4,697 research outputs found
Sensitivity to thermal noise of atomic Einstein-Podolsky-Rosen entanglement
We examine the prospect of demonstrating Einstein-Podolsky-Rosen (EPR) entanglement for massive particles using spin-changing collisions in a spinor Bose-Einstein condensate. Such a demonstration has recently been attempted by Gross et al. [Nature (London) 480, 219 (2011)] using a condensate of Rb-87 atoms trapped in an optical lattice potential. For the condensate initially prepared in the (F, m(F)) = (2,0) hyperfine state, with no population in the m(F) = +/- 1 states, we predict a significant suppression of the product of inferred quadrature variances below the Heisenberg uncertainty limit, implying strong EPR entanglement. However, such EPR entanglement is lost when the collisions are initiated in the presence of a small (currently undetectable) thermal population (n) over bar (th) in the m(F) = +/- 1 states. For condensates containing 150-200 atoms, we predict an upper bound of (n) over bar (th) similar or equal to 1 that can be tolerated in this experiment before EPR entanglement is lost
Limits on the quiescent radio emission from the black hole binaries GRO J1655-40 and XTE J1550-564
We present the results of radio observations of the black hole binaries GRO
J1655-40 and XTE J1550-564 in quiescence, with the upgraded Australia Telescope
Compact Array. Neither system was detected. Radio flux density upper limits (3
sigma) of 26 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for GRO J1655-40,
and 1.4 mJy (at 1.75 GHz), 27 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for
XTE J1550-564 were measured. In conjunction with quasi-simultaneous Chandra
X-ray observations (in the case of GRO J1655-40) and Faulkes Telescope optical
observations (XTE J1550-564) we find that these systems provide the first
evidence of relatively `radio quiet' black hole binaries at low luminosities;
indicating that the scatter observed in the hard state X-ray:radio correlation
at higher luminosities may also extend towards quiescent levels.Comment: Accepted for publication in MNRA
Newton-Hooke spacetimes, Hpp-waves and the cosmological constant
We show explicitly how the Newton-Hooke groups act as symmetries of the
equations of motion of non-relativistic cosmological models with a cosmological
constant. We give the action on the associated non-relativistic spacetimes and
show how these may be obtained from a null reduction of 5-dimensional
homogeneous pp-wave Lorentzian spacetimes. This allows us to realize the
Newton-Hooke groups and their Bargmann type central extensions as subgroups of
the isometry groups of the pp-wave spacetimes. The extended Schrodinger type
conformal group is identified and its action on the equations of motion given.
The non-relativistic conformal symmetries also have applications to
time-dependent harmonic oscillators. Finally we comment on a possible
application to Gao's generalization of the matrix model.Comment: 21 page
Red-sequence galaxies with young stars and dust: The cluster Abell 901/902 seen with COMBO-17
We report the discovery of a rich component of dusty star-forming galaxies
contaminating the red-sequence in the supercluster system comprising Abell
901a, 901b and A902 at redshift ~0.17. These galaxies do not fit into the
colour-density relation, because their preferred habitat is different from that
of regular red-sequence galaxies, which are typically dust-poor, old and
passively evolving. The dusty red galaxies prefer the medium-density outskirts
of clusters while being rare in both the low-density field and the high-density
cluster cores. This new result is based on the information content in the
medium-band photometry of the COMBO-17 survey. The photo-z accuracy of the ~800
brightest cluster galaxies is <0.01 and of the order of the velocity dispersion
of the cluster. This enables us to select a rich and clean cluster sample, in
which we can trace age-sensitive and dust-sensitive spectral features
independently with the detailed medium-band SED data. We find the red colour of
the dusty galaxies to be a result of dust extinction combined with relatively
old stellar ages. We speculate that the dusty red galaxies could either be a
product of minor mergers between established old red cluster galaxies with
infalling blue field galaxies, or mark a period in the internal transformation
of blue field galaxies into red cluster galaxies, which is triggered by the
environmental influences experienced during cluster infall.Comment: accepted version, only minor changes and typos corrected, 17 pages in
A&A print forma
Community prevalence of SARS-CoV-2 in England from April to November, 2020: results from the ONS Coronavirus Infection Survey
Background:
Decisions about the continued need for control measures to contain the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rely on accurate and up-to-date information about the number of people testing positive for SARS-CoV-2 and risk factors for testing positive. Existing surveillance systems are generally not based on population samples and are not longitudinal in design.
Methods:
Samples were collected from individuals aged 2 years and older living in private households in England that were randomly selected from address lists and previous Office for National Statistics surveys in repeated cross-sectional household surveys with additional serial sampling and longitudinal follow-up. Participants completed a questionnaire and did nose and throat self-swabs. The percentage of individuals testing positive for SARS-CoV-2 RNA was estimated over time by use of dynamic multilevel regression and poststratification, to account for potential residual non-representativeness. Potential changes in risk factors for testing positive over time were also assessed. The study is registered with the ISRCTN Registry, ISRCTN21086382.
Findings:
Between April 26 and Nov 1, 2020, results were available from 1 191 170 samples from 280 327 individuals; 5231 samples were positive overall, from 3923 individuals. The percentage of people testing positive for SARS-CoV-2 changed substantially over time, with an initial decrease between April 26 and June 28, 2020, from 0·40% (95% credible interval 0·29–0·54) to 0·06% (0·04–0·07), followed by low levels during July and August, 2020, before substantial increases at the end of August, 2020, with percentages testing positive above 1% from the end of October, 2020. Having a patient-facing role and working outside your home were important risk factors for testing positive for SARS-CoV-2 at the end of the first wave (April 26 to June 28, 2020), but not in the second wave (from the end of August to Nov 1, 2020). Age (young adults, particularly those aged 17–24 years) was an important initial driver of increased positivity rates in the second wave. For example, the estimated percentage of individuals testing positive was more than six times higher in those aged 17–24 years than in those aged 70 years or older at the end of September, 2020. A substantial proportion of infections were in individuals not reporting symptoms around their positive test (45–68%, dependent on calendar time.
Interpretation:
Important risk factors for testing positive for SARS-CoV-2 varied substantially between the part of the first wave that was captured by the study (April to June, 2020) and the first part of the second wave of increased positivity rates (end of August to Nov 1, 2020), and a substantial proportion of infections were in individuals not reporting symptoms, indicating that continued monitoring for SARS-CoV-2 in the community will be important for managing the COVID-19 pandemic moving forwards.
Funding:
Department of Health and Social Care
The Panchromatic Hubble Andromeda Treasury XI: The Spatially-Resolved Recent Star Formation History of M31
We measure the recent star formation history (SFH) across M31 using optical
images taken with the \texit{Hubble Space Telescope} as part of the
Panchromatic Hubble Andromeda Treasury (PHAT). We fit the color-magnitude
diagrams in ~9000 regions that are ~100 pc 100 pc in projected size,
covering a 0.5 square degree area (~380 kpc, deprojected) in the NE
quadrant of M31. We show that the SFHs vary significantly on these small
spatial scales but that there are also coherent galaxy-wide fluctuations in the
SFH back to ~500 Myr, most notably in M31's 10-kpc star-forming ring. We find
that the 10-kpc ring is at least 400 Myr old, showing ongoing star formation
over the past ~500 Myr. This indicates the presence of molecular gas in the
ring over at least 2 dynamical times at this radius. We also find that the
ring's position is constant throughout this time, and is stationary at the
level of 1 km/s, although there is evidence for broadening of the ring due to
diffusion of stars into the disk. Based on existing models of M31's ring
features, the lack of evolution in the ring's position makes a purely
collisional ring origin highly unlikely. We find that the global SFR has been
fairly constant over the last ~500 Myr, though it does show a small increase at
50 Myr that is 1.3 times the average SFR over the past 100 Myr. During the last
~500 Myr, ~60% of all SF occurs in the 10-kpc ring. Finally, we find that in
the past 100 Myr, the average SFR over the PHAT survey area is
M yr with an average deprojected intensity of M yr kpc, which yields a total SFR of ~0.7
M yr when extrapolated to the entire area of M31's disk. This
SFR is consistent with measurements from broadband estimates. [abridged]Comment: 23 pages, 17 figures, 2 tables, accepted for publication in Ap
Great Circle tidal streams: evidence for a nearly spherical massive dark halo around the Milky Way
An all high-latitude sky survey for cool carbon giant stars in the Galactic
halo has revealed 75 such stars, of which the majority are new detections. Of
these, more than half are clustered on a Great Circle on the sky which
intersects the center of Sagittarius dwarf galaxy (Sgr) and is parallel to its
proper motion vector, while many of the remainder are outlying Magellanic Cloud
C-stars. A pole-count analysis of the carbon star distribution clearly
indicates that the Great Circle stream we have isolated is statistically
significant, being a 5-6 sigma over-density. These two arguments strongly
support our conclusion that a large fraction of the Halo carbon stars
originated in Sgr. The stream orbits the Galaxy between the present location of
Sgr, 16 kpc from the Galactic center, and the most distant stream carbon star,
at ~60 kpc. It follows neither a polar nor a Galactic plane orbit, so that a
large range in both Galactic R and z distances are probed. That the stream is
observed as a Great Circle indicates that the Galaxy does not exert a
significant torque upon the stream, so the Galactic potential must be nearly
spherical in the regions probed by the stream. We present N-body experiments
simulating this disruption process as a function of the distribution of mass in
the Galactic halo. A likelihood analysis shows that, in the Galactocentric
distance range 16 kpc < R < 60 kpc, the dark halo is most likely almost
spherical. We rule out, at high confidence levels, the possibility that the
Halo is significantly oblate, with isodensity contours of aspect q_m < 0.7.
This result is quite unexpected and contests currently popular galaxy formation
models. (Abridged)Comment: 26 pages, 13 figures (6 in color, 8 chunky due to PS compression),
minor revisions, accepted by Ap
Relativistic Symmetry Suppresses Quark Spin-Orbit Splitting
Experimental data indicate small spin-orbit splittings in hadrons. For
heavy-light mesons we identify a relativistic symmetry that suppresses these
splittings. We suggest an experimental test in electron-positron annihilation.
Furthermore, we argue that the dynamics necessary for this symmetry are
possible in QCD.Comment: 16 pages, LaTeX. Two postscript figures. Final version to be
published in Physical Review Letter
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