Bubbles of Nothing in Flux Compactifications

We construct a simple AdS_4 x S^1 flux compactification stabilized by a complex scalar field winding the extra dimension and demonstrate an instability via nucleation of a bubble of nothing. This occurs when the Kaluza -- Klein dimension degenerates to a point, defining the bubble surface. Because the extra dimension is stabilized by a flux, the bubble surface must be charged, in this case under the axionic part of the complex scalar. This smooth geometry can be seen as a de Sitter topological defect with asymptotic behavior identical to the pure compactification. We discuss how a similar construction can be implemented in more general Freund -- Rubin compactifications.Comment: 16 pages, 5 figures References adde

Total electron scattering cross sections from thiophene for the (1-300 eV) impact energy range

Experimental electron scattering cross sections for thiophene in the impact energy range from 1 to 300 eV have been measured with a magnetically confined electron transmission-beam apparatus. Random uncertainty limits have been estimated to be less than 5%, and systematic errors derived from acceptance angle limitations have also been identified and evaluated. Experimental values are compared with our previous low energy (1-15 eV) R-matrix and intermediate/high energy (15-300 eV) IAM-SCAR+I calculations finding reasonable agreement, within the combined uncertainty limits. Some of the low energy shape and core-excited resonances predicted by previous calculations are experimentally confirmed in this study

Optimal Carbon Taxes for Emissions Targets in the Electricity Sector

The most dangerous effects of anthropogenic climate change can be mitigated by using emissions taxes or other regulatory interventions to reduce greenhouse gas (GHG) emissions. This paper takes a regulatory viewpoint and describes the Weighted Sum Bisection method to determine the lowest emission tax rate that can reduce the anticipated emissions of the power sector below a prescribed, regulatorily-defined target. This bi-level method accounts for a variety of operating conditions via stochastic programming and remains computationally tractable for realistically large planning test systems, even when binary commitment decisions and multi-period constraints on conventional generators are considered. Case studies on a modified ISO New England test system demonstrate that this method reliably finds the minimum tax rate that meets emissions targets. In addition, it investigates the relationship between system investments and the tax-setting process. Introducing GHG emissions taxes increases the value proposition for investment in new cleaner generation, transmission, and energy efficiency; conversely, investing in these technologies reduces the tax rate required to reach a given emissions target

The Near-Infrared Photometric Properties of Bright Giants in the Central Regions of the Galactic Bulge

Images recorded through broad (J, H, K), and narrow (CO, and 2.2micron continuum) band filters are used to investigate the photometric properties of bright (K < 13.5) stars in a 6 x 6 arcmin field centered on the SgrA complex. The giant branch ridgelines in the (K, J-K) and (K, H-K) color-magnitude diagrams are well matched by the Baade's Window (BW) M giant sequence if the mean extinction is A_K ~ 2.8 mag. Extinction measurements for individual stars are estimated using the M_K versus infrared color relations defined by M giants in BW, and the majority of stars have A_K between 2.0 and 3.5 mag. The extinction is locally high in the SgrA complex, where A_K ~ 3.1 mag. Reddening-corrected CO indices, CO_o, are derived for over 1300 stars with J, H, and K brightnesses, and over 5300 stars with H and K brightnesses. The distribution of CO_o values for stars with K_o between 11.25 and 7.25 can be reproduced using the M_K versus CO_o relation defined by M giants in BW. The data thus suggest that the most metal-rich giants in the central regions of the bulge and in BW have similar photometric properties and 2.3micron CO strengths. Hence, it appears that the central region of the bulge does not contain a population of stars that are significantly more metal-rich than what is seen in BW.Comment: 29 pages, including 14 figure

Cosmic string formation by flux trapping

We study the formation of cosmic strings by confining a stochastic magnetic field into flux tubes in a numerical simulation. We use overdamped evolution in a potential that is minimized when the flux through each face in the simulation lattice is a multiple of the fundamental flux quantum. When the typical number of flux quanta through a correlation-length-sized region is initially about 1, we find a string network similar to that generated by the Kibble-Zurek mechanism. With larger initial flux, the loop distribution and the Brownian shape of the infinite strings remain unchanged, but the fraction of length in infinite strings is increased. A 2D slice of the network exhibits bundles of strings pointing in the same direction, as in earlier 2D simulations. We find, however, that strings belonging to the same bundle do not stay together in 3D for much longer than the correlation length. As the initial flux per correlation length is decreased, there is a point at which infinite strings disappear, as in the Hagedorn transition.Comment: 16 pages and 9 figures. (Minor changes and new references added

Magnetic ordering in GdNi2B2C revisited by resonant x-ray scattering: evidence for the double-q model

Recent theoretical efforts aimed at understanding the nature of antiferromagnetic ordering in GdNi2B2C predicted double-q ordering. Here we employ resonant elastic x-ray scattering to test this theory against the formerly proposed, single-q ordering scenario. Our study reveals a satellite reflection associated with a mixed-order component propagation wave vector, viz., (q_a,2q_b,0) with q_b = q_a approx= 0.55 reciprocal lattice units, the presence of which is incompatible with single-q ordering but is expected from the double-q model. A (3q_a,0,0) wave vector (i.e., third-order) satellite is also observed, again in line with the double-q model. The temperature dependencies of these along with that of a first-order satellite are compared with calculations based on the double-q model and reasonable qualitative agreement is found. By examining the azimuthal dependence of first-order satellite scattering, we show the magnetic order to be, as predicted, elliptically polarized at base temperature and find the temperature dependence of the "out of a-b plane" moment component to be in fairly good agreement with calculation. Our results provide qualitative support for the double-q model and thus in turn corroborate the explanation for the "magnetoelastic paradox" offered by this model.Comment: 8 pages, 5 figures. Submitted to Phys. Rev.