Electrified Fuzzy Spheres and Funnels in Curved Backgrounds

We use the non-Abelian DBI action to study the dynamics of $N$ coincident $Dp$-branes in an arbitrary curved background, with the presence of a homogenous world-volume electric field. The solutions are natural extensions of those without electric fields, and imply that the spheres will collapse toward zero size. We then go on to consider the $D1-D3$ intersection in a curved background and find various dualities and automorphisms of the general equations of motion. It is possible to map the dynamical equation of motion to the static one via Wick rotation, however the additional spatial dependence of the metric prevents this mapping from being invertible. Instead we find that a double Wick rotation leaves the static equation invariant. This is very different from the behaviour in Minkowski space. We go on to construct the most general static fuzzy funnel solutions for an arbitrary metric either by solving the static equations of motion, or by finding configurations which minimise the energy. As a consistency check we construct the Abelian $D3$-brane world-volume theory in the same generic background and find solutions consistent with energy minimisation. In the $NS$5-brane background we find time dependent solutions to the equations of motion, representing a time dependent fuzzy funnel. These solutions match those obtained from the $D$-string picture to leading order suggesting that the action in the large $N$ limit does not need corrections. We conclude by generalising our solutions to higher dimensional fuzzy funnels.Comment: 38 pages, Latex; references adde

Tolerance to the Effects of Morphine on Intestinal Motility of Unanesthetized Dogs1

ABSTRACT Weisbrodt, Norma

Interactions between U(1)U(1) Cosmic Strings: An Analytical Study

We derive analytic expressions for the interaction energy between two general $U(1)$ cosmic strings as the function of their relative orientation and the ratio of the coupling constants in the model. The results are relevant to the statistic description of strings away from critical coupling and shed some light on the mechanisms involved in string formation and the evolution of string networks.Comment: 31 pages,REVTEX, Imperial/TP/93-94/3

Cosmic Strings and Superstrings

Cosmic strings are predicted by many field-theory models, and may have been formed at a symmetry-breaking transition early in the history of the universe, such as that associated with grand unification. They could have important cosmological effects. Scenarios suggested by fundamental string theory or M-theory, in particular the popular idea of brane inflation, also strongly suggest the appearance of similar structures. Here we review the reasons for postulating the existence of cosmic strings or superstrings, the various possible ways in which they might be detected observationally, and the special features that might discriminate between ordinary cosmic strings and superstrings.Comment: Minor errors corrected and some references added, 34 pages, 6 figure

Phase Space Analysis of Quintessence Cosmologies with a Double Exponential Potential

We use phase space methods to investigate closed, flat, and open Friedmann-Robertson-Walker cosmologies with a scalar potential given by the sum of two exponential terms. The form of the potential is motivated by the dimensional reduction of M-theory with non-trivial four-form flux on a maximally symmetric internal space. To describe the asymptotic features of run-away solutions we introduce the concept of a `quasi fixed point.' We give the complete classification of solutions according to their late-time behavior (accelerating, decelerating, crunch) and the number of periods of accelerated expansion.Comment: 46 pages, 5 figures; v2: minor changes, references added; v3: title changed, refined classification of solutions, 3 references added, version which appeared in JCA

From training to artisanal practice : rethinking choreographic relationships in modern dance

In the first part of the twentieth century early modern dancers created both a new art form and the forms of group social organisation that were its condition of possibility. This paper critically examines the balletic and disciplinary ‘training’ model of dancer formation and proposes that the assumption of training in dance can obscure other ways of understanding dance-making relationships and other values in early modern dance. An ‘artisanal’ mode of production and knowledge transmission based on a non-binary relationship between ‘master’ and apprentice and occurring in a quasi-domestic and personalised space of some intimacy is proposed as a more pertinent way to think the enabling conditions of modern dance creation

Correspondence between kinematical backreaction and scalar field cosmologies - the `morphon field'

Spatially averaged inhomogeneous cosmologies in classical general relativity can be written in the form of effective Friedmann equations with sources that include backreaction terms. In this paper we propose to describe these backreaction terms with the help of a homogeneous scalar field evolving in a potential; we call it the `morphon field'. This new field links classical inhomogeneous cosmologies to scalar field cosmologies, allowing to reinterpret, e.g., quintessence scenarios by routing the physical origin of the scalar field source to inhomogeneities in the Universe. We investigate a one-parameter family of scaling solutions to the backreaction problem. Subcases of these solutions (all without an assumed cosmological constant) include scale-dependent models with Friedmannian kinematics that can mimic the presence of a cosmological constant or a time-dependent cosmological term. We explicitly reconstruct the scalar field potential for the scaling solutions, and discuss those cases that provide a solution to the Dark Energy and coincidence problems. In this approach, Dark Energy emerges from morphon fields, a mechanism that can be understood through the proposed correspondence: the averaged cosmology is characterized by a weak decay (quintessence) or growth (phantom quintessence) of kinematical fluctuations, fed by `curvature energy' that is stored in the averaged 3-Ricci curvature. We find that the late-time trajectories of those models approach attractors that lie in the future of a state that is predicted by observational constraints.Comment: 36 pages and 6 Figures, matches published version in Class.Quant.Gra

Generalized Chaplygin gas model: Cosmological consequences and statefinder diagnosis

The generalized Chaplygin gas (GCG) model in spatially flat universe is investigated. The cosmological consequences led by GCG model including the evolution of EoS parameter, deceleration parameter and dimensionless Hubble parameter are calculated. We show that the GCG model behaves as a general quintessence model. The GCG model can also represent the pressureless CDM model at the early time and cosmological constant model at the late time. The dependency of transition from decelerated expansion to accelerated expansion on the parameters of model is investigated. The statefinder parameters $r$ and $s$ in this model are derived and the evolutionary trajectories in $s-r$ plane are plotted. Finally, based on current observational data, we plot the evolutionary trajectories in $s-r$ and $q-r$ planes for best fit values of the parameters of GCG model. It has been shown that although, there are similarities between GCG model and other forms of chaplygin gas in statefinder plane, but the distance of this model from the $\Lambda$CDM fixed point in $s-r$ diagram is shorter compare with standard chaplygin gas model.Comment: 10 pages, 5 figures, accepted in Astrophys Space Sci. (2011

Signatures of Short Distance Physics in the Cosmic Microwave Background

We systematically investigate the effect of short distance physics on the spectrum of temperature anistropies in the Cosmic Microwave Background produced during inflation. We present a general argument-assuming only low energy locality-that the size of such effects are of order H^2/M^2, where H is the Hubble parameter during inflation, and M is the scale of the high energy physics. We evaluate the strength of such effects in a number of specific string and M theory models. In weakly coupled field theory and string theory models, the effects are far too small to be observed. In phenomenologically attractive Horava-Witten compactifications, the effects are much larger but still unobservable. In certain M theory models, for which the fundamental Planck scale is several orders of magnitude below the conventional scale of grand unification, the effects may be on the threshold of detectability. However, observations of both the scalar and tensor fluctuation contributions to the Cosmic Microwave Background power spectrum-with a precision near the cosmic variance limit-are necessary in order to unambiguously demonstrate the existence of these signatures of high energy physics. This is a formidable experimental challenge.Comment: 49 pages, 2 figures. References added, minor typos correcte

Statefinder diagnostic and stability of modified gravity consistent with holographic and new agegraphic dark energy

Recently one of us derived the action of modified gravity consistent with the holographic and new-agegraphic dark energy. In this paper, we investigate the stability of the Lagrangians of the modified gravity as discussed in [M. R. Setare, Int. J. Mod. Phys. D 17 (2008) 2219; M. R. Setare, Astrophys. Space Sci. 326 (2010) 27]. We also calculate the statefinder parameters which classify our dark energy model.Comment: 12 pages, 2 figures, accepted by Gen. Relativ. Gravi