236 research outputs found
An open--quantum--system formulation of particle decay
We consider an open quantum system which contains unstable states. The time
evolution of the system can be described by an effective non-hermitian
Hamiltonian H_{eff}, in accord with the Wigner--Weisskopf approximation, and an
additional term of the Lindblad form, the socalled dissipator. We show that,
after enlarging the original Hilbert space by states which represent the decay
products of the unstable states, the non-hermitian part of H_{eff} --the
``particle decay''-- can be incorporated into the dissipator of the enlarged
space via a specific Lindblad operator. Thus the new formulation of the time
evolution on the enlarged space has a hermitian Hamiltonian and is probability
conserving. The equivalence of the new formulation with the original one
demonstrates that the time evolution which is governed by a non-hermitian
Hamiltonian and a dissipator of the Lindblad form is nevertheless completely
positive, just as systems with hermitian Hamiltonians.Comment: 8 page
Hawking Radiation via Gravitational Anomalies in Non-spherical Topologies
We study the method of calculating the Hawking radiation via gravitational
anomalies in gravitational backgrounds of constant negative curvature. We apply
the method to topological black holes and also to topological black holes
conformally coupled to a scalar field.Comment: 25 pages, no figures, version to be published in Phys. Rev.
Canonical Formalism for a 2n-Dimensional Model with Topological Mass Generation
The four-dimensional model with topological mass generation that was found by
Dvali, Jackiw and Pi has recently been generalized to any even number of
dimensions (2n-dimensions) in a nontrivial manner in which a Stueckelberg-type
mass term is introduced [S. Deguchi and S. Hayakawa, Phys. Rev. D 77, 045003
(2008), arXiv:0711.1446]. The present paper deals with a self-contained model,
called here a modified hybrid model, proposed in this 2n-dimensional
generalization and considers the canonical formalism for this model. For the
sake of convenience, the canonical formalism itself is studied for a model
equivalent to the modified hybrid model by following the recipe for treating
constrained Hamiltonian systems. This formalism is applied to the canonical
quantization of the equivalent model in order to clarify observable and
unobservable particles in the model. The equivalent model (with a gauge-fixing
term) is converted to the modified hybrid model (with a corresponding
gauge-fixing term) in a Becchi-Rouet-Stora-Tyutin (BRST)-invariant manner.
Thereby it is shown that the Chern-Pontryagin density behaves as an observable
massive particle (or field). The topological mass generation is thus verified
at the quantum-theoretical level.Comment: 29 pages, no figures, minor corrections, published versio
Decoherence of entangled kaons and its connection to entanglement measures
We study the time evolution of the entangled kaon system by considering the
Liouville - von Neumann equation with an additional term which allows for
decoherence. We choose as generators of decoherence the projectors to the
2-particle eigenstates of the Hamiltonian. Then we compare this model with the
data of the CPLEAR experiment and find in this way an upper bound on the
strength of the decoherence. We also relate to an effective
decoherence parameter considered previously in literature. Finally we
discuss our model in the light of different measures of entanglement, i.e. the
von Neumann entropy , the entanglement of formation and the concurrence
, and we relate the decoherence parameter to the loss of
entanglement: .Comment: comments and references added, 18 pages, 1 figur
Can an odd number of fermions be created due to chiral anomaly?
We describe a possibility of creation of an odd number of fractionally
charged fermions in 1+1 dimensional Abelian Higgs model. We point out that for
1+1 dimensions this process does not violate any symmetries of the theory, nor
makes it mathematically inconsistent. We construct the proper definition of the
fermionic determinant in this model and underline its non-trivial features that
are of importance for realistic 3+1 dimensional models with fermion number
violation.Comment: 12 pages revtex, 2 figure
Commuting multiparty quantum observables and local compatibility
A formula for the commutator of tensor product matrices is used to shows
that, for qubits, compatibility of quantum multiparty observables almost never
implies local compatibility at each site and to predict when this happens/does
not happen in a concise manner. In particular, it is shown that two ``fully
nontrivial'' -qubit observables are compatible locally and globally if and
only if they are equal up to sign. In addition, the formula gives insight into
the construction of new paradoxes of the type of the Kochen-Specker Theorem,
which can then be easily rephrased into proposals for new no hidden variable
experiments of the type of the ``Bell Theorem without inequalities''.Comment: 6 page
Quantitative complementarity in two-path interferometry
The quantitative formulation of Bohr's complementarity proposed by
Greenberger and Yasin is applied to some physical situations for which
analytical expressions are available. This includes a variety of conventional
double-slit experiments, but also particle oscillations, as in the case of the
neutral-kaon system, and Mott scattering of identical nuclei. For all these
cases, a unified description can be achieved including a new parameter, ,
which quantifies the effective number of fringes one can observe in each
specific interferometric set-up.Comment: 11 RevTex pages, 5 figure
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