Effective-Field-Theory Approach to Top-Quark Production and Decay

We discuss new physics in top-quark interactions, using an effective field theory approach. We consider top-quark decay, single top production, and top-quark pair production. We identify 15 dimension-six operators that contribute to these processes, and we compute the deviation from the Standard Model induced by these operators. The results provide a systematic way of searching for (or obtaining bounds on) physics beyond the Standard Model.Comment: 24 pages, 12 figures; references added, typos correcte

Scalable solid-state quantum computation in decoherence-free subspaces with trapped ions

We propose a decoherence-free subspaces (DFS) scheme to realize scalable quantum computation with trapped ions. The spin-dependent Coulomb interaction is exploited, and the universal set of unconventional geometric quantum gates is achieved in encoded subspaces that are immune from decoherence by collective dephasing. The scalability of the scheme for the ion array system is demonstrated, either by an adiabatic way of switching on and off the interactions, or by a fast gate scheme with comprehensive DFS encoding and noise decoupling techniques.Comment: 4 pages, 1 figur

O-V-S-Z and friends: Non-Gaussianity from inhomogeneous reionization

We calculate the cosmic microwave background (CMB) bispectrum due to inhomogeneous reionization. We calculate all the terms that can contribute to the bispectrum that are products of first order terms on all scales in conformal Newtonian gauge. We also correctly account for the de-correlation between the matter density and initial conditions using perturbation theory up to third order. We find that the bispectrum is of local type as expected. For a reasonable model of reionization, in which the Universe is completely ionized by redshift z_{ri} ~ 8 with optical depth to the last scattering surface \tau_0=0.087 the signal to noise for detection of the CMB temperature bispectrum is S/N ~ 0.1 and confusion in the estimation of primordial non-Gaussianity is f_{NL} ~ -0.1. For an extreme model with z_{ri} ~ 12.5, \tau_0=0.14 we get S/N ~ 0.5 and f_{NL} ~ -0.2.Comment: Published versio

The Nature of the Warm/Hot Intergalactic Medium I. Numerical Methods, Convergence, and OVI Absorption

We perform a series of cosmological simulations using Enzo, an Eulerian adaptive-mesh refinement, N-body + hydrodynamical code, applied to study the warm/hot intergalactic medium. The WHIM may be an important component of the baryons missing observationally at low redshift. We investigate the dependence of the global star formation rate and mass fraction in various baryonic phases on spatial resolution and methods of incorporating stellar feedback. Although both resolution and feedback significantly affect the total mass in the WHIM, all of our simulations find that the WHIM fraction peaks at z ~ 0.5, declining to 35-40% at z = 0. We construct samples of synthetic OVI absorption lines from our highest-resolution simulations, using several models of oxygen ionization balance. Models that include both collisional ionization and photoionization provide excellent fits to the observed number density of absorbers per unit redshift over the full range of column densities (10^13 cm-2 <= N_OVI <= 10^15 cm^-2). Models that include only collisional ionization provide better fits for high column density absorbers (N_OVI > 10^14 cm^-2). The distribution of OVI in density and temperature exhibits two populations: one at T ~ 10^5.5 K (collisionally ionized, 55% of total OVI) and one at T ~ 10^4.5 K (photoionized, 37%) with the remainder located in dense gas near galaxies. While not a perfect tracer of hot gas, OVI provides an important tool for a WHIM baryon census.Comment: 22 pages, 21 figures, emulateapj, accepted for publication in Ap

Studying the WHIM Content of the Galaxy Large-Scale Structures along the Line of Sight to H 2356-309

We make use of a 500ks Chandra HRC-S/LETG spectrum of the blazar H2356-309, combined with a lower S/N spectrum of the same target, to search for the presence of warm-hot absorbing gas associated with two Large-Scale Structures (LSSs) crossed by this sightline at z=0.062 (the Pisces-Cetus Supercluster, PCS) and at z=0.128 ("Farther Sculptor Wall", FSW). No statistically significant (>=3sigma) individual absorption is detected from any of the strong He- or H-like transitions of C, O and Ne at the redshifts of the structures. However we are still able to constrain the physical and geometrical parameters of the associated putative absorbing gas, by performing joint spectral fit of marginal detections and upper limits of the strongest expected lines with our self-consistent hybrid ionization WHIM spectral model. At the redshift of the PCS we identify a warm phase with logT=5.35_-0.13^+0.07 K and log N_H =19.1+/-0.2 cm^-2 possibly coexisting with a hotter and less significant phase with logT=6.9^+0.1_-0.8 K and log N_H=20.1^+0.3_-1.7 cm^-2 (1sigma errors). For the FSW we estimate logT=6.6_-0.2^+0.1 K and log N_H=19.8_-0.8^+0.4 cm^-2. Our constraints allow us to estimate the cumulative number density per unit redshifts of OVII WHIM absorbers. We also estimate the cosmological mass density obtaining Omega_b(WHIM)=(0.021^+0.031_-0.018) (Z/Z_sun)^-1, consistent with the mass density of the intergalactic 'missing baryons' for high metallicities.Comment: 29 pages, 8 figures, 4 tables. Accepted for publication in Ap

Predicting human protein function with multitask deep neural networks

Machine learning methods for protein function prediction are urgently needed, especially now that a substantial fraction of known sequences remains unannotated despite the extensive use of functional assignments based on sequence similarity. One major bottleneck supervised learning faces in protein function prediction is the structured, multi-label nature of the problem, because biological roles are represented by lists of terms from hierarchically organised controlled vocabularies such as the Gene Ontology. In this work, we build on recent developments in the area of deep learning and investigate the usefulness of multitask deep neural networks (MTDNN), which consist of upstream shared layers upon which are stacked in parallel as many independent modules (additional hidden layers with their own output units) as the number of output GO terms (the tasks). MTDNN learns individual tasks partially using shared representations and partially from task-specific characteristics. When no close homologues with experimentally validated functions can be identified, MTDNN gives more accurate predictions than baseline methods based on annotation frequencies in public databases or homology transfers. More importantly, the results show that MTDNN binary classification accuracy is higher than alternative machine learning-based methods that do not exploit commonalities and differences among prediction tasks. Interestingly, compared with a single-task predictor, the performance improvement is not linearly correlated with the number of tasks in MTDNN, but medium size models provide more improvement in our case. One of advantages of MTDNN is that given a set of features, there is no requirement for MTDNN to have a bootstrap feature selection procedure as what traditional machine learning algorithms do. Overall, the results indicate that the proposed MTDNN algorithm improves the performance of protein function prediction. On the other hand, there is still large room for deep learning techniques to further enhance prediction ability

Evolution of Lyman Break Galaxies Beyond Redshift Four

The formation rate of luminous galaxies seems to be roughly constant from z~2 to z~4 from the recent observations of Lyman break galaxies (LBGs) (Steidel et al 1999). The abundance of luminous quasars, on the other hand, appears to drop off by a factor of more than twenty from z~2 to z~5 (Warren, Hewett, & Osmer 1994; Schmidt, Schneider, & Gunn 1995). The difference in evolution between these two classes of objects in the overlapping, observed redshift range, z=2-4, can be explained naturally, if we assume that quasar activity is triggered by mergers of luminous LBGs and one quasar lifetime is ~10^{7-8} yrs. If this merger scenario holds at higher redshift, for the evolutions of these two classes of objects to be consistent at z>4, the formation rate of luminous LBGs is expected to drop off at least as rapidly as exp(-(z-4)^{6/5}) at z>4.Comment: in press, ApJ Letters, 15 latex pages plus 1 fi

Contribution of capecitabine for therapy of patients with gastroesophageal cancer: an update of recent phase III results

Putao Cen, Eric D Tetzlaff, Jaffer A AjaniDepartment of Gastrointestinal Medical Oncology in the Division of Cancer Medicine at the University of Texas MD Anderson Cancer Center, Houston, TX, USABackground: Capecitabine, an orally administered fluoropyrimidines, is widely used in the treatment of multiple malignancies. It has been extensively evaluated in patients with gastroesophageal carcinoma. Since recent reviews have discussed phase I/II trials (Cancer 107:221&amp;ndash;231, 2006; Drugs 67:601&amp;ndash;610, 2007), we focus on the impact of the results of the most current phase III trials using capectiabine in the treatment of advanced gastroesophageal cancers, primarily in the first-line setting.Methods: To find published phase III trials, Medline was searched for English-language clinical trials published from 1996 through June 2007 along with relevant abstracts presented at the American Society of Clinical Oncology, and meetings of the European Cancer Conference and European Society of Medical Oncology. Only representative trials were chosen for this manuscript.Results: The most frequently investigated combinations are capecitabine with taxanes, platinols, and camptothecins. Recent results of a large phase III trial (REAL-2) in untreated patients with gastroesophageal cancer suggest that capecitabine is a non-inferior substitute for intravenous 5-fluorouracil. These results of REAL-2 trial are substantiated by a smaller phase III trial. Previous analysis of multiple trials had suggested that capecitabine, when combined in doses lower than 1250 mg/m2 twice daily, consistently resulted in lower frequency of Grade 3 or 4 toxic effects.Conclusions: Capecitabine provides much needed convenience to patients with gastroesophageal cancer. The recent data derived from two phase III trials confirm that capecitabine is a suitable substitute for intravenous 5-fluorouracil in patients whose swallowing is not greatly affected. Capecitabine remains a subject of further investigations in this group of patients with interest.Keywords: capecitabine, gastroesophageal cancer, oral fluoropyrimidine

A Constraint on the Gravitational Lensing Magnification and Age of the Redshift z=6.28 Quasar SDSS 1030+0524

The recent discovery of bright quasars around redshift z=6 suggests that black holes (BHs) with masses in excess of 10^9 Msun have already assembled at a very early stage in the evolution of the universe. An alternative interpretation is that these quasars are powered by less massive BHs, but their fluxes are strongly magnified through gravitational lensing by intervening galaxies. Here we analyze the flux distribution of the Ly alpha emission of the quasar with the highest known redshift, SDSS 1030+0524, at z=6.28. We show that this object could not have been magnified by lensing by more than a factor of five. The constraint arises from the large observed size, 30 (comoving) Mpc, of the ionized region around this quasar, and relies crucially only on the assumption that the quasar is embedded in a largely neutral IGM. Based on the line/continuum ratio of SDSS 1030+0524, we argue further that this quasar also cannot be beamed by a significant factor. We conclude that the minimum mass for its resident BH is 4 x 10^8 Msun (for magnification by a factor of five); if the mass is this low, then the quasars had to switch on prior to redshift z=9. From the size of the ionized region, we are also able to place an absolute lower bound on the age of this quasar at t > 2 x 10^7 years.Comment: Submitted to ApJL, 2 figures include