23,103 research outputs found
Spacetime: Arena or Reality?
For small values of the mass (in relation to the angular momentum and
electric charge), the Kerr-Newman (KN) solution of Einstein equation reduces to
a naked singularity of circular shape. By considering the Hawking and Ellis
extended interpretation of the KN spacetime, as well as Wheeler's idea of
"charge without charge", the non-trivial topological structure of the extended
KN spatial section is found to represent gravitational states with
half-integral angular momentum. As a consequence, it can be consistently
interpreted as a model for the electron-positron system, in which the concepts
of mass, charge and spin emerge from the spacetime geometry. According to this
model, therefore, instead of a simple arena, spacetime must have a concrete
existence, being responsible -- through its highly non-trivial topological
structures -- for the building blocks of (at least some of) the existing matter
in the universe.Comment: Chapter in the book "Relativity and the Dimensionality of the World",
Springer series "Fundamental Theories of Physics", Vol. 153 (2007). Volume
Editor: Vesselin Petko
Kerr-Newman solution as a Dirac particle
For m^2 < a^2 + q^2, with m, a, and q respectively the source mass, angular
momentum per unit mass, and electric charge, the Kerr--Newman (KN) solution of
Einstein's equation reduces to a naked singularity of circular shape, enclosing
a disk across which the metric components fail to be smooth. By considering the
Hawking and Ellis extended interpretation of the KN spacetime, it is shown
first that, similarly to the electron-positron system, this solution presents
four inequivalent classical states. Next, it is shown that due to the
topological structure of the extended KN spacetime it does admit states with
half-integral angular momentum. This last property is corroborated by the fact
that, under a rotation of the space coordinates, those inequivalent states
transform into themselves only after a 4pi rotation. As a consequence, it
becomes possible to naturally represent them in a Lorentz spinor basis. The
state vector representing the whole KN solution is then constructed, and its
evolution is shown to be governed by the Dirac equation. The KN solution can
thus be consistently interpreted as a model for the electron-positron system,
in which the concepts of mass, charge and spin become connected with the
spacetime geometry. Some phenomenological consequences of the model are
explored.Comment: 19 pages, 6 figures. References added, section 2 enhanced, an
appendix and one figure adde
Boundary versus bulk behavior of time-dependent correlation functions in one-dimensional quantum systems
We study the influence of reflective boundaries on time-dependent responses
of one-dimensional quantum fluids at zero temperature beyond the low-energy
approximation. Our analysis is based on an extension of effective mobile
impurity models for nonlinear Luttinger liquids to the case of open boundary
conditions. For integrable models, we show that boundary autocorrelations
oscillate as a function of time with the same frequency as the corresponding
bulk autocorrelations. This frequency can be identified as the band edge of
elementary excitations. The amplitude of the oscillations decays as a power law
with distinct exponents at the boundary and in the bulk, but boundary and bulk
exponents are determined by the same coupling constant in the mobile impurity
model. For nonintegrable models, we argue that the power-law decay of the
oscillations is generic for autocorrelations in the bulk, but turns into an
exponential decay at the boundary. Moreover, there is in general a nonuniversal
shift of the boundary frequency in comparison with the band edge of bulk
excitations. The predictions of our effective field theory are compared with
numerical results obtained by time-dependent density matrix renormalization
group (tDMRG) for both integrable and nonintegrable critical spin- chains
with , and .Comment: 20 pages, 12 figure
Gravitomagnetic Moments of the Fundamental Fields
The quadratic form of the Dirac equation in a Riemann spacetime yields a
gravitational gyromagnetic ratio \kappa_S = 2 for the interaction of a Dirac
spinor with curvature. A gravitational gyromagnetic ratio \kappa_S = 1 is also
found for the interaction of a vector field with curvature. It is shown that
the Dirac equation in a curved background can be obtained as the square--root
of the corresponding vector field equation only if the gravitational
gyromagnetic ratios are properly taken into account.Comment: 8 pages, RevTeX Style, no figures, changed presentation -- now
restricted to fields of spin 0, 1/2 and 1 -- some references adde
Non universality of entanglement convertibility
Recently, it has been suggested that operational properties connected to
quantum computation can be alternative indicators of quantum phase transitions.
In this work we systematically study these operational properties in 1D systems
that present phase transitions of different orders. For this purpose, we
evaluate the local convertibility between bipartite ground states. Our results
suggest that the operational properties, related to non-analyticities of the
entanglement spectrum, are good detectors of explicit symmetries of the model,
but not necessarily of phase transitions. We also show that thermodynamically
equivalent phases, such as Luttinger liquids, may display different
convertibility properties depending on the underlying microscopic model.Comment: 5 pages + references, 4 figures - improved versio
Magnetically-controlled impurities in quantum wires with strong Rashba coupling
We investigate the effect of strong spin-orbit interaction on the electronic
transport through non-magnetic impurities in one-dimensional systems. When a
perpendicular magnetic field is applied, the electron spin polarization becomes
momentum-dependent and spin-flip scattering appears, to first order in the
applied field, in addition to the usual potential scattering. We analyze a
situation in which, by tuning the Fermi level and the Rashba coupling, the
magnetic field can suppress the potential scattering. This mechanism should
give rise to a significant negative magnetoresistance in the limit of large
barriers.Comment: 4 pages, 2 figure
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