183 research outputs found
Observational constraints on the Internal Structure and Dynamics of the Vela Pulsar
We show that the short spin-up time observed for the Vela pulsar during the
1988 ``Christmas'' glitch implies that the coupling time of the pulsar core to
its crust is less than 10 seconds. Ekman pumping cannot explain the fast
core-crust coupling and a more effective coupling is necessary. The internal
magnetic field of the Vela pulsar can provide the necessary coupling if the
field threads the core with a magnitude that exceeds Gauss for a
normal interior and Gauss for a superconducting interior. These
lower bounds favor the hypothesis that the interior of neutron stars contains
superfluid neutrons and protons and challenge the notion that pulsar magnetic
fields decay over million year time scales or that magnetic flux is expelled
from the core as the star slows.Comment: Latex with aasms4 style file, 15 pages, 1 ps figur
Hydrodynamic Detonation Instability in Electroweak and QCD Phase Transitions
The hydrodynamic stability of deflagration and detonation bubbles for a first
order electroweak and QCD phase transition has been discussed recently with the
suggestion that detonations are stable. We examine here the case of a
detonation more carefully. We find that in front of the bubble wall
perturbations do not grow with time, but behind the wall modes exist which grow
exponentially. We briefly discuss the possible meaning of this instability.Comment: 12 pages, 3 figures available on request, Latex,
FERMILAB--PUB--93/098--
Fluctuations and Bubble Dynamics in First-Order Phase Transitions
We numerically examine the effect of thermal fluctuations on a first-order
phase transition in 2+1 dimensions. By focusing on the expansion of a single
bubble we are able to calculate changes in the bubble wall's velocity as well
as changes in its structure relative to the standard case where the bubble
expands into a homogeneous background. Not only does the wall move faster, but
the transition from the symmetric to the asymmetric phase is no longer smooth,
even for a fairly strong transition. We discuss how these results affect the
standard picture of electroweak baryogenesis.Comment: Latex, 30 pages, 11 ps figures, short discussion added in conclusions
and minor clarifications, accepted to Phys Rev
Pulsar Constraints on Neutron Star Structure and Equation of State
With the aim of constraining the structural properties of neutron stars and
the equation of state of dense matter, we study sudden spin-ups, glitches,
occurring in the Vela pulsar and in six other pulsars. We present evidence that
glitches represent a self-regulating instability for which the star prepares
over a waiting time. The angular momentum requirements of glitches in Vela
indicate that at least 1.4% of the star's moment of inertia drives these
events. If glitches originate in the liquid of the inner crust, Vela's
`radiation radius' must exceed ~12 km for a mass of 1.4 solar masses.
Observational tests of whether other neutron stars obey this constraint will be
possible in the near future.Comment: 5 pages, including figures. To appear in Physical Review Letter
On Bubble Growth and Droplet Decay in Cosmological Phase Transitions
We study spherically symmetric bubble growth and droplet decay in first order
cosmological phase transitions, using a numerical code including both the
complete hydrodynamics of the problem and a phenomenological model for the
microscopic entropy producing mechanism at the phase transition surface. The
small-scale effects of finite wall width and surface tension are thus
consistently incorporated. We verify the existence of the different
hydrodynamical growth modes proposed recently and investigate the problem of a
decaying quark droplet in the QCD phase transition. We find that the decaying
droplet leaves behind no rarefaction wave, so that any baryon number
inhomogeneity generated previously should survive the decay.Comment: 10 pages (revtex), 10 figures as uuencoded postscrip
Reconstructing Single Field Inflationary Actions From CMBR Data
This paper describes a general program for deriving the action of single
field inflation models with nonstandard kinetic energy terms using CMBR power
spectrum data. This method assumes that an action depends on a set of
undetermined functions, each of which is a function of either the inflaton wave
function or its time derivative. The scalar, tensor and non-gaussianity of the
curvature perturbation spectrum are used to derive a set of reconstruction
equations whose solution set can specify up to three of the undetermined
functions. The method is then used to find the undetermined functions in
various types of actions assuming power law type scalar and tensor spectra. In
actions that contain only two unknown functions, the third reconstruction
equation implies a consistency relation between the non-gaussianty, sound speed
and slow roll parameters. In particular we focus on reconstructing a
generalized DBI action with an unknown potential and warp factor. We find that
for realistic scalar and tensor spectra, the reconstructed warp factor and
potential are very similar to the theoretically derived result. Furthermore,
physical consistency of the reconstructed warp factor and potential imposes
strict constraints on the scalar and tensor spectral indices.Comment: 33 pages, 3 figures: v3 - References adde
Stochastic Production Of Kink-Antikink Pairs In The Presence Of An Oscillating Background
We numerically investigate the production of kink-antikink pairs in a
dimensional field theory subject to white noise and periodic driving.
The twin effects of noise and periodic driving acting in conjunction lead to
considerable enhancement in the kink density compared to the thermal
equilibrium value, for low dissipation coefficients and for a specific range of
frequencies of the oscillating background. The dependence of the kink-density
on the temperature of the heat bath, the amplitude of the oscillating
background and value of the dissipation coefficient is also investigated. An
interesting feature of our result is that kink-antikink production occurs even
though the system always remains in the broken symmetry phase.Comment: Revtex, 21 pages including 7 figures; more references adde
Distribution of \u3cem\u3eCotesia rubecula\u3c/em\u3e (Hymenoptera: Braconidae) and Its Displacement of \u3cem\u3eCotesia glomerata\u3c/em\u3e in Eastern North America
A survey was conducted from May to Oct of 2011 of the parasitoid community of the imported cabbageworm, Pieris rapae (Lepidoptera: Pieridae), in cole crops in part of the eastern United States and southeastern Canada. The findings of our survey indicate that Cotesia rubecula (Hymenoptera: Braconidae) now occurs as far west as North Dakota and has become the dominant parasitoid of P. rapae in the northeastern and north central United States and adjacent parts of southeastern Canada, where it has displaced the previously common parasitoid Cotesia glomerata (Hymenoptera: Braconidae). Cotesia glomerata remains the dominant parasitoid in the mid-Atlantic states, from Virginia to North Carolina and westward to southern Illinois, below latitude N 38° 48′. This pattern suggests that the released populations of C. rubecula presently have a lower latitudinal limit south of which they are not adapted
Expanding Bubbles in a Thermal Background
Real scalar field models incorporating asymmetric double well potentials will
decay to the state of lowest energy. While the eventual nature of the system
can be discerned, the determination of the dynamics of the bubble wall provides
many difficulties. In the present study we investigate numerically the
evolution of spherically symmetric expanding bubbles coupled to a thermal bath
in 3+1 dimensions. A Markovian Langevin equation is employed to describe the
interaction between bubble and bath. We find the shape and velocity of the wall
to be independent of temperature, yet extremely sensitive to both asymmetry and
viscosity.Comment: RevTeX, 9 pages (multicols), 9 figures, submitted to Phys. Rev.
Magnetic Field Generation in Stars
Enormous progress has been made on observing stellar magnetism in stars from
the main sequence through to compact objects. Recent data have thrown into
sharper relief the vexed question of the origin of stellar magnetic fields,
which remains one of the main unanswered questions in astrophysics. In this
chapter we review recent work in this area of research. In particular, we look
at the fossil field hypothesis which links magnetism in compact stars to
magnetism in main sequence and pre-main sequence stars and we consider why its
feasibility has now been questioned particularly in the context of highly
magnetic white dwarfs. We also review the fossil versus dynamo debate in the
context of neutron stars and the roles played by key physical processes such as
buoyancy, helicity, and superfluid turbulence,in the generation and stability
of neutron star fields.
Independent information on the internal magnetic field of neutron stars will
come from future gravitational wave detections. Thus we maybe at the dawn of a
new era of exciting discoveries in compact star magnetism driven by the opening
of a new, non-electromagnetic observational window.
We also review recent advances in the theory and computation of
magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo
theory. These advances offer insight into the action of stellar dynamos as well
as processes whichcontrol the diffusive magnetic flux transport in stars.Comment: 41 pages, 7 figures. Invited review chapter on on magnetic field
generation in stars to appear in Space Science Reviews, Springe
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