Cosmic reionization constraints on the nature of cosmological perturbations

We study the reionization history of the Universe in cosmological models with non-Gaussian density fluctuations, taking them to have a renormalized $\chi^2$ probability distribution function parametrized by the number of degrees of freedom, $\nu$. We compute the ionization history using a simple semi-analytical model, considering various possibilities for the astrophysics of reionization. In all our models we require that reionization is completed prior to $z=6$, as required by the measurement of the Gunn--Peterson optical depth from the spectra of high-redshift quasars. We confirm previous results demonstrating that such a non-Gaussian distribution leads to a slower reionization as compared to the Gaussian case. We further show that the recent WMAP three-year measurement of the optical depth due to electron scattering, $\tau=0.09 \pm 0.03$, weakly constrains the allowed deviations from Gaussianity on the small scales relevant to reionization if a constant spectral index is assumed. We also confirm the need for a significant suppression of star formation in mini-halos, which increases dramatically as we decrease $\nu$

The Cluster Abundance in Flat and Open Cosmologies

We use the galaxy cluster X-ray temperature distribution function to constrain the amplitude of the power spectrum of density inhomogeneities on the scale corresponding to clusters. We carry out the analysis for critical density universes, for low density universes with a cosmological constant included to restore spatial flatness and for genuinely open universes. That clusters with the same present temperature but different formation times have different virial masses is included. We model cluster mergers using two completely different approaches, and show that the final results from each are extremely similar. We give careful consideration to the uncertainties involved, carrying out a Monte Carlo analysis to determine the cumulative errors. For critical density our result agrees with previous papers, but we believe the result carries a larger uncertainty. For low density universes, either flat or open, the required amplitude of the power spectrum increases as the density is decreased. If all the dark matter is taken to be cold, then the cluster abundance constraint remains compatible with both galaxy correlation data and the {\it COBE} measurement of microwave background anisotropies for any reasonable density.Comment: Uuencoded package containing LaTeX file (uses mn.sty) plus 7 postscript figures incorporated using epsf. Total length 10 pages. Final version, to appear MNRAS. COBE comparison changed to 4yr data. No change to results or conclusion

Cold dark matter models with high baryon content

Recent results have suggested that the density of baryons in the Universe, OmegaB, is much more uncertain than previously thought, and may be significantly higher. We demonstrate that a higher OmegaB increases the viability of critical-density cold dark matter (CDM) models. High baryon fraction offers the twin benefits of boosting the first peak in the microwave anisotropy power spectrum and of suppressing short-scale power in the matter power spectrum. These enable viable CDM models to have a larger Hubble constant than otherwise possible. We carry out a general exploration of high OmegaB CDM models, varying the Hubble constant h and the spectral index n. We confront a variety of observational constraints and discuss specific predictions. Although some observational evidence may favour baryon fractions as high as 20 per cent, we find that values around 10 to 15 per cent provide a reasonable fit to a wide range of data. We suggest that models with OmegaB in this range, with h about 0.5 and n about 0.8, are currently the best critical-density CDM models.Comment: 14 pages, LaTeX, with 9 included figures, to appear in MNRAS. Revised version includes updated references, some changes to section 4. Conclusions unchange

Apparent and actual galaxy cluster temperatures

The redshift evolution of the galaxy cluster temperature function is a powerful probe of cosmology. However, its determination requires the measurement of redshifts for all clusters in a catalogue, which is likely to prove challenging for large catalogues expected from XMM--Newton, which may contain of order 2000 clusters with measurable temperatures distributed around the sky. In this paper we study the apparent cluster temperature, which can be obtained without cluster redshifts. We show that the apparent temperature function itself is of limited use in constraining cosmology, and so concentrate our focus on studying how apparent temperatures can be combined with other X-ray information to constrain the redshift. We also briefly study the circumstances in which non-thermal spectral features can give redshift information.Comment: 7 pages LaTeX file with 13 figures incorporated (uses mn.sty and epsf). Minor changes to match MNRAS accepted versio

A Bayesian study of the primordial power spectrum from a novel closed universe model

We constrain the shape of the primordial power spectrum using recent measurements of the cosmic microwave background (CMB) from the Wilkinson Microwave Anisotropy Probe (WMAP) 7-year data and other high-resolution CMB experiments. We also include observations of the matter power spectrum from the luminous red galaxy (LRG) subset DR7 of the Sloan Digital Sky Survey (SDSS). We consider two different models of the primordial power spectrum. The first is the standard nearly scale-invariant spectrum in the form of a generalised power-law parameterised in terms of the spectral amplitude $A_{\rm s}$, the spectral index $n_{\rm s}$ and (possibly) the running parameter $n_{\rm run}$. The second spectrum is derived from the Lasenby and Doran (LD) model. The LD model is based on the restriction of the total conformal time available in a closed Universe and the predicted primordial power spectrum depends upon just two parameters. An important feature of the LD spectrum is that it naturally incorporates an exponential fall-off on large scales, which might provide a possible explanation for the lower-than-expected power observed at low multipoles in the CMB. In addition to parameter estimation, we compare both models using Bayesian model selection. We find there is a significant preference for the LD model over a simple power-law spectrum for a CMB-only dataset, and over models with an equal number of parameters for all the datasets considered.Comment: minor corrections to match accepted version to MNRA

Layzer-Irvine equation: new perspectives and the role of interacting dark energy

We derive the Layzer-Irvine equation in the presence of a homogeneous (or quasi-homogeneous) dark energy component with an arbitrary equation of state. We extend the Layzer-Irvine equation to homogeneous and isotropic universes with an arbitrary number of dimensions and obtain the corresponding virial relation for sufficiently relaxed objects. We find analogous equations describing the dynamics of cosmic string loops and other p-branes of arbitrary dimensionality, discussing the corresponding relativistic and non-relativistic limits. Finally, we generalize the Layzer-Irvine equation to account for a non-minimal interaction between dark matter and dark energy, discussing its practical use as a signature of such an interaction.Comment: 4 page

Lessons from Youth in Focus

Youth in Focus (YIF) is a Big Lottery Fund initiative aimed at supporting vulnerable young people through difficult changes in their lives. Beyond Youth Custody (BYC) is one of three England-wide learning and awareness projects funded under the Big Lottery Fund’s YIF programme. BYC has been designed to challenge, advance, and promote better thinking in policy and practice for the effective resettlement of young people after release from custody. BYC brings together Nacro, the social justice charity, with three research and evaluation partners: ARCS (UK), and Salford and Bedfordshire universities, all of which have exceptional track records in action-based research focusing on youth offending and resettlement. The programme was initially funded for a five-year period ending in April 2017. During that period, the partnership delivered a multi-faceted programme of research, networking, publicity and awareness-raising activities. The BYC team produced a wide range of publications and resources for practitioners, policy-makers and researchers. The YIF programme also funded service delivery projects across the country to work with three different client groups: young care-leavers, young carers and young custody-leavers. There were 15 individual YIF projects that worked with young custody-leavers, although some of these projects also worked with care-leavers and young carers. The BYC work focused specifically on young people leaving custody, working alongside these projects and supporting them to evaluate and monitor their own service and compare and contrast different models of resettlement, facilitating young people’s participation and providing ongoing feedback about effective practice and lessons learnt through the research. A key part of BYC’s work involved close and regular involvement with individual YIF projects that worked with young custody-leavers, focusing on issues concerning data collection and evaluation but also on wider practice and policy issues. That involvement with YIF projects generated a substantial set of evidence concerning the implementation and effectiveness of resettlement practice and informed the team’s critical understanding of key resettlement issues

The Fate of the Accelerating Universe

The presently accelerating universe may keep accelerating forever, eventually run into the event horizon problem, and thus be in conflict with the superstring idea. In the other way around, the current accelerating phase as well as the fate of the universe may be swayed by a negative cosmological constant, which dictates a big crunch. Based on the current observational data, in this paper we investigate how large the magnitude of a negative cosmological constant is allowed to be. In addition, for distinguishing the sign of the cosmological constant via observations, we point out that a measure of the evolution of the dark energy equation of state may be a good discriminator. Hopefully future observations will provide much more detailed information about dark energy and thereby indicates the sign of the cosmological constant as well as the fate of the presently accelerating universe.Comment: 16 pages, 5 figures, LaTe