de Sitter geodesics: reappraising the notion of motion

The de Sitter spacetime is transitive under a combination of translations and proper conformal transformations. Its usual family of geodesics, however, does not take into account this property. As a consequence, there are points in de Sitter spacetime which cannot be joined to each other by any one of these geodesics. By taking into account the appropriate transitivity properties in the variational principle, a new family of maximizing trajectories is obtained, whose members are able to connect any two points of the de Sitter spacetime. These geodesics introduce a new notion of motion, given by a combination of translations and proper conformal transformations, which may possibly become important at very-high energies, where conformal symmetry plays a significant role.Comment: 9 pages. V2: Presentation changes aiming at clarifying the text; version accepted for publication in Gen. Rel. Gra

de Sitter relativity: a natural scenario for an evolving Lambda

The dispersion relation of de Sitter special relativity is obtained in a simple and compact form, which is formally similar to the dispersion relation of ordinary special relativity. It is manifestly invariant under change of scale of mass, energy and momentum, and can thus be applied at any energy scale. When applied to the universe as a whole, the de Sitter special relativity is found to provide a natural scenario for the existence of an evolving cosmological term, and agrees in particular with the present-day observed value. It is furthermore consistent with a conformal cyclic view of the universe, in which the transition between two consecutive eras occurs through a conformal invariant spacetime.Comment: V1: 11 pages. V2: Presentation changes, new discussion added, 13 page

de Sitter special relativity

A special relativity based on the de Sitter group is introduced, which is the theory that might hold up in the presence of a non-vanishing cosmological constant. Like ordinary special relativity, it retains the quotient character of spacetime, and a notion of homogeneity. As a consequence, the underlying spacetime will be a de Sitter spacetime, whose associated kinematics will differ from that of ordinary special relativity. The corresponding modified notions of energy and momentum are obtained, and the exact relationship between them, which is invariant under a re-scaling of the involved quantities, explicitly exhibited. Since the de Sitter group can be considered a particular deformation of the Poincar\'e group, this theory turns out to be a specific kind of deformed (or doubly) special relativity. Some experimental consequences, as well as the causal structure of spacetime--modified by the presence of the de Sitter horizon--are briefly discussed.Comment: V2: Some presentation changes; a new section introduced, with a discussion about possible phenomenological consequences; new references added; version to be published in Classical and Quantum Gravit

To achieve and to conform: Motivational values predict social comparison orientation

As personal motivational values have been shown to associate with personality traits, we explore whether they also predict social comparison orientation (SCO), the proclivity to compare with other people in order to inform self-evaluation judgements. Participants completed the Portrait Values Questionnaire (Schwartz et al., 2001) to measure personal values and INCOM (Gibbons & Buunk, 1999) to assess SCO. Bayesian analyses revealed that the personal values of achievement and conformity strongly predicted SCO. The association between SCO and three other personal values—power, universalism, and benevolence—were mediated by achievement. The findings suggest that the tendency to compare to others is determined by very two different motivational values, gaining personal success through demonstrating competence according to social standards and exercising behaviours and attitudes that adhere to social norm

Fermion Helicity Flip in Weak Gravitational Fields

The helicity flip of a spin-${\textstyle \frac{1}{2}}$ Dirac particle interacting gravitationally with a scalar field is analyzed in the context of linearized quantum gravity. It is shown that massive fermions may have their helicity flipped by gravity, in opposition to massless fermions which preserve their helicity.Comment: RevTeX 3.0, 8 pages, 3 figures (available upon request), Preprint IFT-P.013/9

Exploring the underpinning mechanisms of the proximity effect within a competitive food environment

Objective: One method of influencing an individual's food consumption involves placing unhealthy snacks further away from individuals, known as the “proximity effect”. However, only one laboratory study has explored the effect while both an unhealthy and a healthy option are presented simultaneously. Further, little is known about the potential underpinning mechanisms of the effect. The current study aims to replicate the proximity effect in a competitive environment, and to explore the role of visual salience and effort in the proximity effect. Method: Fifty-six participants were asked to complete a two-part questionnaire under the cover story of a relaxation study. Two bowls were presented to participants, each containing either 250 g chocolate M&M's or 250 g mixed fruit pieces. Each bowl was positioned either 20 cm or 70 cm from the participant, creating four proximity conditions. Consumption of each snack was compared between proximity conditions. Results: No main effects were found. A significant interaction between snack type and chocolate position was found (p = .010, ȵ2 = 0.159), with fruit consumption being significantly higher when chocolate was at located at 20 cm compared to 70 cm (53.35 g vs 22.35 g, p = .042). Higher visual salience of each snack type correlated to more of the snack being consumed, ps < .017. Results were similar when calories consumed were analysed. Conclusions: We found an unconventional proximity effect where the consumption of a snack did not depend on its position, but rather the relative position of another snack. Implications of the study could inform café and supermarket layouts to exploit the interaction between moving healthy items closer in addition to moving unhealthy items further away, in order to maximise choice of healthy item

Exploring the roles of physical effort and visual salience within the proximity effect

Background Recent work has explored the effectiveness of the Proximity Effect, where increasing the physical distance between consumer and snacks reduces intake. Foods requiring less effort to attain, or being more visually appealing, are seen to be consumed more. Relatedly, perceived effort and visual salience are suggested mechanisms for the proximity effect, but no prior studies have directly manipulated these in association with the effect. Two between-subjects studies conducted in university laboratories are presented. Method Twenty chocolate brownies that were either wrapped or unwrapped (Study 1, N = 85), or 250g of M&M's, either colourful or plain brown (Study 2, N = 80), were presented as effort and salience manipulations respectively to participants at either 20 cm or 70 cm. Consumption was measured as ‘likelihood of consumption’ (Yes/No) and ‘actual consumption’ (units/grams). Potential moderating variables including perceived effort and perceived visual salience were also measured. Results Likelihood of consumption was positively predicted by perceived visual salience in both Studies, and by distance in Study 2. Significant main effects of distance, p  70 cm), effort, p  wrapped), and distance × effort interaction, p = .003, ȵ2 = 0.111, were observed in Study 1 for actual consumption. A main effect of distance was found in Study 2 for actual consumption, p  70 cm). Perceived visual salience positively correlated with actual consumption in both Studies. Conclusions Increasing physical effort and placing snacks further away appear to act independently and interactively to reduce snack consumption. Manipulating snack colour does not appear to influence consumption, whereas perceptions of visual salience appear to influence consumption. As such, perceived visual salience and physical effort are thought to be key mechanisms underpinning the proximity effect

Preferences induced by accessibility: Evidence from priming

In one experiment, we studied risky preferences using a semantic-priming paradigm where accessibility is manipulated independently of beliefs about the frequencies of risky events. We compared the risks taken for precautionary decisions primed by relevant information (enhancing accessibility to relevant events) with those taken for unprimed decisions and decisions primed by irrelevant information. We found that both priming and the subjective frequency of beliefs independently influence decision making. The results indicate that decisions are the result of an integration of influences derived from both the description (specified probability) and experience (accessibility to pre-experiment beliefs about event frequencies and temporarily activated relevant events) of risks. People's risk preferences are influenced by the accessibility of events in memory, such that increasing accessibility causes risk aversion to a potential loss to increase. Our research findings are not anticipated by the descriptive invariance axiom of expected utility theory, which states that equivalent formulations of a choice problem give rise to the same preference order