Recombination Induced Softening and Reheating of the Cosmic Plasma

The atomic recombination process leads to a softening of the matter equation of state as reflected by a reduced generalized adiabatic index, with accompanying heat release. We study the effects of this recombination softening and reheating of the cosmic plasma on the ionization history, visibility function, Cold Dark Matter (CDM) transfer function, and the Cosmic Microwave Background (CMB) spectra. The resulting modifications of the CMB spectrm is 1/10 of WMAP's current error and is comparable to PLANCK's error. Therefore, this effect should be considered when data with higher accuracy are analysed.Comment: 11 pages, 6 figures, Accepted for publication in Monthly Notices of the Royal Astronomical Society; as advised by referee, omit high-baryon mode

Persuading giants to be wise: an exploratory study of advice sharing in online games

This study investigates the effects of a browser game as a motivational factor for the sharing of short written reflections. We have analysed 400 anonymous written reflections and conducted 10 interviews in order to get a deeper insight of the game experience. This is an opportunistic investigation and the authors did not have control over the game environment. We have found that there is a predominantly positive attitude towards the approach taken by the game, and a significantly higher level of contributions from participants, as compared to a recent investigation of contributions in social awareness streams. A number of user contributions that clearly do not match the game intentions are being reported and discussed. We draw the conclusion that persuasive tools and techniques can be employed within personal learning environments in order to guide learning. The paper makes a strong argument by example for the use of browser games as a persuasive tool in informal online learning

Eliciting and modelling expertise for serious games in project management

Without achieving a clear understanding of the learning domain, it is difficult to develop a successful serious game that enables users to achieve the desired learning outcomes. Thus, the first step in serious game design is to establish an understanding of the particular learning domain, usually through consultation with domain experts. Whilst game design is inherently a creative process, we believe the capturing of the knowledge domain can be systematised and we present a structured approach to knowledge elicitation and representation as a basis for serious game design. We have adapted and extended the applied cognitive task analysis (ACTA) method and have combined it with additional knowledge representation frameworks. We explain how the outputs of this approach can inform the game mechanic and the development of non-player characters, and apply it to the design of a serious game aimed at reducing time-to-competence in soft project management skills for professionals working in corporate environments. A total of 26 domain experts from five different countries were involved in a two-stage interview process. The interviews yielded more than 300 task elements, and information about the cognition underlying the more challenging tasks. This data was incorporated into several representation frameworks and used to indicate features to be implemented in the game and the game mechanics of the supported features. © 2011 International Federation for Information Processing

Does Bose-Einstein condensation of CMB photons cancel {\mu} distortions created by dissipation of sound waves in the early Universe?

The difference in the adiabatic indices of photons and non-relativistic baryonic matter in the early Universe causes the electron temperature to be slightly lower than the radiation temperature. Thermalization of photons with a colder plasma results in the accumulation of photons in the Rayleigh-Jeans tail, aided by stimulated recoil, while the higher frequency spectrum tries to approach Planck spectrum at the electron temperature T_{\gamma}^{final}=\Te; i.e., Bose-Einstein condensation of photons occurs. We find new solutions of the Kompaneets equation describing this effect. No actual condensate is, in reality, possible since the process is very slow and photons drifting to low frequencies are efficiently absorbed by bremsstrahlung and double Compton processes. The spectral distortions created by Bose-Einstein condensation of photons are within an order of magnitude (for the present range of allowed cosmological parameters), with exactly the same spectrum but opposite in sign, of those created by diffusion damping of the acoustic waves on small scales corresponding to comoving wavenumbers $45< k< 10^4\, Mpc^{-1}$. The initial perturbations on these scales are completely unobservable today due to their being erased completely by Silk damping. There is partial cancellation of these two distortions, leading to suppression of $\mu$ distortions expected in the standard model of cosmology. The net distortion depends on the scalar power index $n_S$ and its running $d n_S/d\ln k$, and may vanish for special values of parameters, for example, for a running spectrum with, $n_S=1,d n_S/d\ln k=-0.038$. We arrive at an intriguing conclusion: even a null result, non-detection of $\mu$-type distortion at a sensitivity of $10^{-9}$, gives a quantitative measure of the primordial small-scale power spectrum.Comment: Published versio

On the coupling between different species during recombination

Measurements of fluctuations in the Cosmic Microwave Background Radiation (CMBR) is one of the most promising methods for measuring the fundamental cosmological parameters. However, in order to infer parameters from precision measurements it is necessary to calculate the theoretical fluctuation spectrum to at least the measurement accuracy. Standard treatments assume that electrons, ions and neutral hydrogen are very tightly coupled during the entire recombination history, and that the baryon-photon plasma can be treated as a two-fluid system consisting of baryons and photons interacting via Thomson scattering. We investigate the validity of this approximation by explicitly writing down and solving the full set of Boltzmann equations for electrons, ions, neutral hydrogen and photons. The main correction to the standard treatment is from including Rayleigh scattering between photons and neutral hydrogen, a change of less than 0.1% in the CMBR power spectrum. Our conclusion is thus that the standard treatment of the baryon-photon system is a very good approximation, better than any possible measurement accuracy.Comment: 17 pages, 4 figs, version to appear in New Astronom

Opening a new window to other worlds with spectropolarimetry

A high level of diversity has already been observed among the planets of our own Solar System. As such, one expects extrasolar planets to present a wide range of distinctive features, therefore the characterisation of Earth- and super Earth-like planets is becoming of key importance in scientific research. The SEARCH (Spectropolarimetric Exoplanet AtmospheRe CHaracerisation) mission proposal of this paper represents one possible approach to realising these objectives. The mission goals of SEARCH include the detailed characterisation of a wide variety of exoplanets, ranging from terrestrial planets to gas giants. More specifically, SEARCH will determine atmospheric properties such as cloud coverage, surface pressure and atmospheric composition, and may also be capable of identifying basic surface features. To resolve a planet with a semi major axis of down to 1.4AU and 30pc distant SEARCH will have a mirror system consisting of two segments, with elliptical rim, cut out of a parabolic mirror. This will yield an effective diameter of 9 meters along one axis. A phase mask coronagraph along with an integral spectrograph will be used to overcome the contrast ratio of star to planet light. Such a mission would provide invaluable data on the diversity present in extrasolar planetary systems and much more could be learned from the similarities and differences compared to our own Solar System. This would allow our theories of planetary formation, atmospheric accretion and evolution to be tested, and our understanding of regions such as the outer limit of the Habitable Zone to be further improved.Comment: 23 pages, accepted for publication in Experimental Astronom

Advanced Three Level Approximation for Numerical Treatment of Cosmological Recombination

New public numerical code for fast calculations of the cosmological recombination of primordial hydrogen-helium plasma is presented. The code is based on the three-level approximation (TLA) model of recombination and allows us to take into account some fine physical effects of cosmological recombination simultaneously with using fudge factors. The code can be found at http://www.ioffe.ru/astro/QC/CMBR/atlant/atlant.htmlComment: 10 pages, 7 figures, 1 table, to be submitted to MNRA

CMB at 2x2 order: the dissipation of primordial acoustic waves and the observable part of the associated energy release

Silk damping of primordial small-scale perturbations in the photon-baryon fluid due to diffusion of photons inevitably creates spectral distortions in the CMB. With the proposed CMB experiment PIXIE it might become possible to measure these distortions and thereby constrain the primordial power spectrum at comoving wavenumbers 50 Mpc^{-1} < k < 10^4 Mpc^{-1}. Since primordial fluctuations in the CMB on these scales are completely erased by Silk damping, these distortions may provide the only way to shed light on otherwise unobservable aspects of inflationary physics. A consistent treatment of the primordial dissipation problem requires going to second order in perturbation theory, while thermalization of these distortions necessitates consideration of second order in Compton scattering energy transfer. Here we give a full 2x2 treatment for the creation and evolution of spectral distortions due to the acoustic dissipation process, consistently including the effect of polarization and photon mixing in the free streaming regime. We show that 1/3 of the total energy (9/4 larger than previous estimates) stored in small-scale temperature perturbations imprints observable spectral distortions, while the remaining 2/3 only raises the average CMB temperature, an effect that is unobservable. At high redshift dissipation is mainly mediated through the quadrupole anisotropies, while after recombination peculiar motions are most important. During recombination the damping of the higher multipoles is also significant. We compute the average distortion for several examples using CosmoTherm, analyzing their dependence on parameters of the primordial power spectrum. For one of the best fit WMAP7 cosmologies, with n_S=1.027 and n_run=-0.034, the cooling of baryonic matter practically compensates the heating from acoustic dissipation in the mu-era. (abridged)Comment: 40 pages, 17 figures, accepted by MNRA