Classical Monopoles Research Articles

All finite-mass Dirac monopoles

We present a "primitive" way of realizing finite-mass Dirac monopoles in $U(1)$ gauge theories involving a single non-minimally interacting scalar field. Typically, the energy density of this type of monopole is not concentrated at its core, but it is distributed in a spherical shell, as we illustrate on several exact solutions in the Bogomol'nyi-Prasad-Sommerfield (BPS) limit. We show that our construction can be interpreted as a limit of infinitely massive $W$ bosons coupled to electromagnetic field-strength via a dipole moment. Combining our approach with ideas of Weinberg and Lee, we present a general landscape of $U(1)$ gauge models that support a finite-mass Dirac monopole. In fact, all classical monopoles, i.e., Wu-Yang, 't Hooft-Polyakov, Cho-Maison, etc., are special points on this landscape.

Possible observation of highly itinerant quantum magnetic monopoles in the frustrated pyrochlore Yb2Ti2O7.

The low-energy elementary excitations in frustrated quantum magnets have fascinated researchers for decades. In frustrated Ising magnets on a pyrochlore lattice possessing macroscopically degenerate spin-ice ground states, the excitations have been discussed in terms of classical magnetic monopoles, which do not contain quantum fluctuations. Here we report unusual behaviours of magneto-thermal conductivity in the disordered spin-liquid regime of pyrochlore Yb2Ti2O7, which hosts frustrated spin-ice correlations with large quantum fluctuations owing to pseudospin-1/2 of Yb ions. The analysis of the temperature and magnetic field dependencies shows the presence of gapped elementary excitations. We find that the gap energy is largely suppressed from that expected in classical monopoles. Moreover, these excitations propagate a long distance without being scattered, in contrast to the diffusive nature of classical monopoles. These results suggests the emergence of highly itinerant quantum magnetic monopole, which is a heavy quasiparticle that propagates coherently in three-dimensional spin liquids.

Status of Searches for Magnetic Monopoles

Searches for magnetic monopoles ([Formula: see text]s) are a fascinating interdisciplinary area with implications for fundamental theories, particle physics, astrophysics, and cosmology. The quantum theory of [Formula: see text]s, and its consistency with electrodynamics, was originally derived by Dirac, marking the beginning of the search for classical monopoles at every new accelerator, including the Large Hadron Collider. [Formula: see text]s are required by Grand Unification Theories (GUTs), but unlike classical monopoles they would be incredibly massive, out of reach for any conceivable accelerator. Significant effort has been made to search for [Formula: see text]s in the cosmic radiation as relic particles from the early Universe in the widest experimentally available range of mass and velocity. In this review, we discuss the status of the searches for classical [Formula: see text]s at accelerators for GUTs, superheavy [Formula: see text]s in the penetrating cosmic radiation, and intermediate-mass [Formula: see text]s at high altitudes, emphasizing the most recent results and future perspectives.

Maxwell’s equations in four-dimensional notation and the classical magnetic monopoles

It is shown that, on account of the commutability of the order of derivation of the electromagnetic 4-potential, the first pair of Maxwell equations, when written in a four dimensional notation, is incompatible with the existence of the classical magnetic monopole. It is hypothesized that the appearance in the past of magnetic monopoles could be accepted only if, in exceptional occurrences, it came to be locally lacking the space homogeneity and isotropy on which the commutability of space derivatives is based. The situation is more complex for massive cosmological monopoles.

New limits on magnetic monopoles searches from accelerator and nonaccelerator experiments

Here, the status of the searches for “classical Dirac” magnetic monopoles (MMs) at accelerators and for GUT MMs in the cosmic radiation is discussed. We present recent analysis for classical Dirac monopoles at accelerators and the lowest flux upper limit for MMs in the mass range 105–1012 GeV obtained with the SLIM experiment at the Chacaltaya high-altitude-laboratory (5290 m a.s.l.).

MF digital AM station antennas

It is very important having the proper antenna, specially in the MF AM band where achieving the necessary bandwidth in the antenna impedance is a difficult task. This problem is critical in the lower frequencies were the antenna matching to the transmission line generally is very sharp and the best match is obtained only at the carrier frequency with an appreciable power reflection in the lateral frequency bands. This problem is not very important in the classical AM transmissions were the maximum transmitted power is located at the carrier frequency and only a fraction in the upper and lower lateral bands. Of course this produces some distortion in the AM transmission but in this case the quality of the audio is not really of high fidelity, like in an FM transmission, due to a lot of factors, one of them the lack of the full audio spectrum. This problem can be corrected with high fidelity audio transmitters and specially with digital transmission in order to achieve CD quality audio and here the transmitting antenna plays an important role. In this paper MF AM antenna systems are analyzed not only from the input impedance point of view, but with consideration of all the factors in order to determine the best system in bandwidth and radiation properties in different parts of the standard AM band. Cylindrical, type A, and Cantilever classical monopoles and the modern dipole type antenna systems are compared, to provide the criteria for choosing an optimum antenna for the future digital AM service. Examples of measured field strength as a function of distance in a flat region are presented in order to show the interesting MF AM possibilities for a digital service.

Spinor theory of general relativity without elementary gravitons

We propose a generally covariant and locally Lorentz invariant theory of a Majorana spinor field ψ μ α . Our theory has no elementary spin-2 quanta, but does reproduce Einstein's general relativity as a classical solution. We compare this situation to the possibility of finding classical monopoles in a gauge theory, even though no such elementary object is introduced at the outset.

Avoiding "Dirac's veto" in monopole theory

Using ideas introduced by Wu and Yang in their recent nonsingular formulation of an action principle for classical Dirac magnetic monopoles, we modify Dirac's original formulation of the problem so as to avoid the difficulties encountered when charged-particle trajectories intersect singular strings.