Hour-glass magnetic spectrum in a stripe-less insulating transition metal oxide

An hour-glass shaped magnetic excitation spectrum appears to be an universal characteristic of the high-temperature superconducting cuprates. Fluctuating charge stripes or alternative band structure approaches are able to explain the origin of these spectra. Recently, an hour- glass spectrum has been observed in an insulating cobaltate, thus, favouring the charge stripe scenario. Here we show that neither charge stripes nor band structure effects are responsible for the hour-glass dispersion in a cobaltate within the checkerboard charge ordered regime of La2-xSrxCoO4. The search for charge stripe ordering reflections yields no evidence for charge stripes in La1.6Sr0.4CoO4 which is supported by our phonon studies. With the observation of an hour-glass-shaped excitation spectrum in this stripe-less insulating cobaltate, we provide experimental evidence that the hour-glass spectrum is neither necessarily connected to charge stripes nor to band structure effects, but instead, probably intimately coupled to frustration and arising chiral or non-collinear magnetic correlations

Supersymmetric Higgs Boson Decays in the MSSM with Explicit CP Violation

Decays into neutralinos and charginos are among the most accessible supersymmetric decay modes of Higgs particles in most supersymmetric extensions of the Standard Model. In the presence of explicitly CP--violating phases in the soft breaking sector of the theory, the couplings of Higgs bosons to charginos and neutralinos are in general complex. Based on a specific benchmark scenario of CP violation, we analyze the phenomenological impact of explicit CP violation in the Minimal Supersymmetric Standard Model on these Higgs boson decays. The presence of CP--violating phases could be confirmed either directly through the measurement of a CP--odd polarization asymmetry of the produced charginos and neutralinos, or through the dependence of CP--even quantities (branching ratios and masses) on these phases.Comment: 14 pages, latex, 4 eps figure

Abundance of Cosmological Relics in Low-Temperature Scenarios

We investigate the relic density n_\chi of non-relativistic long-lived or stable particles \chi in cosmological scenarios in which the temperature T is too low for \chi to achieve full chemical equilibrium. The case with a heavier particle decaying into \chi is also investigated. We derive approximate solutions for n_\chi(T) which accurately reproduce numerical results when full thermal equilibrium is not achieved. If full equilibrium is reached, our ansatz no longer reproduces the correct temperature dependence of the \chi number density. However, it does give the correct final relic density, to an accuracy of about 3% or better, for all cross sections and initial temperatures.Comment: 26 pages, 8 figures, comments added, to appear in Phys. Rev.

Non-universal gaugino masses from non-singlet F-terms in non-minimal unified models

In phenomenological studies of low-energy supersymmetry, running gaugino masses are often taken to be equal near the scale of apparent gauge coupling unification. However, many known mechanisms can avoid this universality, even in models with unified gauge interactions. One example is an F-term vacuum expectation value that is a singlet under the Standard Model gauge group but transforms non-trivially in the symmetric product of two adjoint representations of a group that contains the Standard Model gauge group. Here, I compute the ratios of gaugino masses that follow from F-terms in non-singlet representations of SO(10) and E_6 and their sub-groups, extending well-known results for SU(5). The SO(10) results correct some long-standing errors in the literature.Comment: 13 page

Drosophila nuclear lamin precursor Dm0 is translated from either of two developmentally regulated mRNA species apparently encoded by a single gene.

A cDNA clone encoding a portion of Drosophila nuclear lamins Dm1 and Dm2 has been identified by screening a lambda-gt11 cDNA expression library using Drosophila lamin-specific monoclonal antibodies. Two different developmentally regulated mRNA species were identified by Northern blot analysis using the initial cDNA as a probe, and full-length cDNA clones, apparently corresponding to each message, have been isolated. In vitro transcription of both full-length cDNA clones in a pT7 transcription vector followed by in vitro translation in wheat germ lysate suggests that both clones encode lamin Dm0, the polypeptide precursor of lamins Dm1 and Dm2. Nucleotide sequence analyses confirm the impression that both cDNA clones code for the identical polypeptide, which is highly homologous with human lamins A and C as well as with mammalian intermediate filament proteins. The two clones differ in their 3'-untranslated regions. In situ hybridization of lamin cDNA clones to Drosophila polytene chromosomes shows only a single locus of hybridization at or near position 25F on the left arm of chromosome 2. Southern blot analyses of genomic DNA are consistent with the notion that a single or only a few highly similar genes encoding Drosophila nuclear lamin Dm0 exist in the genome

The development of experimental techniques for the study of helicopter rotor noise

The features of existing wind tunnels involved in noise studies are discussed. The acoustic characteristics of the MIT low noise open jet wind tunnel are obtained by employing calibration techniques: one technique is to measure the decay of sound pressure with distance in the far field; the other technique is to utilize a speaker, which was calibrated, as a sound source. The sound pressure level versus frequency was obtained in the wind tunnel chamber and compared with the corresponding calibrated values. Fiberglas board-block units were installed on the chamber interior. The free field was increased significantly after this treatment and the chamber cut-off frequency was reduced to 160 Hz from the original designed 250 Hz. The flow field characteristics of the rotor-tunnel configuration were studied by using flow visualization techniques. The influence of open-jet shear layer on the sound transmission was studied by using an Aeolian tone as the sound source. A dynamometer system was designed to measure the steady and low harmonics of the rotor thrust. A theoretical Mach number scaling formula was developed to scale the rotational noise and blade slap noise data of model rotors to full scale helicopter rotors

Three-Body Decays of SUSY Particles

We analyze the decays of charginos, neutralinos, gluinos and the first/second generation squarks in the Minimal Supersymmetric extension of the Standard Model, focusing on the three-body decays in scenarios where the ratio $\tan \beta$ of vacuum expectation values of the two Higgs doublet fields is large. We show that the three-body decays of the next-to-lightest neutralinos (lightest charginos) into $b\bar{b},\tau^+\tau^-$ ($\tau \nu$) final states, where third generation sfermion and Higgs boson exchange diagrams play an important role, are dominant. Furthermore, we show that decays of gluinos into $b\bar{b}$ final states and squark decays into lighter sbottoms through gluino exchange can also have sizeable branching fractions, especially in scenarios where the soft SUSY breaking gaugino mass parameters are not unified at the GUT scale.Comment: 10 pages with 5 figures + axodraw.sty, late

What can(not) be measured with ton-scale dark matter direct detection experiments

Direct searches for dark matter have prompted in recent years a great deal of excitement within the astroparticle physics community, but the compatibility between signal claims and null results of different experiments is far from being a settled issue. In this context, we study here the prospects for constraining the dark matter parameter space with the next generation of ton-scale detectors. Using realistic experimental capabilities for a wide range of targets (including fluorine, sodium, argon, germanium, iodine and xenon), the role of target complementarity is analysed in detail while including the impact of astrophysical uncertainties in a self-consistent manner. We show explicitly that a multi-target signal in future direct detection facilities can determine the sign of the ratio of scalar couplings $f_n/f_p$, but not its scale. This implies that the scalar-proton cross-section is left essentially unconstrained if the assumption $f_p\sim f_n$ is relaxed. Instead, we find that both the axial-proton cross-section and the ratio of axial couplings $a_n/a_p$ can be measured with fair accuracy if multi-ton instruments using sodium and iodine will eventually come online. Moreover, it turns out that future direct detection data can easily discriminate between elastic and inelastic scatterings. Finally, we argue that, with weak assumptions regarding the WIMP couplings and the astrophysics, only the dark matter mass and the inelastic parameter (i.e. mass splitting) may be inferred from the recoil spectra -- specifically, we anticipate an accuracy of tens of GeV (tens of keV) in the measurement of the dark matter mass (inelastic parameter).Comment: 31 pages, 7 figures, 7 table

Crystal and magnetic structure of the oxypnictide superconductor LaO(1-x)FxFeAs: evidence for magnetoelastic coupling

High-resolution and high-flux neutron as well as X-ray powder-diffraction experiments were performed on the oxypnictide series LaO(1-x)FxFeAs with 0<x<0.15 in order to study the crystal and magnetic structure. The magnetic symmetry of the undoped compound corresponds to those reported for ReOFeAs (with Re a rare earth) and for AFe2As2 (A=Ba, Sr) materials. We find an ordered magnetic moment of 0.63(1)muB at 2 K in LaOFeAs, which is significantly larger than the values previously reported for this compound. A sizable ordered magnetic moment is observed up to a F-doping of 4.5% whereas there is no magnetic order for a sample with a F concentration of x=0.06. In the undoped sample, several interatomic distances and FeAs4 tetrahedra angles exhibit pronounced anomalies connected with the broad structural transition and with the onset of magnetism supporting the idea of strong magneto-elastic coupling in this material.Comment: 8 pages, 7 figures, regular articl