The Pierre Auger Project and Enhancements

The current status of the scientific results of the Auger Observatory will be discussed which include spectrum, anisotropy in arrival directions, chemical composition analyses, and limits on neutrino and photon fluxes. A review of the Observatory detection systems will be presented. Auger has started the construction of its second phase which encompasses antennae for radio detection of cosmic rays, high-elevation telescopes, and surface plus muon detectors. Details will be presented on the latter, AMIGA (Auger Muons and Infill for the Ground Array), an Auger project consisting of 85 detector pairs each one composed of a surface water-Cherenkov detector and a buried muon counter. The detector pairs are arranged in an array with spacings of 433 and 750 m in order to perform a detailed study of the 10^17 eV to 10^19 eV spectrum region. Preliminary results on the performance of the 750 m array of surface detectors and the first muon counter prototype will be presented.Comment: 10 pages, 8 figures, VIII Latin American Symposium on Nuclear Physics and Applications December 15-19, 2009, Santiago, Chil

Non-demolition measurements of observables with general spectra

It has recently been established that, in a non-demolition measurement of an observable $\mathcal{N}$ with a finite point spectrum, the density matrix of the system approaches an eigenstate of $\mathcal{N}$, i.e., it "purifies" over the spectrum of $\mathcal{N}$. We extend this result to observables with general spectra. It is shown that the spectral density of the state of the system converges to a delta function exponentially fast, in an appropriate sense. Furthermore, for observables with absolutely continuous spectra, we show that the spectral density approaches a Gaussian distribution over the spectrum of $\mathcal{N}$. Our methods highlight the connection between the theory of non-demolition measurements and classical estimation theory.Comment: 22 page

Precision spectroscopy of the molecular ion HD+: control of Zeeman shifts

Precision spectroscopy on cold molecules can potentially enable novel tests of fundamental laws of physics and alternative determination of some fundamental constants. Realizing this potential requires a thorough understanding of the systematic effects that shift the energy levels of molecules. We have performed a complete ab initio calculation of the magnetic field effects for a particular system, the heteronuclear molecular hydrogen ion HD+. Different spectroscopic schemes have been considered, and numerous transitions, all accessible by modern radiation sources and exhibiting well controllable or negligible Zeeman shift, have been found to exist. Thus, HD+ is a perspective candidate for determination of the ratio of electron-to-nuclear reduced mass, and for tests of its time-independence.Comment: A Table added, references and figures update

Sympathetic cooling of 4^4He+^+ ions in a radiofrequency trap

We have generated Coulomb crystals of ultracold $^4$He$^+$ ions in a linear radiofrequency trap, by sympathetic cooling via laser--cooled $^9$Be$^+$. Stable crystals containing up to 150 localized He$^+$ ions at $\sim$20 mK were obtained. Ensembles or single ultracold He$^+$ ions open up interesting perspectives for performing precision tests of QED and measurements of nuclear radii. The present work also indicates the feasibility of cooling and crystallizing highly charged atomic ions using $^9$Be$^+$ as coolant.Comment: 4 pages, 2 figure

Polaron Crystallization and Melting: Effects of the Long-Range Coulomb Forces

On examining the stability of a Wigner crystal in an ionic dielectric, two competitive effects due to the polaron formation are found to be important: (i) the screening of the Coulomb force, which destabilizes the crystal, compensated by (ii) the increase of the carrier mass (polaron mass). The competition between the two effects is carefully studied, and the quantum melting of the polaronic Wigner crystal is examined by varying the density at zero temperature. By calculating the quantum fluctuations of both the electron and the polarization, we show that there is a competition between the dissociation of the polarons at the insulator-to-metal transition (IMT), and a melting towards a polaron liquid. We find that at strong coupling, a liquid state of dielectric polarons cannot exist, and the IMT is driven by the polaron dissociation. Next, taking into account the dipolar interactions between localized carriers, we show that these are responsible for an instability of the transverse vibrational modes of the polaronic Wigner crystal as the density increases. This provides a new mechanism for the IMT in doped dielectrics, which yields interesting dielectric properties below and beyond the transition. An optical signature of such a mechanism for the IMT is provided.Comment: 10 pages, 3 figures, to be published in Int.J.Mod.Phys.

Spectral Geometry of Heterotic Compactifications

The structure of heterotic string target space compactifications is studied using the formalism of the noncommutative geometry associated with lattice vertex operator algebras. The spectral triples of the noncommutative spacetimes are constructed and used to show that the intrinsic gauge field degrees of freedom disappear in the low-energy sectors of these spacetimes. The quantum geometry is thereby determined in much the same way as for ordinary superstring target spaces. In this setting, non-abelian gauge theories on the classical spacetimes arise from the K-theory of the effective target spaces.Comment: 14 pages LaTe

Design of the Pluto Event Generator

We present the design of the simulation package Pluto, aimed at the study of hadronic interactions at SIS and FAIR energies. Its main mission is to offer a modular framework with an object-oriented structure, thereby making additions such as new particles, decays of resonances, new models up to modules for entire changes easily applicable. Overall consistency is ensured by a plugin- and distribution manager. Particular features are the support of a modular structure for physics process descriptions, and the possibility to access the particle stream for on-line modifications. Additional configuration and self-made classes can be attached by the user without re-compiling the package, which makes Pluto extremely configurable.Comment: Presented at the 17th International Conference on Computing in High Energy and Nuclear Physic

Comparing conductance quantization in quantum wires and Quantum Hall systems

We propose a new calculation of the DC conductance of a 1-dimensional electron system described by the Luttinger model. Our approach is based on the ideas of Landauer and B\"{u}ttiker and on the methods of current algebra. We analyse in detail the way in which the system can be coupled to external reservoirs. This determines whether the conductance is renormalized or not. We show that although a quantum wire and a Fractional Quantum Hall system are described by the same effective theory, their coupling to external reservoirs is different. As a consequence, the conductance in the wire is quantized in integer units of $e^2/h$ per spin orientation whereas the Hall conductance allows for fractional quantization.Comment: 3 pages, LaTe