"Single-cycle" ionization effects in laser-matter interaction

We investigate numerically effects related to ``single-cycle'' ionization of dense matter by an ultra-short laser pulse. The strongly non-adiabatic response of electrons leads to generation of a megagauss steady magnetic field in laser-solid interaction. By using two-beam interference, it is possible to create periodic density structures able to trap light and to generate relativistic ionization frontsComment: 12 pages, 6 figures, to be published in Laser and Particle Beam

The generation of images of surface structures by laser-accelerated protons

Ion acceleration by lasers is one of the most important innovations in laser-plasma research in recent years. A mechanism that has gained great attention due to the remarkable properties of the accelerated beam is laser acceleration of protons from the rear surface of solid targets. A striking prediction is that these protons are capable of generating images of micro-structures present on this surface. These images might be useful to measure properties of the accelerated beam. In this article, we address the physics of the generation of images of surface structures imprinted into the target back surface with laser-accelerated protons

Three-dimensional Gross-Pitaevskii solitary waves in optical lattices: stabilization using the artificial quartic kinetic energy induced by lattice shaking

In this Letter, we show that a three-dimensional Bose-Einstein solitary wave can become stable if the dispersion law is changed from quadratic to quartic. We suggest a way to realize the quartic dispersion, using shaken optical lattices. Estimates show that the resulting solitary waves can occupy as little as $\sim 1/20$-th of the Brillouin zone in each of the three directions and contain as many as $N = 10^{3}$ atoms, thus representing a \textit{fully mobile} macroscopic three-dimensional object.Comment: 8 pages, 1 figure, accepted in Phys. Lett.

Primordial helium recombination. I. Feedback, line transfer, and continuum opacity

Precision measurements of the cosmic microwave background temperature anisotropy on scales ℓ>500 will be available in the near future. Successful interpretation of these data is dependent on a detailed understanding of the damping tail and cosmological recombination of both hydrogen and helium. This paper and two companion papers are devoted to a precise calculation of helium recombination. We discuss several aspects of the standard recombination picture, and then include feedback, radiative transfer in He i lines with partial redistribution, and continuum opacity from H i photoionization. In agreement with past calculations, we find that He ii recombination proceeds in Saha equilibrium, whereas He i recombination is delayed relative to Saha due to the low rates connecting excited states of He i to the ground state. However, we find that at z<2200 the continuum absorption by the rapidly increasing H i population becomes effective at destroying photons in the He i 21Po-11S line, causing He i recombination to finish around z≃1800, much earlier than previously estimated

A Signature of Cosmic Strings Wakes in the CMB Polarization

We calculate a signature of cosmic strings in the polarization of the cosmic microwave background (CMB). We find that ionization in the wakes behind moving strings gives rise to extra polarization in a set of rectangular patches in the sky whose length distribution is scale-invariant. The length of an individual patch is set by the co-moving Hubble radius at the time the string is perturbing the CMB. The polarization signal is largest for string wakes produced at the earliest post-recombination time, and for an alignment in which the photons cross the wake close to the time the wake is created. The maximal amplitude of the polarization relative to the temperature quadrupole is set by the overdensity of free electrons inside a wake which depends on the ionization fraction $f$ inside the wake. The signal can be as high as $0.06 {\rm \mu K}$ in degree scale polarization for a string at high redshift (near recombination) and a string tension $\mu$ given by $G \mu = 10^{-7}$.Comment: 8 pages, 3 figure

Brueckner-Goldstone perturbation theory for the half-filled Hubbard model in infinite dimensions

We use Brueckner-Goldstone perturbation theory to calculate the ground-state energy of the half-filled Hubbard model in infinite dimensions up to fourth order in the Hubbard interaction. We obtain the momentum distribution as a functional derivative of the ground-state energy with respect to the bare dispersion relation. The resulting expressions agree with those from Rayleigh-Schroedinger perturbation theory. Our results for the momentum distribution and the quasi-particle weight agree very well with those obtained earlier from Feynman-Dyson perturbation theory for the single-particle self-energy. We give the correct fourth-order coefficient in the ground-state energy which was not calculated accurately enough from Feynman-Dyson theory due to the insufficient accuracy of the data for the self-energy, and find a good agreement with recent estimates from Quantum Monte-Carlo calculations.Comment: 15 pages, 8 fugures, submitted to JSTA

Surface Oscillations in Overdense Plasmas Irradiated by Ultrashort Laser Pulses

The generation of electron surface oscillations in overdense plasmas irradiated at normal incidence by an intense laser pulse is investigated. Two-dimensional (2D) particle-in-cell simulations show a transition from a planar, electrostatic oscillation at $2\omega$, with $\omega$ the laser frequency, to a 2D electromagnetic oscillation at frequency $\omega$ and wavevector $k>\omega/c$. A new electron parametric instability, involving the decay of a 1D electrostatic oscillation into two surface waves, is introduced to explain the basic features of the 2D oscillations. This effect leads to the rippling of the plasma surface within a few laser cycles, and is likely to have a strong impact on laser interaction with solid targets.Comment: 9 pages (LaTeX, Revtex4), 4 GIF color figures, accepted for publication in Phys. Rev. Let

Speakable and unspeakable in cosmology: dark matter vs. gravitational self energies. Hubble's constant, the cosmological term and all that

The inadequacy of the present cosmological picture is underlined. The central issue of energy and particles-photons number conservation is addressed. It is shown that consideration of gravitational self energy is paramount both for matter and for radiation to bring present data estimates of matter and radiation density and the radius of the universe towards agreement with the Planck scale quantities from which it should have consistently evolved. Particle creation is proven to play a fundamental role in the evolution of the Universe. It is argued that we might be living inside an expanding black hole