Non-Abelian Monopoles as the Origin of Dark Matter

We suggest that dark matter may be partially constituted by a dilute 't Hooft-Polyakov monopoles gas. We reach this conclusion by using the Georgi-Glashow model coupled to a dual kinetic mixing term $F{\tilde {\cal G}}$ where $F$ is the electromagnetic field and ${\cal G}$ the 't Hooft tensor. We show that these monopoles carry both (Maxwell) electric and (Georgi-Glashow) magnetic charges and the electric charge quantization condition is modified in terms of a dimensionless real parameter. This parameter could be determined from milli-charged particle experiments.Comment: 5 pp, no figure

The Survival of Planetary Nebulae in the Intracluster Medium

The stellar population stripped from galaxies in clusters evolve under the extreme conditions imposed by the intracluster (IC) medium. Intracluster stars generally suffer very high systemic velocities, and evolve within a rarefied and extremely hot IC medium. We present numerical simulations which aim to explore the evolution and survival of IC Asymptotic Giant Branch (AGB) envelopes and Planetary Nebula (PN) shells. Our models reflect the evolution of a low-mass star under the observed conditions in the Virgo IC medium. We find that the integrated hydrogen-recombination line emission of a PN is dominated by the inner dense shell, whose evolution is unaffected by the environment. Ram pressure stripping affects mainly the outermost IC PN shell, which hardly influences the emission when the PN is observed as a point source. More importantly, we find that a PN with progenitor mass of 1 Msun fades to ~30% and 10% of its maximum emission, in 5,000 and 10,000 yr respectively, disclosing an actual PN lifetime t_PN several times shorter to what is usually adopted (25,000 yr). This result affects the theoretical calculation of the luminosity-specific density of IC PNe, which scales with t_PN. For t_PN=10,000 yr, our more conservative estimate, we obtain that the luminosity-specific density of PNe is in fair agreement with the value obtained from Red Giants. With our more realistic PN lifetime we infer a higher fraction (above 15%) of IC starlight in the Virgo core than current estimates.Comment: Accepted for publication in the Astrophysical Journal 14 pages, including 2 figure

The Circumstellar Extinction of Planetary Nebulae

We analyze the dependence of circumstellar extinction on core mass for the brightest planetary nebulae (PNe) in the Magellanic Clouds and M31. We show that in all three galaxies, a statistically significant correlation exists between the two quantities, such that high core mass objects have greater extinction. We model this behavior, and show that the relation is a simple consequence of the greater mass loss and faster evolution times of high mass stars. The relation is important because it provides a natural explanation for the invariance of the [O III] 5007 planetary nebula luminosity function (PNLF) with population age: bright Population I PNe are extinguished below the cutoff of the PNLF. It also explains the counter-intuitive observation that intrinsically luminous Population I PNe often appear fainter than PNe from older, low-mass progenitors.Comment: 12 pages, 2 figures, accepted for ApJ, April 10, 199

The structures underlying soliton solutions in integrable hierarchies

We point out that a common feature of integrable hierarchies presenting soliton solutions is the existence of some special ``vacuum solutions'' such that the Lax operators evaluated on them, lie in some abelian subalgebra of the associated Kac-Moody algebra. The soliton solutions are constructed out of those ``vacuum solitons'' by the dressing transformation procedure.Comment: Talk given at the I Latin American Symposium on High Energy Physics, I SILAFAE, Merida, Mexico, November/96, 5 pages, LaTeX, needs aipproc.tex, aipproc.sty, aipproc.cls, available from ftp://ftp.aip.org/ems/tex/macros/proceedings/6x9

Chiral Anomaly Beyond Lorentz Invariance

The chiral anomaly in the context of an extended standard model with minimal Lorentz invariance violation is studied. Taking into account bounds from measurements of the speed of light, we argue that the chiral anomaly and its consequences are general results valid even beyond the relativistic symmetry.Comment: Final version. To be published in PR

Shot Noise Enhancement in Resonant Tunneling Structures in a Magnetic Field

We have observed that the shot noise of tunnel current, I, in GaSb-AlSb-InAs-AlSb-GaSb double-barrier structure under a magnetic field can exceed 2qI. The measurements were done at T=4K in fields up to 5T parallel to the current. The noise enhancement occurred at each of the several negative-differential conductance regions induced by the tunneling of holes through Landau levels in the InAs quantum well. The amount of the enhancement increased with the strength of the negative conductance and reached values up to 8qI. These results are explained qualitatively by fluctuations of the density of states in the well, but point out the need for a detailed theory of shot noise enhancement in resonant tunneling devices.Comment: 4 pages, RevTex, 3 figure

Planetary nebulae and stellar kinematics in the flattened elliptical galaxy NGC 1344

We present photometric and kinematic information obtained by measuring 197 planetary nebulae (PNs) discovered in the flattened Fornax elliptical galaxy NGC 1344 (also known as NGC 1340) with an on-band, off-band, grism + on-band filter technique. We build the PN luminosity function (PNLF) and use it to derive a distance modulus m-M=31.4, slightly smaller than, but in good agreement with, the surface brightness fluctuation distance. The PNLF also provides an estimate of the specific PN formation rate: 6x10^-12 PNs per year per solar luminosity. Combining the positional information from the on-band image with PN positions measured on the grism + on-band image, we can measure the radial velocities of 195 PNs, some of them distant more than 3 effective radii from the center of NGC 1344. We complement this data set with stellar kinematics derived from integrated spectra along the major and minor axes, and parallel to the major axis of NGC 1344. The line-of-sight velocity dispersion profile indicates the presence of a dark matter halo around this galaxy.Comment: 45 pages, 18 figures, accepted for publication in Ap