Conservation and persistence of spin currents and their relation to the Lieb-Schulz-Mattis twist operators

Systems with spin-orbit coupling do not conserve "bare" spin current $\bf{j}$. A recent proposal for a conserved spin current $\bf{J}$ [J. Shi {\it et.al} Phys. Rev. Lett. {\bf 96}, 076604 (2006)] does not flow persistently in equilibrium. We suggest another conserved spin current $\bar{\bf{J}}$ that may flow persistently in equilibrium. We give two arguments for the instability of persistent current of the form $\bf{J}$: one based on the equations of motions and another based on a variational construction using Lieb-Schulz-Mattis twist operators. In the absence of spin-orbit coupling, the three forms of spin current coincide.Comment: 5 pages; added references, simplified notation, clearer introductio

Standard Model Muon Magnetic Dipole Moment

The most recent high-precision determination of the hadronic leading order contribution to the muon magnetic dipole moment within the Standard Model of particle physics has revealed a five standard deviation discrepancy with the previous determination with the highest precision. A systematic effect of the luminous volume created during the measurements leading to the determinations seems to be the source of the discrepancy. Correcting for the luminous volume effect allows a consistent determination of the Standard Model muon magnetic dipole moment with precision that is comparable to the latest world average from muon spin precession experiments.Comment: Five pages, three tables, updated following discussions at 6th Plenary Workshop of the Muon g-2 Theory Initiativ

Weighing the Axion with Muon Haloscopy

Recent measurements of muon spin precession confirm a long-standing tension with the Standard Model of particle physics. We argue that axions from the local dark matter halo of the galaxy are responsible for the tension. The argument yields a percent level prediction for the mass of the axion provided that dark matter is made of axions. An analysis of charge asymmetry in kaon decays suggests that at least in the local halo dark matter is made of axions and that axions from the local halo are responsible for the observed violation by these reactions of the combined charge conjugation and spatial inversion symmetry operation. Tabletop experiments to directly detect dark matter in the form of axions with the predicted mass are proposed.Comment: 17 pages, 3 figures, now with atomic clocks and laboratory plasma

Spontaneous Mutations from Terahertz Proton Tunneling

Protons in the gap between base pairs of the double helix store the code of life by breaking the chiral symmetry that swaps the sense strand with its complementary partner. When these hydrogen bonds break during replication and transcription, pairs of protons switch sides restoring chiral symmetry and destroying genetic information. Using time-independent second-order perturbation theory, we show that the observed rate of such spontaneous mutations follows in the sudden approximation for bond breaking provided protons in bonds between bases tunnel across the gap with terahertz frequencies.Comment: 5 pages, 1 figure, updated spontaneous mutation rat

Scaling Analysis and Application: Phase Diagram of Magnetic Nanorings and Elliptical Nanoparticles

The magnetic properties of single-domain nanoparticles with different geometric shapes, crystalline anisotropies and lattice structures are investigated. A recently proposed scaling approach is shown to be universal and in agreement with dimensional analysis coupled with an assumption of {\em incomplete} self-similarity. It is used to obtain phase diagrams of magnetic nanoparticles featuring three competing configurations: in-plane and out-of-plane ferromagnetism and vortex formation. The influence of the vortex core on the scaling behavior and phase diagram is analyzed. Three-dimensional phase diagrams are obtained for cylindrical nanorings, depending on their height, outer and inner radius. The triple points in these phase diagrams are shown to be in linear relationship with the inner radius of the ring. Elliptically shaped magnetic nanoparticles are also studied. A new parametrization for double vortex configurations is proposed, and regions in the phase diagram are identified where the double vortex is a stable ground state.Comment: 9 pages, 7 figures; added references, and discussion, as suggested by referee