28,511 research outputs found
On Epstein's trajectory model of non-relativistic quantum mechanics
In 1952 Bohm presented a theory about non-relativistic point-particles moving
along deterministic trajectories and showed how it reproduces the predictions
of standard quantum theory. This theory was actually presented before by de
Broglie in 1926, but Bohm's particular formulation of the theory inspired
Epstein to come up with a different trajectory model. The aim of this paper is
to examine the empirical predictions of this model. It is found that the
trajectories in this model are in general very different from those in the de
Broglie-Bohm theory. In certain cases they even seem bizarre and rather
unphysical. Nevertheless, it is argued that the model seems to reproduce the
predictions of standard quantum theory (just as the de Broglie-Bohm theory).Comment: 12 pages, no figures, LaTex; v2 minor improvement
A minimalist pilot-wave model for quantum electrodynamics
We present a way to construct a pilot-wave model for quantum electrodynamics.
The idea is to introduce beables corresponding only to the bosonic degrees of
freedom and not to the fermionic degrees of freedom of the quantum state. We
show that this is sufficient to reproduce the quantum predictions. The beables
will be field beables corresponding to the electromagnetic field and they will
be introduced in a similar way to that of Bohm's model for the free
electromagnetic field. Our approach is analogous to the situation in
non-relativistic quantum theory, where Bell treated spin not as a beable but
only as a property of the wavefunction. After presenting this model we also
discuss a simple way for introducing additional beables that represent the
fermionic degrees of freedom.Comment: LaTex, 17 pages, no figures; v2 minor corrections, journal versio
Pilot-wave theory and quantum fields
Pilot-wave theories provide possible solutions to the measurement problem. In
such theories, quantum systems are not only described by the state vector, but
also by some additional variables. These additional variables, also called
beables, can be particle positions, field configurations, strings, etc. In this
paper we focus our attention on pilot-wave theories in which the additional
variables are field configurations. The first such theory was proposed by Bohm
for the free electromagnetic field. Since Bohm, similar pilot-wave theories
have been proposed for other quantum fields. The purpose of this paper is to
present an overview and further development of these proposals. We discuss
various bosonic quantum field theories such as the Schroedinger field, the free
electromagnetic field, scalar quantum electrodynamics and the Abelian Higgs
model. In particular, we compare the pilot-wave theories proposed by Bohm and
by Valentini for the electromagnetic field, finding that they are equivalent.
We further discuss the proposals for fermionic fields by Holland and Valentini.
In the case of Holland's model we indicate that further work is required in
order to show that the model is capable of reproducing the standard quantum
predictions. We also consider a similar model, which does not seem to reproduce
the standard quantum predictions. In the case of Valentini's model we point out
a problem that seems hard to overcome.Comment: 65 pages, no figures, LaTex; v2 minor changes, some extensions; v3
minor improvements; v4 some typos correcte
Molecular modeling for physical property prediction
Multiscale modeling is becoming the standard approach for process study in a broader framework that promotes computer aided integrated product and process design. In addition to usual purity requirements, end products must meet new constraints in terms of environmental impact, safety of goods and people, specific properties. This chapter adresses the use of molecular modeling tools for the prediction of physical property usefull for chemical engineering practice
A Dirac sea pilot-wave model for quantum field theory
We present a pilot-wave model for quantum field theory in which the Dirac sea
is taken seriously. The model ascribes particle trajectories to all the
fermions, including the fermions filling the Dirac sea. The model is
deterministic and applies to the regime in which fermion number is
superselected. This work is a further elaboration of work by Colin, in which a
Dirac sea pilot-wave model is presented for quantum electrodynamics. We extend
his work to non-electromagnetic interactions, we discuss a cut-off
regularization of the pilot-wave model and study how it reproduces the standard
quantum predictions. The Dirac sea pilot-wave model can be seen as a possible
continuum generalization of a lattice model by Bell. It can also be seen as a
development and generalization of the ideas by Bohm, Hiley and Kaloyerou, who
also suggested the use of the Dirac sea for the development of a pilot-wave
model for quantum electrodynamics.Comment: 41 pages, no figures, LaTex, v2 minor improvements and addition
Control of unstable macroscopic oscillations in the dynamics of three coupled Bose condensates
We study the dynamical stability of the macroscopic quantum oscillations
characterizing a system of three coupled Bose-Einstein condensates arranged
into an open-chain geometry. The boson interaction, the hopping amplitude and
the central-well relative depth are regarded as adjustable parameters. After
deriving the stability diagrams of the system, we identify three mechanisms to
realize the transition from an unstable to stable behavior and analyze specific
configurations that, by suitably tuning the model parameters, give rise to
macroscopic effects which are expected to be accessible to experimental
observation. Also, we pinpoint a system regime that realizes a
Josephson-junction-like effect. In this regime the system configuration do not
depend on the model interaction parameters, and the population oscillation
amplitude is related to the condensate-phase difference. This fact makes
possible estimating the latter quantity, since the measure of the oscillating
amplitudes is experimentally accessible.Comment: 25 pages, 12 figure
Coarse-Graining the Lin-Maldacena Geometries
The Lin-Maldacena geometries are nonsingular gravity duals to degenerate
vacuum states of a family of field theories with SU(2|4) supersymmetry. In this
note, we show that at large N, where the number of vacuum states is large,
there is a natural `macroscopic' description of typical states, giving rise to
a set of coarse-grained geometries. For a given coarse-grained state, we can
associate an entropy related to the number of underlying microstates. We find a
simple formula for this entropy in terms of the data that specify the geometry.
We see that this entropy function is zero for the original microstate
geometries and maximized for a certain ``typical state'' geometry, which we
argue is the gravity dual to the zero-temperature limit of the thermal state of
the corresponding field theory. Finally, we note that the coarse-grained
geometries are singular if and only if the entropy function is non-zero.Comment: 29 pages, LaTeX, 3 figures; v2 references adde
Towards classical geometrodynamics from Group Field Theory hydrodynamics
We take the first steps towards identifying the hydrodynamics of group field
theories (GFTs) and relating this hydrodynamic regime to classical
geometrodynamics of continuum space. We apply to GFT mean field theory
techniques borrowed from the theory of Bose condensates, alongside standard GFT
and spin foam techniques. The mean field configuration we study is, in turn,
obtained from loop quantum gravity coherent states. We work in the context of
2d and 3d GFT models, in euclidean signature, both ordinary and colored, as
examples of a procedure that has a more general validity. We also extract the
effective dynamics of the system around the mean field configurations, and
discuss the role of GFT symmetries in going from microscopic to effective
dynamics. In the process, we obtain additional insights on the GFT formalism
itself.Comment: revtex4, 32 pages. Contribution submitted to the focus issue of the
New Journal of Physics on "Classical and Quantum Analogues for Gravitational
Phenomena and Related Effects", R. Schuetzhold, U. Leonhardt and C. Maia,
Eds; v2: typos corrected, references updated, to match the published versio
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