Correlation effects in total energy of transition metals and related properties

We present an accurate implementation of total energy calculations into the local density approximation plus dynamical mean-field theory (LDA+DMFT) method. The electronic structure problem is solved through the full potential linear Muffin-Tin Orbital (FP-LMTO) and Korringa-Kohn-Rostoker (FP-KKR) methods with a perturbative solver for the effective impurity suitable for moderately correlated systems. We have tested the method in detail for the case of Ni and investigated the sensitivity of the results to the computational scheme and to the complete self-consistency. It is demonstrated that the LDA+DMFT method can resolve a long-standing controversy between the LDA/GGA density functional approach and experiment for equilibrium lattice constant and bulk modulus of Mn.Comment: 14 pages, 5 figure

Neutrino production through hadronic cascades in AGN accretion disks

We consider the production of neutrinos in active galactic nuclei (AGN) through hadronic cascades. The initial, high energy nucleons are accelerated in a source above the accretion disk around the central black hole. From the source, the particles diffuse back to the disk and initiate hadronic cascades. The observable output from the cascade are electromagnetic radiation and neutrinos. We use the observed diffuse background X-ray luminosity, which presumably results {}from this process, to predict the diffuse neutrino flux close to existing limits from the Frejus experiment. The resulting neutrino spectrum is $E^{-2}$ down to the \GeV region. We discuss modifications of this scenario which reduce the predicted neutrino flux.Comment: 12 Pages, LaTeX, TK 92 0

Absolute calibration of the LOPES antenna system

Radio emission in extensive air showers arises from an interaction with the geomagnetic field and is subject of theoretical studies. This radio emission has advantages for the detection of high energy cosmic rays compared to secondary particle or fluorescence measurement methods. Radio antennas like the LOPES30 antenna system are suited to investigate this emission process by detecting the radio pulses. The characteristic observable parameters like electric field strength and pulse length require a calibration which was done with a reference radio source resulting in an amplification factor representing the system behavior in the environment of the KASCADE-Grande experiment. Knowing the amplification factor and the gain of the LOPES antennas LOPES30 is calibrated absolutely for systematic analyses of the radio emission.Comment: 5 pages, Proceedings of International Workshop on Acoustic and Radio EeV Neutrino detection Activities: ARENA, May 17-19, 2005, DESY Zeuthe

Spinning compact binary inspiral II: Conservative angular dynamics

We establish the evolution equations of the set of independent variables characterizing the 2PN rigorous conservative dynamics of a spinning compact binary, with the inclusion of the leading order spin-orbit, spin-spin and mass quadrupole - mass monopole effects, for generic (noncircular, nonspherical) orbits. More specifically, we give a closed system of first order ordinary differential equations for the orbital elements of the osculating ellipse and for the angles characterizing the spin orientations with respect to the osculating orbit. We also prove that (i) the relative angle of the spins stays constant for equal mass black holes, irrespective of their orientation, and (ii) the special configuration of equal mass black holes with equal, but antialigned spins, both laying in the plane of motion (leading to the largest recoil found in numerical simulations) is preserved at 2PN level of accuracy, with leading order spin-orbit, spin-spin and mass quadrupolar contributions included.Comment: v2: 19 pages, extended, improved, published versio

Self-consistency over the charge-density in dynamical mean-field theory: a linear muffin-tin implementation and some physical implications

We present a simple implementation of the dynamical mean-field theory approach to the electronic structure of strongly correlated materials. This implementation achieves full self-consistency over the charge density, taking into account correlation-induced changes to the total charge density and effective Kohn-Sham Hamiltonian. A linear muffin-tin orbital basis-set is used, and the charge density is computed from moments of the many body momentum-distribution matrix. The calculation of the total energy is also considered, with a proper treatment of high-frequency tails of the Green's function and self-energy. The method is illustrated on two materials with well-localized 4f electrons, insulating cerium sesquioxide Ce2O3 and the gamma-phase of metallic cerium, using the Hubbard-I approximation to the dynamical mean-field self-energy. The momentum-integrated spectral function and momentum-resolved dispersion of the Hubbard bands are calculated, as well as the volume-dependence of the total energy. We show that full self-consistency over the charge density, taking into account its modification by strong correlations, can be important for the computation of both thermodynamical and spectral properties, particularly in the case of the oxide material.Comment: 20 pages, 6 figures (submitted in The Physical Review B

Spectroscopic signatures of a bandwidth-controlled Mott transition at the surface of 1T-TaSe2_2

High-resolution angle-resolved photoemission (ARPES) data show that a metal-insulator Mott transition occurs at the surface of the quasi-two dimensional compound TaSe$_2$. The transition is driven by the narrowing of the Ta $5d$ band induced by a temperature-dependent modulation of the atomic positions. A dynamical mean-field theory calculation of the spectral function of the half-filled Hubbard model captures the main qualitative feature of the data, namely the rapid transfer of spectral weight from the observed quasiparticle peak at the Fermi surface to the Hubbard bands, as the correlation gap opens up.Comment: 4 pages, 4 figures; one modified figure, added referenc

Contact Discontinuities in Models of Contact Binaries Undergoing Thermal Relaxation Oscillations

In this paper we pursue the suggestion by Shu, Lubow & Anderson (1979) and Wang (1995) that contact discontinuity (DSC) may exist in the secondary in the expansion TRO (thermal relaxation oscillation) state. It is demonstrated that there is a mass exchange instability in some range of mass ratio for the two components. We show that the assumption of {\it constant} volume of the secondary should be relaxed in DSC model. For {\it all} mass ratio the secondary alway satisfies the condition that no mass flow returns to the primary through the inner Lagrangian point. The secondary will expand in order to equilibrate the interaction between the common convective envelope and the secondary. The contact discontinuity in contact binary undergoing thermal relaxation does not violate the second law of thermodynamics. The maintaining condition of contact discontinuity is derived in the time-dependent model. It is desired to improve the TRO model with the advanced contact discontinuity layer in future detailed calculations.Comment: 5 pages in emulateapj, 1 figur

Detection and imaging of atmospheric radio flashes from cosmic ray air showers

The nature of ultrahigh-energy cosmic rays (UHECRs) at energies >10^20 eV remains a mystery. They are likely to be of extragalactic origin, but should be absorbed within ~50 Mpc through interactions with the cosmic microwave background. As there are no sufficient powerful accelerators within this distance from the Galaxy, explanations for UHECRs range from unusual astrophysical sources to exotic string physics. Also unclear is whether UHECRs consist of protons, heavy nuclei, neutrinos or gamma-rays. To resolve these questions, larger detectors with higher duty cycles and which combine multiple detection techniques are needed. Radio emission from UHECRs, on the other hand, is unaffected by attenuation, has a high duty cycle, gives calorimetric measurements and provides high directional accuracy. Here we report the detection of radio flashes from cosmic-ray air showers using low-cost digital radio receivers. We show that the radiation can be understood in terms of the geosynchrotron effect. Our results show that it should be possible to determine the nature and composition of UHECRs with combined radio and particle detectors, and to detect the ultrahigh-energy neutrinos expected from flavour mixing.Comment: Nature, May 19, 2005 issue (PDF, 14 pages), http://www.astro.ru.nl/lopes/?loc=publication

Cosmic Ray Protons and Magnetic Fields in Clusters of Galaxies and their Cosmological Consequences

The masses of clusters of galaxies estimated by gravitational lensing exceed in many cases the mass estimates based on hydrostatic equilibrium. This may suggest the existence of nonthermal pressure. We ask if radio galaxies can heat and support the cluster gas with injected cosmic ray protons and magnetic field densities, which are permitted by Faraday rotation and gamma ray observations of clusters of galaxies. We conclude that they are powerful enough to do this within a cluster radius of roughly 1 Mpc. If present, nonthermal pressures could lead to a revised estimate of the ratio of baryonic mass to total mass, and the apparent baryonic overdensity in clusters would disappear. In consequence, $\Omega_{\rm cold}$, the clumping part of the cosmological density $\Omega_{o}$, would be larger than $0.4\,h_{50}^{-1/2}$.Comment: Accepted by ApJ, 16 pages, LaTeX, 2 figures, epsfig.sty, aaspp4.st