Colored Pseudo-Goldstone Bosons and Gauge Boson Pairs

If the electroweak symmetry breaking sector contains colored particles weighing a few hundred GeV, then they will be copiously produced at a hadron supercollider. Colored technipions can rescatter into pairs of gauge bosons. As proposed by Bagger, Dawson, and Valencia, this leads to gauge boson pair rates far larger than in the standard model. In this note we reconsider this mechanism, and illustrate it in a model in which the rates can be reliably calculated. The observation of both an enhanced rate of gauge-boson-pair events and colored particles would be a signal that the colored particles were pseudo-Goldstone bosons of symmetry breaking.Comment: 10 pages, 2 figures not include

Measurement of 0.25-3.2 GeV antiprotons in the cosmic radiation

The balloon-borne Isotope Matter-Antimatter Experiment (IMAX) was flown from Lynn Lake, Manitoba, Canada on 16–17 July 1992. Using velocity and magnetic rigidity to determine mass, we have directly measured the abundances of cosmic ray antiprotons and protons in the energy range from 0.25 to 3.2 GeV. Both the absolute flux of antiprotons and the antiproton/proton ratio are consistent with recent theoretical work in which antiprotons are produced as secondary products of cosmic ray interactions with the interstellar medium. This consistency implies a lower limit to the antiproton lifetime of ∼10 to the 7th yr

Manifestation of spin-charge separation in the dynamic dielectric response of one--dimensional Sr2CuO3

We have determined the dynamical dielectric response of a one-dimensional, correlated insulator by carrying out electron energy-loss spectroscopy on Sr2CuO3 single crystals. The observed momentum and energy dependence of the low-energy features, which correspond to collective transitions across the gap, are well described by an extended one-band Hubbard model with moderate nearest neighbor Coulomb interaction strength. An exciton-like peak appears with increasing momentum transfer. These observations provide experimental evidence for spin-charge separation in the relevant excitations of this compound, as theoretically expected for the one-dimensional Hubbard model.Comment: RevTex, 4 pages+2 figures, to appear in PRL (July 13

High Speed Phase-Resolved 2-d UBV Photometry of the Crab pulsar

We report a phase-resolved photometric and morphological analysis of UBV data of the Crab pulsar obtained with the 2-d TRIFFID high speed optical photometer mounted on the Russian 6m telescope. By being able to accurately isolate the pulsar from the nebular background at an unprecedented temporal resolution (1 \mu s), the various light curve components were accurately fluxed via phase-resolved photometry. Within the $UBV$ range, our datasets are consistent with the existing trends reported elsewhere in the literature. In terms of flux and phase duration, both the peak Full Width Half Maxima and Half Width Half Maxima decrease as a function of photon energy. This is similarly the case for the flux associated with the bridge of emission. Power-law fits to the various light curve components are as follows; \alpha = 0.07 \pm 0.19 (peak 1), \alpha = -0.06 \pm 0.19 (peak 2) and \alpha = -0.44 \pm 0.19 (bridge) - the uncertainty here being dominated by the integrated CCD photometry used to independently reference the TRIFFID data. Temporally, the main peaks are coincident to \le 10 \mu s although an accurate phase lag with respect to the radio main peak is compromised by radio timing uncertainties. The plateau on the Crab's main peak was definitively determined to be \leq 55 \mu s in extent and may decrease as a function of photon energy. There is no evidence for non-stochastic activity over the light curves or within various phase regions, nor is there evidence of anything akin to the giant pulses noted in the radio. Finally, there is no evidence to support the existence of a reported 60 second modulation suggested to be as a consequence of free precession.Comment: 13 pages, 12 figures, accepted for publication in Astronomy & Astrophysic

Implications of the Optical Observations of Neutron Stars

We show that observations of pulsars with pulsed optical emission indicate that the peak flux scales according to the magnetic field strength at the light cylinder. The derived relationships indicate that the emission mechanism is common across all of the observed pulsars with periods ranging from 33ms to 385 ms and ages of 1000-300,000 years. It is noted that similar trends exist for $\gamma$ ray pulsars. Furthermore the model proposed by Pacini (1971) and developed by Pacini and Salvati (1983,1987) still has validity and gives an adequate explanation of the optical phenomena.Comment: 23 pages, 6 figures, accepted for publication in the Astrophysical Journa

Chemical kinetics and photochemical data for use in stratospheric modeling. Evaluation number 6

Evaluated sets of rate constants and photochemical cross sections are presented. The primary application of the data is in the modeling of stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena

Non-gapped Fermi surfaces, quasiparticles and the anomalous temperature dependence of the near-EFE_F electronic states in the CMR oxide La2−2x_{2-2x}Sr1+2x_{1+2x}Mn2_2O7_7 with x=0.36x=0.36

After years of research into colossal magnetoresistant (CMR) manganites using bulk techniques, there has been a recent upsurge in experiments directly probing the electronic states at or near the surface of the bilayer CMR materials La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ using angle-resolved photoemission or scanning probe microscopy. Here we report new, temperature dependent, angle resolved photoemission data from single crystals with a doping level of $x=0.36$. The first important result is that there is no sign of a pseudogap in the charge channel of this material for temperatures below the Curie temperature $T_C$. The second important result concerns the temperature dependence of the electronic states. The temperature dependent changes in the Fermi surface spectra both at the zone face and zone diagonal regions in $k$-space indicate that the coherent quasiparticle weight disappears for temperatures significantly above $T_C$, and that the $k$-dependence of the T-induced changes in the spectra invalidate an interpretation of these data in terms of the superposition of a `universal' metallic spectrum and an insulating spectrum whose relative weight changes with temperature. In this sense, our data are not compatible with a phase separation scenario.Comment: 6 pages, 4 figure

Chemical kinetics and photochemical data for use in stratospheric modeling

Rate constants and photochemical cross sections are presented. The primary application of the data is for modeling of the stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena