1,807 research outputs found
Proposal for Higgs and Superpartner Searches at the LHCb Experiment
The spectrum of supersymmetric theories with R-parity violation are much more
weakly constrained than that of supersymmetric theories with a stable
neutralino. We investigate the signatures of supersymmetry at the LHCb
experiment in the region of parameter space where the neutralino decay leaves a
displaced vertex. We find sensitivity to squark production up to squark masses
of order 1 TeV. We note that if the Higgs decays to neutralinos in this
scenario, LHCb should see the lightest Higgs boson before ATLAS and CMS.Comment: 7 pages, 5 figure
Top-tagging: A Method for Identifying Boosted Hadronic Tops
A method is introduced for distinguishing top jets (boosted, hadronically
decaying top quarks) from light quark and gluon jets using jet substructure.
The procedure involves parsing the jet cluster to resolve its subjets, and then
imposing kinematic constraints. With this method, light quark or gluon jets
with pT ~ 1 TeV can be rejected with an efficiency of around 99% while
retaining up to 40% of top jets. This reduces the dijet background to heavy
t-tbar resonances by a factor of ~10,000, thereby allowing resonance searches
in t-tbar to be extended into the all-hadronic channel. In addition,
top-tagging can be used in t-tbar events when one of the tops decays
semi-leptonically, in events with missing energy, and in studies of b-tagging
efficiency at high pT.Comment: 4 pages, 4 figures; v2: separate quark and gluon efficiencies
included, figure on helicity angle added, and physics discussion extende
Frame-Dragging Vortexes and Tidal Tendexes Attached to Colliding Black Holes: Visualizing the Curvature of Spacetime
When one splits spacetime into space plus time, the spacetime curvature (Weyl
tensor) gets split into an "electric" part E_{jk} that describes tidal gravity
and a "magnetic" part B_{jk} that describes differential dragging of inertial
frames. We introduce tools for visualizing B_{jk} (frame-drag vortex lines,
their vorticity, and vortexes) and E_{jk} (tidal tendex lines, their tendicity,
and tendexes), and also visualizations of a black-hole horizon's (scalar)
vorticity and tendicity. We use these tools to elucidate the nonlinear dynamics
of curved spacetime in merging black-hole binaries.Comment: 4 pages, 5 figure
Frame-Dragging Vortexes and Tidal Tendexes Attached to Colliding Black Holes: Visualizing the Curvature of Spacetime
When one splits spacetime into space plus time, the spacetime curvature (Weyl
tensor) gets split into an "electric" part E_{jk} that describes tidal gravity
and a "magnetic" part B_{jk} that describes differential dragging of inertial
frames. We introduce tools for visualizing B_{jk} (frame-drag vortex lines,
their vorticity, and vortexes) and E_{jk} (tidal tendex lines, their tendicity,
and tendexes), and also visualizations of a black-hole horizon's (scalar)
vorticity and tendicity. We use these tools to elucidate the nonlinear dynamics
of curved spacetime in merging black-hole binaries.Comment: 4 pages, 5 figure
Visualizing Spacetime Curvature via Frame-Drag Vortexes and Tidal Tendexes I. General Theory and Weak-Gravity Applications
When one splits spacetime into space plus time, the Weyl curvature tensor
(vacuum Riemann tensor) gets split into two spatial, symmetric, and trace-free
(STF) tensors: (i) the Weyl tensor's so-called "electric" part or tidal field,
and (ii) the Weyl tensor's so-called "magnetic" part or frame-drag field. Being
STF, the tidal field and frame-drag field each have three orthogonal
eigenvector fields which can be depicted by their integral curves. We call the
integral curves of the tidal field's eigenvectors tendex lines, we call each
tendex line's eigenvalue its tendicity, and we give the name tendex to a
collection of tendex lines with large tendicity. The analogous quantities for
the frame-drag field are vortex lines, their vorticities, and vortexes. We
build up physical intuition into these concepts by applying them to a variety
of weak-gravity phenomena: a spinning, gravitating point particle, two such
particles side by side, a plane gravitational wave, a point particle with a
dynamical current-quadrupole moment or dynamical mass-quadrupole moment, and a
slow-motion binary system made of nonspinning point particles. [Abstract is
abbreviated; full abstract also mentions additional results.]Comment: 25 pages, 20 figures, matches the published versio
Momentum flow in black-hole binaries: II. Numerical simulations of equal-mass, head-on mergers with antiparallel spins
Research on extracting science from binary-black-hole (BBH) simulations has
often adopted a "scattering matrix" perspective: given the binary's initial
parameters, what are the final hole's parameters and the emitted gravitational
waveform? In contrast, we are using BBH simulations to explore the nonlinear
dynamics of curved spacetime. Focusing on the head-on plunge, merger, and
ringdown of a BBH with transverse, antiparallel spins, we explore numerically
the momentum flow between the holes and the surrounding spacetime. We use the
Landau-Lifshitz field-theory-in-flat-spacetime formulation of general
relativity to define and compute the density of field energy and field momentum
outside horizons and the energy and momentum contained within horizons, and we
define the effective velocity of each apparent and event horizon as the ratio
of its enclosed momentum to its enclosed mass-energy. We find surprisingly good
agreement between the horizons' effective and coordinate velocities. To
investigate the gauge dependence of our results, we compare pseudospectral and
moving-puncture evolutions of physically similar initial data; although
spectral and puncture simulations use different gauge conditions, we find
remarkably good agreement for our results in these two cases. We also compare
our simulations with the post-Newtonian trajectories and near-field
energy-momentum. [Abstract abbreviated; full abstract also mentions additional
results.]Comment: Submitted to Phys. Rev.
A search for fast radio burst-like emission from Fermi gamma-ray bursts
We report the results of the rapid follow-up observations of gamma-ray bursts
(GRBs) detected by the Fermi satellite to search for associated fast radio
bursts. The observations were conducted with the Australian Square Kilometre
Array Pathfinder at frequencies from 1.2-1.4 GHz. A set of 20 bursts, of which
four were short GRBs, were followed up with a typical latency of about one
minute, for a duration of up to 11 hours after the burst. The data was searched
using 4096 dispersion measure trials up to a maximum dispersion measure of 3763
pc cm, and for pulse widths over a range of duration from 1.256 to
40.48 ms. No associated pulsed radio emission was observed above for any of the 20 GRBs.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society Main Journa
Manacled to Identity: Cosmopolitanism, Class, and ‘The Culture Concept’ in Stephen Crane
This article begins with a close reading of Stephen Crane’s short story ‘Manacled’ from 1900, which situates this rarely considered short work within the context of contemporary debates about realism. I then proceed to argue that many of the debates raised by the tale have an afterlife in our own era of American literary studies, which has frequently focused on questions of ‘identity’ and ‘culture’ in its reading of realism and naturalism to the exclusion of the importance of cosmopolitan discourses of diffusion and exchange across national borders. I then offer a brief reading of Crane’s novel George’s Mother, which follows Walter Benn Michaels in suggesting that the recent critical attention paid to particularities of cultural difference in American studies have come to conflate ideas of class and social position with ideas of culture in ways that have ultimately obscured the presence of genuine historical inequalities in US society. In order to challenge this critical commonplace, I situate Crane’s work within a history of transatlantic cosmopolitanism associated with the ideas of Franz Boas and Matthew Arnold to demonstrate the ways in which Crane’s narratives sought out an experience of the universal within their treatments of the particular
Intensive Swift and LCO monitoring of PG 1302102: AGN disk reverberation mapping of a supermassive black hole binary candidate
We present an intensive multiwavelength monitoring campaign of the quasar PG
1302102 with Swift and the Las Cumbres Observatory network telescopes. At
, it tests the limits of the reverberation mapping (RM) technique in
probing the accretion disk around a supermassive black hole (SMBH) and extends
the parameter space to high masses and high accretion rates. This is also the
first time the RM technique has been applied to test disk structures predicted
in the SMBH binary model that has been suggested for this source. PG 1302102
was observed at a daily cadence for months in 14 bands spanning
from X-ray to UV and optical wavelengths, and it shows moderate to significant
levels of variability correlated between wavelengths. We measure the inter-band
time lags which are consistent with a relation as
expected from standard disk reprocessing, albeit with large errors. The disk
size implied by the lag spectrum is consistent with the expected disk size for
its black hole mass within uncertainties. While the source resembles other
reverberation-mapped AGN in many respects, and we do not find evidence
supporting the prevalent hypothesis that it hosts an SMBH binary, we
demonstrate the feasibility of studying SMBH binaries from this novel angle and
suggest possibilities for the LSST Deep Drilling Fields.Comment: 11 pages, 5 figures, 4 tables. Accepted for publication in ApJ. The
full dataset will be available with the ApJ articl
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