Can topological defects mimic the BICEP2 B-mode signal?

We show that the B-mode polarization signal detected at low multipoles by BICEP2 cannot be entirely due to topological defects. This would be incompatible with the high-multipole B-mode polarization data and also with existing temperature anisotropy data. Adding cosmic strings to a model with tensors, we find that B modes on their own provide a comparable limit on the defects to that already coming from Planck satellite temperature data. We note that strings at this limit give a modest improvement to the best fit of the B-mode data, at a somewhat lower tensor-to-scalar ratio of r ≃ 0.15.

Cosmic microwave background anomalies in an open universe.

We argue that the observed large-scale cosmic microwave anomalies, discovered by WMAP and confirmed by the Planck satellite, are most naturally explained in the context of a marginally open universe. Particular focus is placed on the dipole power asymmetry, via an open universe implementation of the large-scale gradient mechanism of Erickcek et al. Open inflation models, which are motivated by the string landscape and which can excite "supercurvature" perturbation modes, can explain the presence of a very-large-scale perturbation that leads to a dipole modulation of the power spectrum measured by a typical observer. We provide a specific implementation of the scenario which appears compatible with all existing constraints.

Non-Gaussianity in axion N-flation models.

We study perturbations in the multifield axion N-flation model, taking account of the full cosine potential. We find significant differences from previous analyses which made a quadratic approximation to the potential. The tensor-to-scalar ratio and the scalar spectral index move to lower values, which nevertheless provide an acceptable fit to observation. Most significantly, we find that the bispectrum non-Gaussianity parameter f{NL} may be large, typically of order 10 for moderate values of the axion decay constant, increasing to of order 100 for decay constants slightly smaller than the Planck scale. Such a non-Gaussian fraction is detectable. We argue that this property is generic in multifield models of hilltop inflation.

Early assembly of the most massive galaxies.

The current consensus is that galaxies begin as small density fluctuations in the early Universe and grow by in situ star formation and hierarchical merging. Stars begin to form relatively quickly in sub-galactic-sized building blocks called haloes which are subsequently assembled into galaxies. However, exactly when this assembly takes place is a matter of some debate. Here we report that the stellar masses of brightest cluster galaxies, which are the most luminous objects emitting stellar light, some 9 billion years ago are not significantly different from their stellar masses today. Brightest cluster galaxies are almost fully assembled 4-5 billion years after the Big Bang, having grown to more than 90 per cent of their final stellar mass by this time. Our data conflict with the most recent galaxy formation models based on the largest simulations of dark-matter halo development. These models predict protracted formation of brightest cluster galaxies over a Hubble time, with only 22 per cent of the stellar mass assembled at the epoch probed by our sample. Our findings suggest a new picture in which brightest cluster galaxies experience an early period of rapid growth rather than prolonged hierarchical assembly.

A novel population health approach: Using fish retinoblastoma gene profiles as a surrogate for humans.

Retinoblastoma, a tumor suppressor gene, is frequently mutated in diverse types of human tumors. We have previously shown that two types of fish tumor, eye and liver, also possess mutant Rb genes. Our aim is to determine if the Rb allele status is linked to environmentally-induced cancer and whether this information in fish can be used to predict future phenotype. This is a proof-of-concept investigation to elucidate if fish may act as surrogates in assessing pollution-induced tumor incidence and inform regulatory authorities of potential long-term population health consequences. Marine flatfish, Limanda limanda, that display either normal liver histopathology, liver adenoma or liver hepatocellular carcinoma were analysed for the presence of Rb gene alterations. Several Rb alterations were detected in the fish displaying adenoma and carcinoma, and not in the surrounding normal tissue from the same individuals. The profile is similar to that reported in humans in that they spread across the gene, particularly exons 8-23, and a functionally important region of the protein. This Rb allele data was then used to build statistical classifier sets, linking Rb status with tumor pathology. Further flatfish caught from coastal-water areas of differing contaminant burden around the UK were subsequently analysed for the presence of Rb alterations. Using novel pattern matching statistics of the classifier sets compared with the coastal samples, the coastal fish were considered more similar to the characterised disease phenotype than the normal phenotype. Preliminary data suggests that using a statistical approach, based on classifying sets of histopathologically-defined tumor states, makes it possible to predict the phenotype of wild fish based on the status of the Rb allele. Since the Rb gene is orthologous, fish populations could act as surrogates for human populations in an eco-epidemiological investigation of the combined roles of genetics and environmental exposures in the tumorigenesis process.

Inflation, dark matter, and dark energy in the string landscape.

We consider the conditions needed to unify the description of dark matter, dark energy, and inflation in the context of the string landscape. We find that incomplete decay of the inflaton field gives the possibility that a single field is responsible for all three phenomena. By contrast, unifying dark matter and dark energy into a single field, separate from the inflaton, appears rather difficult.