431 research outputs found
Detecting a Higgs Pseudoscalar with a Boson at the LHC
We have adopted two Higgs doublet models to study the production of a Higgs
pseudoscalar () in association with a gauge boson from gluon fusion
() at the CERN Large Hadron Collider. The prospects for the
discovery of are investigated with physics
backgrounds and realistic cuts. Promising results are found for m_A \alt 260
GeV in two Higgs doublet models when the heavier Higgs scalar () can decay
into a boson and a Higgs pseudoscalar (). Although the cross section
of is usually small in the minimal supersymmetric standard model,
it can be significantly enhanced in general two Higgs doublet models. This
discovery channel might provide an opportunity to search for a Higgs scalar and
a Higgs pseudoscalar simultaneously at the LHC and could lead to new physics
beyond the Standard Model and the minimal supersymmetric model.Comment: Two tables added for the ratio of signal/backgroun
Binary-black-hole initial data with nearly-extremal spins
There is a significant possibility that astrophysical black holes with
nearly-extremal spins exist. Numerical simulations of such systems require
suitable initial data. In this paper, we examine three methods of constructing
binary-black-hole initial data, focusing on their ability to generate black
holes with nearly-extremal spins: (i) Bowen-York initial data, including
standard puncture data (based on conformal flatness and Bowen-York extrinsic
curvature), (ii) standard quasi-equilibrium initial data (based on the
extended-conformal-thin-sandwich equations, conformal flatness, and maximal
slicing), and (iii) quasi-equilibrium data based on the superposition of
Kerr-Schild metrics. We find that the two conformally-flat methods (i) and (ii)
perform similarly, with spins up to about 0.99 obtainable at the initial time.
However, in an evolution, we expect the spin to quickly relax to a
significantly smaller value around 0.93 as the initial geometry relaxes. For
quasi-equilibrium superposed Kerr-Schild (SKS) data [method (iii)], we
construct initial data with \emph{initial} spins as large as 0.9997. We evolve
SKS data sets with spins of 0.93 and 0.97 and find that the spin drops by only
a few parts in 10^4 during the initial relaxation; therefore, we expect that
SKS initial data will allow evolutions of binary black holes with relaxed spins
above 0.99. [Abstract abbreviated; full abstract also mentions several
secondary results.
Accurate gravitational waveforms for binary-black-hole mergers with nearly extremal spins
Motivated by the possibility of observing gravitational waves from merging
black holes whose spins are nearly extremal (i.e., 1 in dimensionless units),
we present numerical waveforms from simulations of merging black holes with the
highest spins simulated to date: (1) a 25.5-orbit inspiral, merger, and
ringdown of two holes with equal masses and spins of magnitude 0.97 aligned
with the orbital angular momentum; and (2) a previously reported 12.5-orbit
inspiral, merger, and ringdown of two holes with equal masses and spins of
magnitude 0.95 anti-aligned with the orbital angular momentum. First, we
consider the horizon mass and spin evolution of the new aligned-spin
simulation. During the inspiral, the horizon area and spin evolve in remarkably
close agreement with Alvi's analytic predictions, and the remnant hole's final
spin agrees reasonably well with several analytic predictions. We also find
that the total energy emitted by a real astrophysical system with these
parameters---almost all of which is radiated during the time included in this
simulation---would be 10.952% of the initial mass at infinite separation.
Second, we consider the gravitational waveforms for both simulations. After
estimating their uncertainties, we compare the waveforms to several
post-Newtonian approximants, finding significant disagreement well before
merger, although the phase of the TaylorT4 approximant happens to agree
remarkably well with the numerical prediction in the aligned-spin case. We find
that the post-Newtonian waveforms have sufficient uncertainty that hybridized
waveforms will require far longer numerical simulations (in the absence of
improved post-Newtonian waveforms) for accurate parameter estimation of
low-mass binary systems.Comment: 17 pages, 7 figures, submitted to Classical and Quantum Gravit
Assessing the Energetics of Spinning Binary Black Hole Systems
In this work we study the dynamics of spinning binary black hole systems in
the strong field regime. For this purpose we extract from numerical relativity
simulations the binding energy, specific orbital angular momentum, and
gauge-invariant orbital frequency. The goal of our work is threefold: First, we
extract the individual spin contributions to the binding energy, in particular
the spin-orbit, spin-spin, and cubic-in-spin terms. Second, we compare our
results with predictions from waveform models and find that while
post-Newtonian approximants are not capable of representing the dynamics during
the last few orbits before merger, there is good agreement between our data and
effective-one-body approximants as well as the numerical relativity surrogate
models. Finally, we present phenomenological representations for the binding
energy for non-spinning systems with mass ratios up to and for the
spin-orbit interaction for mass ratios up to obtaining accuracies of
and , respectively
Simulating merging binary black holes with nearly extremal spins
Astrophysically realistic black holes may have spins that are nearly extremal
(i.e., close to 1 in dimensionless units). Numerical simulations of binary
black holes are important tools both for calibrating analytical templates for
gravitational-wave detection and for exploring the nonlinear dynamics of curved
spacetime. However, all previous simulations of binary-black-hole inspiral,
merger, and ringdown have been limited by an apparently insurmountable barrier:
the merging holes' spins could not exceed 0.93, which is still a long way from
the maximum possible value in terms of the physical effects of the spin. In
this paper, we surpass this limit for the first time, opening the way to
explore numerically the behavior of merging, nearly extremal black holes.
Specifically, using an improved initial-data method suitable for binary black
holes with nearly extremal spins, we simulate the inspiral (through 12.5
orbits), merger and ringdown of two equal-mass black holes with equal spins of
magnitude 0.95 antialigned with the orbital angular momentum.Comment: 4 pages, 2 figures, updated with version accepted for publication in
Phys. Rev. D, removed a plot that was incorrectly included at the end of the
article in version v
Numerical-relativity surrogate modeling with nearly extremal black-hole spins
Numerical relativity (NR) simulations of binary black hole (BBH) systems
provide the most accurate gravitational wave predictions, but at a high
computational cost -- especially when the black holes have nearly extremal
spins (i.e. spins near the theoretical upper limit) or very unequal masses.
Recently, the technique of Reduced Order Modeling (ROM) has enabled the
construction of surrogate models trained on an existing set of NR waveforms.
Surrogate models enable the rapid computation of the gravitational waves
emitted by BBHs. Typically these models are used for interpolation to compute
gravitational waveforms for BBHs with mass ratios and spins within the bounds
of the training set. Because simulations with nearly extremal spins are so
technically challenging, surrogate models almost always rely on training sets
with only moderate spins. In this paper, we explore how well surrogate models
can extrapolate to nearly extremal spins when the training set only includes
moderate spins. For simplicity, we focus on one-dimensional surrogate models
trained on NR simulations of BBHs with equal masses and equal, aligned spins.
We assess the performance of the surrogate models at higher spin magnitudes by
calculating the mismatches between extrapolated surrogate model waveforms and
NR waveforms, by calculating the differences between extrapolated and NR
measurements of the remnant black-hole mass, and by testing how the surrogate
model improves as the training set extends to higher spins. We find that while
extrapolation in this one-dimensional case is viable for current detector
sensitivities, surrogate models for next-generation detectors should use
training sets that extend to nearly extremal spins
Visualizing Spacetime Curvature via Frame-Drag Vortexes and Tidal Tendexes II. Stationary Black Holes
When one splits spacetime into space plus time, the Weyl curvature tensor
(which equals the Riemann tensor in vacuum) splits into two spatial, symmetric,
traceless tensors: the tidal field , which produces tidal forces, and the
frame-drag field , which produces differential frame dragging. In recent
papers, we and colleagues have introduced ways to visualize these two fields:
tidal tendex lines (integral curves of the three eigenvector fields of ) and
their tendicities (eigenvalues of these eigenvector fields); and the
corresponding entities for the frame-drag field: frame-drag vortex lines and
their vorticities. These entities fully characterize the vacuum Riemann tensor.
In this paper, we compute and depict the tendex and vortex lines, and their
tendicities and vorticities, outside the horizons of stationary (Schwarzschild
and Kerr) black holes; and we introduce and depict the black holes' horizon
tendicity and vorticity (the normal-normal components of and on the
horizon). For Schwarzschild and Kerr black holes, the horizon tendicity is
proportional to the horizon's intrinsic scalar curvature, and the horizon
vorticity is proportional to an extrinsic scalar curvature. We show that, for
horizon-penetrating time slices, all these entities (, , the tendex lines
and vortex lines, the lines' tendicities and vorticities, and the horizon
tendicities and vorticities) are affected only weakly by changes of slicing and
changes of spatial coordinates, within those slicing and coordinate choices
that are commonly used for black holes. [Abstract is abbreviated.]Comment: 19 pages, 7 figures, v2: Changed to reflect published version
(changes made to color scales in Figs 5, 6, and 7 for consistent
conventions). v3: Fixed Ref
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