Vector triplets at the LHC

Several popular extensions of the Standard Model predict extra vector fields that transform as triplets under the gauge group SU(2)_L. These multiplets contain Z' and W' bosons, with masses and couplings related by gauge invariance. We review some model-independent results about these new vector bosons, with emphasis on di-lepton and lepton-plus-missing-energy signals at the LHC.Comment: LaTex 5 pages. Talk by M. Perez-Victoria at LHCP 2013, Barcelona, Spain, May 13-18, 2013. New reference adde

Holographic renormalisation group flows and renormalisation from a Wilsonian perspective

From the Wilsonian point of view, renormalisable theories are understood as submanifolds in theory space emanating from a particular fixed point under renormalisation group evolution. We show how this picture precisely applies to their gravity duals. We investigate the Hamilton-Jacobi equation satisfied by the Wilson action and find the corresponding fixed points and their eigendeformations, which have a diagonal evolution close to the fixed points. The relevant eigendeformations are used to construct renormalised theories. We explore the relation of this formalism with holographic renormalisation. We also discuss different renormalisation schemes and show that the solutions to the gravity equations of motion can be used as renormalised couplings that parametrise the renormalised theories. This provides a transparent connection between holographic renormalisation group flows in the Wilsonian and non-Wilsonian approaches. The general results are illustrated by explicit calculations in an interacting scalar theory in AdS space.Comment: 63 pages. Minor changes and references added. Matches JHEP versio

Wilsonian renormalisation of CFT correlation functions: Field theory

We examine the precise connection between the exact renormalisation group with local couplings and the renormalisation of correlation functions of composite operators in scale-invariant theories. A geometric description of theory space allows us to select convenient non-linear parametrisations that serve different purposes. First, we identify normal parameters in which the renormalisation group flows take their simplest form; normal correlators are defined by functional differentiation with respect to these parameters. The renormalised correlation functions are given by the continuum limit of correlators associated to a cutoff-dependent parametrisation, which can be related to the renormalisation group flows. The necessary linear and non-linear counterterms in any arbitrary parametrisation arise in a natural way from a change of coordinates. We show that, in a class of minimal subtraction schemes, the renormalised correlators are exactly equal to normal correlators evaluated at a finite cutoff. To illustrate the formalism and the main results, we compare standard diagrammatic calculations in a scalar free-field theory with the structure of the perturbative solutions to the Polchinski equation close to the Gaussian fixed point.This work has been supported by the Spanish MICINN project FPA 2013-47836-C3-2-P, the MINECO project FPA2016-78220-C3-1-P and by the European Commission through the contract PITN-GA-2012-316704 (HIGGSTOOLS)

Single-file dynamics with different diffusion constants

We investigate the single-file dynamics of a tagged particle in a system consisting of N hardcore interacting particles (the particles cannot pass each other) which are diffusing in a one-dimensional system where the particles have different diffusion constants. For the two particle case an exact result for the conditional probability density function (PDF) is obtained for arbitrary initial particle positions and all times. The two-particle PDF is used to obtain the tagged particle PDF. For the general N-particle case (N large) we perform stochastic simulations using our new computationally efficient stochastic simulation technique based on the Gillespie algorithm. We find that the mean square displacement for a tagged particle scales as the square root of time (as for identical particles) for long times, with a prefactor which depends on the diffusion constants for the particles; these results are in excellent agreement with very recent analytic predictions in the mathematics literature.Comment: 9 pages, 5 figures. Journal of Chemical Physics (in press

Time walkers and spatial dynamics of ageing information

The distribution of information is essential for living system's ability to coordinate and adapt. Random walkers are often used to model this distribution process and, in doing so, one effectively assumes that information maintains its relevance over time. But the value of information in social and biological systems often decay and must continuously be updated. To capture the spatial dynamics of ageing information, we introduce time walkers. A time walker moves like a random walker, but interacts with traces left by other walkers, some representing older information, some newer. The traces forms a navigable information landscape. We quantify the dynamical properties of time walkers moving on a two-dimensional lattice and the quality of the information landscape generated by their movements. We visualise the self-similar landscape as a river network, and show that searching in this landscape is superior to random searching and scales as the length of loop-erased random walks

Diffusive transport in networks built of containers and tubes

We developed analytical and numerical methods to study a transport of non-interacting particles in large networks consisting of M d-dimensional containers C_1,...,C_M with radii R_i linked together by tubes of length l_{ij} and radii a_{ij} where i,j=1,2,...,M. Tubes may join directly with each other forming junctions. It is possible that some links are absent. Instead of solving the diffusion equation for the full problem we formulated an approach that is computationally more efficient. We derived a set of rate equations that govern the time dependence of the number of particles in each container N_1(t),N_2(t),...,N_M(t). In such a way the complicated transport problem is reduced to a set of M first order integro-differential equations in time, which can be solved efficiently by the algorithm presented here. The workings of the method have been demonstrated on a couple of examples: networks involving three, four and seven containers, and one network with a three-point junction. Already simple networks with relatively few containers exhibit interesting transport behavior. For example, we showed that it is possible to adjust the geometry of the networks so that the particle concentration varies in time in a wave-like manner. Such behavior deviates from simple exponential growth and decay occurring in the two container system.Comment: 21 pages, 18 figures, REVTEX4; new figure added, reduced emphasis on graph theory, additional discussion added (computational cost, one dimensional tubes

Patrones de colonización y ecología de poblaciones de dos bivalvos invasores (mejillón cebra Dreissena polymorpha Pallas, 1771 y almeja asiática Corbicula fluminea Müller, 1774) en un tramo lótico del Ebro medio (Castejón, Navarra).

Los bivalvos dulceacuícolas son un componente importante de la ecología fluvial, fundamentalmente por el papel que desempeñan como organismos filtradores y de remoción del sedimento. Además son un grupo zoológico diverso y amenazado a escala global, en el que se incluyen algunas de las especies invasoras más dañinas. El estudio de sus poblaciones es imprescindible para conocer el estado de conservación de las comunidades bentónicas. Para esto se prospectaron 17 parcelas vadeables y 7 escolleras a lo largo de 7,38 km de meandros del río Ebro en Castejón (Navarra), tanto el cauce principal como en brazos secundarios de corriente permanente y/o temporal. El mejillón cebra Dreissena polymorpha Pallas, 1771 se encontró en 7 escolleras y 6 parcelas. El sustrato preferente fueron rocas (85%), donde la densidad resultó 0,31-5,45 mejillones/m2; el 2,6% se hallaron sobre plásticos agrícolas abandonados. En las escolleras sólo el 3,6% de los ejemplares eran juveniles y un 33% tenían una edad > 4 años. La almeja asiática Corbicula fluminea Müller, 1774 se encontró en todas las parcelas. La densidad resultó muy diferente en los tres tipos de ambientes fluviales con valores máximos de 15.100 almejas/m2, lo que constituye un nuevo máximo fluvial en Europa. Se encontraron subpoblaciones de almeja asiática con diferentes estructuras de edad según los ambientes fluviales, además de poblaciones menos numerosas en el brazo principal del río que en los otros tipos. Los resultados muestran que junto a estas especies alóctonas en expansión, con altas tasas de reclutamiento, se encuentra una estructura poblacional muy precaria para las autóctonas, de las cuales únicamente se localizaron 12 náyades vivas y ningún esférido

Depolarizing metrics for plant samples imaging

Optical methods, as fluorescence microscopy or hyperspectral imaging, are commonly used for plants visualization and characterization. Another powerful collection of optical techniques is the so-called polarimetry, widely used to enhance image contrast in multiple applications. In the botanical applications framework, in spite of some works have already highlighted the depolarizing print that plant structures left on input polarized beams, the potential of polarimetric methods has not been properly exploited. In fact, among the few works dealing with polarization and plants, most of them study light scattered by plants using the Degree of Polarization (DoP) indicator. Other more powerful depolarization metrics are nowadays neglected. In this context, we highlight the potential of different depolarization metrics obtained using the Mueller matrix (MM) measurement: the Depolarization Index and the Indices of Polarimetric Purity. We perform a qualitative and quantitative comparison between DoP- and MM-based images by studying a particular plant, the Hedera maroccana. We show how Mueller-based metrics are generally more suitable in terms of contrast than DoP-based measurements. The potential of polarimetric measurements in the study of plants is highlighted in this work, suggesting they can be applied to the characterization of plants, plant taxonomy, water stress in plants, and other botanical studies