1,720,981 research outputs found
Color-flavor reflection in the continuum limit of two-dimensional lattice gauge theories with scalar fields
Full text linkWe address the interplay between local and global symmetries in determining
the continuum limit of two-dimensional lattice scalar theories characterized by
gauge symmetry and non-Abelian global invariance. We argue
that, when a quartic interaction is present, the continuum limit of these model
corresponds in some cases to the gauged non-linear model field theory
associated with the real Grassmannian manifold ), which is characterized by the invariance under the color-flavor
reflection . Monte Carlo simulations and
Finite-Size Scaling analyses, performed for and several values of
, confirm the emergence of the color-flavor reflection symmetry in the
scaling limit, and support the identification of the continuum limit.Comment: 9 pages, 8 pdf figure
Quantum critical behaviors and decoherence of weakly coupled quantum Ising models within an isolated global system
No full textWe discuss the quantum dynamics of an isolated composite system consisting of weakly interacting manybody subsystems. We focus on one of the subsystems, S, and study the dependence of its quantum correlations and decoherence rate on the state of the weakly-coupled complementary part E, which represents the environment. As a theoretical laboratory, we consider a composite system made of two stacked quantum Ising chains, locally and homogeneously weakly coupled. One of the chains is identified with the subsystem S under scrutiny, and the other one with the environment E. We investigate the behavior of S at equilibrium, when the global system is in its ground state, and under out-of-equilibrium conditions, when the global system evolves unitarily after a quench of the coupling between S and E. When S develops quantum critical correlations in the weak-coupling regime, the associated scaling behavior crucially depends on the quantum state of E, whether it is characterized by short-range correlations (analogous to those characterizing disordered phases in closed systems), algebraically decaying correlations (typical of critical systems), or long-range correlations (typical of magnetized ordered phases). In particular, different scaling behaviors, depending on the state of E, are observed for the decoherence of the subsystem S, as demonstrated by the different power-law divergences of the decoherence susceptibility that quantifies the sensitivity of the coherence to the interaction with E
From learning to new goal generation in a bioinspired robotic setup
No full textIn the field of cognitive bioinspired robotics, we focus on autonomous development, and propose a possible model to explain how humans generate and pursue new goals that are not strictly dictated by survival. Autonomous lifelong learning is an important ability for robots to make them able to acquire new skills, and autonomous goal generation is a basic mechanism for that. The Intentional Distributed Robotic Architecture (IDRA) here presented intends to allow the autonomous development of new goals in situated agents starting from some simple hard-coded instincts. It addresses this capability through an imitation of the neural plasticity, the property of
the cerebral cortex supporting learning. Three main brain areas are involved in goal generation, cerebral cortex, thalamus, and amygdala; these are mimicked at a functional level by the modules of our computational model, namely Deliberative, Working-Memory, Goal-Generator, and Instincts Modules, all connected in a network. IDRA has been designed to be robot independent; we have used it in simulation and on the real Aldebaran NAO humanoid robot. The reported experiments explore how basic capabilities, as active sensing, are obtained by the architecture
Critical crossover phenomena driven by symmetry-breaking defects at quantum transitions
Full text linkWe study the effects of symmetry-breaking defects at continuous quantum
transitions (CQTs), which may arise from localized external fields coupled to
the order-parameter operator. The problem is addressed within
renormalization-group (RG) and finite-size scaling frameworks. We consider the
paradigmatic one-dimensional quantum Ising models at their CQT, in the presence
of defects which break the global symmetry. We show that such
defects can give rise to notable critical crossover regimes where the
ground-state properties experience substantial and rapid changes, from
symmetric conditions to symmetry-breaking boundaries. An effective
characterization of these crossover phenomena driven by defects is achieved by
analyzing the ground-state fidelity associated with small changes of the defect
strength. Within the critical crossover regime, the fidelity susceptibility
shows a power-law divergence when increasing the system size, related to the RG
dimension of the defect strength; in contrast, outside the critical defect
regime, it remains finite. We support the RG scaling arguments with numerical
results.Comment: 13 pages, 11 figure
Quantum many-body spin rings coupled to ancillary spins: The sunburst quantum Ising model
Full text linkWe study the ground-state properties of a quantum "sunburst model", composed
of a quantum Ising spin-ring in a transverse field, symmetrically coupled to a
set of ancillary isolated qubits, to maintain a residual translation invariance
and also a symmetry. The large-size limit is taken in two
different ways: either by keeping the distance between any two neighboring
ancillary qubits fixed, or by fixing their number while increasing the ring
size. Substantially different regimes emerge, depending on the various
Hamiltonian parameters: for small energy scale of the ancillary
subsystem and small ring-qubits interaction , we observe rapid and
nonanalytic changes in proximity of the quantum transitions of the Ising ring,
both first-order and continuous, which can be carefully controlled by
exploiting renormalization-group and finite-size scaling frameworks. Smoother
behaviors are instead observed when keeping fixed and in the Ising
disordered phase. The effect of an increasing number of ancillary spins
turns out to scale proportionally to for sufficiently large values
of .Comment: 15 pages, 16 figures. Corrected fig. 10 and few misprint
The organization of Cortex-Ganglia-Thalamus to generate movements from motor primitives: a model for developmental robotics
Full text linkA bioinspired intentional architecture for situated agents to explore human cognitive abilities
No full textThree-dimensional lattice SU(Nc) gauge theories with multiflavor scalar fields in the adjoint representation
No full textWe consider three-dimensional lattice SU(Nc) gauge theories with multiflavor (Nf>1) scalar fields in theadjoint representation. We investigate their phase diagram, identify the different Higgs phases with their gauge-symmetry pattern, and determine the nature of the transition lines. In particular, we study the role played bythe quartic scalar potential and by the gauge-group representation in determining the Higgs phases and theglobal and gauge-symmetry-breaking patterns characterizing the different transitions. The general argumentsare confirmed by numerical analyses of Monte Carlo results for two representative models that are expected tohave qualitatively different phase diagrams and Higgs phases. We consider the model with Nc=3, Nf=2 and with Nc=2, Nf=4. This second case is interesting phenomenologically to describe some features of cuprate superconductors
Decoherence and energy flow in the sunburst quantum Ising model
Full text linkWe study the post-quench unitary dynamics of a quantum sunburst spin model,
composed of a transverse-field quantum Ising ring which is suddenly coupled to
a set of independent external qubits along the longitudinal direction, in a way
to respect a residual translation invariance and the Ising
symmetry. Starting from the different equilibrium quantum phases of the system,
we characterize the decoherence and the energy storage in the external qubits,
which may be interpreted as a probing apparatus for the inner Ising ring. Our
results show that, in proximity of the quantum transitions of the Ising ring,
either first-order or continuous, it is possible to put forward dynamic FSS
frameworks which unveil peculiar scaling regimes, depending on the way in which
the large-size limit is taken: either by fixing the number of probing
qubits, or their interspace distance . In any case, the dependence of the
various observables on can be reabsorbed into a redefinition of the quench
parameter by a prefactor. We also address the role of a
nearest-neighbor coupling between the external qubits.Comment: 24 pages, 11 figure
Linguistic primitives: A new model for language development in robotics
No full textOften in robotics natural language processing is used simply to improve the human-machine interaction. However, language is not only a powerful communication tool: it is deeply linked to the inner organization of the mind, and it guides its development. The aim of this paper is to take a first step towards a model of language which can be integrated with the diverse abilities of the robot, thus leading to its cognitive development, and eventually speeding up its learning capacity. To this end we propose and implement the Language primitives Model (LPM) to imitate babbling, a phase in the learning process that characterizes a few months old babies. LPM is based on the same principles dictated by the Motor Primitives model. The obtained results positively compare with experimental data and observations about children, so confirming this interest of the new model
- …
