4,156,191 research outputs found
An approach to nonstandard quantum mechanics
We use nonstandard analysis to formulate quantum mechanics in
hyperfinite-dimensional spaces. Self-adjoint operators on
hyperfinite-dimensional spaces have complete eigensets, and bound states and
continuum states of a Hamiltonian can thus be treated on an equal footing. We
show that the formalism extends the standard formulation of quantum mechanics.
To this end we develop the Loeb-function calculus in nonstandard hulls. The
idea is to perform calculations in a hyperfinite-dimensional space, but to
interpret expectation values in the corresponding nonstandard hull. We further
apply the framework to non-relativistic quantum scattering theory. For
time-dependent scattering theory, we identify the starting time and the
finishing time of a scattering experiment, and we obtain a natural separation
of time scales on which the preparation process, the interaction process, and
the detection process take place. For time-independent scattering theory, we
derive rigorously explicit formulas for the M{\o}ller wave operators and the
S-Matrix
R^2 Dark Matter
There is a non-trivial four-derivative extension of the gravitational
spectrum that is free of ghosts and phenomenologically viable. It is the so
called -gravity since it is defined by the only addition of a term
proportional to the square of the scalar curvature. Just the presence of this
term does not improve the ultraviolet behaviour of Einstein gravity but
introduces one additional scalar degree of freedom that can account for the
dark matter of our Universe.Comment: 6 pages, 1 figure, to appear in the Proceedings of the sixth
International Workshop on the Dark Side of the Universe (DSU2010) Leon,
Guanajuato, Mexico 1-6 June 201
Particle motion around magnetized black holes: Preston-Poisson space-time
We analyze motion of massless and massive particles around black holes
immersed in an asymptotically uniform magnetic field and surrounded by some
mechanical structure, which provides the magnetic field. The space-time is
described by Preston-Poisson metric, which is the generalization of the
well-known Ernst metric with a new parameter, tidal force, characterizing the
surrounding structure. The Hamilton-Jacobi equations allow separation of
variables in the equatorial plane. The presence of tidal force from
surroundings considerably changes parameters of the test particle motion: it
increases the radius of circular orbits of particles, increases the binding
energy of massive particles going from a given circular orbits to the innermost
stable orbit near black hole. In addition, it increases the distance of minimal
approach, time delay and bending angle for a ray of light propagating near
black hole.Comment: 6 pages, RevTex, the version accepted for publication in Phys. Rev.
General purpose computer programs for numerically analyzing linear ac electrical and electronic circuits for steady-state conditions
Digital computer programs determine steady-state performance characteristics of active and passive linear circuits. The ac analysis program solves the basic circuit parameters. The compiler program solves these circuit parameters and in addition provides a more versatile program by allowing the user to perform mathematical and logical operations
Recommended from our members
The Potential of Freeform Construction Processes
The level of automation technology and processes control found in modern day construction
lags significantly behind other industries such as automotive and aerospace. The construction
industry has health and safety issues and still uses traditional methods of procurement. These
problems are compounded by diminishing skills in the labour force. Methods of production
must change if these issues are to be resolved and Freeform Construction is a collection of
processes that could have potential impact. This paper outlines some of the major issues
facing construction and sets a context with examples of digital fabrication in construction.
Freeform Construction is defined and potential applications are presented and related to
application scale. The viability of two potential applications are investigated in terms of cost.Mechanical Engineerin
Nflation: multi-field inflationary dynamics and perturbations
We carry out numerical investigations of the dynamics and perturbations in
the Nflation model of Dimopoulos et al. (2005). This model features large
numbers of scalar fields with different masses, which can cooperate to drive
inflation according to the assisted inflation mechanism. We extend previous
work to include random initial conditions for the scalar fields, and explore
the predictions for density perturbations and the tensor-to-scalar ratio. The
tensor-to-scalar ratio depends only on the number of e-foldings and is
independent of the number of fields, their masses, and their initial
conditions. It therefore always has the same value as for a single massive
field. By contrast, the scalar spectral index has significant dependence on
model parameters. While normally multi-field inflation models make predictions
for observable quantities which depend also on the unknown field initial
conditions, we find evidence of a `thermodynamic' regime whereby the predicted
spectral index becomes independent of initial conditions if there are enough
fields. Only in parts of parameter space where the mass spectrum of the fields
is extremely densely packed is the model capable of satisfying the tight
observational constraints from WMAP3 observations.Comment: 6 pages RevTeX4, 4 figures included. Updated to match PRD accepted
version. Analysis and conclusions unchanged. New references, especially
astro-ph/0510441 which was first to give the general r=8/N resul
Some model-independent phenomenological consequences of flexible brane worlds
In this work we will review the main properties of brane-world models with
low tension. Starting from very general principles, it is possible to obtain an
effective action for the relevant degrees of freedom at low energies (branons).
Using the cross sections for high-energy processes involving branons, we set
bounds on the different parameters appearing in these models. We also show that
branons provide a WIMP candidate for dark matter in a natural way. We consider
cosmological constraints on its thermal and non-thermal relic abundances. We
derive direct detection limits and compare those limits with the preferred
parameter region in the case in which the EGRET excess in the diffuse galactic
gamma rays is due to dark matter annihilation. Finally we will discuss the
constraints coming from the precision tests of the Standard Model and the muon
anomalous magnetic moment.Comment: 10 pages, 6 figures. Contribution to the Proceedings of the Second
International Conference on Quantum Theories and Renormalization Group in
Gravity and Cosmology, IRGAC 2006, Barcelona, 11-15 July, 200
- …