On the mass distribution of neutron stars

The distribution of masses for neutron stars is analyzed using the Bayesian statistical inference, evaluating the likelihood of proposed gaussian peaks by using fifty-four measured points obtained in a variety of systems. The results strongly suggest the existence of a bimodal distribution of the masses, with the first peak around $1.37 {M_{\odot}}$, and a much wider second peak at $1.73 {M_{\odot}}$. The results support earlier views related to the different evolutionary histories of the members for the first two peaks, which produces a natural separation (even if no attempt to "label" the systems has been made here), and argues against the single-mass scale viewpoint. The bimodal distribution can also accommodate the recent findings of $\sim M_{\odot}$ masses quite naturally. Finally, we explore the existence of a subgroup around $1.25 {M_{\odot}}$, finding weak, if any, evidence for it. This recently claimed low-mass subgroup, possibly related to $O-Mg-Ne$ core collapse events, has a monotonically decreasing likelihood and does not stand out clearly from the rest of the sample.Comment: 11 pp., 3 figures, submitted to MNRAS Letter

The masses of neutron stars

We present in this article an overview of the problem of neutron star masses. After a brief appraisal of the methods employed to determine the masses of neutron stars in binary systems, the existing sample of measured masses is presented, with a highlight on some very well-determined cases. We discuss the analysis made to uncover the underlying distribution and a few robust results that stand out from them. The issues related to some particular groups of neutron stars originated from different channels of stellar evolution are shown. Our conclusions are that last century's paradigm that there a single, $1.4 M_{\odot}$ scale is too simple. A bimodal or even more complex distribution is actually present. It is confirmed that some neutron stars have masses of $\sim 2 M_{\odot}$, and, while there is still no firm conclusion on the maximum and minimum values produced in nature, the field has entered a mature stage in which all these and related questions can soon be given an answer.Comment: 12 pp., 3 figures, Chapter of forthcoming Handbook of Supernovae, edited by Athem W. Alsabti and Paul Murdi

Thermodynamic constraints on matter creation models

Entropy is a fundamental concept from Thermodynamics and it can be used to study models on context of Creation Cold Dark Matter (CCDM). From conditions on the first ($\dot{S}\geq0$)\footnote{Throughout the present work we will use dots to indicate time derivatives and dashes to indicate derivatives with respect to scale factor.} and second order ($\ddot{S}<0$) time derivatives of total entropy in the initial expansion of Sitter through the radiation and matter eras until the end of Sitter expansion, it is possible to estimate the intervals of parameters. The total entropy ($S_{t}$) is calculated as sum of the entropy at all eras ($S_{\gamma}$ and $S_{m}$) plus the entropy of the event horizon ($S_h$). This term derives from the Holographic Principle where it suggests that all information is contained on the observable horizon. The main feature of this method for these models are that thermodynamic equilibrium is reached in a final de Sitter era. Total entropy of the universe is calculated with three terms: apparent horizon ($S_{h}$), entropy of matter ($S_{m}$) and entropy of radiation ($S_{\gamma}$). This analysis allows to estimate intervals of parameters of CCDM models.Comment: 16 pages, 11 figures. Replaced in order to match accepted versio

Bayesian analysis of CCDM Models

Creation of Cold Dark Matter (CCDM), in the context of Einstein Field Equations, leads to negative creation pressure, which can be used to explain the accelerated expansion of the Universe. In this work we tested six different spatially flat models for matter creation using statistical tools, at light of SN Ia data: Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC) and Bayesian Evidence (BE). These approaches allow to compare models considering goodness of fit and number of free parameters, penalizing excess of complexity. We find that JO model is slightly favoured over LJO/$\Lambda$CDM model, however, neither of these, nor $\Gamma=3\alpha H_0$ model can be discarded from the current analysis. Three other scenarios are discarded either from poor fitting, either from excess of free parameters.Comment: 16 pages, 6 figures, 6 tables. Corrected some text and language in new versio

Identifying Volatility Risk Premium from Fixed Income Asian Options

We provide approximation formulas for at-the-money asian option prices to extract volatility risk premium from a joint dataset of bonds and option prices. The dynamic model generates stochastic volatility and a time-varying volatility risk premium, which explicitly depends on the average cross section of bond yields and on the time series behavior of option prices. When estimated using a joint dataset of Brazilian local bonds and asian options, the model generates bond risk premium strongly correlated (89%) with a widely accepted emerging markets benchmark index, and a negative volatility risk premium implying that investors might be using options as insurance in this market. Volatility premium explains a significant portion (32.5%) of bond premium, confirming that options are indeed important to identify risk premium in dynamic term structure models.

Term Structure Movements Implicit in Option Prices

This paper analyzes how including options in the estimation of a dynamic term structure model impacts the way it captures term structure movements. Two versions of a multi-factor Gaussian model are compared: One adopting only bonds data, and the other adopting a joint dataset of bonds and options. Term structure movements extracted under each version behave distinctly, with slope and curvature presenting higher mean reversion rates when options are adopted. The composition of bond risk premium is also affected, with considerably more weight attributed to the level factor when options are included. The inclusion of options in the estimation of the dynamic model also improves the pricing of out-of-sample options.

Analysis of Abstracts Presented at the Prosthodontic Research Section of IADR General Sessions 2004–2005: Demographics, Publication Rates, and Factors Contributing to Publication

Purpose: The purposes of this study were to describe the demographics of abstracts presented at the prosthodontics section of IADR General Sessions from 2004 to 2005, evaluate the publication rate of abstracts, and analyze the relationship between variables in abstracts and publication. Materials and Methods: Prosthodontics research section abstracts from the IADR General Session in 2004 and 2005 were evaluated for: number of authors, presentation type, origin, affiliation, topic, study design, statistics, study outcome, and funding. The publication rate was calculated following a PubMed search. The journal of publication, year of publication, and the length of time before publication were analyzed. Descriptive statistics were used for the data analysis; the relationships between presentation type, study design, study outcome, statistics, funding, and publication were analyzed using logistic regression (α= 0.05). Results: From 346 abstracts, 37.0% were published. For oral presentations, 40.7% were published; 35.8% of poster presentations were published. The mean duration before publication was 26.4 months. North America had the most abstracts, and Europe had the most publications. Fixed prosthodontic research had the highest number and proportion for publication. A significant association with publication was noted for neutral study outcomes (p= 0.018), studies with funding (p= 0.035), and abstracts from Europe (p= 0.001). Conclusions: The majority of abstracts from the prosthodontics research section of IADR General Sessions from 2004 and 2005 remain unpublished. A significant association for publication was noted with neutral outcomes, funding, and abstracts from Europe

Enabling conditions for integrated crop and livestock systems in the United States, Brazil, and New Zealand: A comparative analysis of incentives and barriers across three regions.

In this study we examine the institutional environment for sustainable agriculture in the United States, Brazil, and New Zealand. In particular we ask whether or not the overall policy context is enabling or inhibitory of integrated crop and livestock systems (ICLS) and which policy changes are likely to have the most enabling influence on the adoption of ICLS