The stochastic gravitational-wave background from massive black hole binary systems: implications for observations with Pulsar Timing Arrays

Massive black hole binary systems, with masses in the range ~10^4-10^10 \msun, are among the primary sources of gravitational waves in the frequency window ~10^-9 Hz - 0.1 Hz. Pulsar Timing Arrays (PTAs) and the Laser Interferometer Space Antenna (LISA) are the observational means by which we will be able to observe gravitational radiation from these systems. We carry out a systematic study of the generation of the stochastic gravitational-wave background from the cosmic population of massive black hole binaries. We consider a wide variety of assembly scenarios and we estimate the range of signal strength in the frequency band accessible to PTAs. We show that, taking into account the uncertainties surrounding the actual key model parameters, the amplitude lies in the interval h_c(f = 10^-8 Hz)~5x10^-16 - 8x10^-15. The most optimistic predictions place the signal level at a factor of ~3 below the current sensitivity of Pulsar Timing Arrays, but within the detection range of the complete Parkes PTA for a wide variety of models, and of the future Square-Kilometer-Array PTA for all the models considered here. We also show that at frequencies >10^-8 Hz the frequency dependency of the generated background follows a power-law significantly steeper than f^-2/3, that has been considered so far. Finally we show that LISA observations of individual resolvable massive black hole binaries are complementary and orthogonal to PTA observations of a stochastic background from the whole population in the Universe. In fact, the detection of gravitational radiation in both frequency windows will enable us to fully characterise the cosmic history of massive black holes.Comment: 21 pages, 14 figures, minor revisions, accepted for publication in MNRA

Damasus Winzen Lecture

In lieu of an abstract, below is the essay\u27s first paragraph. It was my good fortune recently to acquire some long unavailable commentaries on the sacred liturgy by some of the pioneers of the liturgical movement. Among these are Dame Aemiliana Löhr‘s The Mass Through the Year – the latter being a German Benedictine nun of Herstelle where Dom Odo Casel of Maria Laach served as chaplain. Of course, it is from Maria Laach that the person in whose name this lecture is presented came with two companions to found this monastery of Mt. Savior. And it was he who wrote the foreword to the English translation of Löhr‘s work in 1958. I would like to begin this lecture, therefore, with a brief but profound passage from that introduction

Stochastic background from extra dimensions

The existence of extra dimensions is a common feature in almost all quantum theories of gravity. These extra dimensions, whose size and number vary from theory to theory, have a signature on the gravitational stochastic background. Here we review the predictions of the individual theories and the hope of revealing such signals with earthbound detectors

The Second Vatican Council Fifty Years Later: Achievements and Challenges

In lieu of an abstract, below is the essay\u27s first paragraph. I would like to begin this lecture with a personal perspective followed by some introductory comments concerning the ongoing “clash of interpretations” surrounding Vatican II and its documents, followed by a brief survey of each document noting some of its achievements and, in my opinion, ongoing challenges

Triduum: A Drama in Three Acts

In lieu of an abstract, below is the essay\u27s first paragraph. And to think he called them friends. If anyone ever had a right to say, “With friends like mine, who needs enemies?” it was Jesus Christ. Just look at those so-called “friends” around the table with him that night: There’s Peter, who denied him three times. There’s Thomas who doubted him -- the same Thomas who told him the night of the Supper he didn’t know Jesus was the way to the Father. Philip too was there that night – Philip who didn’t know that by seeing Jesus he could see the Father who sent him. James and John were there as well: the two brothers who vied to be first in the kingdom, though they slept through Jesus’ agony in the garden later that night

MOTIVATION STRATEGIES FOR KNOWLEDGE WORKERS: EVIDENCES AND CHALLENGES

Many studies have been performed previously to investigate different theories of motivation and, more specifically, how to motivate technical professionals. Through a questionnaire survey carried out on 376 development engineers, identified as "knowledge workers" by managers in their firms, this study identifies what methods are used in industry to motivate these individuals , what works and what does not. While many aspects of standard incentives and reward systems used to motivate technical professionals in general are also motivating for technical visionaries, these results indicate that they are motivated by additional factors not generally discussed in the literature

Italian research on the Antarctic atmosphere

In this work after a short introduction on the structure of Programma Nazionale di Ricerche in Antartide, the different researches on atmospheric physics developed by Italian scientists are presented. The international activities are described, with particular attention both to APE experiment and the setting up of the new base in Dome-C. The results obtained are also discussed and the new projects proposed by SCAR or other international bodies are recalled. The reduction of funds and fall in young people interested in scientifi c studies represent the main problems for the future work

The Reggio Childhood Studies PhD as a learning community

Exploring visions and methods to pursue high level education means to study how each person is allowed to develop new intellectual, aesthetic, and operational perspective, as well as grasp new insights for growth and enrichment of one’s understanding of the world. The authors present the pilot phase of an analysis of the first industrial doctorate in Reggio Chilhood Studies, organized by the University of Modena and Reggio Emilia in collaboration with the Reggio Children Foundation: its socio-constructivist matrix is highlighted. In fact, constructing a community of learners allows cross-fertilization among diverse disciplinary knowledge and many cultures. The study hereby presented explores the variables of such learning community, through the analysis of in-depth interviews of the PhD fellows. Results show factors and variables that can affect and challenge the existence of the community. Recommendations are made to continue exploring the doctoral community, bringing in the picture all the stakeholders involved