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Articles 1 - 5 of 5
Full-Text Articles in Physical Sciences and Mathematics
Fluctuations In A Cosmology With A Spacelike Singularity And Their Gauge Theory Dual Description, Robert H. Brandenberger, Elisa G. M. Ferreira, Ian A. Morrison, Yi-Fu Cai, Sumit R. Das, Yi Wang
Fluctuations In A Cosmology With A Spacelike Singularity And Their Gauge Theory Dual Description, Robert H. Brandenberger, Elisa G. M. Ferreira, Ian A. Morrison, Yi-Fu Cai, Sumit R. Das, Yi Wang
Physics and Astronomy Faculty Publications
We consider a time-dependent deformation of anti–de Sitter (AdS) space-time which contains a spacelike “singularity”—a spacelike region of high curvature. Making use of the AdS/CFT correspondence we can map the bulk dynamics onto the boundary. The boundary theory has a time dependent coupling constant which becomes small at times when the bulk space-time is highly curved. We investigate the propagation of small fluctuations of a test scalar field from early times before the bulk singularity to late times after the singularity. Under the assumption that the AdS/CFT correspondence extends to deformed AdS space-times, we can map the bulk evolution of …
The Baryon Cycle At High Redshifts: Effects Of Galactic Winds On Galaxy Evolution In Overdense And Average Regions, Raphael Sadoun, Isaac Shlosman, Jun-Hwan Choi, Emilio Romano-Díaz
The Baryon Cycle At High Redshifts: Effects Of Galactic Winds On Galaxy Evolution In Overdense And Average Regions, Raphael Sadoun, Isaac Shlosman, Jun-Hwan Choi, Emilio Romano-Díaz
Physics and Astronomy Faculty Publications
We employ high-resolution cosmological zoom-in simulations focusing on a high-sigma peak and an average cosmological field at z ~ 6–12 in order to investigate the influence of environment and baryonic feedback on galaxy evolution in the reionization epoch. Strong feedback, e.g., galactic winds, caused by elevated star formation rates (SFRs) is expected to play an important role in this evolution. We compare different outflow prescriptions: (i) constant wind velocity (CW), (ii) variable wind scaling with galaxy properties (VW), and (iii) no outflows (NW). The overdensity leads to accelerated evolution of dark matter and baryonic structures, absent from the "normal" region, …
H-, He-Like Recombination Spectra ‒ Ii. L-Changing Collisions For He Rydberg States, Francisco Guzmán, N. R. Badnell, R. J. R. Williams, P. A. M. Van Hoof, Marios Chatzikos, Gary J. Ferland
H-, He-Like Recombination Spectra ‒ Ii. L-Changing Collisions For He Rydberg States, Francisco Guzmán, N. R. Badnell, R. J. R. Williams, P. A. M. Van Hoof, Marios Chatzikos, Gary J. Ferland
Physics and Astronomy Faculty Publications
Cosmological models can be constrained by determining primordial abundances. Accurate predictions of the He i spectrum are needed to determine the primordial helium abundance to a precision of < 1 per cent in order to constrain big bang nucleosynthesis models. Theoretical line emissivities at least this accurate are needed if this precision is to be achieved. In the first paper of this series, which focused on H ι, we showed that differences in l-changing collisional rate coefficients predicted by three different theories can translate into 10 per cent changes in predictions for H ι spectra. Here, we consider the more complicated case of He atoms, where low-l subshells are not energy degenerate. A criterion for deciding when the energy separation between l subshells is small enough to apply energy-degenerate collisional theories is given. Moreover, for certain conditions, the Bethe approximation originally proposed by …
H, He-Like Recombination Spectra – I. L-Changing Collisions For Hydrogen, Francisco Guzmán, N. R. Badnell, R. J. R. Williams, P. A. M. Van Hoof, Marios Chatzikos, Gary J. Ferland
H, He-Like Recombination Spectra – I. L-Changing Collisions For Hydrogen, Francisco Guzmán, N. R. Badnell, R. J. R. Williams, P. A. M. Van Hoof, Marios Chatzikos, Gary J. Ferland
Physics and Astronomy Faculty Publications
Hydrogen and helium emission lines in nebulae form by radiative recombination. This is a simple process which, in principle, can be described to very high precision. Ratios of He I and H I emission lines can be used to measure the He+/H+ abundance ratio to the same precision as the recombination rate coefficients. This paper investigates the controversy over the correct theory to describe dipole l-changing collisions (nl → nl′ = l ± 1) between energy-degenerate states within an n-shell. The work of Pengelly & Seaton has, for half-a-century, been considered the definitive …
Direct Collapse To Supermassive Black Hole Seeds: Comparing The Amr And Sph Approaches, Yang Luo, Kentaro Nagamine, Isaac Shlosman
Direct Collapse To Supermassive Black Hole Seeds: Comparing The Amr And Sph Approaches, Yang Luo, Kentaro Nagamine, Isaac Shlosman
Physics and Astronomy Faculty Publications
We provide detailed comparison between the adaptive mesh refinement (AMR) code ENZO-2.4 and the smoothed particle hydrodynamics (SPH)/N-body code GADGET-3 in the context of isolated or cosmological direct baryonic collapse within dark matter (DM) haloes to form supermassive black holes. Gas flow is examined by following evolution of basic parameters of accretion flows. Both codes show an overall agreement in the general features of the collapse; however, many subtle differences exist. For isolated models, the codes increase their spatial and mass resolutions at different pace, which leads to substantially earlier collapse in SPH than in AMR cases due …