Towards (3+1) gravity through Drinfel'd doubles with cosmological constant

We present the generalisation to (3+1) dimensions of a quantum deformation of the (2+1) (Anti)-de Sitter and Poincar\'e Lie algebras that is compatible with the conditions imposed by the Chern-Simons formulation of (2+1) gravity. Since such compatibility is automatically fulfilled by deformations coming from Drinfel'd double structures, we believe said structures are worth being analysed also in the (3+1) scenario as a possible guiding principle towards the description of (3+1) gravity. To this aim, a canonical classical $r$-matrix arising from a Drinfel'd double structure for the three (3+1) Lorentzian algebras is obtained. This $r$-matrix turns out to be a twisted version of the one corresponding to the (3+1) $\kappa$-deformation, and the main properties of its associated noncommutative spacetime are analysed. In particular, it is shown that this new quantum spacetime is not isomorphic to the $\kappa$-Minkowski one, and that the isotropy of the quantum space coordinates can be preserved through a suitable change of basis of the quantum algebra generators. Throughout the paper the cosmological constant appears as an explicit parameter, thus allowing the (flat) Poincar\'e limit to be straightforwardly obtained.Comment: 12 pages. References and comments added. One misprint correcte

Access to Credit and the Effect of Credit Constraints on Costa Rican Manufacturing Firms

This paper examines the finances and the effect of credit limitations on the behavior and performance of firms in Costa Rica. The study is based on a survey of manufacturing firms conducted by the authors during 2001. The paper characterizes the profile firms’ finances, examines the determinants of firms’ access to banking credit and tries to assess the effect of credit constraints on the behavior and performance of firms. The paper finds that while banks are the main source of credit for larger firms, non-banking credit (trade plus informal credit) remains the leading source of funds for smaller firms. Moreover, own funds and informal credit is a leading form of credit for newly created firms. It is also found that the probability of having banking credit and the fraction of banking credit/total debt is mostly affected by (if anything) characteristics of the firm and not by those of their owners. Indeed, the firm’s value and age, and whether it keeps formal accounting procedures appear as the most relevant determinants of access to banking credit. With respect to the starting up finances of firms, the data is not conclusive on the determinants of banking credit, yet it suggests a negative relationship with the previous entrepreneurship experience of the owner. The paper discusses different explanations, all of which highlight the importance of credit constraints. Adopting ideas from the econometric literature on treatment effects, the paper explores the effect of banking credit on the behavior and performance of firms. Two different methods are used to correct for selection biases: a parametric two-step point method and a non-parametric method that estimates upper and lower bounds for the effects. While the results are not statistically conclusive, both methods do suggest that having access to banking credit positively affects firms’ performance.

τ\tau-Flavour Violation at the LHC

We study the conditions required for $\chi_2 \to \chi + \tau^\pm \mu^\mp$ decays to yield observable tau flavour violation at the LHC, for cosmologically interesting values of the neutralino relic density. These condition can be achieved in the framework of a SU(5) model with a see-saw mechanism that allows a possible coexistence of a LHC signal a low prediction for radiative LFV decays.Comment: 7 pages, 5 figures, Prepared for the proceedings of the workshop: "LC09: $e^+ e^-$ Physics at the TeV Scale and the Dark Matter Connection", 21-24 September 2009, Perugia, Ital

Niche divergence and limits to expansion in the high polyploid Dianthus broteri complex

Niche evolution in plant polyploids remains controversial and evidence for alternative patterns has been reported. Using the autopolyploid Dianthus broteri complex (2×, 4×, 6× and 12×) as a model, we aimed to integrate three scenarios – competitive exclusion, recurrent origins of cytotypes and niche filling – into a single framework of polyploid niche evolution. We hypothesized that high polyploids would tend to evolve towards extreme niches when low ploidy cytotypes have nearly filled the niche space. We used several ecoinformatics and phylogenetic comparative analyses to quantify differences in the ecological niche of each cytotype and to evaluate alternative models of niche evolution. Each cytotype in this complex occupied a distinct ecological niche. The distributions were mainly constrained by soil characteristics, temperature and drought stress imposed by the Mediterranean climate. Tetraploids had the highest niche breadth and overlap due to their multiple origins, whereas the higher ploidy cytotypes were found in different, restricted, nonoverlapping niches. Niche evolution analyses suggested a scenario with one niche optimum for each ploidy, including the two independent tetraploid lineages.Our results suggest that the fate of nascent polyploids could not be predicted without accounting for phylogenetic relatedness, recurrent origins or the niche occupied by ancestors.Aridos La Melera S.L. (FIUS project 2234/0724

Non-equilibrium Effects in the Thermal Switching of Underdamped Josephson Junctions

We study the thermal escape problem in the low damping limit. We find that finiteness of the barrier is crucial for explaining the thermal activation results. In this regime low barrier non-equilibrium corrections to the usual theories become necessary. We propose a simple theoretical extension accounting for these non-equilibrium processes which agrees numerical results. We apply our theory to the understanding of switching current curves in underdamped Josephson junctions.Comment: 4 pages + 4 figure