Lyman-alpha constraints on warm and on warm-plus-cold dark matter models

We revisit Lyman-alpha bounds on the dark matter mass in Lambda Warm Dark Matter (Lambda-WDM) models, and derive new bounds in the case of mixed Cold plus Warm models (Lambda-CWDM), using a set up which is a good approximation for several theoretically well-motivated dark matter models. We combine WMAP5 results with two different Lyman-alpha data sets, including observations from the Sloan Digital Sky Survey. We pay a special attention to systematics, test various possible sources of error, and compare the results of different statistical approaches. Expressed in terms of the mass of a non-resonantly produced sterile neutrino, our bounds read m_NRP > 8 keV (frequentist 99.7% confidence limit) or m_NRP > 12.1 keV (Bayesian 95% credible interval) in the pure Lambda-WDM limit. For the mixed model, we obtain limits on the mass as a function of the warm dark matter fraction F_WDM. Within the mass range studied here (5 keV < m_NRP < infinity), we find that any mass value is allowed when F_WDM < 0.6 (frequentist 99.7% confidence limit); similarly, the Bayesian joint probability on (F_WDM, 1/m_NRP) allows any value of the mass at the 95% confidence level, provided that F_WDM < 0.35.Comment: 55 pages, 14 figures. References added, discussion of the data analysis expanded. Final version to appear in JCA

On general features of warm dark matter with reduced relativistic gas

Reduced Relativistic Gas (RRG) is a useful approach to describe the warm dark matter (WDM) or the warmness of baryonic matter in the approximation when the interaction between the particles is irrelevant. The use of Maxwell distribution leads to the complicated equation of state of the J\"{u}ttner model of relativistic ideal gas. The RRG enables one to reproduce the same physical situation but in a much simpler form. For this reason RRG can be a useful tool for the theories with some sort of a "new Physics". On the other hand, even without the qualitatively new physical implementations, the RRG can be useful to describe the general features of WDM in a model-independent way. In this sense one can see, in particular, to which extent the cosmological manifestations of WDM may be dependent on its Particle Physics background. In the present work RRG is used as a complementary approach to derive the main observational exponents for the WDM in a model-independent way. The only assumption concerns a non-negligible velocity $v$ for dark matter particles which is parameterized by the warmness parameter $b$. The relatively high values of $b$ ( $b^2\gtrsim 10^{-6}$) erase the radiation (photons and neutrinos) dominated epoch and cause an early warm matter domination after inflation. Furthermore, RRG approach enables one to quantify the lack of power in linear matter spectrum at small scales and in particular, reproduces the relative transfer function commonly used in context of WDM with accuracy of $\lesssim 1\%$. A warmness with $b^2\lesssim 10^{-6}$ (equivalent to $v\lesssim 300 km/s$) does not alter significantly the CMB power spectrum and is in agreement with the background observational tests.Comment: 15 pages, 8 figures. Essential improvements in style and presentatio

Predictors of posttraumatic stress disorder among firefighters

A dissertation submitted to the Faculty of Humanities in partial fulfilment of the requirements of the degree of Master of Arts Organisational Psychology University of the Witwatersrand March 2016Emergency first responders such as firefighters are exposed to higher levels of traumatic events through the course of their work. Accordingly, chances of such exposure resulting in negative psychological consequences are elevated. Previous research implicates the experience of trauma incident(s) and other organisational factors, among other factors, as causes of the development of consequences such as posttraumatic stress disorder and the variance thereof. However, research exploring these implications is limited. As a result, firefighters in the Emergency Medical Services were surveyed in the attempt to identify experiences of posttraumatic stress symptoms resulting from history of exposure to work-related traumatic events, perceived life threat during those incidents, general work-related stress and their perceived organisational support. The purpose of this study was to explore the predictive relationship PTSD symptoms and four predictors namely; perceived life threat, perceived organisational support, history of trauma and job-related stress, among Johannesburg firefighters. The sample was drawn from the City of Johannesburg Emergency Medical Services. A sample (N=100) of trauma-exposed firefighters was recruited for the study. Participants were recruited using a non-probability, convenience sampling strategy in which participation in the study was voluntary. The sample was made of 89 male participants and 11 female participants. All variables included in the study were measured using self-report instruments. Participants completed a demographic questionnaire to gather information pertaining to gender, age, organisational tenure and race. The following questionnaires were used to ascertain scores for the predictor variables: Survey of perceived Organisational Support, General Work Stress scale, Life Threat scale and a self-developed history of trauma scale. The Revised Impact of Event scale was used to measure the firefighters’ experience of PTSD related symptoms. Participants reported an average score of 29 on the IES-R scale indicating a stress reaction with the possibility of posttraumatic stress disorder. However, using a multiple regression analysis, this present study found that the four predictor variables explored did not have a substantial impact on the development of PTSD among firefighters. Secondary analyses were conducted to explore the individual association between each independent variable and PTSD. The results are reported. Overall, the results yielded suggest that there are other factors that exert a greater impact on the development of PTSD among firefighters. Future research among firefighters could focus on exploring other risk and protective factors associated with the development of PTSD. Alternatively, if this study is to be replicated, the researcher could employ a longitudinal, qualitative approach to explore the predictive relationship between history of trauma, perceived life threat, perceived organisational support, work-related stress and PTSD related symptoms. KEYWORDS: Post-traumatic stress disorder, perceived life threat, perceived organisational support, job-related stress, history of traum

Metastable GeV-scale particles as a solution to the cosmological lithium problem

The persistent discrepancy between observations of 7Li with putative primordial origin and its abundance prediction in Big Bang Nucleosynthesis (BBN) has become a challenge for the standard cosmological and astrophysical picture. We point out that the decay of GeV-scale metastable particles X may significantly reduce the BBN value down to a level at which it is reconciled with observations. The most efficient reduction occurs when the decay happens to charged pions and kaons, followed by their charge exchange reactions with protons. Similarly, if X decays to muons, secondary electron antineutrinos produce a similar effect. We consider the viability of these mechanisms in different classes of new GeV-scale sectors, and find that several minimal extensions of the Standard Model with metastable vector and/or scalar particles are capable of solving the cosmological lithium problem. Such light states can be a key to the explanation of recent cosmic ray anomalies and can be searched for in a variety of high-intensity medium-energy experiments.Comment: 50 pages, 13 figures; references added, typo correcte

Features and New Physical Scales in Primordial Observables: Theory and Observation

All cosmological observations to date are consistent with adiabatic, Gaussian and nearly scale invariant initial conditions. These findings provide strong evidence for a particular symmetry breaking pattern in the very early universe (with a close to vanishing order parameter, $\epsilon$), widely accepted as conforming to the predictions of the simplest realizations of the inflationary paradigm. However, given that our observations are only privy to perturbations, in inferring something about the background that gave rise to them, it should be clear that many different underlying constructions project onto the same set of cosmological observables. Features in the primordial correlation functions, if present, would offer a unique and discriminating window onto the parent theory in which the mechanism that generated the initial conditions is embedded. In certain contexts, simple linear response theory allows us to infer new characteristic scales from the presence of features that can break the aforementioned degeneracies among different background models, and in some cases can even offer a limited spectroscopy of the heavier degrees of freedom that couple to the inflaton. In this review, we offer a pedagogical survey of the diverse, theoretically well grounded mechanisms which can imprint features into primordial correlation functions in addition to reviewing the techniques one can employ to probe observations. These observations include cosmic microwave background anisotropies and spectral distortions as well as the matter two and three point functions as inferred from large-scale structure and potentially, 21 cm surveys.Comment: Invited review to IJMPD, 101 pages + 2 appendices, 29 figures, references added, matches journal versio