Scalar field phase dynamics in preheating

We study the model of a massive inflaton field $\phi$ coupled to another scalar filed $\chi$ with interaction term $g^2\phi^2\chi^2$ for the first stage of preheating. We obtain the the behavior of the phase in terms of the iteration of a simple family of circle maps. When expansion of the universe is taken into account the qualitative behavior of the phase and growth number evolution is reminiscent of the behavior found in the case without expansion.Comment: 4 pages, 4 figures, LaTeX; submitted to the Proceedings of Eleventh Marcel Grossmann Meetin

Reheating induced by competing decay modes

We address the problem of studying the decay of the inflaton field $\phi$ to another scalar field $\chi$ through parametric resonance in the case of a coupling that involves several decay modes. This amounts to the presence of extra harmonic terms in the perturbation of the $\chi$ field dynamics. For the case of two frequencies we compute the geometry of the resonance regions, which is significantly altered due to the presence of non-cuspidal resonance regions associated to higher harmonics and to the emergence of instability `pockets'. We discuss the effect of this change in the efficiency of the energy transfer process for the simplest case of a coupling given by a combination of the two interaction terms of homogeneous degree usually considered in the literature. We find that the presence of higher harmonics has limited cosmological implications.Comment: 14 pages, 4 figures Added references. Corrected typo

Comparison of engagement and emotional responses of older and younger adults interacting with 3D cultural heritage artefacts on personal devices

The availability of advanced software and less expensive hardware allows museums to preserve and share artefacts digitally. As a result, museums are frequently making their collections accessible online as interactive, 3D models. This could lead to the unique situation of viewing the digital artefact before the physical artefact. Experiencing artefacts digitally outside of the museum on personal devices may affect the user's ability to emotionally connect to the artefacts. This study examines how two target populations of young adults (18–21 years) and the elderly (65 years and older) responded to seeing cultural heritage artefacts in three different modalities: augmented reality on a tablet, 3D models on a laptop, and then physical artefacts. Specifically, the time spent, enjoyment, and emotional responses were analysed. Results revealed that regardless of age, the digital modalities were enjoyable and encouraged emotional responses. Seeing the physical artefacts after the digital ones did not lessen their enjoyment or emotions felt. These findings aim to provide an insight into the effectiveness of 3D artefacts viewed on personal devices and artefacts shown outside of the museum for encouraging emotional responses from older and younger people

Scaling solutions from interacting fluids

We examine the dynamical implications of an interaction between some of the fluid components of the universe. We consider the combination of three matter components, one of which is a perfect fluid and the other two are interacting. The interaction term generalizes the cases found in scalar field cosmologies with an exponential potential. We find that attracting scaling solutions are obtained in several regions of parameter space, that oscillating behaviour is possible, and that new curvature scaling solutions exist. We also discuss the inflationary behaviour of the solutions and present some of the constraints on the strength of the coupling, namely those arising from nucleosynthesis.Comment: RevTeX, 21 pages, 8 figure

9/11: Seven Years into History

The after-effects of the 9/11 attacks continue to reverberate around the world. It is much too soon to draw any definitive conclusions about its long-term impact, let alone its place in history. But five years is long enough to ask some preliminary questions and suggest some tentative answers. This article addresses only two of the many possible questions. First, did 9/11 represent a "Revolution in Terrorism Affairs"? That is, did it amount to such a profound break with the past practice of terrorism that the world now confronts an unprecedented threat? Second, did it "alter the course of history"? Did it initiate any significant events or have consequences which otherwise would not have occurred? The development of terrorism over the last three decades calls into question the notion that al-Qaeda and 9/11 marked a ‘revolutionary’ change in the nature of terrorism. In many respects, they seem to constitute a ‘paradigm shift’ rather than a ‘quantum leap’ – more evolutionary than revolutionary. There are plenty of factors that suggest 9/11 was a ‘world-changing event’: the launching of a "Global War on Terrorism"; the consequent invasions and occupations of Iraq and Afghanistan; the rise of major insurgencies in both countries; radicalization of expatriate Muslim communities; the fracturing of the trans-Atlantic alliance; the adoption of harsh anti-terrorism measures by liberal democratic states; and finally, the American adoption of the strategy of ‘preventive war.’ While it is tempting to suggest that none of this would have happened without 9/11, the truth of the matter is less clear-cut than one might think. Granted that five years is still much too close to place an event in its proper historical context, the evidence thus far suggests first, that 9/11 may have been less earth-shaking in its strategic consequences than first imagined, and second, that reactions to it contain some ‘genetic markers’ of longer-term trends that pre-date that event. Its strategic significance will probably be determined by three factors: the outcome of the war in Iraq; the extent to which ‘pre-emptive war’ becomes an accepted model of international crisis management; and the ability of democracies to balance security and civil liberties in the face of a prolonged war. At this juncture, perhaps all that we can say with any certainty is that history is a continuum and that 9/11 represents neither a beginning nor an end