81,687 research outputs found
Towards a General Theory of Quantized Fields on the Anti-de Sitter Space-Time
We propose a general framework for studying quantum field theory on the
anti-de-Sitter space-time, based on the assumption of positivity of the
spectrum of the possible energy operators. In this framework we show that the
n-point functions are analytic in suitable domains of the complex AdS manifold,
that it is possible to Wick rotate to the Euclidean manifold and come back, and
that it is meaningful to restrict AdS quantum fields to Poincare' branes. We
give also a complete characterization of two-point functions which are the
simplest example of our theory. Finally we prove the existence of the AdS-Unruh
effect for uniformly accelerated observers on trajectories crossing the
boundary of AdS at infinity, while that effect does not exist for all the other
uniformly accelerated trajectories.Comment: LaTex, 43 pages, 2 figures. New introduction. Discussion of the
AdS-Unruh effect expanded. Final section added. To be published on CM
Model Reduction for Quantum Systems: Discrete-time Quantum Walks and Open Markov Dynamics
A general approach to obtain reduced models for a wide class of discrete-time
quantum systems is proposed. The obtained models not only reproduce exactly the
output of a given quantum model, but are also guaranteed to satisfy physical
constraints, namely complete positivity and preservation of total probability.
A fundamental framework for exact model reduction of quantum systems is
constructed leveraging on algebraic methods, as well as novel results on
quantum conditional expectations in finite-dimensions. The proposed reduction
algorithm is illustrated and tested on prototypical examples, including the
quantum walk realizing Grover's algorithm.Comment: 16 page
Reflection Positivity and Monotonicity
We prove general reflection positivity results for both scalar fields and
Dirac fields on a Riemannian manifold, and comment on applications to quantum
field theory. As another application, we prove the inequality
between Dirichlet and Neumann covariance operators on a manifold with a
reflection.Comment: 11 page
On the Debate Concerning the Proper Characterisation of Quantum Dynamical Evolution
There has been a long-standing and sometimes passionate debate between
physicists over whether a dynamical framework for quantum systems should
incorporate not completely positive (NCP) maps in addition to completely
positive (CP) maps. Despite the reasonableness of the arguments for complete
positivity, we argue that NCP maps should be allowed, with a qualification:
these should be understood, not as reflecting 'not completely positive'
evolution, but as linear extensions, to a system's entire state space, of CP
maps that are only partially defined. Beyond the domain of definition of a
partial-CP map, we argue, much may be permitted.Comment: To be presented at the 2012 biennial meeting of the Philosophy of
Science Association (PSA), San Diego, Californi
Irreversibility and dissipation in neutral B-meson decays
The propagation and decay of neutral B-mesons can be described in terms of
quantum dynamical semigroups; they provide generalized time-evolutions that
take into account possible non-standard effects leading to loss of phase
coherence and dissipation. These effects can be fully parametrized in terms of
six phenomenological constants. A detailed analysis of selected B-meson decays
shows that present and future dedicated experiments, both at colliders and
B-factories, will be able to put stringent bounds on these non-standard
parameters.Comment: 33 pages, plain-TeX, no figure
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