magnetic field and in electron accelerators, where electron trajectories are far from being circular. Full article

We describe the Adler function in Quantum Chromodynamics using a transseries representation within a resurgent framework. The approach is based on a Borel-Ecalle resummation of the infrared renormalons combined with an effective running for the strong coupling. The new approach is flexible enough to give values in agreement with the current Adler function determinations. We then apply our finding to the muon’s anomalous magnetic moment studying the possibility of saturating, solely in terms of the vacuum polarization function, the current discrepancy between the best Standard Model value for the muon’s anomalous magnetic moment and the experimental value obtained by the most recent muon $g-2$ collaboration. The latter shows that the Adler function’s new representation can also be consistent with recent lattice determinations. Full article

Based on density functional theory, we studied the electronic, magnetic, and mechanical properties of Co_3−xCr_xAl (x = 0, 1, 2, 3) Heusler compounds with the generalized gradient approximation (GGA) for the exchange-correlation potential. In this study, we report two principal spin-related phenomena, namely, the anomalous Hall effect and current spin polarization of the Co_3−xCr_xAl Heusler compounds in the L2₁ crystal structure. Heusler compounds, both ideally and inversely ordered, were considered. We found that the calculated magnetic moment of Co_3−xCr_xAl decreased with an increase in the Cr concentration for both ideally and inversely ordered structures, except for Cr₃Al. We also found that the spin polarization for all Co_3−xCr_xAl was larger than 50%, except for Cr₂CoAl in the inverse structure. All the considered Heusler compounds were mechanically stable except for the regular Cr₂CoAl. The Hall current spin polarization was also calculated. We found that Co₂CrAl in the XA structure had the largest spin Hall conductivity of 370 ($\hslash \mathrm{S}/\mathrm{e} \mathrm{cm}$), and the spin polarization of the induced Hall current was high. Full article

We consider a QCD cold-plasma-motivated Equation of State (EOS) to examine the impact of an Anomalous Magnetic Moment (AMM) coupling and small shape deformations on the static oblate and prolate core shapes of quark stars. Using the Fogaça QCD-motivated EOS, which shifts from the high-temperature, low-chemical-potential quark–gluon plasma environment to the low-temperature, high-chemical-potential quark stellar core environment, we consider the impact of an AMM coupling with a metric-induced shape deformation parameter in the Tolman–Oppenheimer–Volkov (TOV) equations. The AMM coupling includes a phenomenological scaling that accounts for the weak and strong field characteristics in dense matter. The EOS is developed using a hard gluon and soft gluon decomposition of the gluon field tensor and using a mean-field effective mass for the gluons. The AMM is considered using the Dirac spin tensor coupled to the EM field tensor with quark-flavor-based magnetic moments. The shape parameter is introduced in a metric ansatz that represents oblate and prolate static stellar cores for modified TOV equations. These equations are numerically solved for the final mass and radius states, representing the core collapse of a massive star with a phase transition leading to an unbound quark–gluon plasma. We find that the combined shape parameter and AMM effects can alter the coupled EOS–TOV equations, resulting in an increase in the final mass and a decrease in the final equatorial radius without collapsing the core into a black hole and without violating causality constraints; we find maximum mass values in the range 1.6 M_ʘ < M < 2.5 M_ʘ. These states are consistent with some astrophysical, high-mass magnetar/pulsar and gravity wave systems and may provide evidence for a core that has undergone a quark–gluon phase transition such as PSR 0943 + 10 and the secondary from the GW 190814 event. Full article