321 research outputs found
ARES:Adaptive receding-horizon synthesis of optimal plans
We introduce ARES, an efficient approximation algorithm for generating optimal plans (action sequences) that take an initial state of a Markov Decision Process (MDP) to a state whose cost is below a specified (convergence) threshold. ARES uses Particle Swarm Optimization, with adaptive sizing for both the receding horizon and the particle swarm. Inspired by Importance Splitting, the length of the horizon and the number of particles are chosen such that at least one particle reaches a next-level state, that is, a state where the cost decreases by a required delta from the previous-level state. The level relation on states and the plans constructed by ARES implicitly define a Lyapunov function and an optimal policy, respectively, both of which could be explicitly generated by applying ARES to all states of the MDP, up to some topological equivalence relation. We also assess the effectiveness of ARES by statistically evaluating its rate of success in generating optimal plans. The ARES algorithm resulted from our desire to clarify if flying in V-formation is a flocking policy that optimizes energy conservation, clear view, and velocity alignment. That is, we were interested to see if one could find optimal plans that bring a flock from an arbitrary initial state to a state exhibiting a single connected V-formation. For flocks with 7 birds, ARES is able to generate a plan that leads to a V-formation in 95% of the 8,000 random initial configurations within 63 s, on average. ARES can also be easily customized into a model-predictive controller (MPC) with an adaptive receding horizon and statistical guarantees of convergence. To the best of our knowledge, our adaptive-sizing approach is the first to provide convergence guarantees in receding-horizon techniques
Reconciling neutrino anomalies in a simple four-neutrino scheme with R-parity violation
We propose a simple extension of the MSSM based on extra compact dimensions
which includes an singlet superfield. The fermion present
in this superfield is the sterile neutrino, which combines with one linear
combination of to form a Dirac pair whose mass
accounts for the LSND anomaly. Its small mass can be ascribed to a volume
suppression factor associated with extra compact dimensions. On the other hand
the sterile neutrino scalar partner can trigger the spontaneous violation of
R-parity, thereby inducing the necessary mass splittings to fit also the solar
and atmospheric neutrino data. Thus the model can explain all neutrino
oscillation data. It leads to four predictions for the neutrino oscillation
parameters and implies that the atmospheric neutrino problem must include at
least some oscillations, which will be testable in the
near future. Moreover it also predicts that the lightest supersymmetric
particle (LSP) decays visibly via lepton number violating modes, which could be
searched for at present and future accelerators.Comment: 15 pages, requires axodraw.sty and elsart.cl
Neutrinoless Double Beta Decay from Singlet Neutrinos in Extra Dimensions
We study the model-building conditions under which a sizeable
-decay signal to the recently reported level of~0.4 eV is due
to Kaluza--Klein singlet neutrinos in theories with large extra dimensions. Our
analysis is based on 5-dimensional singlet-neutrino models compactified on an
orbifold, where the Standard--Model fields are localized on a
3-brane. We show that a successful interpretation of a positive signal within
the above minimal 5-dimensional framework would require a non-vanishing shift
of the 3-brane from the orbifold fixed points by an amount smaller than the
typical scale (100 MeV) characterizing the Fermi nuclear momentum. The
resulting 5-dimensional models predict a sizeable effective Majorana-neutrino
mass that could be several orders of magnitude larger than the light neutrino
masses. Most interestingly, the brane-shifted models with only one bulk sterile
neutrino also predict novel trigonometric textures leading to mass scenarios
with hierarchical active neutrinos and large - and
- mixings that can fully explain the current atmospheric and
solar neutrino data.Comment: 33 pages, LaTeX, minor rewordings, references adde
Neutrino Masses and Mixing: Evidence and Implications
Measurements of various features of the fluxes of atmospheric and solar
neutrinos have provided evidence for neutrino oscillations and therefore for
neutrino masses and mixing. We review the phenomenology of neutrino
oscillations in vacuum and in matter. We present the existing evidence from
solar and atmospheric neutrinos as well as the results from laboratory
searches, including the final status of the LSND experiment. We describe the
theoretical inputs that are used to interpret the experimental results in terms
of neutrino oscillations. We derive the allowed ranges for the mass and mixing
parameters in three frameworks: First, each set of observations is analyzed
separately in a two-neutrino framework; Second, the data from solar and
atmospheric neutrinos are analyzed in a three active neutrino framework; Third,
the LSND results are added, and the status of accommodating all three signals
in the framework of three active and one sterile light neutrinos is presented.
We review the theoretical implications of these results: the existence of new
physics, the estimate of the scale of this new physics and the lessons for
grand unified theories, for supersymmetric models with R-parity violation, for
models of extra dimensions and singlet fermions in the bulk, and for flavor
models.Comment: Added note on the effects of KamLAND results. Two new figure
Mechanosensory interactions drive collective behaviour in Drosophila.
Collective behaviour enhances environmental sensing and decision-making in groups of animals. Experimental and theoretical investigations of schooling fish, flocking birds and human crowds have demonstrated that simple interactions between individuals can explain emergent group dynamics. These findings indicate the existence of neural circuits that support distributed behaviours, but the molecular and cellular identities of relevant sensory pathways are unknown. Here we show that Drosophila melanogaster exhibits collective responses to an aversive odour: individual flies weakly avoid the stimulus, but groups show enhanced escape reactions. Using high-resolution behavioural tracking, computational simulations, genetic perturbations, neural silencing and optogenetic activation we demonstrate that this collective odour avoidance arises from cascades of appendage touch interactions between pairs of flies. Inter-fly touch sensing and collective behaviour require the activity of distal leg mechanosensory sensilla neurons and the mechanosensory channel NOMPC. Remarkably, through these inter-fly encounters, wild-type flies can elicit avoidance behaviour in mutant animals that cannot sense the odour--a basic form of communication. Our data highlight the unexpected importance of social context in the sensory responses of a solitary species and open the door to a neural-circuit-level understanding of collective behaviour in animal groups
Observation of associated near-side and away-side long-range correlations in âsNN=5.02ââTeV proton-lead collisions with the ATLAS detector
Two-particle correlations in relative azimuthal angle (ÎÏ) and pseudorapidity (Îη) are measured in âsNN=5.02ââTeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1ââÎŒb-1 of data as a function of transverse momentum (pT) and the transverse energy (ÎŁETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Îη|<5) ânear-sideâ (ÎÏâŒ0) correlation that grows rapidly with increasing ÎŁETPb. A long-range âaway-sideâ (ÎÏâŒÏ) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ÎŁETPb, is found to match the near-side correlation in magnitude, shape (in Îη and ÎÏ) and ÎŁETPb dependence. The resultant ÎÏ correlation is approximately symmetric about Ï/2, and is consistent with a dominant cosâĄ2ÎÏ modulation for all ÎŁETPb ranges and particle pT
- âŠ