Living on the edge: cosmology on the boundary of anti-de Sitter space

We sketch a particularly simple and compelling version of D-brane cosmology. Inspired by the semi-phenomenological Randall--Sundrum models, and their cosmological generalizations, we develop a variant that contains a single (3+1)-dimensional D-brane which is located on the boundary of a single bulk (4+1)-dimensional region. The D-brane boundary is itself to be interpreted as our visible universe, with ordinary matter (planets, stars, galaxies) being trapped on this D-brane by string theory effects. The (4+1)-dimensional bulk is, in its simplest implementation, adS_{4+1}, anti-de Sitter space. We demonstrate that a k=+1 closed FLRW universe is the most natural option, though the scale factor could quite easily be so large as to make it operationally indistinguishable from a k=0 spatially flat universe. (With minor loss of elegance, spatially flat and hyperbolic FLRW cosmologies can also be accommodated.) We demonstrate how this model can be made consistent with standard cosmology, and suggest some possible observational tests.Comment: LaTeX2e, 17 pages; Revised (references added, physics unchanged). To appear in Physics Letters

Quantum Interest in (3+1) dimensional Minkowski space

The so-called "Quantum Inequalities", and the "Quantum Interest Conjecture", use quantum field theory to impose significant restrictions on the temporal distribution of the energy density measured by a time-like observer, potentially preventing the existence of exotic phenomena such as "Alcubierre warp-drives" or "traversable wormholes". Both the quantum inequalities and the quantum interest conjecture can be reduced to statements concerning the existence or non-existence of bound states for a certain one-dimensional quantum mechanical pseudo-Hamiltonian. Using this approach, we shall provide a simple proof of one version of the Quantum Interest Conjecture in (3+1) dimensional Minkowski space.Comment: V1: 8 pages, revtex4; V2: 10 pages, some technical changes in details of the argument, no change in physics conclusions, this version essentially identical to published versio

The Small-Is-Very-Small Principle

The central result of this paper is the small-is-very-small principle for restricted sequential theories. The principle says roughly that whenever the given theory shows that a property has a small witness, i.e. a witness in every definable cut, then it shows that the property has a very small witness: i.e. a witness below a given standard number. We draw various consequences from the central result. For example (in rough formulations): (i) Every restricted, recursively enumerable sequential theory has a finitely axiomatized extension that is conservative w.r.t. formulas of complexity $\leq n$. (ii) Every sequential model has, for any $n$, an extension that is elementary for formulas of complexity $\leq n$, in which the intersection of all definable cuts is the natural numbers. (iii) We have reflection for $\Sigma^0_2$-sentences with sufficiently small witness in any consistent restricted theory $U$. (iv) Suppose $U$ is recursively enumerable and sequential. Suppose further that every recursively enumerable and sequential $V$ that locally inteprets $U$, globally interprets $U$. Then, $U$ is mutually globally interpretable with a finitely axiomatized sequential theory. The paper contains some careful groundwork developing partial satisfaction predicates in sequential theories for the complexity measure depth of quantifier alternations

Inverse Source Identification based on Acoustic Particle Velocity Measurements

A general applicable acoustic source identification method is the inverse frequency response function technique (IFRF). In the standard IFRF method acoustic pressures measured on a grid in the nearfield of the acoustic source are used. To relate the measured field pressures to the normal velocities on the surface of the source, a transfer matrix is calculated with a boundary element method. The resulting system of equations is ill-conditioned and can only be solved by applying regularization techniques. In this paper, it is described how the nearfield particle velocities can be used instead of pressures to reconstruct the original source vibrations. By means of a simulated experiment, a comparison is made between pressure based and velocity based IFRF

Explicit form of the Mann-Marolf surface term in (3+1) dimensions

The Mann-Marolf surface term is a specific candidate for the "reference background term" that is to be subtracted from the Gibbons-Hawking surface term in order make the total gravitational action of asymptotically flat spacetimes finite. That is, the total gravitational action is taken to be: (Einstein-Hilbert bulk term) + (Gibbons-Hawking surface term) - (Mann-Marolf surface term). As presented by Mann and Marolf, their surface term is specified implicitly in terms of the Ricci tensor of the boundary. Herein I demonstrate that for the physically interesting case of a (3+1) dimensional bulk spacetime, the Mann-Marolf surface term can be specified explicitly in terms of the Einstein tensor of the (2+1) dimensional boundary.Comment: 4 pages; revtex4; V2: Now 5 pages. Improved discussion of the degenerate case where some eigenvalues of the Einstein tensor are zero. No change in physics conclusions. This version accepted for publication in Physical Review

Policy voting, projection, and persuasion: an application of balance theory to electoral behavior

In this article differences between rational, policy-based, and rationalized voting are discussed, and it is argued that these forms of electoral decision making are not properly analyzed in existing electoral studies. Policy voting, persuasion, and projection are then redefined as three possible ways of restoring balance among imbalanced triads of political beliefs and attitudes. With the help of the Chernobyl nuclear plants issue it is shown that persuasion and projection are far more important ways of restoring balance than policy voting