Mass mortality and extraterrestrial impacts

The discovery of iridium enrichment at the Cretaceous/Tertiary boundary resulted in formulation of hypothesis of a cometary or asteroid impact as the cause of the biological extinctions at this boundary. Subsequent discoveries of geochemical anomalies at major stratigraphic boundaries like the Precambrian/Cambrian, Permian/Triassic, Middle/Late Jurassic, resulted in the application of similar extraterrestrial impact theories to explain biological changes at these boundaries. Until recently the major physical evidence, as is the location of the impact crater site, to test the impact induced biological extinction was lacking. The diameter of such a crater would be in the range of 60 to 100 km. The recent discovery of the first impact crater in the ocean provide the first opportunity to test the above theory. The crater, named Montagnais and located on the outer shelf off Nova Scotia, Canada, has a minimum diameter of 42 km, with some evidence to a diameter of more than 60 km. At the Montagnais impact site, micropaleontological analysis of the uppermost 80 m of the fall-back breccia represented by a mixture of pre-impact sediments and basement rocks which fills the crater and of the basal 50 m of post-impact marine sediments which overly the impact deposits, revealed presence of diversified foraminiferal and nannoplankton assemblages. The sediments which are intercalated within the uppermost part of the fall-back breccia, had to be deposited before the meteorite impact. The post-impact deposits were laid down almost immediately after the impact as also supported by the micropaleontological data. In conclusion, micropaleontological studies of sediments from the first submarine impact crater site identified in the ocean did not reveal any mass extinction or significant biological changes at the impact site or in the proximal deep ocean basin

Electronic structure of unidirectional superlattices in crossed electric and magnetic fields and related terahertz oscillations

We have studied Bloch electrons in a perfect unidirectional superlattice subject to crossed electric and magnetic fields, where the magnetic field is oriented ``in-plane'', i.e. in parallel to the sample plane. Two orientation of the electric field are considered. It is shown that the magnetic field suppresses the intersubband tunneling of the Zener type, but does not change the frequency of Bloch oscillations, if the electric field is oriented perpendicularly to both the sample plane and the magnetic field. The electric field applied in-plane (but perpendicularly to the magnetic field) yields the step-like electron energy spectrum, corresponding to the magnetic-field-tunable oscillations alternative to the Bloch ones.Comment: 7 pages, 1 figure, accepted for publication in Phys. Rev.

Vortex Plasma in a Superconducting Film with Magnetic Dots

We consider a superconducting film, placed upon a magnetic dot array. Magnetic moments of the dots are normal to the film and randomly oriented. We determine how the concentration of the vortices in the film depends on the magnetic moment of a dot at low temperatures. The concentration of the vortices, bound to the dots, is proportional to the density of the dots and depends on the magnetization of a dot in a step-like way. The concentration of the unbound vortices oscillates about a value, proportional to the magnetic moment of the dots. The period of the oscillations is equal to the width of a step in the concentration of the bound vortices.Comment: RevTeX, 4 page

Finite size effects in quantum field theories with boundary from scattering data

We derive a relation between leading finite size corrections for a 1+1 dimensional quantum field theory on a strip and scattering data, which is very similar in spirit to the approach pioneered by Luscher for periodic boundary conditions. The consistency of the results is tested both analytically and numerically using thermodynamic Bethe Ansatz, Destri-de Vega nonlinear integral equation and classical field theory techniques. We present strong evidence that the relation between the boundary state and the reflection factor one-particle couplings, noticed earlier by Dorey et al. in the case of the Lee-Yang model extends to any boundary quantum field theory in 1+1 dimensions.Comment: 24 pages, 1 eps figure. Clarifying comments and a reference adde

Large distance behaviour of light cone operator product in perturbative and nonperturbative QCD regimes

We evaluate the coordinate space dependence of the matrix elements of the commutator of the electromagnetic and gluon currents in the vicinity of the light-cone but at large distances within the parton model, DGLAP, the resummation approaches to the small x behaviour of DIS processes, and for the Unitarity Bound. We find that an increase of the commutator with relative distance $py$ as $\propto (py)f(py,y^2=t^2-r^2)$ is the generic property of QCD at small but fixed space-time interval $y^2=t^2-r^2$ in perturbative and nonperturbative QCD regimes. We explain that the factor $py$ follows within the dipole model (QCD factorization theorem) from the properties of Lorents transformation. The increase of $f(r)$ disappeares at central impact parameters if cross section of DIS may achieve the Unitarity Limit. We argue that such long range forces are hardly consistent with thermodynamic equilibrium while a Unitarity Limit may signal equilibration. Possible implications of this new long range interaction are briefly discussed.Comment: 23 page

Nemesis Reconsidered

The hypothesis of a companion object (Nemesis) orbiting the Sun was motivated by the claim of a terrestrial extinction periodicity, thought to be mediated by comet showers. The orbit of a distant companion to the Sun is expected to be perturbed by the Galactic tidal field and encounters with passing stars, which will induce variation in the period. We examine the evidence for the previously proposed periodicity, using two modern, greatly improved paleontological datasets of fossil biodiversity. We find that there is a narrow peak at 27 My in the cross-spectrum of extinction intensity time series between these independent datasets. This periodicity extends over a time period nearly twice that for which it was originally noted. An excess of extinction events are associated with this periodicity at 99% confidence. In this sense we confirm the originally noted feature in the time series for extinction. However, we find that it displays extremely regular timing for about 0.5 Gy. The regularity of the timing compared with earlier calculations of orbital perturbation would seem to exclude the Nemesis hypothesis as a causal factor.Comment: 10 pages, 2 figures, accepted for publication in Monthly Notices of the Royal Astronomical Societ

Orthogonal Linear Combinations of Gaussian Type Orbitals

The set of Gaussian Type Orbitals g(n1,n2,n3) of order (n+1)(n+2)/2, of common n=n1+n2+n3<=7, common center and exponential, is customized to define a set of 2n+1 linear combinations t(n,m) (-n<=m<=n) such that each t(n,m) depends on the azimuthal and polar angle of the spherical coordinate system like the real or imaginary part of the associated Spherical Harmonic. (Results cover both Hermite and Cartesian Gaussian Type Orbitals.) Overlap, kinetic energy and Coulomb energy matrix elements are presented for generalized basis functions of the type r^s*t(n,m) (s=0,2,4,...). In addition, normalization integrals int |g(n1,n2,n3)|d^3r are calculated up to n=7 and normalization integrals int |r^s*t(n,m)|d^3r up to n=5.Comment: 13 pages, no figures, REVTeX4. Corrected eqs. (23) and (C4

LEVEL CORRELATIONS DRIVEN BY WEAK LOCALIZATION IN 2-D SYSTEMS

We consider the two-level correlation function in two-dimensional disordered systems. In the non-ergodic diffusive regime, at energy $\epsilon>E_{c}$ ($E_{c}$ is the Thouless energy), it is shown to be completely determined by the weak localization effects, thus being extremely sensitive to time-reversal and spin symmetry breaking: it decreases drastically in the presence of magnetic field or magnetic impurities and changes its sign in the presence of a spin-orbit interaction. In contrast to this, the variance of the levels number fluctuations is shown to be almost unaffected by the weak localization effects.Comment: 4 pages, 2 figures, in self-ectracting uuencoded file, submitted to Phys. Rev. Letters

Equation of state of a strongly magnetized hydrogen plasma

The influence of a constant uniform magnetic field on the thermodynamic properties of a partially ionized hydrogen plasma is studied. Using the method of Green' s function various interaction contributions to the thermodynamic functions are calculated. The equation of state of a quantum magnetized plasma is presented within the framework of a low density expansion up to the order e^4 n^2 and, additionally, including ladder type contributions via the bound states in the case of strong magnetic fields (2.35*10^{5} T << B << 2.35*10^{9} T). We show that for high densities (n=10^{27-30} m^{-3}) and temperatures T=10^5 - 10^6 K typical for the surface of neutron stars nonideality effects as, e.g., Debye screening must be taken into account.Comment: 12 pages, 2 Postscript figures. uses revtex, to appear in Phys. Rev.