1,973 research outputs found
State reconstruction of finite dimensional compound systems via local projective measurements and one-way classical communication
For a finite dimensional discrete bipartite system, we find the relation
between local projections performed by Alice, and Bob post-selected state
dependence on the global state submatrices. With this result the joint state
reconstruction problem for a bipartite system can be solved with strict local
projections and one-way classical communication. The generalization to
multipartite systems is straightforward.Comment: 4 pages, 1 figur
Fourth post-Newtonian effective-one-body Hamiltonians with generic spins
In a compact binary coalescence, the spins of the compact objects can have a significant effect on the orbital motion and gravitational-wave (GW) emission. For generic spin orientations, the orbital plane precesses, leading to characteristic modulations of the GW signal. The observation of precession effects is crucial to discriminate among different binary formation scenarios, and to carry out precise tests of General Relativity. Here, we work toward an improved description of spin effects in binary inspirals, within the effective-one-body (EOB) formalism, which is commonly used to build waveform models for LIGO and Virgo data analysis. We derive EOB Hamiltonians including the complete fourth post-Newtonian (4PN) conservative dynamics, which is the current state of the art. We place no restrictions on the spin orientations or magnitudes, or on the type of compact object (e.g., black hole or neutron star), and we produce the first generic-spin EOB Hamiltonians complete at 4PN order. We consider multiple spinning EOB Hamiltonians, which are more or less direct extensions of the varieties found in previous literature, and we suggest another simplified variant. Finally, we compare the circular-orbit, aligned-spin binding-energy functions derived from the EOB Hamiltonians to numerical-relativity simulations of the late inspiral. While finding that all proposed Hamiltonians perform reasonably well, we point out some interesting differences, which could guide the selection of a simpler, and thus faster-to-evolve EOB Hamiltonian to be used in future LIGO and Virgo inference studies
Reduced Hamiltonian for next-to-leading order Spin-Squared Dynamics of General Compact Binaries
Within the post Newtonian framework the fully reduced Hamiltonian (i.e., with
eliminated spin supplementary condition) for the next-to-leading order
spin-squared dynamics of general compact binaries is presented. The Hamiltonian
is applicable to the spin dynamics of all kinds of binaries with
self-gravitating components like black holes and/or neutron stars taking into
account spin-induced quadrupolar deformation effects in second post-Newtonian
order perturbation theory of Einstein's field equations. The corresponding
equations of motion for spin, position and momentum variables are given in
terms of canonical Poisson brackets. Comparison with a nonreduced potential
calculated within the Effective Field Theory approach is made.Comment: 11 pages, minor changes to match published version at CQ
An improved effective-one-body Hamiltonian for spinning black-hole binaries
Building on a recent paper in which we computed the canonical Hamiltonian of
a spinning test particle in curved spacetime, at linear order in the particle's
spin, we work out an improved effective-one-body (EOB) Hamiltonian for spinning
black-hole binaries. As in previous descriptions, we endow the effective
particle not only with a mass m, but also with a spin S*. Thus, the effective
particle interacts with the effective Kerr background (having spin S_Kerr)
through a geodesic-type interaction and an additional spin-dependent
interaction proportional to S*. When expanded in post-Newtonian (PN) orders,
the EOB Hamiltonian reproduces the leading order spin-spin coupling and the
spin-orbit coupling through 2.5PN order, for any mass-ratio. Also, it
reproduces all spin-orbit couplings in the test-particle limit. Similarly to
the test-particle limit case, when we restrict the EOB dynamics to spins
aligned or antialigned with the orbital angular momentum, for which circular
orbits exist, the EOB dynamics has several interesting features, such as the
existence of an innermost stable circular orbit, a photon circular orbit, and a
maximum in the orbital frequency during the plunge subsequent to the inspiral.
These properties are crucial for reproducing the dynamics and
gravitational-wave emission of spinning black-hole binaries, as calculated in
numerical relativity simulations.Comment: 22 pages, 9 figures. Minor changes to match version accepted for
publication in PR
Entanglement and nonclassical properties of hypergraph states
Hypergraph states are multi-qubit states that form a subset of the locally
maximally entangleable states and a generalization of the well--established
notion of graph states. Mathematically, they can conveniently be described by a
hypergraph that indicates a possible generation procedure of these states;
alternatively, they can also be phrased in terms of a non-local stabilizer
formalism. In this paper, we explore the entanglement properties and
nonclassical features of hypergraph states. First, we identify the equivalence
classes under local unitary transformations for up to four qubits, as well as
important classes of five- and six-qubit states, and determine various
entanglement properties of these classes. Second, we present general conditions
under which the local unitary equivalence of hypergraph states can simply be
decided by considering a finite set of transformations with a clear
graph-theoretical interpretation. Finally, we consider the question whether
hypergraph states and their correlations can be used to reveal contradictions
with classical hidden variable theories. We demonstrate that various
noncontextuality inequalities and Bell inequalities can be derived for
hypergraph states.Comment: 29 pages, 5 figures, final versio
On the comparison of results regarding the post-Newtonian approximate treatment of the dynamics of extended spinning compact binaries
A brief review is given of all the Hamiltonians and effective potentials
calculated hitherto covering the post-Newtonian (pN) dynamics of a two body
system. A method is presented to compare (conservative) reduced Hamiltonians
with nonreduced potentials directly at least up to the next-to-leading-pN
order.Comment: Conference proceedings for the 7th International Conference on
Gravitation and Cosmology (ICGC2011), 4 page
On Robust Discursive Equality
This paper explores the idea of robust discursive equality on which respect-based conceptions of justificatory reciprocity often draw. I distinguish between formal and substantive discursive equality and argue that if justificatory reciprocity requires that people be accorded formally equal discursive standing, robust discursive equality should not be construed as requiring standing that is equal substantively, or in terms of its discursive purchase. Still, robust discursive equality is purchase sensitive: it does not obtain when discursive standing is impermissibly unequal in purchase. I then showcase different candidate conceptions of purchase justice, and draw conclusions about the substantive commitments of justificatory reciprocity
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