Entanglement Scaling in the One-Dimensional Hubbard Model at Criticality

We derive exact expressions for the local entanglement entropy E in the ground state of the one-dimensional Hubbard model at a quantum phase transition driven by a change in magnetic field h or chemical potential u. The leading divergences of dE/dh and dE/du are shown to be directly related to those of the zero-temperature spin and charge susceptibilities. Logarithmic corrections to scaling signal a change in the number of local states accessible to the system as it undergoes the transition.Comment: 4+ pages, 2 figures. Fig. 2 and minor typos correcte

Persistent currents through a quantum impurity: Protection through integrability

We consider an integrable model of a one-dimensional mesoscopic ring with the conduction electrons coupled by a spin exchange to a magnetic impurity. A symmetry analysis based on a Bethe Ansatz solution of the model reveals that the current is insensitive to the presence of the impurity. We argue that this is true for any integrable impurity-electron interaction, independent of choice of physical parameters or couplings. We propose a simple physical picture of how the persistent current gets protected by integrability.Comment: 5 pages, minor update

The effect of multiple paternity on genetic diversity during and after colonisation

In metapopulations, genetic variation of local populations is influenced by the genetic content of the founders, and of migrants following establishment. We analyse the effect of multiple paternity on genetic diversity using a model in which the highly promiscuous marine snail Littorina saxatilis expands from a mainland to colonise initially empty islands of an archipelago. Migrant females carry a large number of eggs fertilised by 1 - 10 mates. We quantify the genetic diversity of the population in terms of its heterozygosity: initially during the transient colonisation process, and at long times when the population has reached an equilibrium state with migration. During colonisation, multiple paternity increases the heterozygosity by 10 - 300 % in comparison with the case of single paternity. The equilibrium state, by contrast, is less strongly affected: multiple paternity gives rise to 10 - 50 % higher heterozygosity compared with single paternity. Further we find that far from the mainland, new mutations spreading from the mainland cause bursts of high genetic diversity separated by long periods of low diversity. This effect is boosted by multiple paternity. We conclude that multiple paternity facilitates colonisation and maintenance of small populations, whether or not this is the main cause for the evolution of extreme promiscuity in Littorina saxatilis.Comment: 7 pages, 5 figures, electronic supplementary materia

Fermi-LAT Detection of a Break in the Gamma-Ray Spectrum of the Supernova Remnant Cassiopeia A

We report on observations of the supernova remnant Cassiopeia A in the energy range from 100 MeV to 100 GeV using 44 months of observations from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. We perform a detailed spectral analysis of this source and report on a low-energy break in the spectrum at $1.72^{+1.35}_{-0.89}$ GeV. By comparing the results with models for the gamma-ray emission, we find that hadronic emission is preferred for the GeV energy range.Comment: 18 pages, 5 figures, 2 tables, to be published in Ap

Cystic fibrosis gene mutations and gastrointestinal diseases

Background: This study examined if CF mutation heterozygosity is associated with diseases of gastrointestinal epithelial barrier function. Design and methods: Swedish registers identified 865 patients with a diagnosis of CF between 1968 and 2003 and matched with 8101 individuals without CF. Gastrointestinal disease risk was examined among 1534 biological parents and 1396 siblings of CF patients, compared with 15,526 parents and 15,542 siblings of individuals without CF. Results: First-degree relatives of CF patients were not at lower risk of the gastrointestinal diseases, in contrast with a raised risk among CF patients. Conclusion: Heterozygosity for CF gene mutations does not protect against gastrointestinal diseases where impaired barrier function may be relevant. © 2010 European Cystic Fibrosis Society

Cancer risk among patients with cystic fibrosis and their first-degree relatives

Patients with cystic fibrosis (CF) are at increased risk of some cancers. Little is known about the cancer risks among carriers heterozygous for the CF mutation and it is hypothesized this may be associated with reduced cancer risk. Using Swedish general population-based registers, we identified 884 patients with CF from 1968 to 2003 and 3,033 of their first-degree relatives The subjects were followed from birth of index persons or 1958, whichever came later, until death, emigration or 2003, whichever came first. Cancer risks were compared with the general Swedish population using standardized incidence ratios (SIR) with 95% confidence intervals (CI). Patients, followed for an average of 21 years, were at a higher overall risk of cancer. Some 26 cancer diagnoses, after excluding multiple diagnoses of nonmelanoma skin cancer in one man, produced an overall SIR of 3.2 (95%CI 2.1-4.6).We found statistically significantly increased risks for kidney, thyroid, endocrine, lymphoma and nonmelanoma skin cancer. There was no modification of cancer risk among parents and siblings, with an average of 21 years of follow-up. This study did not identify a heterozygote advantage for CF gene mutations in relation to cancer risk. © 2009 UICC

Energy Injection in GRB Afterglow Models

We extend the standard fireball model, widely used to interpret gamma-ray burst (GRB) afterglow light curves, to include energy injections, and apply the model to the afterglow light curves of GRB 990510, GRB 000301C and GRB 010222. We show that discrete energy injections can cause temporal variations in the optical light curves and present fits to the light curves of GRB 000301C as an example. A continuous injection may be required to interpret other bursts such as GRB 010222. The extended model accounts reasonably well for the observations in all bands ranging from X-rays to radio wavelengths. In some cases, the radio light curves indicate that additional model ingredients may be needed.Comment: Accepted for publication in the Astrophysical Journa