443 research outputs found
Massive and massless higher spinning particles in odd dimensions
We study actions for massive bosonic particles of higher spins by
dimensionally reducing an action for massless particles. For the latter we take
a model with a SO(N) extended local supersymmetry on the worldline, that is
known to describe massless (conformal) particles of higher spins in flat
spacetimes of even dimensions. Dimensional reduction produces an action for
massive spinning particles in odd dimensions. The field equations that emerge
in a quantization a la Dirac are shown to be equivalent to the Fierz-Pauli
ones. The massless limit generates a multiplet of massless states with higher
spins, whose first quantized field equations have a geometric form with fields
belonging to various types of Young tableaux. These geometric equations can be
partially integrated to show their equivalence with the standard
Fronsdal-Labastida equations. We covariantize our model to check whether an
extension to curved spacetimes can be achieved. Restricting to (A)dS spaces, we
find that the worldline gauge algebra becomes nonlinear, but remains first
class. This guarantees consistency on such backgrounds. A light cone analysis
confirms the presence of the expected propagating degrees of freedom. A
covariant analysis is worked out explicitly for the massive case, which is seen
to give rise to the Fierz-Pauli equations extended to (A)dS spaces. It is worth
noting that in D=3 the massless limit of our model when N goes to infinity has
the same field content of the Vasiliev's theory that accommodates each spin
exactly once.Comment: 31 page
Particles with non abelian charges
Efficient methods for describing non abelian charges in worldline approaches
to QFT are useful to simplify calculations and address structural properties,
as for example color/kinematics relations. Here we analyze in detail a method
for treating arbitrary non abelian charges. We use Grassmann variables to take
into account color degrees of freedom, which however are known to produce
reducible representations of the color group. Then we couple them to a U(1)
gauge field defined on the worldline, together with a Chern-Simons term, to
achieve projection on an irreducible representation. Upon gauge fixing there
remains a modulus, an angle parametrizing the U(1) Wilson loop, whose
dependence is taken into account exactly in the propagator of the Grassmann
variables. We test the method in simple examples, the scalar and spin 1/2
contribution to the gluon self energy, and suggest that it might simplify the
analysis of more involved amplitudes.Comment: 14 page
Furan-PNA : a mildly inducible irreversible interstrand crosslinking system targeting single and double stranded DNA
We here report on the design and synthesis of tailor-made furan-modified peptide nucleic acid (PNA) probes for covalent targeting of single stranded DNA through a crosslinking strategy. After introducing furan-containing building blocks into a PNA sequence, hybridization and furan-oxidation based crosslinking to DNA is investigated. The structure of the crosslinked products is characterized and preliminary investigations concerning the application of these systems to double stranded DNA are shown
Adaptation is a Game
Control data variants of game models such as Interface Automata are suitable for the design and analysis of self-adaptive systems
Modelling and analyzing adaptive self-assembling strategies with Maude
Building adaptive systems with predictable emergent behavior is a challenging task and it is becoming a critical need. The research community has accepted the challenge by introducing approaches of various nature: from software architectures, to programming paradigms, to analysis techniques. We recently proposed a conceptual framework for adaptation centered around the role of control data. In this paper we show that it can be naturally realized in a reflective logical language like Maude by using the Reflective Russian Dolls model. Moreover, we exploit this model to specify, validate and analyse a prominent example of adaptive system: robot swarms equipped with self-assembly strategies. The analysis exploits the statistical model checker PVeStA
Event structures for Petri nets with persistence
Event structures are a well-accepted model of concurrency. In a seminal paper by Nielsen, Plotkin and Winskel, they are used to establish a bridge between the theory of domains and the approach to concurrency proposed by Petri. A basic role is played by an unfolding construction that maps (safe) Petri nets into a subclass of event structures, called prime event structures, where each event has a uniquely determined set of causes. Prime event structures, in turn, can be identified with their domain of configurations. At a categorical level, this is nicely formalised by Winskel as a chain of coreflections. Contrary to prime event structures, general event structures allow for the presence of disjunctive causes, i.e., events can be enabled by distinct minimal sets of events. In this paper, we extend the connection between Petri nets and event structures in order to include disjunctive causes. In particular, we show that, at the level of nets, disjunctive causes are well accounted for by persistent places. These are places where tokens, once generated, can be used several times without being consumed and where multiple tokens are interpreted collectively, i.e., their histories are inessential. Generalising the work on ordinary nets, Petri nets with persistence are related to a new subclass of general event structures, called locally connected, by means of a chain of coreflections relying on an unfolding construction
A Conceptual Framework for Adapation
This paper presents a white-box conceptual framework for adaptation that promotes a neat separation of the adaptation logic from the application logic through a clear identification of control data and their role in the adaptation logic. The framework provides an original perspective from which we survey archetypal approaches to (self-)adaptation ranging from programming languages and paradigms, to computational models, to engineering solutions
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