1,292 research outputs found
Quantum Stability of (2+1)-Spacetimes with Non-Trivial Topology
Quantum fields are investigated in the (2+1)-open-universes with non-trivial
topologies by the method of images. The universes are locally de Sitter
spacetime and anti-de Sitter spacetime. In the present article we study
spacetimes whose spatial topologies are a torus with a cusp and a sphere with
three cusps as a step toward the more general case. A quantum energy momentum
tensor is obtained by the point stripping method. Though the cusps are no
singularities, the latter cusps cause the divergence of the quantum field. This
suggests that only the latter cusps are quantum mechanically unstable. Of
course at the singularity of the background spacetime the quantum field
diverges. Also the possibility of the divergence of topological effect by a
negative spatial curvature is discussed. Since the volume of the negatively
curved space is larger than that of the flat space, one see so many images of a
single source by the non-trivial topology. It is confirmed that this divergence
does not appear in our models of topologies. The results will be applicable to
the case of three dimensional multi black hole\cite{BR}.Comment: 17 pages, revtex, 3 uuencoded figures containe
Quantum Complex Scalar Field in the Two-Dimensional Spacetime with Closed Timelike Curves and a Time-Machine Problem
It is considered the quantum complex scalar field which obeys the
authomorphic condition in the two-dimensional spacetime with closed timelike
curves and the chronology horizon. The renormalized stress-energy tensor is
obtained. It is shown that the value of the stress-energy tensor is regular at
the chronology horizon for specific authomorphic parameters. Thus the
particular example of field configuration is given for which the Hawking's
chronology protection conjecture is violated.Comment: 21(Latex)Postscript file of the figure may be received from author,
CQG-94-100
Formalising the Continuous/Discrete Modeling Step
Formally capturing the transition from a continuous model to a discrete model
is investigated using model based refinement techniques. A very simple model
for stopping (eg. of a train) is developed in both the continuous and discrete
domains. The difference between the two is quantified using generic results
from ODE theory, and these estimates can be compared with the exact solutions.
Such results do not fit well into a conventional model based refinement
framework; however they can be accommodated into a model based retrenchment.
The retrenchment is described, and the way it can interface to refinement
development on both the continuous and discrete sides is outlined. The approach
is compared to what can be achieved using hybrid systems techniques.Comment: In Proceedings Refine 2011, arXiv:1106.348
Divergences in the Effective Action for Acausal Spacetimes
The 1--loop effective Lagrangian for a massive scalar field on an arbitrary
causality violating spacetime is calculated using the methods of Euclidean
quantum field theory in curved spacetime. Fields of spin 1/2, spin 1 and
twisted field configurations are also considered. In general, we find that the
Lagrangian diverges to minus infinity at each of the nth polarised
hypersurfaces of the spacetime with a structure governed by a DeWitt-Schwinger
type expansion.Comment: 17 pages, Late
Pressure Induced Charge Disproportionation in LaMnO
We present a total energy study as a function of volume in the cubic phase of
LaMnO. A charge disproportionated state into planes of
MnO/MnO was found. It is argued that the pressure
driven localisation/delocalisation transition might go smoothly through a
region of Mn and Mn coexistence.Comment: 3 pages, 1 figure, Conference Proceedings: Nanospintronics: Design
and Realization (Kyoto, Japan 24-28 May, 2004
Casimir Effect in closed spaces
As it is well known the topology of space is not totally determined by
Einstein's equations. It is considered a massless scalar quantum field in a
static Euclidean space of dimension 3. The expectation value for the energy
density in all compact orientable Euclidean 3-spaces are obtained in this work
as a finite summation of Epstein type zeta functions. The Casimir energy
density for these particular manifolds is independent of the type of coupling
with curvature. A numerical plot of the result inside each Dirichlet region is
obtained.Comment: Version accepted for publication. The most general coupling with
curvature is chose
Stripe phases in the two-dimensional Falicov-Kimball model
The observation of charge stripe order in the doped nickelate and cuprate
materials has motivated much theoretical effort to understand the underlying
mechanism of the stripe phase. Numerical studies of the Hubbard model show two
possibilities: (i) stripe order arises from a tendency toward phase separation
and its competition with the long-range Coulomb interaction or (ii) stripe
order inherently arises as a compromise between itinerancy and magnetic
interactions. Here we determine the restricted phase diagrams of the
two-dimensional Falicov-Kimball model and see that it displays rich behavior
illustrating both possibilities in different regions of the phase diagram.Comment: (5 pages, 3 figures
Towards a method for rigorous development of generic requirements patterns
We present work in progress on a method for the engineering, validation and verification of generic requirements using domain engineering and formal methods. The need to develop a generic requirement set for subsequent system instantiation is complicated by the addition of the high levels of verification demanded by safety-critical domains such as avionics. Our chosen application domain is the failure detection and management function for engine control systems: here generic requirements drive a software product line of target systems. A pilot formal specification and design exercise is undertaken on a small (twosensor) system element. This exercise has a number of aims: to support the domain analysis, to gain a view of appropriate design abstractions, for a B novice to gain experience in the B method and tools, and to evaluate the usability and utility of that method.We also present a prototype method for the production and verification of a generic requirement set in our UML-based formal notation, UML-B, and tooling developed in support. The formal verification both of the structural generic requirement set, and of a particular application, is achieved via translation to the formal specification language, B, using our U2B and ProB tools
Hawking temperature in the eternal BTZ black hole: an example of Holography in AdS spacetime
We review the relation between AdS spacetime in 1+2 dimensions and the BTZ
black hole. Later we show that a ground state in AdS spacetime becomes a
thermal state in the BTZ black hole. We show that this is true in the bulk and
in the boundary of AdS spacetime. The existence of this thermal state is
tantamount to say that the Unruh effect exists in AdS spacetime and becomes the
Hawking effect for an eternal BTZ black hole. In order to make this we use the
correspondence introduced in Algebraic Holography between algebras of
quasi-local observables associated to wedges and doble cones regions in the
bulk of AdS spacetime and its conformal boundary respectively. Also we give the
real scalar quantum field as a concrete heuristic realization of this
formalism.Comment: 29 page
Quantum time machine
The continuation of Misner space into the Euclidean region is seen to imply
the topological restriction that the period of the closed spatial direction
becomes time-dependent. This restriction results in a modified Lorentzian
Misner space in which the renormalized stress-energy tensor for quantized
complex massless scalar fields becomes regular everywhere, even on the
chronology horizon. A quantum-mechanically stable time machine with just the
sub-microscopic size may then be constructed out of the modified Misner space,
for which the semiclassical Hawking's chronology protection conjecture is no
longer an obstruction.Comment: 6 pages, RevTe
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