Deterring a Nuclear Iran: The Devil in the Details

Explores the technical requirements for a deterrence regime against Iran should it acquire a nuclear weapons capability. Considers red lines, treaty arrangements, force deployment and bases, military assistance to Iran's neighbors, and crisis management

Flaw Selection Strategies for Partial-Order Planning

Several recent studies have compared the relative efficiency of alternative flaw selection strategies for partial-order causal link (POCL) planning. We review this literature, and present new experimental results that generalize the earlier work and explain some of the discrepancies in it. In particular, we describe the Least-Cost Flaw Repair (LCFR) strategy developed and analyzed by Joslin and Pollack (1994), and compare it with other strategies, including Gerevini and Schubert's (1996) ZLIFO strategy. LCFR and ZLIFO make very different, and apparently conflicting claims about the most effective way to reduce search-space size in POCL planning. We resolve this conflict, arguing that much of the benefit that Gerevini and Schubert ascribe to the LIFO component of their ZLIFO strategy is better attributed to other causes. We show that for many problems, a strategy that combines least-cost flaw selection with the delay of separable threats will be effective in reducing search-space size, and will do so without excessive computational overhead. Although such a strategy thus provides a good default, we also show that certain domain characteristics may reduce its effectiveness.Comment: See http://www.jair.org/ for an online appendix and other files accompanying this articl

A Consistent Effective Theory of Long-Wavelength Cosmological Perturbations

Effective field theory provides a perturbative framework to study the evolution of cosmological large-scale structure. We investigate the underpinnings of this approach, and suggest new ways to compute correlation functions of cosmological observables. We find that, in contrast with quantum field theory, the appropriate effective theory of classical cosmological perturbations involves interactions that are nonlocal in time. We describe an alternative to the usual approach of smoothing the perturbations, based on a path-integral formulation of the renormalization group equations. This technique allows for improved handling of short-distance modes that are perturbatively generated by long-distance interactions.Comment: submitted to Phys. Rev. D; corrected typ

How Decoherence Affects the Probability of Slow-Roll Eternal Inflation

Slow-roll inflation can become eternal if the quantum variance of the inflaton field around its slowly rolling classical trajectory is converted into a distribution of classical spacetimes inflating at different rates, and if the variance is large enough compared to the rate of classical rolling that the probability of an increased rate of expansion is sufficiently high. Both of these criteria depend sensitively on whether and how perturbation modes of the inflaton interact and decohere. Decoherence is inevitable as a result of gravitationally-sourced interactions whose strength are proportional to the slow-roll parameters. However, the weakness of these interactions means that decoherence is typically delayed until several Hubble times after modes grow beyond the Hubble scale. We present perturbative evidence that decoherence of long-wavelength inflaton modes indeed leads to an ensemble of classical spacetimes with differing cosmological evolutions. We introduce the notion of per-branch observables---expectation values with respect to the different decohered branches of the wave function---and show that the evolution of modes on individual branches varies from branch to branch. Thus single-field slow-roll inflation fulfills the quantum-mechanical criteria required for the validity of the standard picture of eternal inflation. For a given potential, the delayed decoherence can lead to slight quantitative adjustments to the regime in which the inflaton undergoes eternal inflation.Comment: 27 pages, 3 figures; v2 reflects peer review process and has new results in Section

Sport is king: an investigation into local media coverage of women's sport in the UK East Midlands

There has been a recent interest in research into national media coverage of female sport, particularly single events, but on-going sporting activities by women are rarely reported. This paper attempts to examine this subject at the local level, looking in general at women’s sport and in particular at women’s football in the East Midlands region of the UK. Quantitative methods were used to survey local newspapers and radio stations and interviews were carried out with a range of people relevant to the field of study. The topic of sports media is framed here with reference to research into masculinities and a socialist feminist approach is used to address problems. The data showed there was a significant and on-going imbalance in the amount of coverage and even some signs of a decline in women’s football reporting, in spite of a national resurgence of the sport itself. The authors try to account for this and suggest further areas of future study

De Sitter Space Without Dynamical Quantum Fluctuations

We argue that, under certain plausible assumptions, de Sitter space settles into a quiescent vacuum in which there are no dynamical quantum fluctuations. Such fluctuations require either an evolving microstate, or time-dependent histories of out-of-equilibrium recording devices, which we argue are absent in stationary states. For a massive scalar field in a fixed de Sitter background, the cosmic no-hair theorem implies that the state of the patch approaches the vacuum, where there are no fluctuations. We argue that an analogous conclusion holds whenever a patch of de Sitter is embedded in a larger theory with an infinite-dimensional Hilbert space, including semiclassical quantum gravity with false vacua or complementarity in theories with at least one Minkowski vacuum. This reasoning provides an escape from the Boltzmann brain problem in such theories. It also implies that vacuum states do not uptunnel to higher-energy vacua and that perturbations do not decohere while slow-roll inflation occurs, suggesting that eternal inflation is much less common than often supposed. On the other hand, if a de Sitter patch is a closed system with a finite-dimensional Hilbert space, there will be Poincare recurrences and dynamical Boltzmann fluctuations into lower-entropy states. Our analysis does not alter the conventional understanding of the origin of density fluctuations from primordial inflation, since reheating naturally generates a high-entropy environment and leads to decoherence, nor does it affect the existence of non-dynamical vacuum fluctuations such as those that give rise to the Casimir effect.Comment: version accepted for publication in Foundations of Physic

Why Boltzmann Brains Don't Fluctuate Into Existence From the De Sitter Vacuum

Many modern cosmological scenarios feature large volumes of spacetime in a de Sitter vacuum phase. Such models are said to be faced with a "Boltzmann Brain problem" - the overwhelming majority of observers with fixed local conditions are random fluctuations in the de Sitter vacuum, rather than arising via thermodynamically sensible evolution from a low-entropy past. We argue that this worry can be straightforwardly avoided in the Many-Worlds (Everett) approach to quantum mechanics, as long as the underlying Hilbert space is infinite-dimensional. In that case, de Sitter settles into a truly stationary quantum vacuum state. While there would be a nonzero probability for observing Boltzmann-Brain-like fluctuations in such a state, "observation" refers to a specific kind of dynamical process that does not occur in the vacuum (which is, after all, time-independent). Observers are necessarily out-of-equilibrium physical systems, which are absent in the vacuum. Hence, the fact that projection operators corresponding to states with observers in them do not annihilate the vacuum does not imply that such observers actually come into existence. The Boltzmann Brain problem is therefore much less generic than has been supposed.Comment: Based on a talk given by SMC at, and to appear in the proceedings of, the Philosophy of Cosmology conference in Tenerife, September 201

Extending Foster Care to Age 21: Weighing the Costs to Government against the Benefits to Youth

The Fostering Connections to Success and Increasing Adoptions Act of 2008 allows states to claim federal reimbursement for the costs of caring for and supervising Title IV-E eligible foster youth until their 21st birthday. This issue brief provides preliminary estimates of what the potential costs to government and the benefits to young people would be if states extend foster care to age 21. The analysis focuses on the increase in postsecondary educational attainment associated with allowing foster youth to remain in care until they are 21 years old and the resulting increase in lifetime earnings associated with postsecondary education. Researchers estimate that lifetime earnings would increase an average of two dollars for every dollar spent on keeping foster youth in care beyond age 18

Demonstration of the Zero-Crossing Phasemeter with a LISA Test-bed Interferometer

The Laser Interferometer Space Antenna (LISA) is being designed to detect and study in detail gravitational waves from sources throughout the Universe such as massive black hole binaries. The conceptual formulation of the LISA space-borne gravitational wave detector is now well developed. The interferometric measurements between the sciencecraft remain one of the most important technological and scientific design areas for the mission. Our work has concentrated on developing the interferometric technologies to create a LISA-like optical signal and to measure the phase of that signal using commercially available instruments. One of the most important goals of this research is to demonstrate the LISA phase timing and phase reconstruction for a LISA-like fringe signal, in the case of a high fringe rate and a low signal level. We present current results of a test-bed interferometer designed to produce an optical LISA-like fringe signal previously discussed in the literature.Comment: find minor corrections in the CQG versio