Supersymmetric Reflection Matrices

We briefly review the general structure of integrable particle theories in 1+1 dimensions having N=1 supersymmetry. Examples are specific perturbed superconformal field theories (of Yang-Lee type) and the N=1 supersymmetric sine-Gordon theory. We comment on the modifications that are required when the N=1 supersymmetry algebra contains non-trivial topological charges.Comment: 7 pages, Revtex, 2 figures, talk given at the International Seminar on Supersymmetry and Quantum Field Theory, dedicated to the memory of D.V.Volkov, Kharkov (Ukraine), January 5-7, 199

Charge carrier induced lattice strain and stress effects on As activation in Si

We studied lattice expansion coefficient due to As using density functional theory with particular attention to separating the impact of electrons and ions. Based on As deactivation mechanism under equilibrium conditions, the effect of stress on As activation is predicted. We find that biaxial stress results in minimal impact on As activation, which is consistent with experimental observations by Sugii et al. [J. Appl. Phys. 96, 261 (2004)] and Bennett et al.[J. Vac. Sci. Tech. B 26, 391 (2008)]

Characterization of Si/Si_(1-y)C_y superlattices grown by surfactant assisted molecular beam epitaxy

Si/Si_(0.97)C_(0.03) superlattices grown on Si(001) substrates by Sb surfactant assisted molecular beam epitaxy are characterized by in situ reflection high energy electron diffraction (RHEED), atomic force microscopy, transmission electron microscopy (TEM), and high resolution x‐ray diffraction. The RHEED shows that, in the absence of Sb, the growth front roughens during Si_(0.97)C_(0.03) growth and smooths during subsequent Si growth. In contrast, when Sb is present, the growth front remains smooth throughout the growth. This observation is confirmed by cross‐sectional TEM, which reveals that for samples grown without the use of Sb, the Si/Si_(0.97)C_(0.03) interfaces (Si_(0.97)C_(0.03) on Si) are much more abrupt than the Si_(0.97)C_(0.03)/Si interfaces. In the case of Sb assisted growth, there is no observable difference in abruptness between the two types of interfaces. Atomic force microscopy micrographs of the Si_(0.97)C_(0.03) surface reveal features that could be the source of the roughness observed by RHEED and TEM

Sb-surfactant-mediated growth of Si/Si1–yCy superlattices by molecular-beam epitaxy

Si/Si0.97C0.03 superlattices were grown on Si(001) substrates by molecular beam epitaxy (MBE) to study the use of Sb as a surfactant during Si1–yCy growth. In situ reflection high energy electron diffraction (RHEED) shows that while carbon easily disrupts the two-dimensional growth of homoepitaxial Si, such disruption is suppressed for layers grown on Sb-terminated Si(001) surfaces. Cross-sectional transmission electron microscopy (TEM) reveals that for samples grown without the use of Sb, the Si/Si0.97C0.03 interfaces (Si0.97C0.03 on Si) were much more abrupt than Si0.97C0.03/Si interfaces. In the case of Sb-mediated growth, differences in abruptness between the two types of interfaces were not readily observable

Atomic scale lattice distortions and domain wall profiles

We present an atomic scale theory of lattice distortions using strain related variables and their constraint equations. Our approach connects constrained {\it atomic length} scale variations to {\it continuum} elasticity and describes elasticity at several length scales. We apply the approach to a two-dimensional square lattice with a monatomic basis, and find the elastic deformations and hierarchical atomic relaxations in the vicinity of a domain wall between two different homogeneous strain states. We clarify the microscopic origin of gradient terms, some of which are included phenomenologically in Ginzburg-Landau theory, by showing that they are anisotropic.Comment: 6 figure

Nonlinear Bias of Cosmological Halo Formation in the Early Universe

We present estimates of the nonlinear bias of cosmological halo formation, spanning a wide range in the halo mass from $\sim 10^{5} M_\odot$ to $\sim 10^{12} M_\odot$, based upon both a suite of high-resolution cosmological N-body simulations and theoretical predictions. The halo bias is expressed in terms of the mean bias and stochasticity as a function of local overdensity ($\delta$), under different filtering scales, which is realized as the density of individual cells in uniform grids. The sampled overdensities span a range wide enough to provide the fully nonlinear bias effect on the formation of haloes. A strong correlation between $\delta$ and halo population overdensity $\delta_h$ is found, along with sizable stochasticity. We find that the empirical mean halo bias matches, with good accuracy, the prediction by the peak-background split method based on the excursion set formalism, as long as the empirical, globally-averaged halo mass function is used. Consequently, this bias formalism is insensitive to uncertainties caused by varying halo identification schemes, and can be applied generically. We also find that the probability distribution function of biased halo numbers has wider distribution than the pure Poisson shot noise, which is attributed to the sub-cell scale halo correlation. We explicitly calculate this correlation function and show that both overdense and underdense regions have positive correlation, leading to stochasticity larger than the Poisson shot noise in the range of haloes and halo-collapse epochs we study.Comment: 18 pages, 8 figures, in press for publication in MNRAS; supplementary material (additional 16 figures) separately supplied (supplement.pdf) as a part of source file

Implications of WMAP 3 Year Data for the Sources of Reionization

New results on the anisotropy of the cosmic microwave background (CMB) and its polarization based on the first 3 years of data from the Wilkinson Microwave Anisotropy Probe (WMAP) have revised the electron scattering optical depth downward from tau_es=0.17+0.08-0.07 to tau_es=0.09+/-0.03. This implies a shift of the effective reionization redshift from z_r~17 to z_r~11. Previous attempts to explain the high redshift of reionization inferred from the WMAP 1 year data have led to widespread speculation that the sources of reionization must have been much more efficient than those associated with the star formation observed at low redshift. This is consistent, for example, with the suggestion that early star formation involved massive, Population III stars that early on produced most of the ionizing radiation escaping from halos. It is therefore tempting to interpret the new WMAP results as implying that we can now relax those previous high demands on the efficiency of the sources of reionization and perhaps even turn the argument around as evidence against such high efficiency. We show that this is not the case, however. The new WMAP results also find that the primordial density fluctuation power spectrum has a lower amplitude, sigma_8, and departs substantially from the scale-invariant spectrum. We show that these effects combine to cancel the impact of the later reionization implied by the new value of tau_es on the required ionizing efficiency per collapsed baryon. The delay of reionization is surprisingly well matched by a comparable delay (by a factor of ~1.4 in scale factor) in the formation of the halos responsible for reionization.Comment: 4 pages, 3 figures, Published in ApJ Letters, revised to match published versio