761 research outputs found
Instability of a gapless color superconductor with respect to inhomogeneous fluctuations
We systematically apply density functional theory to determine the kind of
inhomogeneities that spontaneously develop in a homogeneous gapless phase of
neutral two-flavor superfluid quark matter. We consider inhomogeneities in the
quark and electron densities and in the phases and amplitude of the order
parameter. These inhomogeneities are expected to lead the gapless phase to a
BCS-normal coexisting phase, a Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state
with phase oscillations alone, and a LOFF state with amplitude oscillations. We
find that which of them the homogeneous system tends towards depends
sensitively on the chemical potential separation between up and down quarks and
the gradient energies.Comment: 15 pages, 3 figures; corrected Eq. (36) and changed content
associated with d quark clustering instabilit
Disk wind feedback from high-mass protostars
We perform a sequence of 3D magnetohydrodynamic (MHD) simulations of the
outflow-core interaction for a massive protostar forming via collapse of an
initial cloud core of . This allows us to characterize the
properties of disk wind driven outflows from massive protostars, which can
allow testing of different massive star formation theories. It also enables us
to assess quantitatively the impact of outflow feedback on protostellar core
morphology and overall star formation efficiency. We find that the opening
angle of the flow increases with increasing protostellar mass, in agreement
with a simple semi-analytic model. Once the protostar reaches
the outflow's opening angle is so wide that it has blown
away most of the envelope, thereby nearly ending its own accretion. We thus
find an overall star formation efficiency of , similar to that
expected from low-mass protostellar cores. Our simulation results therefore
indicate that the MHD disk wind outflow is the dominant feedback mechanism for
helping to shape the stellar initial mass function from a given prestellar core
mass function.Comment: Accepted for publication in Ap
Non-Abelian Stokes Theorem and Quark Confinement in SU(3) Yang-Mills Gauge Theory
We derive a new version of SU(3) non-Abelian Stokes theorem by making use of
the coherent state representation on the coset space , the flag space. Then we outline a derivation of the area law of the
Wilson loop in SU(3) Yang-Mills theory in the maximal Abelian gauge (The
detailed exposition will be given in a forthcoming article). This derivation is
performed by combining the non-Abelian Stokes theorem with the reformulation of
the Yang-Mills theory as a perturbative deformation of a topological field
theory recently proposed by one of the authors. Within this framework, we show
that the fundamental quark is confined even if is broken by partial
gauge fixing into just as is broken to . An
origin of the area law is related to the geometric phase of the Wilczek-Zee
holonomy for U(2). Abelian dominance is an immediate byproduct of these results
and magnetic monopole plays the dominant role in this derivation.Comment: 14 pages, Latex, no figures, version accepted for publication in Mod.
Phys. Lett. A (some comments are added in the final parts
The Impact of Feedback in Massive Star Formation. II. Lower Star Formation Efficiency at Lower Metallicity
We conduct a theoretical study of the formation of massive stars over a wide
range of metallicities from 1e-5 to 1Zsun and evaluate the star formation
efficiencies (SFEs) from prestellar cloud cores taking into account multiple
feedback processes. Unlike for simple spherical accretion, in the case of disk
accretion feedback processes do not set upper limits on stellar masses. At
solar metallicity, launching of magneto-centrifugally-driven outflows is the
dominant feedback process to set SFEs, while radiation pressure, which has been
regarded to be pivotal, has only minor contribution even in the formation of
over-100Msun stars. Photoevaporation becomes significant in over-20Msun star
formation at low metallicities of <1e-2Zsun, where dust absorption of ionizing
photons is inefficient. We conclude that if initial prestellar core properties
are similar, then massive stars are rarer in extremely metal-poor environments
of 1e-5 - 1e-3Zsun. Our results give new insight into the high-mass end of the
initial mass function and its potential variation with galactic and
cosmological environments.Comment: 13 pages, 9 figures, accepted for publication in The Astrophysical
Journa
Outflow-Confined HII regions. II. The Early Break-Out Phase
In this series of papers, we model the formation and evolution of the
photoionized region and its observational signatures during massive star
formation. Here we focus on the early break out of the photoionized region into
the outflow cavity. Using results of 3-D magnetohydrodynamic-outflow
simulations and protostellar evolution calculations, we perform post-processing
radiative-transfer. The photoionized region first appears at a protostellar
mass of 10Msun in our fiducial model, and is confined to within 10-100AU by the
dense inner outflow, similar to some observed very small hypercompact HII
regions. Since the ionizing luminosity of the massive protostar increases
dramatically as Kelvin-Helmholz (KH) contraction proceeds, the photoionized
region breaks out to the entire outflow region in <10,000yr. Accordingly, the
radio free-free emission brightens significantly in this stage. In our fiducial
model, the radio luminosity at 10 GHz changes from 0.1 mJy kpc2 at m=11Msun to
100 mJy kpc2 at 16Msun, while the infrared luminosity increases by less than a
factor of two. The radio spectral index also changes in the break-out phase
from the optically thick value of 2 to the partially optically thin value of
0.6. Additionally, we demonstrate that short-timescale variation in free-free
flux would be induced by an accretion burst. The outflow density is enhanced in
the accretion burst phase, which leads to a smaller ionized region and weaker
free-free emission. The radio luminosity may decrease by one order of magnitude
during such bursts, while the infrared luminosity is much less affected, since
internal protostellar luminosity dominates over accretion luminosity after KH
contraction starts. Such variability may be observable on timescales as short
10-100 yr, if accretion bursts are driven by disk instabilities.Comment: 9 pages, 5 figures, accepted for publication in Ap
Conductance of a single molecule anchored by an isocyanide substituent to gold electrodes
The effect of anchoring group on the electrical conductance of a single
molecule bridging two Au electrodes was studied using di-substituted
(isocyanide (CN-), thiol (S-) or cyanide (NC-)) benzene. The conductance of a
single Au/1,4-diisocyanobenzene/Au junction anchored by isocyanide via a C atom
(junction with the Au-CN bond) was (). The
value was comparable to of a single
Au/1,4-benzenedithiol/Au junction with the Au-S bond. The
Au/1,4-dicyanobenzene/Au molecular junction with the Au-NC bond did not show
well-defined conductance values. The metal-molecule bond strength was estimated
by the distance over which the molecular junction was stretched before
breakdown. The stretched length of the molecular junction with the Au-CN bond
was comparable to that of the Au junction, indicating that the Au-CN bond was
stronger than the Au-Au bond.Comment: 3 figures, to be appear in Appl. Phys. Let
GMC Collisions as Triggers of Star Formation. V. Observational Signatures
We present calculations of molecular, atomic and ionic line emission from
simulations of giant molecular cloud (GMC) collisions. We post-process
snapshots of the magneto-hydrodynamical simulations presented in an earlier
paper in this series by Wu et al. (2017) of colliding and non-colliding GMCs.
Using photodissociation region (PDR) chemistry and radiative transfer we
calculate the level populations and emission properties of CO ,
[CI] at m, [CII] m and [OI]
transition at m. From integrated
intensity emission maps and position-velocity diagrams, we find that
fine-structure lines, particularly the [CII] m, can be used as a
diagnostic tracer for cloud-cloud collision activity. These results hold even
in more evolved systems in which the collision signature in molecular lines has
been diminished.Comment: 10 pages, 7 figures, accepted for publication in ApJ, comments
welcom
Magnetohydrodynamic Simulations of A Rotating Massive Star Collapsing to A Black Hole
We perform two-dimensional, axisymmetric, magnetohydrodynamic simulations of
the collapse of a rotating star of 40 Msun and in the light of the collapsar
model of gamma-ray burst. Considering two distributions of angular momentum, up
to \sim 10^{17} cm^2/s, and the uniform vertical magnetic field, we investigate
the formation of an accretion disk around a black hole and the jet production
near the hole. After material reaches to the black hole with the high angular
momentum, the disk is formed inside a surface of weak shock. The disk becomes
in a quasi-steady state for stars whose magnetic field is less than 10^{10} G
before the collapse. We find that the jet can be driven by the magnetic fields
even if the central core does not rotate as rapidly as previously assumed and
outer layers of the star has sufficiently high angular momentum. The magnetic
fields are chiefly amplified inside the disk due to the compression and the
wrapping of the field. The fields inside the disk propagate to the polar region
along the inner boundary near the black hole through the Alfv{\'e}n wave, and
eventually drive the jet. The quasi-steady disk is not an advection-dominated
disk but a neutrino cooling-dominated one. Mass accretion rates in the disks
are greater than 0.01 Msun/sec with large fluctuations. The disk is transparent
for neutrinos. The dense part of the disk, which locates near the hole, emits
neutrino efficiently at a constant rate of < 8 \times 10^{51} erg/s. The
neutrino luminosity is much smaller than those from supernovae after the
neutrino burst.Comment: 42 pages, accepted for publication in the Astrophysical Journal. A
paper with higher-resolution figures available at
http://www.ec.knct.ac.jp/~fujimoto/collapsar/mhd-color.pd
Massive Protostellar Disks as a Hot Laboratory of Silicate Grain Evolution
Typical accretion disks around massive protostars are hot enough for water
ice to sublimate. We here propose to utilize the massive protostellar disks for
investigating the collisional evolution of silicate grains with no ice mantle,
which is an essential process for the formation of rocky planetesimals in
protoplanetary disks around lower-mass stars. We for the first time develop a
model of massive protostellar disks that includes the coagulation,
fragmentation, and radial drift of dust. We show that the maximum grain size in
the disks is limited by collisional fragmentation rather than by radial drift.
We derive analytic formulas that produce the radial distribution of the maximum
grain size and dust surface density in the steady state. Applying the analytic
formulas to the massive protostellar disk of GGD27-MM1, where the grain size is
constrained from a millimeter polarimetric observation, we infer that the
silicate grains in this disk fragment at collision velocities above ~ 10 m/s.
The inferred fragmentation threshold velocity is lower than the maximum grain
collision velocity in typical protoplanetary disks around low-mass stars,
implying that coagulation alone may not lead to the formation of rocky
planetesimals in those disks. With future measurements of grain sizes in
massive protostellar disks, our model will provide more robust constraints on
the sticking property of silicate grains.Comment: 17 pages, 5 figures,accepted for publication to The Astrophysical
Journa
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