12,090 research outputs found
The role of positivity and causality in interactions involving higher spin
It is shown that the recently introduced positivity and causality preserving string-local quantum field theory (SLFT) resolves most No-Go situations in higher spin problems. This includes in particular the Velo–Zwanziger causality problem which turns out to be related in an interesting way to the solution of zero mass Weinberg–Witten issue. In contrast to the indefinite metric and ghosts of gauge theory, SLFT uses only positivity-respecting physical degrees of freedom. The result is a fully Lorentz-covariant and causal string field theory in which light- or space-like linear strings transform covariant under Lorentz transformation.
The cooperation of causality and quantum positivity in the presence of interacting
particles leads to remarkable conceptual changes. It turns out that the presence of H-selfinteractions in the Higgs model is not the result of SSB on a postulated Mexican hat potential, but solely the consequence of the implementation of positivity and causality. These principles (and not the imposed gauge symmetry) account also for the Lie-algebra structure of the leading contributions of selfinteracting vector mesons.
Second order consistency of selfinteracting vector mesons in SLFT requires the presence of H-particles; this, and not SSB, is the raison d'être for H.
The basic conceptual and calculational tool of SLFT is the S-matrix. Its string-independence is a powerful restriction which determines the form of interaction densities in terms of the model-defining particle content and plays a fundamental role in the construction of pl observables and sl interpolating fields
Classical-Quantum Coexistence: a `Free Will' Test
Von Neumann's statistical theory of quantum measurement interprets the
instantaneous quantum state and derives instantaneous classical variables. In
realty, quantum states and classical variables coexist and can influence each
other in a time-continuous way. This has been motivating investigations since
longtime in quite different fields from quantum cosmology to optics as well as
in foundations. Different theories (mean-field, Bohm, decoherence, dynamical
collapse, continuous measurement, hybrid dynamics, e.t.c.) emerged for what I
call `coexistence of classical continuum with quantum'. I apply to these
theories a sort of `free will' test to distinguish `tangible' classical
variables useful for causal control from useless ones.Comment: 7pp, based on talk at Conf. on Emergent Quantum Mechanics, Heinz von
Foerster Congress (Vienna University, Nov 11-13, 2011
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