39,016 research outputs found
The Carnegie-Irvine Galaxy Survey. V. Statistical study of bars and buckled bars
Simulations have shown that bars are subject to a vertical buckling
instability that transforms thin bars into boxy or peanut-shaped structures,
but the physical conditions necessary for buckling to occur are not fully
understood. We use the large sample of local disk galaxies in the
Carnegie-Irvine Galaxy Survey to examine the incidence of bars and buckled bars
across the Hubble sequence. Depending on the disk inclination angle (), a
buckled bar reveals itself as either a boxy/peanut-shaped bulge (at high )
or as a barlens structure (at low ). We visually identify bars,
boxy/peanut-shaped bulges, and barlenses, and examine the dependence of bar and
buckled bar fractions on host galaxy properties, including Hubble type, stellar
mass, color, and gas mass fraction. We find that the barred and unbarred disks
show similar distributions in these physical parameters. The bar fraction is
higher (70\%--80\%) in late-type disks with low stellar mass () and high gas mass ratio. In contrast, the buckled bar
fraction increases to 80\% toward massive and early-type disks (), and decreases with higher gas mass ratio. These
results suggest that bars are more difficult to grow in massive disks that are
dynamically hotter than low-mass disks. However, once a bar forms, it can
easily buckle in the massive disks, where a deeper potential can sustain the
vertical resonant orbits. We also find a probable buckling bar candidate (ESO
506G004) that could provide further clues to understand the timescale of the
buckling process.Comment: 9 pages, 7 figures, 2 tables. Accepted for publication in The
Astrophysical Journa
Discovery and Identification of W' and Z' in SU(2) x SU(2) x U(1) Models at the LHC
We explore the discovery potential of W' and Z' boson searches for various
SU(2) x SU(2) x U(1) models at the Large Hadron Collider (LHC), after taking
into account the constraints from low energy precision measurements and direct
searches at both the Tevatron (1.96 TeV) and the LHC (7 TeV). In such models,
the W' and Z' bosons emerge after the electroweak symmetry is spontaneously
broken. Two patterns of the symmetry breaking are considered in this work: one
is SU(2)_L x SU(2)_2 x U(1)_X to SU(2)_L x U(1)_Y (BP-I), another is SU(2)_1 x
SU(2)_2 x U(1)_Y to SU(2)_L x U(1)_Y (BP-II). Examining the single production
channel of W' and Z' with their subsequent leptonic decays, we find that the
probability of detecting W' and Z' bosons in the considered models at the LHC
(with 14 TeV) is highly limited by the low energy precision data constraints.
We show that observing Z' alone, without seeing a W', does not rule out new
physics models with non-Abelian gauge extension, such as the phobic models in
BP-I. Models in BP-II would predict the discovery of degenerate W' and Z'
bosons at the LHC.Comment: 29 pages, including 11 figures, 3 tables, added references for
introductio
Spin superconductor in ferromagnetic graphene
We show a spin superconductor (SSC) in ferromagnetic graphene as the
counterpart to the charge superconductor, in which a spin-polarized
electron-hole pair plays the role of the spin `Cooper pair' with
a neutral charge. We present a BCS-type theory for the SSC. With the
`London-type equations' of the super-spin-current density, we show the
existence of an electric `Meissner effect' against a spatial varying electric
field. We further study a SSC/normal conductor/SSC junction and predict a
spin-current Josephson effect.Comment: 6 pages, 4 figure
Efficient two-step entanglement concentration for arbitrary W states
We present two two-step practical entanglement concentration protocols (ECPs)
for concentrating an arbitrary three-particle less-entangled W state into a
maximally entangled W state assisted with single photons. The first protocol
uses the linear optics and the second protocol adopts the cross-Kerr
nonlinearity to perform the protocol. In the first protocol, based on the
post-selection principle, three parties say Alice, Bob and Charlie in different
distant locations can obtain the maximally entangled W state from the arbitrary
less-entangled W state with a certain success probability. In the second
protocol, it dose not require the parties to posses the sophisticated
single-photon detectors and the concentrated photon pair can be retained after
performing this protocol successfully. Moreover, the second protocol can be
repeated to get a higher success probability. Both protocols may be useful in
practical quantum information applications.Comment: 10 pages, 4 figure
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