22,636 research outputs found
Self-completeness and spontaneous dimensional reduction
A viable quantum theory of gravity is one of the biggest challenges facing
physicists. We discuss the confluence of two highly expected features which
might be instrumental in the quest of a finite and renormalizable quantum
gravity -- spontaneous dimensional reduction and self-completeness. The former
suggests the spacetime background at the Planck scale may be effectively
two-dimensional, while the latter implies a condition of maximal compression of
matter by the formation of an event horizon for Planckian scattering. We
generalize such a result to an arbitrary number of dimensions, and show that
gravity in higher than four dimensions remains self-complete, but in lower
dimensions it is not. In such a way we established an "exclusive disjunction"
or "exclusive or" (XOR) between the occurrence of self-completeness and
dimensional reduction, with the goal of actually reducing the unknowns for the
scenario of the physics at the Planck scale. Potential phenomenological
implications of this result are considered by studying the case of a
two-dimensional dilaton gravity model resulting from dimensional reduction of
Einstein gravity.Comment: 12 pages, 3 figures; v3: final version in press on Eur. Phys. J. Plu
Composition of Jupiter irregular satellites sheds light on their origin
Irregular satellites of Jupiter with their highly eccentric, inclined and
distant orbits suggest that their capture took place just before the giant
planet migration. We aim to improve our understanding of the surface
composition of irregular satellites of Jupiter to gain insight into a narrow
time window when our Solar System was forming. We observed three Jovian
irregular satellites, Himalia, Elara, and Carme, using a medium-resolution
0.8-5.5 micro m spectrograph on the National Aeronautics and Space
Administration (NASA) Infrared Telescope Facility (IRTF). Using a linear
spectral unmixing model we have constrained the major mineral phases on the
surface of these three bodies. Our results confirm that the surface of Himalia,
Elara, and Carme are dominated by opaque materials such as those seen in
carbonaceous chondrite meteorites. Our spectral modeling of NIR spectra of
Himalia and Elara confirm that their surface composition is the same and
magnetite is the dominant mineral. A comparison of the spectral shape of
Himalia with the two large main C-type asteroids, Themis (D 176 km) and Europa
(D 352 km), suggests surface composition similar to Europa. The NIR spectrum of
Carme exhibits blue slope up to 1.5 microm and is spectrally distinct from
those of Himalia and Elara. Our model suggests that it is compositionally
similar to amorphous carbon. Himalia and Elara are compositionally similar but
differ significantly from Carme. These results support the hypotheses that the
Jupiter irregular satellites are captured bodies that were subject to further
breakup events and clustered as families based on their similar physical and
surface compositions
The postlarval phase of bivalve mollusks: A review of functional ecology and new records of postlarval drifting of Chesapeake Bay bivalves
Many bivalve mollusks have one or more separate post-metamorphic stages which are functionally distinct from the late juvenile or the adult. The benthic plantigrade and the planktonic postlarva are defined and reviewed here. The plantigrade is a developmentally obligatory stage in mast bivalves. Various anatomical or conchological features, depending on taxa, are intermediate between the veliger and the juvenile. The plantigrade is benthic but highly mobile, via the foot and byssus, relative to the adult, although in some highly mobile bivalves, the plantigrade is functionally similar to the adult. The plantigrade may enter the water column briefly, but not nearly to the extent that the postlarva does. The planktonic postlarva is a non-obligatory stage, usually developmentally synonymous with the plantigrade, but functionally distinct. A specialized byssus or similar drogue is used by the postlarva for extended planktonic drifting. The plantigrade may serve simply as a developmentally intermediate stage between the larva and the juvenile, it may increase a species\u27 options when selecting a habitat by its ability to relocate, or it may occupy a different habitat than later stages. The planktonic postlarva can either increase the dispersal ability of a bivalve, or, like the plantigrade phase, it can permit an ontogenetic niche shift. Planktonic postlarvae for three species not previously shown to exhibit this phase (Anadara transversa, Geukensia demissa, and Tellina agilis) are reported and described here
Quasiclassical Equations of Motion for Nonlinear Brownian Systems
Following the formalism of Gell-Mann and Hartle, phenomenological equations
of motion are derived from the decoherence functional formalism of quantum
mechanics, using a path-integral description. This is done explicitly for the
case of a system interacting with a ``bath'' of harmonic oscillators whose
individual motions are neglected. The results are compared to the equations
derived from the purely classical theory. The case of linear interactions is
treated exactly, and nonlinear interactions are compared using classical and
quantum perturbation theory.Comment: 24 pages, CALT-68-1848 (RevTeX 2.0 macros
Exotic fermion multiplets as a solution to baryon asymmetry, dark matter and neutrino masses
We propose an extension to the standard model where three exotic fermion
5-plets and one scalar 6-plet are added to the particle content. By demanding
that all interactions are renormalizable and standard model gauge invariant, we
show that the lightest exotic particle in this model can be a dark matter
candidate as long as the new 6-plet scalar does not develop a nonzero vacuum
expectation value. Furthermore, light neutrino masses are generated radiatively
at one-loop while the baryon asymmetry is produced by the CP-violating decays
of the second lightest exotic particle. We have demonstrated using concrete
examples that there is a parameter space where a consistent solution to the
problems of baryon asymmetry, dark matter and neutrino masses can be obtained.Comment: 17 pages, 2 figures (REVTeX4.1), v2: some refs added, v3: typos
corrected, Sec.VI.B, C modified, this version to appear in PR
Decoherent Histories Quantum Mechanics with One 'Real' Fine-Grained History
Decoherent histories quantum theory is reformulated with the assumption that
there is one "real" fine-grained history, specified in a preferred complete set
of sum-over-histories variables. This real history is described by embedding it
in an ensemble of comparable imagined fine-grained histories, not unlike the
familiar ensemble of statistical mechanics. These histories are assigned
extended probabilities, which can sometimes be negative or greater than one. As
we will show, this construction implies that the real history is not completely
accessible to experimental or other observational discovery. However,
sufficiently and appropriately coarse-grained sets of alternative histories
have standard probabilities providing information about the real fine-grained
history that can be compared with observation. We recover the probabilities of
decoherent histories quantum mechanics for sets of histories that are recorded
and therefore decohere. Quantum mechanics can be viewed as a classical
stochastic theory of histories with extended probabilities and a well-defined
notion of reality common to all decoherent sets of alternative coarse-grained
histories.Comment: 11 pages, one figure, expanded discussion and acknowledgment
N-body Gravity and the Schroedinger Equation
We consider the problem of the motion of bodies in a self-gravitating
system in two spacetime dimensions. We point out that this system can be mapped
onto the quantum-mechanical problem of an N-body generalization of the problem
of the H molecular ion in one dimension. The canonical gravitational
N-body formalism can be extended to include electromagnetic charges. We derive
a general algorithm for solving this problem, and show how it reduces to known
results for the 2-body and 3-body systems.Comment: 15 pages, Latex, references added, typos corrected, final version
that appears in CQ
Gapless Hartree-Fock Resummation Scheme for the O(N) Model
A modified selfconsistent Hartree-Fock approximation to the lambda*phi^4
theory with spontaneously broken O(N) symmetry is proposed. It preserves all
the desirable features, like conservation laws and thermodynamic consistency,
of the selfconsistent Dyson scheme generated from a 2PI functional, also known
as the Phi-derivable scheme, while simultaneously respecting the
Nambu-Goldstone theorem in the chiral-symmetry broken phase. Various
approximate resummation schemes are discussed.Comment: 13 pages, 10 figures / Version accepted by Phys. Rev. D: the
introduction has been expanded by a few remarks in order to further clarify
the goal of the pape
The 1987 update on leased grounds near the US 17 bridge over Chuckatuck Creek
This report is an update of a study made in June to mid-august 1979. This study was made by the Virginia Institute of Marine Science of the College of William and Mary for the Department of Highways and Transportation, Suffolk, Virginia. The previous study provided: 1) a description of the shellfish resource prior to construction of a new bridge; 2) an estimate of the value of the oysters and shell on leased areas within the right-of-way; and 3) a basis for a later study after construction to evaluate possible environmental changes.
Since 1979 the Commonwealth has purchased the right-of-way and the VMRC has opened it to public fishing. There is no shellfish resources in the right-of-way. Therefore, the study describes the present shellfish resource in the adjacent leases, within 600 ft. of the center of the bridge, which might be affected by construction activity
A resurvey of the Hampton Roads corridor area adjacent to the proposed site of the I-664 bridge-tunnel
On July 2 and 3, 1985, a survey was conducted by the Virginia Institute of Marine Science (VIMS) on Drewery-Register (formerly Melzer) leased bottom (48.37 acres) off Newport News Point, Virginia (Figure 1). The study was done at the request of the Virginia Department of Highways and Transportation, Suffolk, Virginia in relation to the construction of I-664, Project 066!!-121-102, RW-201.
The objective of this study was to determine the extent and value of the molluscan resource on the Dewery - Register lease prior to construction activity
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