Magnetic Monopoles in Field Theory and Cosmology

The existence of magnetic monopoles is predicted by many theories of particle physics beyond the Standard Model. However, in spite of extensive searches, there is no experimental or observational sign of them. I review the role of magnetic monopoles in quantum field theory and discuss their implications for particle physics and cosmology. I also highlight their differences and similarities with monopoles found in frustrated magnetic systems, and discuss how experiments carried out in these systems could help us understand the physics of fundamental monopoles.Comment: 15 pages, no figures. Based on a talk given at the discussion meeting "Emergent magnetic monopoles in frustrated magnetic systems" at the Kavli Royal Society International Centre, 17-18 October 2011. To be published in Philosophical Transactions of the Royal Society

On the formation/dissolution of equilibrium droplets

We consider liquid-vapor systems in finite volume $V\subset\R^d$ at parameter values corresponding to phase coexistence and study droplet formation due to a fixed excess $\delta N$ of particles above the ambient gas density. We identify a dimensionless parameter $\Delta\sim(\delta N)^{(d+1)/d}/V$ and a \textrm{universal} value \Deltac=\Deltac(d), and show that a droplet of the dense phase occurs whenever \Delta>\Deltac, while, for \Delta<\Deltac, the excess is entirely absorbed into the gaseous background. When the droplet first forms, it comprises a non-trivial, \textrm{universal} fraction of excess particles. Similar reasoning applies to generic two-phase systems at phase coexistence including solid/gas--where the ``droplet'' is crystalline--and polymorphic systems. A sketch of a rigorous proof for the 2D Ising lattice gas is presented; generalizations are discussed heuristically.Comment: An announcement of a forthcoming rigorous work on the 2D Ising model; to appear in Europhys. Let

Spin current and magneto-electric effect in non-collinear magnets

A new microscopic mechanism of the magneto-electric (ME) effect based on the spin supercurrent is theoretically presented for non-collinear magnets. The close analogy between the superconductors (charge current) and magnets (spin current) is drawn to derive the distribution of the spin supercurrent and the resultant electric polarization. Application to the spiral spin structure is discussed.Comment: 5 pages, 2 figure

Phenomenological approach to the critical dynamics of the QCD phase transition revisited

The phenomenological dynamics of the QCD critical phenomena is revisited. Recently, Son and Stephanov claimed that the dynamical universality class of the QCD phase transition belongs to model H. In their discussion, they employed a time-dependent Ginzburg-Landau equation for the net baryon number density, which is a conserved quantity. We derive the Langevin equation for the net baryon number density, i.e., the Cahn-Hilliard equation. Furthermore, they discussed the mode coupling induced through the {\it irreversible} current. Here, we show the {\it reversible} coupling can play a dominant role for describing the QCD critical dynamics and that the dynamical universality class does not necessarily belong to model H.Comment: 13 pages, the Curie principle is discussed in S.2, to appear in J.Phys.

Dissipation Enhanced Asymmetric Transport in Quantum Ratchets

Quantum mechanical motion of a particle in a periodic asymmetric potential is studied theoretically at zero temperature. It is shown based on semi-classical approximation that the tunneling probability from one local minimum to the next becomes asymmetric in the presence of weak oscillating field, even though there is no macroscopic field gradient in average. Dissipation enhances this asymmetry, and leads to a steady unidirectional current, resulting in a quantum ratchet system.Comment: 12 pages, 2 Figures, submitted to J. Phys. Soc. Jp

Thermodynamic basis of the concept of "recombination resistances"

The concept of "recombination resistance" introduced by Shockley and Read (Phys. Rev. 87, 835 (1952)) is discussed within the framework of the thermodynamics of irreversible processes ruled by the principle of the minimum rate of entropy production. It is shown that the affinities of recombination processes represent "voltages" in a thermodynamic Ohm-like law where the net rates of recombinations represent the "currents". The quantities thus found allow for the definition of the "dissipated power" which is to be related to the rate of entropy production of the recombination processes dealt with.Comment: Submitted to Phys. Rev.

The Free Will Theorem

On the basis of three physical axioms, we prove that if the choice of a particular type of spin 1 experiment is not a function of the information accessible to the experimenters, then its outcome is equally not a function of the information accessible to the particles. We show that this result is robust, and deduce that neither hidden variable theories nor mechanisms of the GRW type for wave function collapse can be made relativistic. We also establish the consistency of our axioms and discuss the philosophical implications.Comment: 31 pages, 6figure

Gyrokinetic Simulations Compared with Magnetic Fluctuations Diagnosed with a Faraday-Effect Radial Interferometer-Polarimeter in the DIII-D pedestal

Experimental data on electromagnetic fluctuations in DIII-D, made available by the Faraday-effect Radial Interferometer-Polarimeter (RIP) diagnostic, is examined in comparison with detailed gyrokinetic simulations using Gyrokinetic Electromagnetic Numerical Experiment (GENE). The diagnostic has the unique capability of making internal measurements of fluctuating magnetic fields $\frac{\int n_e \delta B_r dR}{\int n_e dR}$. Local linear simulations identify microtearing modes (MTMs) over a substantial range of toroidal mode numbers (peaking at $n=15$) with frequencies in good agreement with the experimental data. Local nonlinear simulations reinforce this result by producing a magnetic frequency spectrum in good agreement with that diagnosed by RIP. Simulated heat fluxes are in the range of experimental expectations. However, magnetic fluctuation amplitudes are substantially lower than the experimental expectations. Possible sources of this discrepancy are discussed, notably the fact that the diagnostics are localized at the mid-plane -- the poloidal location where the simulations predict the fluctuation amplitudes to be smallest. Despite some discrepancies, several connections between simulations and experiments, combined with general criteria discriminating between potential pedestal instabilities, strongly point to MTMs as the source of the observed magnetic fluctuations

Introduction to Magnetic Monopoles

One of the most basic properties of magnetism is that a magnet always has two poles, north and south, which cannot be separated into isolated poles, i.e., magnetic monopoles. However, there are strong theoretical arguments why magnetic monopoles should exist. In spite of extensive searches they have not been found, but they have nevertheless played a central role in our understanding of physics at the most fundamental level.Comment: 22 pages, 7 figures. To be published in Contemporary Physic

Critical phenomena: 150 years since Cagniard de la Tour

Critical phenomena were discovered by Cagniard de la Tour in 1822, who died 150 years ago. In order to mark this anniversary, the context and the early history of his discovery is reviewed. We then follow with a brief sketch of the history of critical phenomena, indicating the main lines of development until the present date. Os fen\'omenos cr\'{\i}ticos foram descobertos pelo Cagniard de la Tour em Paris em 1822. Para comemorar os 150 anos da sua morte, o contexto e a hist\'oria initial da sua descoberta \'e contada. Conseguimos com uma descri\c{c}\~ao breve da hist\'oria dos fen\'emenos cr\'{\i}ticos, indicando as linhas principais do desenvolvimento at\'e o presente.Comment: Latex2e, 8 pp, 3 eps figures include