Origin of the Glacial Cycles: A Collection of Articles

This collection of articles describes a new theory of glacial cycles and its application to a number of data sets that represent conditions during glacial times. The widely held conventional theory of glacial cycles, which is due to Milankovitch, attributes cycles in the earth's ice cover to perturbations in the motion of the earth and the resulting changes of insolation (solar heating) in the Northern Hemisphere. The strongest effects are expected to come from changes in the earth's obliquity (tilt of the earth's spin axis with respect to its orbit) and from the precession term that accounts for the delay between summer solstice (when the pole faces the sun) and perihelion (when the earth is closest to the sun). Perturbations of the earth's motion come from gravitational effects of the planets and the moon, and can be calculated with precision back at least 10 million years. Another parameter describing the motion of the earth is the inclination i of the earth's orbital plane with respect to the invariable plane of the planetary systems. The invariable plane of the solar system is a plane perpendicular to the total angular momentum vector of the planets. Over the past one million years, the inclination has varied from about half a degree to about 3 degrees. During the time of low inclination, the earth accretes interplanetary dust at a greater rate than at times of high inclination. The dust particles, under the gravitational pull of the perturbing planets, tend to be concentrated in the invariable plane. Dust particles can affect climate by altering the amount of solar radiation reaching the lower part of the atmosphere. At the high altitudes where the dust particles enter the atmosphere, the particles themselves can attenuate the incoming solar radiation, can sweep up water vapor which is a warming greenhouse gas, and can nucleate water particles to form high-altitude (noctilucent) clouds. The clouds would themselves reflect radiation. While the detailed mechanisms of how astronomical dust can influence climate have not been completely worked out, this collection of articles shows that variation in inclination provides a better match for data sets on climate proxies than do variations of eccentricity. The theory also requires that density of dust in the vicinity of the variable plane varies with time. Beginning about one million years ago, the 100-kyr cycle became the dominating feature of variations in the total volume of ice covering the earth. Before that time, weaker variations are seen with 40-kyr and 20-kyr periods, consistent with variations in obliquity and precession

Spectrum of 100-kyr glacial cycle: Orbital inclination, not eccentricity

Spectral analysis of climate data shows a strong narrow peak with period ≈100 kyr, attributed by the Milankovitch theory to changes in the eccentricity of the earth’s orbit. The narrowness of the peak does suggest an astronomical origin; however the shape of the peak is incompatible with both linear and nonlinear models that attribute the cycle to eccentricity or (equivalently) to the envelope of the precession. In contrast, the orbital inclination parameter gives a good match to both the spectrum and bispectrum of the climate data. Extraterrestrial accretion from meteoroids or interplanetary dust is proposed as a mechanism that could link inclination to climate, and experimental tests are described that could prove or disprove this hypothesis

Perturbative spectrum of Trapped Weakly Interacting Bosons in Two Dimensions

We study a trapped Bose-Einstein condensate under rotation in the limit of weak, translational and rotational invariant two-particle interactions. We use the perturbation-theory approach (the large-N expansion) to calculate the ground-state energy and the excitation spectrum in the asymptotic limit where the total number of particles N goes to infinity while keeping the total angular momentum L finite. Calculating the probabilities of different configurations of angular momentum in the exact eigenstates gives us a clear view of the physical content of excitations. We briefly discuss the case of repulsive contact interaction.Comment: Revtex, 10 pages, 1 table, to appear in Phys. Rev.

Current-Induced Torques in Magnetic Metals: Beyond Spin Transfer

Current-induced torques on ferromagnetic nanoparticles and on domain walls in ferromagnetic nanowires are normally understood in terms of transfer of conserved spin angular momentum between spin-polarized currents and the magnetic condensate. In a series of recent articles we have discussed a microscopic picture of current-induced torques in which they are viewed as following from exchange fields produced by the misaligned spins of current carrying quasiparticles. This picture has the advantage that it can be applied to systems in which spin is not approximately conserved. More importantly, this point of view makes it clear that current-induced torques can also act on the order parameter of an antiferromagnetic metal, even though this quantity is not related to total spin. In this informal and intentionally provocative review we explain this picture and discuss its application to antiferromagnets.Comment: 5 figures, to appear in Journal of Magnetism and

Exact Mesonic Vacua From Matrix Models

We investigate in detail the structure of mesonic vacua of N=1 U(Nc) supersymmetric gauge theory with Nf flavors from the matrix model. We show that the Witten index from the matrix model calculation agrees with a result from field theoretical analysis. We also discuss the relationship between a diagrammatic summation and direct matrix integration with insertion of a variable changing delta function. Using this formalism, we obtain the quantum moduli space and evidence of the Seiberg duality from the matrix models.Comment: 14 pages, 1 figure, typos corrected and note on the quamtum moduli space adde

The interaction of a gap with a free boundary in a two dimensional dimer system

Let $\ell$ be a fixed vertical lattice line of the unit triangular lattice in the plane, and let \Cal H be the half plane to the left of $\ell$. We consider lozenge tilings of \Cal H that have a triangular gap of side-length two and in which $\ell$ is a free boundary - i.e., tiles are allowed to protrude out half-way across $\ell$. We prove that the correlation function of this gap near the free boundary has asymptotics $\frac{1}{4\pi r}$, $r\to\infty$, where $r$ is the distance from the gap to the free boundary. This parallels the electrostatic phenomenon by which the field of an electric charge near a conductor can be obtained by the method of images.Comment: 34 pages, AmS-Te

“Trunk-like” heavy ion structures observed by the Van Allen Probes

Dynamic ion spectral features in the inner magnetosphere are the observational signatures of ion acceleration, transport, and loss in the global magnetosphere. We report “trunk-like” ion structures observed by the Van Allen Probes on 2 November 2012. This new type of ion structure looks like an elephant's trunk on an energy-time spectrogram, with the energy of the peak flux decreasing Earthward. The trunks are present in He+ and O+ ions but not in H+. During the event, ion energies in the He+ trunk, located at L = 3.6–2.6, magnetic local time (MLT) = 9.1–10.5, and magnetic latitude (MLAT) = −2.4–0.09°, vary monotonically from 3.5 to 0.04 keV. The values at the two end points of the O+ trunk are energy = 4.5–0.7 keV, L = 3.6–2.5, MLT = 9.1–10.7, and MLAT = −2.4–0.4°. Results from backward ion drift path tracings indicate that the trunks are likely due to (1) a gap in the nightside ion source or (2) greatly enhanced impulsive electric fields associated with elevated geomagnetic activity. Different ion loss lifetimes cause the trunks to differ among ion species

Tidal friction in close-in satellites and exoplanets. The Darwin theory re-visited

This report is a review of Darwin's classical theory of bodily tides in which we present the analytical expressions for the orbital and rotational evolution of the bodies and for the energy dissipation rates due to their tidal interaction. General formulas are given which do not depend on any assumption linking the tidal lags to the frequencies of the corresponding tidal waves (except that equal frequency harmonics are assumed to span equal lags). Emphasis is given to the cases of companions having reached one of the two possible final states: (1) the super-synchronous stationary rotation resulting from the vanishing of the average tidal torque; (2) the capture into a 1:1 spin-orbit resonance (true synchronization). In these cases, the energy dissipation is controlled by the tidal harmonic with period equal to the orbital period (instead of the semi-diurnal tide) and the singularity due to the vanishing of the geometric phase lag does not exist. It is also shown that the true synchronization with non-zero eccentricity is only possible if an extra torque exists opposite to the tidal torque. The theory is developed assuming that this additional torque is produced by an equatorial permanent asymmetry in the companion. The results are model-dependent and the theory is developed only to the second degree in eccentricity and inclination (obliquity). It can easily be extended to higher orders, but formal accuracy will not be a real improvement as long as the physics of the processes leading to tidal lags is not better known.Comment: 30 pages, 7 figures, corrected typo

Nonequilibrium Dynamics in Low Dimensional Systems

In these lectures we give an overview of nonequilibrium stochastic systems. In particular we discuss in detail two models, the asymmetric exclusion process and a ballistic reaction model, that illustrate many general features of nonequilibrium dynamics: for example coarsening dynamics and nonequilibrium phase transitions. As a secondary theme we shall show how a common mathematical structure, the q-deformed harmonic oscillator algebra, serves to furnish exact results for both systems. Thus the lectures also serve as a gentle introduction to things q-deformed.Comment: 48 pages LaTeX2e with 9 figures and using elsart.cls (included); Lectures at the International Summer School on Fundamental Problems in Statistical Physics X, August-September 2001, Altenberg, Germany. v2 corrects some errors and includes further discussion/reference