Emergent SO(5)SO(5) Symmetry at the N\'eel to Valence-Bond-Solid Transition

We show numerically that the `deconfined' quantum critical point between the N\'eel antiferromagnet and the columnar valence-bond-solid, for a square lattice of spin-1/2s, has an emergent $SO(5)$ symmetry. This symmetry allows the N\'eel vector and the valence-bond-solid order parameter to be rotated into each other. It is a remarkable 2+1-dimensional analogue of the $SO(4)= [SU(2)\times SU(2)]/Z_2$ symmetry that appears in the scaling limit for the spin-1/2 Heisenberg chain. The emergent $SO(5)$ is strong evidence that the phase transition in the 2+1D system is truly continuous, despite the violations of finite-size scaling observed previously in this problem. It also implies surprising relations between correlation functions at the transition. The symmetry enhancement is expected to apply generally to the critical two-component Abelian Higgs model (non-compact $CP^1$ model). The result indicates that in three dimensions there is an $SO(5)$-symmetric conformal field theory which has no relevant singlet operators, so is radically different to conventional Wilson-Fisher-type conformal field theories.Comment: 4+epsilon pages, 6 figure

Is regionalism better for economic integration? : nations, regions, and risk sharing

Our analysis yields some conclusions about the political role of regions in the formation of supranational economic areas, which turns out to be quite di®erent from the role of nations. The claim that regions have more incentives than nations to attain a ¯scal agreement implying full economic integration is likely to be correct when nations are economic stable arrangements, i.e. when the rich region of a nation is not \exploited" by the poor region. When, on the other hand, it is not on the interest of a rich region to be part of a nation, attempts to achieve full economic integration among a group of nations is more likely to be successful if nations, instead of regions, are the decision makers

A theoretical model of nations, regions and fiscal integration

This paper analyzes how the incentives of regions differ from those of nations when choosing a supranational fiscal arrangement. Two types of fiscal arrangements are studied: a Union of nations and a Federation of nations. Under the Union, there is full fiscal integration, and under the Federation, there is only partial fiscal integration and partial insurance against local risks. We show that the claim that regions have stronger incentives than nations to form a supranational Union rather than a Federation might be true only in the case where regions have strong incentives to be part of a centralized nation.Ortuno-Ortin gratefully acknowledges financial support from Spanish Ministry of Science and Technology, Project SEJ2004-00968, Fundacion BBVA-3-04x and CAM 06/HSE/0157/2004Publicad

3D loop models and the CP^{n-1} sigma model

Many statistical mechanics problems can be framed in terms of random curves; we consider a class of three-dimensional loop models that are prototypes for such ensembles. The models show transitions between phases with infinite loops and short-loop phases. We map them to $CP^{n-1}$ sigma models, where $n$ is the loop fugacity. Using Monte Carlo simulations, we find continuous transitions for $n=1,2,3$, and first order transitions for $n\geq 5$. The results are relevant to line defects in random media, as well as to Anderson localization and $(2+1)$-dimensional quantum magnets.Comment: Published versio

Deconfined Quantum Criticality, Scaling Violations, and Classical Loop Models

Numerical studies of the N\'eel to valence-bond solid phase transition in 2D quantum antiferromagnets give strong evidence for the remarkable scenario of deconfined criticality, but display strong violations of finite-size scaling that are not yet understood. We show how to realise the universal physics of the Neel-VBS transition in a 3D classical loop model (this includes the interference effect that suppresses N\'eel hedgehogs). We use this model to simulate unprecedentedly large systems (of size $L\leq 512$). Our results are compatible with a direct continuous transition at which both order parameters are critical, and we do not see conventional signs of first-order behaviour. However, we find that the scaling violations are stronger than previously realised and are incompatible with conventional finite-size scaling over the size range studied, even if allowance is made for a weakly/marginally irrelevant scaling variable. In particular, different determinations of the anomalous dimensions $\eta_\text{VBS}$ and $\eta_\text{N\'eel}$ yield very different results. The assumption of conventional finite-size scaling gives estimates which drift to negative values at large $L$, in violation of unitarity bounds. In contrast, the behaviour of correlators on scales much smaller than $L$ is consistent with large positive anomalous dimensions. Barring an unexpected reversal in behaviour at still larger sizes, this implies that the transition, if continuous, must show unconventional finite-size scaling, e.g. from a dangerously irrelevant scaling variable. Another possibility is an anomalously weak first-order transition. By analysing the renormalisation group flows for the non-compact $CP^{n-1}$ model ($n$-component Abelian Higgs model) between two and four dimensions, we give the simplest scenario by which an anomalously weak first-order transition can arise without fine-tuning of the Hamiltonian.Comment: 20 pages, 19 figure

Evaluation of Bacterial Resistance to Antibiotics in Stool Samples Obtained from Guinea Pigs (Cavia porcellus) in Family and Family-commercial Farms

The inappropriate use of antimicrobial agents in guinea pigs to control enteric pathogens affects the nutritional sustainability of the rural population. Therefore, it is important to identify the pathogen, its resistance, and the appropriate antimicrobial agent for its control. The present investigation was carried out in family and family-commercial guinea pig farms, in eight rural parishes of the Gualaceo canton, Azuay province, Ecuador, from which 384 samples were obtained by rectal swabbing of guinea pigs from production units with enteric problems (diarrhea), the same ones that were transferred to the laboratory of the Faculty of Agricultural Sciences of the University of Cuenca, in order to identify the bacterial agents present in fecal samples of guinea pigs. There the isolation of culture media and identification of pathogens were carried out, they were subsequently exposed to an antibiogram, in order to qualitatively assess their bacterial resistance. The data were tabulated and analyzed in SPSS, finding the presence of Escherichia coli (49.4%), Salmonella typhimurium (24.6%), Shigella flexneri (14.3%), and Klebsiella pneumoniae (11.7%). The Chi-square test determined that of the five antimicrobials used, only tetracycline had a relationship between bacterial presence and resistance. It was also found that Escherichia coli presented a higher percentage of resistance, for enrofloxacin 22.5%, neomycin 14.2%, sulfamethoxazole - trimethoprim 33.3%, tetracyclines 29.2%. Data were analyzed at a confidence level of 95% with a 5% error, concluding that the identified pathogens have low resistance to the antimicrobials used, but are still susceptible. Keywords: bacterial resistance, antibiogram, enteric infection, antibiotics. Resumen El uso inadecuado de agentes antimicrobianos en cobayos para controlar patógenos entéricos, afectan la sustentabilidad alimenticia de la población rural, por ello es importante identificar el patógeno, su resistencia y el agente antimicrobiano adecuado para su control. La presente investigación se realizó en explotaciones de cobayos de tipo familiar y familiar – comercial, en ocho parroquias rurales del cantón Gualaceo provincia del Azuay, Ecuador de donde se obtuvo 384 muestras mediante hisopado rectal de cobayos provenientes de unidades productoras con problemas entéricos (diarrea), las mismas que fueron trasladadas al laboratorio de la Facultad de Ciencias Agropecuarias de la Universidad de Cuenca, con el fin de identificar los agentes bacterianos presentes en muestras fecales de cobayos, ahí se realizó la infección de medios de cultivo e identificación de agentes patógenos, mismos que posteriormente fueron expuestos a un antibiograma, con la finalidad de evaluar cualitativamente su resistencia bacteriana. Los datos fueron tabulados y analizados en SPSS, encontrándose la presencia de Escherichia coli (49,4%), Salmonella typhimurium (24,6%), Shigella flexneri (14,3%) y Klebsiella pneumoniae (11,7%). En la prueba de chi 2, se determinó que de los cinco antimicrobianos usados, solamente la Tetraciclina tiene relación entre la presencia bacteriana y la resistencia; también se encontró que Escherichia coli presentó mayor porcentaje de resistencia, para Enrofloxacina 22,5%, Neomicina 14,2%, Sulfametoxazol – trimetoprim 33,3%, Tetraciclinas 29,2%, datos que fueron analizados a un nivel de confianza del 95% con un 5% de error, concluyendo que los patógenos identificados presentan baja resistencia a los antimicrobianos utilizados, pero aún son susceptibles. Palabras Clave: resistencia bacteriana, antibiograma, infección entérica, antibióticos

Effects of many-electron jumps in relaxation and conductivity of Coulomb glasses

A numerical study of the energy relaxation and conductivity of the Coulomb glass is presented. The role of many-electron transitions is studied by two complementary methods: a kinetic Monte Carlo algorithm and a master equation in configuration space method. A calculation of the transition rate for two-electron transitions is presented, and the proper extension of this to multi-electron transitions is discussed. It is shown that two-electron transitions are important in bypassing energy barriers which effectively block sequential one-electron transitions. The effect of two-electron transitions is also discussed.Comment: 8 pages, 6 figure

Fluctuations of the correlation dimension at metal-insulator transitions

We investigate numerically the inverse participation ratio, $P_2$, of the 3D Anderson model and of the power-law random banded matrix (PRBM) model at criticality. We found that the variance of $\ln P_2$ scales with system size $L$ as $\sigma^2(L)=\sigma^2(\infty)-A L^{-D_2/2d}$, being $D_2$ the correlation dimension and $d$ the system dimension. Therefore the concept of a correlation dimension is well defined in the two models considered. The 3D Anderson transition and the PRBM transition for $b=0.3$ (see the text for the definition of $b$) are fairly similar with respect to all critical magnitudes studied.Comment: RevTex, 5 pages, 4 eps figures, to be published in Phys. Rev. Let

Statistical keyword detection in literary corpora

Understanding the complexity of human language requires an appropriate analysis of the statistical distribution of words in texts. We consider the information retrieval problem of detecting and ranking the relevant words of a text by means of statistical information referring to the "spatial" use of the words. Shannon's entropy of information is used as a tool for automatic keyword extraction. By using The Origin of Species by Charles Darwin as a representative text sample, we show the performance of our detector and compare it with another proposals in the literature. The random shuffled text receives special attention as a tool for calibrating the ranking indices.Comment: Published version. 11 pages, 7 figures. SVJour for LaTeX2

Active tectonics of the Alhama de Murcia fault, Betic Cordillera, Spain

We present an overview of the knowledge of the structure and the seismic behavior of the Alhama de Murcia Fault (AMF). We utilize a fault traces map created from a LIDAR DEM combined with the geodynamic setting, the analysis of the morphology, the distribution of seismicity, the geological information from E 1:50000 geological maps and the available paleoseismic data to describe the recent activity of the AMF. We discuss the importance of uncertainties regarding the structure and kinematics of the AMF applied to the interpretation and spatial correlation of the paleoseismic data. In particular, we discuss the nature of the faults dipping to the SE (antithetic to the main faults of the AMF) in several segments that have been studied in the previous paleoseismic works. A special chapter is dedicated to the analysis of the tectonic source of the Lorca 2011 earthquake that took place in between two large segments of the fault