208 research outputs found

### TASI Lectures on Gravitational Waves from the Early Universe

These lectures discuss how the direct detection of gravitational waves can be
used to probe the very early Universe. We review the main cosmological
mechanisms which could have produced relic gravitational waves, and compare
theoretical predictions with capabilities and time scales of current and
upcoming experiments.Comment: 37 pages, 8 figures; typos correcte

### Effective action and tension renormalization for cosmic and fundamental strings

We derive the effective action for classical strings coupled to dilatonic,
gravitational, and axionic fields. We show how to use this effective action
for: (i) renormalizing the string tension, (ii) linking ultraviolet divergences
to the infrared (long-range) interaction between strings, (iii) bringing
additional light on the special cancellations that occur for fundamental
strings, and (iv) pointing out the limitations of Dirac's celebrated
field-energy approach to renormalization.Comment: 13 pages, RevTex, one paragraph added at the en

### Modeling dynamical scalarization with a resummed post-Newtonian expansion

Despite stringent constraints set by astrophysical observations, there remain
viable scalar-tensor theories that could be distinguished from general
relativity with gravitational-wave detectors. A promising signal predicted in
these alternative theories is dynamical scalarization, which can dramatically
affect the evolution of neutron-star binaries near merger. Motivated by the
successful treatment of spontaneous scalarization, we develop a formalism that
partially resums the post-Newtonian expansion to capture dynamical
scalarization in a mathematically consistent manner. We calculate the
post-Newtonian order corrections to the equations of motion and scalar mass of
a binary system. Through comparison with quasi-equilibrium configuration
calculations, we verify that this new approximation scheme can accurately
predict the onset and magnitude of dynamical scalarization.Comment: 24 pages, 8 figures; recolored figures, fixed typos, added emai

### The dynamics of precessing binary black holes using the post-Newtonian approximation

We investigate the (conservative) dynamics of binary black holes using the
Hamiltonian formulation of the post-Newtonian (PN) equations of motion. The
Hamiltonian we use includes spin-orbit coupling, spin-spin coupling, and mass
monopole/spin-induced quadrupole interaction terms. In the case of both
quasi-circular and eccentric orbits, we search for the presence of chaos (using
the method of Lyapunov exponents) for a large variety of initial conditions.
For quasi-circular orbits, we find no chaotic behavior for black holes with
total mass 10 - 40 solar masses when initially at a separation corresponding to
a Newtonian gravitational-wave frequency less than 150 Hz. Only for rather
small initial radial distances, for which spin-spin induced oscillations in the
radial separation are rather important, do we find chaotic solutions, and even
then they are rare. Moreover, these chaotic quasi-circular orbits are of
questionable astrophysical significance, since they originate from direct
parametrization of the equations of motion rather than from widely separated
binaries evolving to small separations under gravitational radiation reaction.
In the case of highly eccentric orbits, which for ground-based interferometers
are not astrophysically favored, we again find chaotic solutions, but only at
pericenters so small that higher order PN corrections, especially higher spin
PN corrections, should also be taken into account.Comment: 18 pages, 26 figure

### Third post-Newtonian spin-orbit effect in the gravitational radiation flux of compact binaries

Gravitational waves contain tail effects that are due to the backscattering
of linear waves in the curved space-time geometry around the source. The
knowledge as well as the accuracy of the two-body inspiraling post-Newtonian
(PN) dynamics and of the gravitational-wave signal has been recently improved,
notably by computing the spin-orbit (SO) terms induced by tail effects in the
gravitational-wave energy flux at the 3PN order. Here we sketch this
derivation, which yields the phasing formula including SO tail effects through
the same 3PN order. Those results can be employed to improve the accuracy of
analytical templates aimed at describing the whole process of inspiral, merger,
and ringdown.Comment: 6 pages; proceeding of the 9th LISA Symposium, Pari

### Detection template families for gravitational waves from the final stages of binary--black-hole inspirals: Nonspinning case

We investigate the problem of detecting gravitational waves from binaries of
nonspinning black holes with masses m = 5--20 Msun, moving on quasicircular
orbits, which are arguably the most promising sources for first-generation
ground-based detectors. We analyze and compare all the currently available
post--Newtonian approximations for the relativistic two-body dynamics; for
these binaries, different approximations predict different waveforms. We then
construct examples of detection template families that embed all the
approximate models, and that could be used to detect the true
gravitational-wave signal (but not to characterize accurately its physical
parameters). We estimate that the fitting factor for our detection families is
>~0.95 (corresponding to an event-rate loss <~15%) and we estimate that the
discretization of the template family, for ~10^4 templates, increases the loss
to <~20%.Comment: 58 pages, 38 EPS figures, final PRD version; small corrections to GW
flux terms as per Blanchet et al., PRD 71, 129902(E)-129904(E) (2005

### Quasiequilibrium sequences of binary neutron stars undergoing dynamical scalarization

We calculate quasiequilibrium sequences of equal-mass, irrotational binary
neutron stars (BNSs) in a scalar-tensor (ST) theory of gravity that admits
dynamical scalarization. We model neutron stars with realistic equations of
state (notably through piecewise polytropic equations of state). Using these
quasiequilibrium sequences we compute the binary's scalar charge and binding
energy versus orbital angular frequency. We find that the absolute value of the
binding energy is smaller than in general relativity (GR), differing at most by
~14% at high frequencies for the cases considered. We use the newly computed
binding energy and the balance equation to estimate the number of
gravitational-wave (GW) cycles during the adiabatic, quasicircular inspiral
stage up to the end of the sequence, which is the last stable orbit or the
mass-shedding point, depending on which comes first. We find that, depending on
the ST parameters, the number of GW cycles can be substantially smaller than in
GR. In particular, we obtain that when dynamical scalarization sets in around a
GW frequency of ~130 Hz, the sole inclusion of the ST binding energy causes a
reduction of GW cycles from ~120 Hz up to the end of the sequence (~1200 Hz) of
~11% with respect to the GR case. We estimate that when the ST energy flux is
also included the reduction in GW cycles becomes of ~24%. Quite interestingly,
dynamical scalarization can produce a difference in the number of GW cycles
with respect to the GR point-particle case that is much larger than the effect
due to tidal interactions, which is on the order of only a few GW cycles. These
results further clarify and confirm recent studies that have evolved BNSs
either in full numerical relativity or in post-Newtonian theory, and point out
the importance of developing accurate ST-theory waveforms for systems composed
of strongly self-gravitating objects, such as BNSs.Comment: 16 pages, 14 figures, 2 tables, updated to match the published
versio

### Spin effects on gravitational waves from inspiraling compact binaries at second post-Newtonian order

We calculate the gravitational waveform for spinning, precessing compact
binary inspirals through second post-Newtonian order in the amplitude. When
spins are collinear with the orbital angular momentum and the orbits are
quasi-circular, we further provide explicit expressions for the
gravitational-wave polarizations and the decomposition into spin-weighted
spherical-harmonic modes. Knowledge of the second post-Newtonian spin terms in
the waveform could be used to improve the physical content of analytical
templates for data analysis of compact binary inspirals and for more accurate
comparisons with numerical-relativity simulations.Comment: 15 pages, expressions available in mathematica format upon reques

### Gravitational waves

These lectures are envisioned to be an introductory, basic course in
gravitational-wave physics.Comment: 50 pages, 13 figures; to appear in the Proceedings of Les Houches
Summer School, Particle Physics and Cosmology: The Fabric of Spacetime, Les
Houches, France, 31 Jul - 25 Aug 200

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