6,188 research outputs found
Extreme recoils: impact on the detection of gravitational waves from massive black hole binaries
Recent numerical simulations of coalescences of highly spinning massive black
hole binaries (MBHBs) suggest that the remnant can suffer a recoil velocity of
the order of few thousands km/s. We study here, by means of dedicated
simulations of black holes build--up, how such extreme recoils could affect the
cosmological coalescence rate of MBHBs, placing a robust lower limit for the
predicted number of gravitational wave (GW) sources detectable by future
space--borne missions (such as LISA). We consider two main routes for black
hole formation: one where seeds are light remnants of Population III stars
(~10^2 \msun), and one where seeds are much heavier (>~10^4 \msun), formed via
the direct gas collapse in primordial nuclear disks. We find that extreme
recoil velocities do not compromise the efficient MBHB detection by LISA. If
seeds are already massive and/or relatively rare, the detection rate is reduced
by only ~15%. The number of detections drops substantially (by ~60%) if seeds
are instead light and abundant, but in this case the number of predicted
coalescences is so high that at least ~10 sources in a three year observation
are guaranteed.Comment: 5 pages, 4 figures, replaced with final versio
Three-family oscillations using neutrinos from muon beams at very long baseline
The planned LBL experiments will be able to prove the hypothesis of flavor
oscillation between muon and tau neutrinos. We explore the possibility of a
second generation long baseline experiment at very long baseline, i.e. L in the
range 5000-7000 km. This distance requires intense neutrino beams that could be
available from very intense muon beams as those needed for colliders.
Such baselines allow the study of neutrino oscillations with with neutrinos of energy , i.e.
above tau threshold. Moreover, matter effects inside the Earth could lead to
observable effects in oscillations. These effects are
interchanged between neutrinos and antineutrinos, and therefore they can be
tested by comparing the oscillated spectra obtained running the storage ring
with positive and negative muons.Comment: 14 pages, 4 figure
A medium baseline search for oscillations at a beam from muon decays
The accurate knowledge of the beam produced in
decays and the absence of contamination, make a future
muon storage ring the ideal place to look for \numunue (\numubarnuebar)
oscillations. Using a detector capable of electron and muon identification with
charge discrimination (e.g., the presently running NOMAD experiment), good
sensitivities to \numunue (\numubarnuebar) oscillations could be achieved.
With the CERN-PS as a proton driver for a muon storage ring of the kind
envisaged for a -collider, the LSND claim would be confirmed or disproved
in a few years of running.Comment: 10 pages, 4 figure
Making use of geometrical invariants in black hole collisions
We consider curvature invariants in the context of black hole collision
simulations. In particular, we propose a simple and elegant combination of the
Weyl invariants I and J, the {\sl speciality index} . In the context
of black hole perturbations provides a measure of the size of the
distortions from an ideal Kerr black hole spacetime. Explicit calculations in
well-known examples of axisymmetric black hole collisions demonstrate that this
quantity may serve as a useful tool for predicting in which cases perturbative
dynamics provide an accurate estimate of the radiation waveform and energy.
This makes particularly suited to studying the transition from
nonlinear to linear dynamics and for invariant interpretation of numerical
results.Comment: 4 pages, 3 eps figures, Revte
A Complete Statistical Analysis for the Quadrupole Amplitude in an Ellipsoidal Universe
A model of Universe with a small eccentricity due to the presence of a
magnetic field at the decoupling time (i.e. an Ellipsoidal Universe) has been
recently proposed for the solution of the low quadrupole anomaly of the angular
power spectrum of cosmic microwave background anisotropies. We present a
complete statistical analysis of that model showing that the probability of
increasing of the amplitude of the quadrupole is larger than the probability of
decreasing in the whole parameters' space.Comment: 5 pages, 3 figure
On the energy and baseline optimization to study effects related to the δ-phase (CP-/T-violation) in neutrino oscillations at a neutrino factory
In this paper we discuss the detection of CP- and T-violation effects in the framework of a neutrino factory. We introduce three quantities, which are good discriminants for a non-vanishing complex phase (δ) in the 3 Ă 3 neutrino mixing matrix: Îδ, ÎCP and ÎT. We find that these three discriminants (in vacuum) all scale with L/Ev, where L is the baseline and Ev the neutrino energy. Matter effects modify the scaling, but these effects are large enough to spoil the sensitivity only for baselines larger than 5000 km. So, in the hypothesis of constant neutrino factory power (i.e., number of muons inversely proportional to muon energy), the sensitivity on the δ-phase is independent of the baseline chosen. Specially interesting is the direct measurement of T-violation from the "wrong-sign" electron channel (i.e., the ÎT discriminant), which involves a comparison of the ve â vÎź and vÎź â ve oscillation rates. However, the vÎź â ve measurement requires magnetic discrimination of the electron charge, experimentally very challenging in a neutrino detector. Since the direction of the electron curvature has to be estimated before the start of the electromagnetic shower, low-energy neutrino beams and hence short baselines, are preferred. In this paper we show, as an example, the exclusion regions in the Îm212-δ plane using the ÎCP and ÎT discriminants for two concrete cases keeping the same L/Ev ratio (730 km/7.5 GeV and 2900 km/30 GeV). We obtain a similar excluded region provided that the electron detection efficiency is âź20% and the charge confusion 0.1%. The Îm212 compatible with the LMA solar data can be tested with a flux of 5 Ă 1021 muons. We compare these results with the fit of the visible energy distributions. Š 2002 Elsevier Science B.V. All rights reserved
Evolution of Magnetic Fields in Freely Decaying Magnetohydrodynamic Turbulence
We study the evolution of magnetic fields in freely decaying
magnetohydrodynamic turbulence. By quasi-linearizing the Navier-Stokes
equation, we solve analytically the induction equation in quasi-normal
approximation. We find that, if the magnetic field is not helical, the magnetic
energy and correlation length evolve in time respectively as E_B \propto
t^{-2(1+p)/(3+p)} and \xi_B \propto t^{2/(3+p)}, where p is the index of
initial power-law spectrum. In the helical case, the magnetic helicity is an
almost conserved quantity and forces the magnetic energy and correlation length
to scale as E_B \propto (log t)^{1/3} t^{-2/3} and \xi_B \propto (log t)^{-1/3}
t^{2/3}.Comment: 4 pages, 2 figures; accepted for publication in PR
The flavor of neutrinos in muon decays at a neutrino factory and the LSND puzzle
The accurate prediction of the neutrino beam produced in muon decays and the
absence of opposite helicity contamination for a particular neutrino flavor
make a future neutrino factory the ideal place to look for the lepton flavor
violating (LFV) decays of the kind \mu^+\ra e^+\nuebar\numu and lepton number
violating (LNV) processes like \mu^-\ra e^-\nue\numu. Excellent sensitivities
can be achieved using a detector capable of muon and/or electron identification
with charge discrimination. This would allow to set experimental limits that
improve current ones by more than two orders of magnitude and test the
hypothesis that the LSND excess is due to such anomalous decays, rather than
neutrino flavor oscillations in vacuum.Comment: 19 pages, 4 figure
Close encounters of three black holes
We present the first fully relativistic longterm numerical evolutions of
three equal-mass black holes in a system consisting of a third black hole in a
close orbit about a black-hole binary. We find that these
close-three-black-hole systems have very different merger dynamics from
black-hole binaries. In particular, we see complex trajectories, a
redistribution of energy that can impart substantial kicks to one of the holes,
distinctive waveforms, and suppression of the emitted gravitational radiation.
We evolve two such configurations and find very different behaviors. In one
configuration the binary is quickly disrupted and the individual holes follow
complicated trajectories and merge with the third hole in rapid succession,
while in the other, the binary completes a half-orbit before the initial merger
of one of the members with the third black hole, and the resulting
two-black-hole system forms a highly elliptical, well separated binary that
shows no significant inspiral for (at least) the first t~1000M of evolution.Comment: 4 pages, 5 figure
The Lazarus project: A pragmatic approach to binary black hole evolutions
We present a detailed description of techniques developed to combine 3D
numerical simulations and, subsequently, a single black hole close-limit
approximation. This method has made it possible to compute the first complete
waveforms covering the post-orbital dynamics of a binary black hole system with
the numerical simulation covering the essential non-linear interaction before
the close limit becomes applicable for the late time dynamics. To determine
when close-limit perturbation theory is applicable we apply a combination of
invariant a priori estimates and a posteriori consistency checks of the
robustness of our results against exchange of linear and non-linear treatments
near the interface. Once the numerically modeled binary system reaches a regime
that can be treated as perturbations of the Kerr spacetime, we must
approximately relate the numerical coordinates to the perturbative background
coordinates. We also perform a rotation of a numerically defined tetrad to
asymptotically reproduce the tetrad required in the perturbative treatment. We
can then produce numerical Cauchy data for the close-limit evolution in the
form of the Weyl scalar and its time derivative
with both objects being first order coordinate and tetrad invariant. The
Teukolsky equation in Boyer-Lindquist coordinates is adopted to further
continue the evolution. To illustrate the application of these techniques we
evolve a single Kerr hole and compute the spurious radiation as a measure of
the error of the whole procedure. We also briefly discuss the extension of the
project to make use of improved full numerical evolutions and outline the
approach to a full understanding of astrophysical black hole binary systems
which we can now pursue.Comment: New typos found in the version appeared in PRD. (Mostly found and
collected by Bernard Kelly
- âŚ