434 research outputs found
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
Dissimilar bouncy walkers
We consider the dynamics of a one-dimensional system consisting of dissimilar
hardcore interacting (bouncy) random walkers. The walkers' (diffusing
particles') friction constants xi_n, where n labels different bouncy walkers,
are drawn from a distribution rho(xi_n). We provide an approximate analytic
solution to this recent single-file problem by combining harmonization and
effective medium techniques. Two classes of systems are identified: when
rho(xi_n) is heavy-tailed, rho(xi_n)=A xi_n^(-1-\alpha) (0<alpha<1) for large
xi_n, we identify a new universality class in which density relaxations,
characterized by the dynamic structure factor S(Q,t), follows a Mittag-Leffler
relaxation, and the the mean square displacement of a tracer particle (MSD)
grows as t^delta with time t, where delta=alpha/(1+\alpha). If instead rho is
light-tailedsuch that the mean friction constant exist, S(Q,t) decays
exponentially and the MSD scales as t^(1/2). We also derive tracer particle
force response relations. All results are corroborated by simulations and
explained in a simplified model.Comment: 11 pages, to appear in Journal of Chemical Physic
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)
Polarization tailored novel vector beams based on conical refraction
Coherent vector beams with involved states of polarization (SOP) are
widespread in the literature, having applications in laser processing,
super-resolution imaging and particle trapping. We report novel vector beams
obtained by transforming a Gaussian beam passing through a biaxial crystal, by
means of the conical refraction phenomenon. We analyze both experimentally and
theoretically the SOP of the different vector beams generated and demonstrate
that the SOP of the input beam can be used to control both the shape and the
SOP of the transformed beam. We also identify polarization singularities of
such beams for the first time and demonstrate their control by the SOP of an
input beam
First-passage dynamics of obstructed tracer particle diffusion in one-dimensional systems
The standard setup for single-file diffusion is diffusing particles in one
dimension which cannot overtake each other, where the dynamics of a tracer
(tagged) particle is of main interest. In this article we generalise this
system and investigate first-passage properties of a tracer particle when
flanked by crowder particles which may, besides diffuse, unbind (rebind) from
(to) the one-dimensional lattice with rates (). The
tracer particle is restricted to diffuse with rate on the lattice. Such a
model is relevant for the understanding of gene regulation where regulatory
proteins are searching for specific binding sites ona crowded DNA. We quantify
the first-passage time distribution, ( is time), numerically using
the Gillespie algorithm, and estimate it analytically. In terms of our key
parameter, the unbinding rate , we study the bridging of two known
regimes: (i) when unbinding is frequent the particles may effectively pass each
other and we recover the standard single particle result
with a renormalized diffusion constant, (ii) when unbinding is rare we recover
well-known single-file diffusion result . The intermediate
cases display rich dynamics, with the characteristic -peak and the
long-time power-law slope both being sensitive to
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
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
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