6,125 research outputs found
Gravitational Geons Revisited
A careful analysis of the gravitational geon solution found by Brill and
Hartle is made. The gravitational wave expansion they used is shown to be
consistent and to result in a gauge invariant wave equation. It also results in
a gauge invariant effective stress-energy tensor for the gravitational waves
provided that a generalized definition of a gauge transformation is used. To
leading order this gauge transformation is the same as the usual one for
gravitational waves. It is shown that the geon solution is a self-consistent
solution to Einstein's equations and that, to leading order, the equations
describing the geometry of the gravitational geon are identical to those
derived by Wheeler for the electromagnetic geon. An appendix provides an
existence proof for geon solutions to these equations.Comment: 18 pages, ReVTeX. To appear in Physical Review D. Significant changes
include more details in the derivations of certain key equations and the
addition of an appendix containing a proof of the existence of a geon
solution to the equations derived by Wheeler. Also a reference has been added
and various minor changes have been mad
Three-Dimensional Gravity and String Ghosts
It is known that much of the structure of string theory can be derived from
three-dimensional topological field theory and gravity. We show here that, at
least for simple topologies, the string diffeomorphism ghosts can also be
explained in terms of three-dimensional physics.Comment: 6 page
The Fermionic Projector, Entanglement, and the Collapse of the Wave Function
After a brief introduction to the fermionic projector approach, we review how
entanglement and second quantized bosonic and fermionic fields can be described
in this framework. The constructions are discussed with regard to decoherence
phenomena and the measurement problem. We propose a mechanism leading to the
collapse of the wave function in the quantum mechanical measurement process.Comment: 17 pages, LaTeX, 2 figures, minor changes (published version
Emergence of classical behavior from the quantum spin
Classical Hamiltonian system of a point moving on a sphere of fixed radius is
shown to emerge from the constrained evolution of quantum spin. The constrained
quantum evolution corresponds to an appropriate coarse-graining of the quantum
states into equivalence classes, and forces the equivalence classes to evolve
as single units representing the classical states. The coarse-grained quantum
spin with the constrained evolution in the limit of the large spin becomes
indistinguishable from the classical system
Partial domain wall partition functions
We consider six-vertex model configurations on an n-by-N lattice, n =< N,
that satisfy a variation on domain wall boundary conditions that we define and
call "partial domain wall boundary conditions". We obtain two expressions for
the corresponding "partial domain wall partition function", as an
(N-by-N)-determinant and as an (n-by-n)-determinant. The latter was first
obtained by I Kostov. We show that the two determinants are equal, as expected
from the fact that they are partition functions of the same object, that each
is a discrete KP tau-function, and, recalling that these determinants represent
tree-level structure constants in N=4 SYM, we show that introducing 1-loop
corrections, as proposed by N Gromov and P Vieira, preserves the determinant
structure.Comment: 30 pages, LaTeX. This version, which appeared in JHEP, has an
abbreviated abstract and some minor stylistic change
Understanding light quanta: First quantization of the free electromagnetic field
The quantization of the electromagnetic field in vacuum is presented without
reference to lagrangean quantum field theory. The equal time commutators of the
fields are calculated from basic principles. A physical discussion of the
commutators suggest that the electromagnetic fields are macroscopic emergent
properties of more fundamental physical system: the photons
Electrodynamics of balanced charges
In this work we modify the wave-corpuscle mechanics for elementary charges
introduced by us recently. This modification is designed to better describe
electromagnetic (EM) phenomena at atomic scales. It includes a modification of
the concept of the classical EM field and a new model for the elementary charge
which we call a balanced charge (b-charge). A b-charge does not interact with
itself electromagnetically, and every b-charge possesses its own elementary EM
field. The EM energy is naturally partitioned as the interaction energy between
pairs of different b-charges. We construct EM theory of b-charges (BEM) based
on a relativistic Lagrangian with the following properties: (i) b-charges
interact only through their elementary EM potentials and fields; (ii) the field
equations for the elementary EM fields are exactly the Maxwell equations with
proper currents; (iii) a free charge moves uniformly preserving up to the
Lorentz contraction its shape; (iv) the Newton equations with the Lorentz
forces hold approximately when charges are well separated and move with
non-relativistic velocities. The BEM theory can be characterized as
neoclassical one which covers the macroscopic as well as the atomic spatial
scales, it describes EM phenomena at atomic scale differently than the
classical EM theory. It yields in macroscopic regimes the Newton equations with
Lorentz forces for centers of well separated charges moving with
nonrelativistic velocities. Applied to atomic scales it yields a hydrogen atom
model with a frequency spectrum matching the same for the Schrodinger model
with any desired accuracy.Comment: Manuscript was edited to improve the exposition and to remove noticed
typo
East-central Florida pre-Columbian wood sculpture: Radiocarbon dating, wood identification and strontium isotope studies
A suite of scientific approaches are applied to four pre- Columbian wood sculptures from east-central Florida, comprising new radiocarbon determinations, wood identification and strontium isotope analysis. The dates for three large zoomorphic carvings recovered from the St. Johns River at Hontoon Island place them between ca. AD 1300 and 1600, suggesting that they belonged to a tradition of erecting largescale pine carvings spanning at least some centuries. Two of the carvings have strontium isotope signals consistent with the immediate vicinity of the site, while the third differs significantly. Baseline data for biologically available strontium from sampled modern trees indicates considerable isotopic variability over short distances, making it difficult to determine the source of the wood used for this third carving. The only anthropomorphic sculpture, recovered from the vicinity of Tomoka State Park, dates to a similar time period, ca. AD 1440-1620. Our study confirms the wood's previous identification as belonging to the genus Peltophorum, a tropical hardwood thought not to be native to Florida. Its strontium isotope value is consistent with its find location, but equally may be found over much of southern Florida, where perhaps the species grew in the past. The results clarify the chronology for a stylistically distinctive carving tradition, as well as raising questions concerning the exchange of organic materials over varying distances. Highlights • 14C results for four east-central Florida carvings (Hontoon Island; Tomoka State Park) range ca. AD 1300-1600, spanning the proto-historic/historic periods • 87Sr/86Sr results for two of the three Hontoon carvings are consistent with the immediate locale, while the third suggests a different provenance • Pinus sp. was used at Hontoon, while Peltophorum sp., currently not native to Florida, was used at Tomoka</p
Loop Quantum Cosmology II: Volume Operators
Volume operators measuring the total volume of space in a loop quantum theory
of cosmological models are constructed. In the case of models with rotational
symmetry an investigation of the Higgs constraint imposed on the reduced
connection variables is necessary, a complete solution of which is given for
isotropic models; in this case the volume spectrum can be calculated
explicitly. It is observed that the stronger the symmetry conditions are the
smaller is the volume spectrum, which can be interpreted as level splitting due
to broken symmetries. Some implications for quantum cosmology are presented.Comment: 21 page
Naturalizing Dasein and other (Alleged) Heresies
First paragraph: To my mind, being wrong is nowhere near as disheartening as being boring, so I am encouraged by the fact that, in the four chapters immediately preceding this one, four thinkers for whom I have nothing but the utmost intellectual respect have found my ongoing project to articulate the philosophical groundwork for a genuinely Heideggerian cognitive science interesting enough that they have taken the trouble to explain precisely why it is flawed. Just how deep the supposed flaws go depends on which set of criticisms one chooses to read. For Ratcliffe and Rehberg they go very deep indeed, since, for these thinkers, there is a sense in which the very idea of a Heideggerian cognitive science borders on the incoherent. Dreyfus and Rietveld, on the other hand, seem to agree with me that something worth calling a Heideggerian cognitive science is certainly possible; it's just that my version of it is seriously defective
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