7,814 research outputs found
Dark matter as integration constant in Horava-Lifshitz gravity
In the non-relativistic theory of gravitation recently proposed by Horava,
the Hamiltonian constraint is not a local equation satisfied at each spatial
point but an equation integrated over a whole space. The global Hamiltonian
constraint is less restrictive than its local version, and allows a richer set
of solutions than in general relativity. We show that a component which behaves
like pressureless dust emerges as an "integration constant" of dynamical
equations and momentum constraint equations. Consequently, classical solutions
to the infrared limit of Horava-Lifshitz gravity can mimic general relativity
plus cold dark matter.Comment: 16 pages; (non-)conservation equation for "dark matter" added (v2);
note added to comment on some recent preprints (v3); version accepted for
publication in PRD (v4
Spacetime Foam, Holographic Principle, and Black Hole Quantum Computers
Spacetime foam, also known as quantum foam, has its origin in quantum
fluctuations of spacetime. Arguably it is the source of the holographic
principle, which severely limits how densely information can be packed in
space. Its physics is also intimately linked to that of black holes and
computation. In particular, the same underlying physics is shown to govern the
computational power of black hole quantum computers.Comment: 8 pages, LaTeX; Talk given by Jack Ng, in celebration of Paul
Frampton's 60th birthday, at the Coral Gables Conference (in Fort Lauderdale,
Florida on December 17, 2003). To appear in the Proceedings of the 2003 Coral
Gables Conferenc
Quantum Entanglement and Communication Complexity
We consider a variation of the multi-party communication complexity scenario
where the parties are supplied with an extra resource: particles in an
entangled quantum state. We show that, although a prior quantum entanglement
cannot be used to simulate a communication channel, it can reduce the
communication complexity of functions in some cases. Specifically, we show
that, for a particular function among three parties (each of which possesses
part of the function's input), a prior quantum entanglement enables them to
learn the value of the function with only three bits of communication occurring
among the parties, whereas, without quantum entanglement, four bits of
communication are necessary. We also show that, for a particular two-party
probabilistic communication complexity problem, quantum entanglement results in
less communication than is required with only classical random correlations
(instead of quantum entanglement). These results are a noteworthy contrast to
the well-known fact that quantum entanglement cannot be used to actually
simulate communication among remote parties.Comment: 10 pages, latex, no figure
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