75 research outputs found
Can Cosmic Shear Shed Light on Low Cosmic Microwave Background Multipoles?
The lowest multipole moments of the cosmic microwave background (CMB) are
smaller than expected for a scale-invariant power spectrum. One possible
explanation is a cutoff in the primordial power spectrum below a comoving scale
of Mpc. This would affect not only the
CMB but also the cosmic-shear (CS) distortion of the CMB. Such a cutoff
increases significantly the cross-correlation between the large-angle CMB and
cosmic-shear patterns. The cross-correlation may be detectable at
which, when combined with the low CMB moments, may tilt the balance between a
result and a firm detection of a large-scale power-spectrum cutoff.
As an aside, we also note that the cutoff increases the large-angle
cross-correlation between the CMB and low-redshift tracers of the mass
distribution.Comment: 5 pages, 3 figures, revised statistical analysis, submitted to PR
The spin expansion for binary black hole merger: new predictions and future directions
In a recent paper arXiv:0709.0299, we introduced a spin expansion that
provides a simple yet powerful way to understand aspects of binary black hole
(BBH) merger. This approach relies on the symmetry properties of initial and
final quantities like the black hole mass m, kick velocity {\bf k}, and spin
vector {\bf s}, rather than a detailed understanding of the merger dynamics. In
this paper, we expand on this proposal, examine how well its predictions agree
with current simulations, and discuss several future directions that would make
it an even more valuable tool. The spin expansion yields many new predictions,
including several exact results that may be useful for testing numerical codes.
Some of these predictions have already been confirmed, while others await
future simulations. We explain how a relatively small number of simulations --
10 equal-mass simulations, and 16 unequal-mass simulations -- may be used to
calibrate all of the coefficients in the spin expansion up to second order at
the minimum computational cost. For a more general set of simulations of given
covariance, we derive the minimum-variance unbiased estimators for the spin
expansion coefficients. We discuss how this calibration would be interesting
and fruitful for general relativity and astrophysics. Finally, we sketch the
extension to eccentric orbits.Comment: 32 pages, 8 figures, matches Phys. Rev. D version. Added new
appendix: "Minimum-variance estimators for the spin coefficients
Explaining LIGO's observations via isolated binary evolution with natal kicks
We compare binary evolution models with different assumptions about
black-hole natal kicks to the first gravitational-wave observations performed
by the LIGO detectors. Our comparisons attempt to reconcile merger rate,
masses, spins, and spin-orbit misalignments of all current observations with
state-of-the-art formation scenarios of binary black holes formed in isolation.
We estimate that black holes (BHs) should receive natal kicks at birth of the
order of (50) km/s if tidal processes do (not) realign
stellar spins. Our estimate is driven by two simple factors. The natal kick
dispersion is bounded from above because large kicks disrupt too many
binaries (reducing the merger rate below the observed value). Conversely, the
natal kick distribution is bounded from below because modest kicks are needed
to produce a range of spin-orbit misalignments. A distribution of misalignments
increases our models' compatibility with LIGO's observations, if all BHs are
likely to have natal spins. Unlike related work which adopts a concrete BH
natal spin prescription, we explore a range of possible BH natal spin
distributions. Within the context of our models, for all of the choices of
used here and within the context of one simple fiducial parameterized
spin distribution, observations favor low BH natal spin.Comment: 19 pages, 14 figures, as published in PR
An ecological approach to problems of Dark Energy, Dark Matter, MOND and Neutrinos
Modern astronomical data on galaxy and cosmological scales have revealed
powerfully the existence of certain dark sectors of fundamental physics, i.e.,
existence of particles and fields outside the standard models and inaccessible
by current experiments. Various approaches are taken to modify/extend the
standard models. Generic theories introduce multiple de-coupled fields A, B, C,
each responsible for the effects of DM (cold supersymmetric particles), DE
(Dark Energy) effect, and MG (Modified Gravity) effect respectively. Some
theories use adopt vanilla combinations like AB, BC, or CA, and assume A, B, C
belong to decoupled sectors of physics. MOND-like MG and Cold DM are often
taken as opposite frameworks, e.g. in the debate around the Bullet Cluster.
Here we argue that these ad hoc divisions of sectors miss important clues from
the data. The data actually suggest that the physics of all dark sectors is
likely linked together by a self-interacting oscillating field, which governs a
chameleon-like dark fluid, appearing as DM, DE and MG in different settings. It
is timely to consider an interdisciplinary approach across all semantic
boundaries of dark sectors, treating the dark stress as one identity, hence
accounts for several "coincidences" naturally.Comment: 12p, Proceedings to the 6-th Int. Conf. of Gravitation and Cosmology.
Neutrino section expande
Multi-timescale analysis of phase transitions in precessing black-hole binaries
This is the author accepted manuscript. The final version is available from APS via http://dx.doi.org/10.1103/PhysRevD.92.064016The dynamics of precessing binary black holes (BBHs) in the post-Newtonian
regime has a strong timescale hierarchy: the orbital timescale is very short
compared to the spin-precession timescale which, in turn, is much shorter than
the radiation-reaction timescale on which the orbit is shrinking due to
gravitational-wave emission. We exploit this timescale hierarchy to develop a
multi-scale analysis of BBH dynamics elaborating on the analysis of Kesden et
al. (2015). We solve the spin-precession equations analytically on the
precession time and then implement a quasi-adiabatic approach to evolve these
solutions on the longer radiation-reaction time. This procedure leads to an
innovative "precession-averaged" post-Newtonian approach to studying precessing
BBHs. We use our new solutions to classify BBH spin precession into three
distinct morphologies, then investigate phase transitions between these
morphologies as BBHs inspiral. These precession-averaged post-Newtonian
inspirals can be efficiently calculated from arbitrarily large separations,
thus making progress towards bridging the gap between astrophysics and
numerical relativity.D.G. is supported by the UK STFC and the Isaac Newton Studentship of the University of Cambridge. M.K. is supported by Alfred P. Sloan Foundation grant FG-2015-65299. R.O'S. is supported by NSF grants PHY-0970074 and PHY-1307429. E.B. is sup- ported by NSF CAREER Grant PHY-1055103 and by FCT contract IF/00797/2014/CP1214/CT0012 under the IF2014 Programme. U.S. is supported by FP7- PEOPLE-2011-CIG Grant No. 293412, FP7-PEOPLE- 2011-IRSES Grant No.295189, H2020 ERC Consolida- tor Grant Agreement No. MaGRaTh-646597, SDSC and TACC through XSEDE Grant No. PHY-090003 by the NSF, Finis Terrae through Grant No. ICTS- CESGA-249, STFC Roller Grant No. ST/L000636/1 and DiRAC's Cosmos Shared Memory system through BIS Grant No. ST/J005673/1 and STFC Grant Nos. ST/H008586/1, ST/K00333X/1
Gravitational lensing as a contaminant of the gravity wave signal in CMB
Gravity waves (GW) in the early universe generate B-type polarization in the
cosmic microwave background (CMB), which can be used as a direct way to measure
the energy scale of inflation. Gravitational lensing contaminates the GW signal
by converting the dominant E polarization into B polarization. By
reconstructing the lensing potential from CMB itself one can decontaminate the
B mode induced by lensing. We present results of numerical simulations of B
mode delensing using quadratic and iterative maximum-likelihood lensing
reconstruction methods as a function of detector noise and beam. In our
simulations we find the quadratic method can reduce the lensing B noise power
by up to a factor of 7, close to the no noise limit. In contrast, the iterative
method shows significant improvements even at the lowest noise levels we
tested. We demonstrate explicitly that with this method at least a factor of 40
noise power reduction in lensing induced B power is possible, suggesting that
T/S=10^-6 may be achievable in the absence of sky cuts, foregrounds, and
instrumental systematics. While we do not find any fundamental lower limit due
to lensing, we find that for high-sensitivity detectors residual lensing noise
dominates over the detector noise.Comment: 6 pages, 2 figures, submitted to PR
Gravitational-Wave Signature of an Inspiral into a Supermassive Horizonless Object
Event horizons are among the most intriguing of general relativity's
predictions. Although on firm theoretical footing, direct indications of their
existence have yet to be observed. With this motivation in mind, we explore
here the possibility of finding a signature for event horizons in the
gravitational waves (GWs) produced during the inspiral of stellar-mass compact
objects (COs) into the supermassive () objects that lie at
the center of most galaxies. Such inspirals will be a major source for LISA,
the future space-based GW observatory. We contrast supermassive black holes
with models in which the central object is a supermassive boson star (SMBS).
Provided the COs interact only gravitationally with the SMBS, stable orbits
exist not just outside the Schwarzschild radius but also inside the surface of
the SMBS as well. The absence of an event horizon allows GWs from these orbits
to be observed. Here we solve for the metric in the interior of a fairly
generic class of SMBS and evolve the trajectory of an inspiraling CO from the
Schwarzschild exterior through the plunge into the exotic SMBS interior. We
calculate the approximate waveforms for GWs emitted during this inspiral.
Geodesics within the SMBS surface will exhibit extreme pericenter precession
and other features making the emitted GWs readily distinguishable from those
emitted during an inspiral into a black hole.Comment: 20 pages, 9 figures, submitted to PR
Distinguishing black-hole spin-orbit resonances by their gravitational wave signatures. II. Full parameter estimation
Gravitational waves from coalescing binary black holes encode the evolution of their spins prior to merger. In the post-Newtonian regime and on the precession time scale, this evolution has one of three morphologies, with the spins either librating around one of two fixed points ("resonances") or circulating freely. In this paper we perform full parameter estimation on resonant binaries with fixed masses and spin magnitudes, changing three parameters: a conserved "projected effective spin" ξ and resonant family ΔΦ=0,π (which uniquely label the source); the inclination θJN of the binary's total angular momentum with respect to the line of sight (which determines the strength of precessional effects in the waveform); and the signal amplitude. We demonstrate that resonances can be distinguished for a wide range of binaries, except for highly symmetric configurations where precessional effects are suppressed. Motivated by new insight into double-spin evolution, we introduce new variables to characterize precessing black hole binaries which naturally reflects the time scale separation of the system and therefore better encode the dynamical information carried by gravitational waves.D.T. is partially supported by the National Science Foundation through awards PHY-1067985, PHY-1404139, PHY-1055103 and PHY-1307020. D.T. is grateful for the support and hospitality of V. Kalogera's group and the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) at Northwestern University, where this project was conceived. D.G. is supported by the UK STFC and the Isaac Newton Studentship of the University of Cambridge. E.B. is supported by NSF CAREER Grant PHY-1055103 and by FCT contract IF/00797/2014/CP1214/CT0012 under the IF2014 Programme. M.K. is supported by Alfred P. Sloan Foundation grant FG-2015-65299. T.B.L. acknowledges NSF award PHY-1307020. U.S. is supported by FP7-PEOPLE-2011-CIG Grant No. 293412, FP7-PEOPLE-2011-IRSES Grant No.295189, H2020-MSCA-RISE-2015 Grant No. StronGrHEP-690904, H2020 ERC Consolidator Grant Agreement No. MaGRaTh-646597, SDSC and TACC through XSEDE Grant No. PHY-090003 by the NSF, Finis Terrae through Grant No. ICTS-CESGA-249, STFC Roller Grant No. ST/L000636/1 and DiRAC's Cosmos Shared Memory system through BIS Grant No. ST/J005673/1 and STFC Grant Nos. ST/H008586/1, ST/K00333X/1. Computational resources were provided by the Northwestern University Grail cluster (CIERA) through NSF MRI award PHY-1126812, by the Atlas cluster at AEI Hannover, supported by the Max Planck Institute and by the Nemo 20 at cluster through NSF-092340
A Lensing Reconstruction of Primordial Cosmic Microwave Background Polarization
We discuss a possibility to directly reconstruct the CMB polarization field
at the last scattering surface by accounting for modifications imposed by the
gravitational lensing effect. The suggested method requires a tracer field of
the large scale structure lensing potentials that deflected propagating CMB
photons from the last scattering surface. This required information can come
from a variety of observations on the large scale structure matter
distribution, including convergence reconstructed from lensing shear studies
involving galaxy shapes. In the case of so-called curl, or B,-modes of CMB
polarization, the reconstruction allows one to identify the distinct signature
of inflationary gravitational waves.Comment: 6 pages, 2 figures; PRD submitte
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