3,043 research outputs found
Uses of a small field value which falls from a metastable maximum over cosmological times
We consider a small, metastable maximum vacuum expectation value of
order of a few eV, for a pseudoscalar Goldstone-like field, which is related to
the scalar inflaton field in an idealized model of a cosmological,
spontaneously-broken chiral symmetry. The b field allows for relating
semi-quantitatively three distinct quantities in a cosmological context.
(1) A very small, residual vacuum energy density or effective cosmological
constant of ~ lambda b_0^4 ~ 2.7 x 10^{-47}GeV^4, for lambda ~ 3 x 10^{-14},
the same as an empirical inflaton self-coupling.
(2) A tiny neutrino mass, less then b_0.
(3) A possible small variation downward of the proton to electron mass ratio
over cosmological time. The latter arises from the motion downward of the
field over cosmological time, toward a nonzero limiting value as . Such behavior is consistent with an equation of motion.
We argue that hypothetical b quanta, potentially inducing new long-range
forces, are absent, because of negative, effective squared mass in an equation
of motion for -field fluctuations.Comment: version accepted for publication in Mod.Phys.Lett.
Recommended from our members
The systemic environment: at the interface of aging and adult neurogenesis.
Aging results in impaired neurogenesis in the two neurogenic niches of the adult mammalian brain, the dentate gyrus of the hippocampus and the subventricular zone of the lateral ventricle. While significant work has characterized intrinsic cellular changes that contribute to this decline, it is increasingly apparent that the systemic environment also represents a critical driver of brain aging. Indeed, emerging studies utilizing the model of heterochronic parabiosis have revealed that immune-related molecular and cellular changes in the aging systemic environment negatively regulate adult neurogenesis. Interestingly, these studies have also demonstrated that age-related decline in neurogenesis can be ameliorated by exposure to the young systemic environment. While this burgeoning field of research is increasingly garnering interest, as yet, the precise mechanisms driving either the pro-aging effects of aged blood or the rejuvenating effects of young blood remain to be thoroughly defined. Here, we review how age-related changes in blood, blood-borne factors, and peripheral immune cells contribute to the age-related decline in adult neurogenesis in the mammalian brain, and posit both direct neural stem cell and indirect neurogenic niche-mediated mechanisms
The fish fauna of the Iwokrama Forest
Fishes were collected from the rivers in and around the Iwokrama Forest during January-February and November-December 1997. Four hundred species of fish were recorded from forty families in ten orders. Many of these fishes are newly recorded from Guyana and several are thought to be endemic. The number of species recorded for the area is surprising given the low level of effort and suggests that this area may be particularly important from a fish diversity perspective. This paper focuses on species of particular interest from a management perspective including those considered economically important, rare or endangered. The paper is also the basis for developing fisheries management systems in the Iwokrama Forest and Rupununi Wetlands
Initial data for black hole-neutron star binaries: a flexible, high-accuracy spectral method
We present a new numerical scheme to solve the initial value problem for
black hole-neutron star binaries. This method takes advantage of the
flexibility and fast convergence of a multidomain spectral representation of
the initial data to construct high-accuracy solutions at a relatively low
computational cost. We provide convergence tests of the method for both
isolated neutron stars and irrotational binaries. In the second case, we show
that we can resolve the small inconsistencies that are part of the
quasi-equilibrium formulation, and that these inconsistencies are significantly
smaller than observed in previous works. The possibility of generating a wide
variety of initial data is also demonstrated through two new configurations
inspired by results from binary black holes. First, we show that choosing a
modified Kerr-Schild conformal metric instead of a flat conformal metric allows
for the construction of quasi-equilibrium binaries with a spinning black hole.
Second, we construct binaries in low-eccentricity orbits, which are a better
approximation to astrophysical binaries than quasi-equilibrium systems.Comment: 19 pages, 11 figures, Modified to match final PRD versio
Big Bang Nucleosynthesis Constraints on the Self-Gravity of Pressure
Using big bang nucleosynthesis and present, high-precision measurements of
light element abundances, we constrain the self-gravity of radiation pressure
in the early universe. The self-gravity of pressure is strictly non-Newtonian,
and thus the constraints we set provide a direct test of this prediction of
general relativity and of the standard, Robertson-Walker-Friedmann cosmology.Comment: 5 pages, 1 figure. This paper was developed from an earlier version
which was posted as arXiv:0707.358
Clonally related, Notch-differentiated spinal neurons integrate into distinct circuits
Shared lineage has diverse effects on patterns of neuronal connectivity. In mammalian cortex, excitatory sister neurons assemble into shared microcircuits. I
- …