Dark Matter Seeding in Neutron Stars

We present a mechanism that may seed compact stellar objects with stable lumps of quark matter, or {\it strangelets}, through the self-annihilation of gravitationally accreted WIMPs. We show that dark matter particles with masses above a few GeV may provide enough energy in the nuclear medium for quark deconfinement and subsequent strangelet formation. If this happens this effect may then trigger a partial or full conversion of the star into a strange star. We set a new limit on the WIMP mass in the few-GeV range that seems to be consistent with recent indications in dark matter direct detection experiments.Comment: 3 pages, 1 figure. Prepared for 19th Particles and Nuclei International Conference (PANIC 2011), Boston, USA 25-29 Jul 201

Ages of Elliptical Galaxies: Single versus Multi Population Interpretation

New calibrations of spectrophotometric indices of elliptical galaxies as functions of spectrophotometric indices are presented, permitting estimates of mean stellar population ages and metallicities. These calibrations are based on evolutionary models including a two-phase interstellar medium, infall and a galactic wind.Free parameters were fixed by requiring that models reproduce the mean trend of data in the color-magnitude diagram as well as in the plane of indices Hbeta-Mg2 and Mg2-. To improve the location of faint ellipticals(MB > -20) in the Hbeta-Mg2 diagram, down-sizing was introduced. An application of our calibrations to a sample of ellipticals and a comparison with results derived from single stellar population models is given. Our models indicate that mean population ages span an interval of 7-12 Gyr and are correlated with metallicities, which range from approximately half up to three times solar.Comment: 10 pages and 6 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa

A late-time transition in the equation of state versus Lambda-CDM

We study a model of the dark energy which exhibits a rapid change in its equation of state w(z), such as occurs in vacuum metamorphosis. We compare the model predictions with CMB, large scale structure and supernova data and show that a late-time transition is marginally preferred over standard Lambda-CDM.Comment: 4 pages, 1 figure, to appear in the proceedings of XXXVIIth Rencontres de Moriond, "The Cosmological Model", March 200

Measuring the Radiative Histories of QSOs with the Transverse Proximity Effect

Since the photons that stream from QSOs alter the ionization state of the gas they traverse, any changes to a QSO's luminosity will produce outward-propagating ionization gradients in the surrounding intergalactic gas. This paper shows that at redshift z~3 the gradients will alter the gas's Lyman-alpha absorption opacity enough to produce a detectable signature in the spectra of faint background galaxies. By obtaining noisy (S:N~4) low-resolution (~7A) spectra of a several dozen background galaxies in an R~20' field surrounding an isotropically radiating 18th magnitude QSO at z=3, it should be possible to detect any order-of-magnitude changes to the QSO's luminosity over the previous 50--100 Myr and to measure the time t_Q since the onset of the QSO's current luminous outburst with an accuracy of ~5 Myr for t_Q<~50 Myr. Smaller fields-of-view are acceptable for shorter QSO lifetimes. The major uncertainty, aside from cosmic variance, will be the shape and orientation of the QSO's ionization cone. This can be determined from the data if the number of background sources is increased by a factor of a few. The method will then provide a direct test of unification models for AGN.Comment: Accepted for publication in the ApJ. 16 page

Out-of-plane thermopower of strongly correlated layered systems: an application to Bi_2(Sr,La)_2CaCu_2O_{8+\delta}

We calculate the out-of-plane thermopower in a quasi-two dimensional system, and argue that this quantity is an effective probe of the asymmetry of the single-particle spectral function. We find that the temperature and doping dependence of the out-of-plane thermopower in Bi_2(Sr,La)_2CaCu_2O_{8+\delta} single crystals is broadly consistent with the behavior of the spectral function determined from ARPES and tunneling experiments. We also investigate the relationship between out-of-plane thermopower and entropy in a quasi-two dimensional material. We present experimental evidence that at moderate temperatures, there is a qualitative correspondence between the out-of-plane thermopower in Bi_2(Sr,La)_2CaCu_2O_{8+\delta}, and the entropy obtained from specific heat measurements. Finally, we argue that the derivative of the entropy with respect to particle number may be the more appropriate quantity to compare with the thermopower, rather than the entropy per particle.Comment: 11 pages, 5 figures. v2: substantially rewritten, including a more detailed analysis of the relationship between thermopower and entrop

The AGN-starburst connection, Galactic superwinds, and M_BH - sigma

Recent observations of young galaxies at redshifts z ~ 3 have revealed simultaneous AGN and starburst activity, as well as galaxy-wide superwinds. I show that there is probably a close connection between these phenomena by extending an earlier treatment of the M_BH - sigma relation (King, 2003). As the black hole grows, an outflow drives a shell into the surrounding gas. This stalls after a dynamical time at a size determined by the hole's current mass and thereafter grows on the Salpeter timescale. The gas trapped inside this bubble cools and forms stars and is recycled as accretion and outflow. The consequent high metallicity agrees with that commonly observed in AGN accretion. Once the hole reaches a critical mass this region attains a size such that the gas can no longer cool efficiently. The resulting energy-driven flow expels the remaining gas as a superwind, fixing both the M_BH - sigma relation and the total stellar bulge mass at values in good agreement with observation. Black hole growth thus produces starbursts and ultimately a superwind.Comment: ApJ, in press, 4 page