9,444 research outputs found
Stability criterion for self-similar solutions with a scalar field and those with a stiff fluid in general relativity
A stability criterion is derived in general relativity for self-similar
solutions with a scalar field and those with a stiff fluid, which is a perfect
fluid with the equation of state . A wide class of self-similar
solutions turn out to be unstable against kink mode perturbation. According to
the criterion, the Evans-Coleman stiff-fluid solution is unstable and cannot be
a critical solution for the spherical collapse of a stiff fluid if we allow
sufficiently small discontinuity in the density gradient field in the initial
data sets. The self-similar scalar-field solution, which was recently found
numerically by Brady {\it et al.} (2002 {\it Class. Quantum. Grav.} {\bf 19}
6359), is also unstable. Both the flat Friedmann universe with a scalar field
and that with a stiff fluid suffer from kink instability at the particle
horizon scale.Comment: 15 pages, accepted for publication in Classical and Quantum Gravity,
typos correcte
Jamming transitions in a schematic model of suspension rheology
We study the steady-state response to applied stress in a simple scalar model
of sheared colloids. Our model is based on a schematic (F2) model of the glass
transition, with a memory term that depends on both stress and shear rate. For
suitable parameters, we find transitions from a fluid to a nonergodic, jammed
state, showing zero flow rate in an interval of applied stress. Although the
jammed state is a glass, we predict that jamming transitions have an analytical
structure distinct from that of the conventional mode coupling glass
transition. The static jamming transition we discuss is also distinct from
hydrodynamic shear thickening.Comment: 7 pages; 3 figures; improved version with added references. Accepted
for publication in Europhysics Letter
Fractal to Nonfractal Phase Transition in the Dielectric Breakdown Model
A fast method is presented for simulating the dielectric-breakdown model
using iterated conformal mappings. Numerical results for the dimension and for
corrections to scaling are in good agreement with the recent RG prediction of
an upper critical , at which a transition occurs between branching
fractal clusters and one-dimensional nonfractal clusters.Comment: 5 pages, 7 figures; corrections to scaling include
Gauge symmetry breaking on orbifolds
We discuss a new method for gauge symmetry breaking in theories with one
extra dimension compactified on the orbifold S^1/Z_2. If we assume that fields
and their derivatives can jump at the orbifold fixed points, we can implement a
generalized Scherk-Schwarz mechanism that breaks the gauge symmetry. We show
that our model with discontinuous fields is equivalent to another with
continuous but non periodic fields; in our scheme localized lagrangian terms
for bulk fields appear.Comment: 6 pages, 2 figures. Talk given at the XXXVIIth Rencontres de Moriond,
"Electroweak interactions and unified theories", Les Arcs, France, 9-16 Mar
2002. Minor changes, one reference adde
Magnitude and Timing of Extreme Continental Extension, Central Death Valley Region, California
New geochronologic, stratigraphic, and sedimentologic
data indicate extreme late Cenozoic extension across the
central Death Valley region (fig. 9). ^(40)Ar/^(39)Ar geochronology
of sanidine from tuffs intercalated with steeply tilted
sediments along the eastern margin of the central Death Valley
region, including sections near Chicago Pass and at
Eagle Mountain, indicates deposition from approximately
15 to 11.7 Ma (fig. 10). Clasts of marble, orthoquartzite,
fusilinid limestone, and leucogabbro are prominent at both
locations. The only known source in the Death Valley
region for this clast assemblage is in the southern
Cotton wood Mountains, more than 100 km away on the
western flank of the Death Valley region. U/Pb geochronology
of baddeleyite confirms that leucogabbro clasts from
both sections have the same igneous crystallization age
(~180 Ma) as the leucogabbroic phase of the Hunter Mountain
batholith, in the southern Cottonwood Mountains. The
sediments include debris flows, flood deposits, and monolithic
boulder beds of large leucogabbro clasts (>1 m), suggesting
deposition in an alluvial fan setting. Sedimentary
transport of these deposits is unlikely to have exceeded 20
km. Restoration of the Eagle Mountain and Chicago Valley deposits to a position just east of the southern Cotton wood
Mountains results in approximate net translations of 80 km
and 104 km, respectively, at an azimuth of N. 67° W. (fig.
11). This suggests overall extension magnitudes of at least
500 percent across the Death Valley region since 12 Ma,
with strain rates that approached 10^(-14)/s during maximum
extension. These results support previous reconstructions
based on isopachs and Mesozoic structural features. (See,
for example, Wernicke and others, 1988.
The central density of a neutron star is unaffected by a binary companion at linear order in
Recent numerical work by Wilson, Mathews, and Marronetti [J. R. Wilson, G. J.
Mathews and P. Marronetti, Phys. Rev. D 54, 1317 (1996)] on the coalescence of
massive binary neutron stars shows a striking instability as the stars come
close together: Each star's central density increases by an amount proportional
to 1/(orbital radius). This overwhelms any stabilizing effects of tidal
coupling [which are proportional to 1/(orbital radius)^6] and causes the stars
to collapse before they merge. Since the claimed increase of density scales
with the stars' mass, it should also show up in a perturbation limit where a
point particle of mass orbits a neutron star. We prove analytically that
this does not happen; the neutron star's central density is unaffected by the
companion's presence to linear order in . We show, further, that the
density increase observed by Wilson et. al. could arise as a consequence of not
faithfully maintaining boundary conditions.Comment: 3 pages, REVTeX, no figures, submitted to Phys Rev D as a Rapid
Communicatio
Matching of the continuous gravitational wave in an all sky search
We investigate the matching of continuous gravitational wave (CGW) signals in
an all sky search with reference to Earth based laser interferometric
detectors. We consider the source location as the parameters of the signal
manifold and templates corresponding to different source locations. It has been
found that the matching of signals from locations in the sky that differ in
their co-latitude and longitude by radians decreases with source
frequency. We have also made an analysis with the other parameters affecting
the symmetries. We observe that it may not be relevant to take care of the
symmetries in the sky locations for the search of CGW from the output of
LIGO-I, GEO600 and TAMA detectors.Comment: 16 pages, 7 figures, 3 Tables, To appear in Int. J. Mod. Phys.
Magnetic Response of a Single, Isolated Gold Loop
Measurements have been made of the low-temperature magnetic response of single, isolated, micron-size Au loops. The magnetic response is found to contain a component which oscillates with the applied magnetic flux with a fundamental period of Ί0=h/e. The amplitude of the oscillatory component corresponds to a persistent current of â(0.3â2.0)evF/L, 1 to 2 orders of magnitude larger than predicted by current theories
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