Phases of supersymmetric O(N) theories

We perform a global renormalization group study of O(N) symmetric Wess-Zumino theories and their phases in three euclidean dimensions. At infinite N the theory is solved exactly. The phases and phase transitions are worked out for finite and infinite short-distance cutoffs. A distinctive new feature arises at strong coupling, where the effective superfield potential becomes multi-valued, signalled by divergences in the fermion-boson interaction. Our findings resolve the long-standing puzzle about the occurrence of degenerate O(N) symmetric phases. At finite N, we find a strongly-coupled fixed point in the local potential approximation and explain its impact on the phase transition. We also examine the possibility for a supersymmetric Bardeen-Moshe-Bander phenomenon, and relate our findings with the spontaneous breaking of supersymmetry in other models.Comment: 23 pages, 18 figure

Entropy-driven phase transition in a polydisperse hard-rods lattice system

We study a system of rods on the 2d square lattice, with hard-core exclusion. Each rod has a length between 2 and N. We show that, when N is sufficiently large, and for suitable fugacity, there are several distinct Gibbs states, with orientational long-range order. This is in sharp contrast with the case N=2 (the monomer-dimer model), for which Heilmann and Lieb proved absence of phase transition at any fugacity. This is the first example of a pure hard-core system with phases displaying orientational order, but not translational order; this is a fundamental characteristic feature of liquid crystals

Traumatic dental injuries and socioeconomic position – findings from the Children's Dental Health Survey 2013

OBJECTIVES: The aim of this study was to assess whether traumatic dental injuries (TDI) were socially graded among children and adolescents in England, Wales and Northern Ireland, using nationally representative data from the Children's Dental Health Survey (CDHS) 2013. METHODS: This cross-sectional study used data from the Children's Dental Health Survey 2013 which was conducted among a nationally representative sample of schoolchildren in England, Wales and Northern Ireland. Children's family socioeconomic position (SEP) was measured through free school meal eligibility and relative area deprivation using the Indices of Multiple Deprivation. The analytical sample included 6707 schoolchildren aged 8, 12 and 15. Multiple logistic regression was used to model the associations between experience of TDI and the two markers of SEP, after adjusting for sex and age. RESULTS: The overall prevalence of traumatic dental injuries to permanent incisors was 9% (n = 590). There were no statistically significant associations between TDI and either SEP measure. Further subgroup analyses (n = 2650) showed also no significant associations between TDI and additional SEP markers (parental education and social class). The odds of having sustained a traumatic dental injury were higher for boys than for girls and were greater in older age groups. CONCLUSIONS: This study found no significant relationships between the experience of traumatic dental injuries and two markers of family socioeconomic position among children living in England, Wales and Northern Ireland. This implies that rather than specifically targeting the more deprived sectors of society, TDI prevention policies should use upstream public health strategies incorporating a whole-population approach

A Class of Parameter Dependent Commuting Matrices

We present a novel class of real symmetric matrices in arbitrary dimension $d$, linearly dependent on a parameter $x$. The matrix elements satisfy a set of nontrivial constraints that arise from asking for commutation of pairs of such matrices for all $x$, and an intuitive sufficiency condition for the solvability of certain linear equations that arise therefrom. This class of matrices generically violate the Wigner von Neumann non crossing rule, and is argued to be intimately connected with finite dimensional Hamiltonians of quantum integrable systems.Comment: Latex, Added References, Typos correcte

A projection method for statics and dynamics of lattice spin systems

A method based on Monte Carlo sampling of the probability flows projected onto the subspace of one or more slow variables is proposed for investigation of dynamic and static properties of lattice spin systems. We illustrate the method by applying it, with projection onto the order-parameter subspace, to the three-dimensional 3-state Potts model in equilibrium and to metastable decay in a three-dimensional 3-state kinetic Potts model.Comment: 4 pages, 3 figures, RevTex, final version to appear in Phys. Rev. Let

Communities of wood-inhabiting bryophytes and fungi on dead beech logs in Europe - reflecting substrate quality or shaped by climate and forest conditions?

Aim: Fungi are drivers of wood decay in forested ecosystem, while bryophytes use dead wood as a platform for their autotrophic lifestyle. We tested the hypothesis that fungal communities on beech logs are mainly structured by substrate quality, while bryophyte communities are structured by climatic gradients. In addition, we tested whether community structure in both organism groups is altered along a gradient from nearly pristine forest to forests heavily affected by management and human disturbance in the past. Location: Europe. Methods: We surveyed 1207 fallen beech logs in 26 of the best-preserved forest stands across six European countries, representing a gradient in overall naturalness of the forest landscape. Recorded species were classified into ecological guilds. Indirect ordination and variation partitioning was used to analyse the relationship between species composition and environmental variables, recorded at log or site level. Results: In total, 10,367 bryophyte and 15,575 fungal records were made, representing 157 and 272 species, respectively. Fungal communities were more clearly structured by substrate quality than were bryophyte communities. In both groups a distinct turnover in species composition was evident along a longitudinal gradient from Central to Western Europe. Fungi specialized in trunk rot and specialized epixylic bryophytes were scarcely represented in Atlantic regions, and partly replaced by species belonging to less specialized guilds. Variables related to climate and forest conditions were confounded along this main geographical gradient in community composition. Main conclusions: We found that bryophyte and fungal communities co-occurring on fallen beech logs in European beech forest reserves differed in their responses to biogeographical drivers and local-scale habitat filters. Both groups responded to major gradients in climate and forest conditions, but the loss of specialist guilds in degraded forest landscapes points to a functionally important effect of forest landscape degradation at the European continental scale. © 2014 John Wiley & Sons Ltd

Enhancing quantum transport in a photonic network using controllable decoherence

Transport phenomena on a quantum scale appear in a variety of systems, ranging from photosynthetic complexes to engineered quantum devices. It has been predicted that the efficiency of quantum transport can be enhanced through dynamic interaction between the system and a noisy environment. We report the first experimental demonstration of such environment-assisted quantum transport, using an engineered network of laser-written waveguides, with relative energies and inter-waveguide couplings tailored to yield the desired Hamiltonian. Controllable decoherence is simulated via broadening the bandwidth of the input illumination, yielding a significant increase in transport efficiency relative to the narrowband case. We show integrated optics to be suitable for simulating specific target Hamiltonians as well as open quantum systems with controllable loss and decoherence.Comment: 6 pages, 3 figure