Equilibrium phases of dipolar lattice bosons in the presence of random diagonal disorder

Ultracold gases offer an unprecedented opportunity to engineer disorder and interactions in a controlled manner. In an effort to understand the interplay between disorder, dipolar interaction and quantum degeneracy, we study two-dimensional hard-core dipolar lattice bosons in the presence of on-site bound disorder. Our results are based on large-scale path-integral quantum Monte Carlo simulations by the Worm algorithm. We study the ground state phase diagram at fixed half-integer filling factor for which the clean system is either a superfluid at lower dipolar interaction strength or a checkerboard solid at larger dipolar interaction strength. We find that, even for weak dipolar interaction, superfluidity is destroyed in favor of a Bose glass at relatively low disorder strength. Interestingly, in the presence of disorder, superfluidity persists for values of dipolar interaction strength for which the clean system is a checkerboard solid. At fixed disorder strength, as the dipolar interaction is increased, superfluidity is destroyed in favor of a Bose glass. As the interaction is further increased, the system eventually develops extended checkerboard patterns in the density distribution. Due to the presence of disorder, though, grain boundaries and defects, responsible for a finite residual compressibility, are present in the density distribution. Finally, we study the robustness of the superfluid phase against thermal fluctuations

Equilibrium Phases of Tilted Dipolar Lattice Bosons

The recent advances in creating nearly degenerate quantum dipolar gases in optical lattices are opening the doors for the exploration of equilibrium physics of quantum systems with anisotropic and long-range dipolar interactions. In this paper we study the zero- and finite-temperature phase diagrams of a system of hard-core dipolar bosons at half-filling, trapped in a two-dimensional optical lattice. The dipoles are aligned parallel to one another and tilted out of the optical lattice plane by means of an external electric field. At zero-temperature, the system is a superfluid at all tilt angles $\theta$ provided that the strength of dipolar interaction is below a critical value $V_c(\theta)$. Upon increasing the interaction strength while keeping $\theta$ fixed, the superfluid phase is destabilized in favor of a checkerboard or a stripe solid depending on the tilt angle. We explore the nature of the phase transition between the two solid phases and find evidence of a micro-emulsion phase, following the Spivak-Kivelson scenario, separating these two solid phases. Additionally, we study the stability of these quantum phases against thermal fluctuations and find that the stripe solid is the most robust, making it the best candidate for experimental observation.Comment: 7 pages, 6 figure

Gauge and Averaging in Gravitational Self-force

A difficulty with previous treatments of the gravitational self-force is that an explicit formula for the force is available only in a particular gauge (Lorenz gauge), where the force in other gauges must be found through a transformation law once the Lorenz gauge force is known. For a class of gauges satisfying a ``parity condition'' ensuring that the Hamiltonian center of mass of the particle is well-defined, I show that the gravitational self-force is always given by the angle-average of the bare gravitational force. To derive this result I replace the computational strategy of previous work with a new approach, wherein the form of the force is first fixed up to a gauge-invariant piece by simple manipulations, and then that piece is determined by working in a gauge designed specifically to simplify the computation. This offers significant computational savings over the Lorenz gauge, since the Hadamard expansion is avoided entirely and the metric perturbation takes a very simple form. I also show that the rest mass of the particle does not evolve due to first-order self-force effects. Finally, I consider the ``mode sum regularization'' scheme for computing the self-force in black hole background spacetimes, and use the angle-average form of the force to show that the same mode-by-mode subtraction may be performed in all parity-regular gauges. It appears plausible that suitably modified versions of the Regge-Wheeler and radiation gauges (convenient to Schwarzschild and Kerr, respectively) are in this class

Improving the dependability of research in personality and social psychology: recommendations for research and educational practice

pre-printThe Society for Personality and Social Psychology (SPSP) Presidential Task Force on Publication and Research Practices was appointed in response to concerns about the dependability and replicability of research findings in personality and social psychology, a problem that also plagues fields as diverse as physics, economics, biochemistry, medicine and cell biology. In this article the Task Force offers a brief statistical primer and recommendations for improving the dependability of scientific research. Recommendations for research practice include (1) describing and addressing the choice of N (sample size) and consequent issues of statistical power, (2) reporting effect sizes and 95% confidence intervals for findings, (3) avoiding "questionable research practices" that can undermine the assumptions underlying statistical procedures and inflate the probability of Type I error, (4) making available research materials necessary to replicate reported results, (5) adhering to SPSP's data sharing policy, (6) encouraging publication of high quality replication studies, and (7), maintaining flexibility and openness to alternative standards and methods when evaluating research. Recommendations for educational practice include (1) encouraging a culture of "getting it right" rather than "finding significant results," (2) teaching and encouraging transparency of data reporting, (3) improving methodological instruction on topics such as effect size, confidence intervals, statistical power, replication, and the effects of questionable research practices, and (4) modeling sound science and supporting junior researchers who seek to "get it right." The hope is that these recommendations can help lead the way to improved research practices and a more transparent research culture, throughout all of science

Supersolid phase with cold polar molecules on a triangular lattice

We study a system of heteronuclear molecules on a triangular lattice and analyze the potential of this system for the experimental realization of a supersolid phase. The ground state phase diagram contains superfluid, solid and supersolid phases. At finite temperatures and strong interactions there is an additional emulsion region, in contrast to similar models with short-range interactions. We derive the maximal critical temperature $T_c$ and the corresponding entropy $S/N = 0.04(1)$ for supersolidity and find feasible experimental conditions for its realization.Comment: 4 pages, 4 figure

The sentiment analysis of tweets as a new tool to measure public perception of male erectile and ejaculatory dysfunctions

Twitter is a social network based on "tweets," short messages of up to 280 characters. Social media has been investigated in health care research to ascertain positive or negative feelings associated with several conditions but never in sexual medicin

Sport, doping and male fertility

It is universally accepted that lifestyle interventions are the first step towards a good overall, reproductive and sexual health. Cessation of unhealthy habits, such as tobacco, alcohol and drug use, poor nutrition and sedentary behavior, is suggested in order to preserve/improve fertility in humans. However, the possible risks of physical exercise per se or sports on male fertility are less known. Being fit does not only improve the sense of well-being, but also has beneficial effects on general health: in fact physical exercise is by all means a low-cost, high-efficacy method for preventing or treating several conditions, ranging from purely physical (diabetes and obesity) to psychological (depression and anxiety), highly influencing male reproduction. If male sexual and reproductive health could be positively affected by a proper physical activity, inadequate bouts of strength - both excessive intensity and duration of exercise training - are more likely to have detrimental effects. In addition, the illicit use of prohibited drugs (i.e. doping) has reached pandemic proportions, and their actions, unfortunately very often underestimated by both amateur and professional athletes, are known to disrupt at different levels and throughout various mechanisms the male hypothalamic-pituitary-gonadal axis, resulting in hypogonadism and infertility

Household preferences for Socially Responsible Investments

We analyze revealed and stated household preferences for socially responsible investments (SRI). Using a questionnaire specifically designed for this purpose and administered to a Dutch representative household panel, we investigate the actual and latent demand for SRI products. Respondents reported whether they owned SRI products and why or why not, but also answered stated choice questions on traditional investments and hypothetical socially responsible products with an explicit return penalty and/or an in- kind compensation associated with lower return. Our results show that investors attracted by socially responsible financial products are more interested in the social product as such and show little interest in compensation. The magnitude of the penalty for investing in SRI is not diluting their investment intentions