A Supernova Brane Scan

We consider a `brane-world scenario' recently introduced by Dvali, Gabadadze and Porrati, and subsequently proposed as an alternative to a cosmological constant in explaining the current acceleration of the universe. We show that, contrary to these claims, this proposal is already strongly disfavoured by the available Type Ia Supernovae, Cosmic Microwave Background and cluster data.Comment: Further cosmetic changes; to appear in The Astrophysical Journal, v56

Mobi algebra as an abstraction to the unit interval and its comparison to rings

We introduce a new algebraic structure, called mobi algebra, consisting of three constants and one ternary operation. The canonical example of a mobi algebra is the unit interval with the three constants 0, 1, and 1/2 and the ternary operation given by the formula x−yx+yz. We study some of its properties and prove that every unitary ring with one half uniquely determines and is uniquely determined by a mobi algebra with one double. Another algebraic structure, called involutive medial monoid (IMM), is considered to establish the passage between rings and mobi algebras.info:eu-repo/semantics/publishedVersio

Vorton Formation

In this paper we present the first analytic model for vorton formation. We start by deriving the microscopic string equations of motion in Witten's superconducting model, and show that in the relevant chiral limit these coincide with the ones obtained from the supersonic elastic models of Carter and Peter. We then numerically study a number of solutions of these equations of motion and thereby suggest criteria for deciding whether a given superconducting loop configuration can form a vorton. Finally, using a recently developed model for the evolution of currents in superconducting strings we conjecture, by comparison with these criteria, that string networks formed at the GUT phase transition should produce no vortons. On the other hand, a network formed at the electroweak scale can produce vortons accounting for up to 6% of the critical density. Some consequences of our results are discussed.Comment: 41 pages; color figures 3-6 not included, but available from authors. To appear in Phys. Rev.