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    Emotions before actions: When children see costs as causal
    (Elsevier, 2024) Sehl, Claudia G.; Friedman, Ori; Denison, Stephanie
    Adults expect people to be biased by sunk costs, but young children do not. We tested between two accounts for why children overlook the sunk cost bias. On one account, children do not see sunk costs as causal. The other account posits that children see sunk costs as causal, but unlike adults, think future actions cannot make up for sunk costs. These accounts make opposing predictions about whether children should see sunk costs as affecting emotions. Across three experiments, 4–7-year-olds (total N = 320) and adults (total N = 429) saw stories about characters who collected items that were easy or difficult to obtain, and predicted characters' emotions and actions. At all ages, participants anticipated that characters would feel sadder about high-cost objects, but only adults predicted that characters would keep high-cost objects. Our findings show that children see incurred costs as causal, and that costs are integrated children's and adults' theory of emotions. Moreover, the findings suggest that developmental differences in sunk cost reasoning may rest in children's incomplete mental accounting. We also discuss children's reasoning about rational and irrational action.
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    Sunk cost predictions as theory of mind
    (Cambridge University Press, 2024) Howard, Amy; Sehl, Claudia G.; Denison, Stephanie; Friedman, Ori
    People often predict that they, and others, will be biased by sunk costs—they think that investing in an object or goal increases how much one values or wants it. In this article, we use sunk cost predictions to look at people’s theory of mind and their conceptions of mental life. More specifically, we ask which mental states and motivations are seen as underlying the bias. To investigate this, participants in two preregistered experiments predicted whether different kinds of agents would be biased by sunk costs, and also assessed the agents’ mental abilities. Participants predicted that some kinds of agents (e.g., human adults and children, robots) would show the sunk cost bias and that others would not (e.g., raccoons and human babies). These predictions were strongly related to the participants’ assessments of whether the different kinds of agents are capable of seeing actions as wasteful, but also related to their assessments of the agents’ capacities to feel regret and frustration.
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    Statistical segment length in complex-Langevin field-theoretic simulations
    (American Institute of Physics (AIP), 2026) Willis, J. D.; Matsen, M. W.
    A method is introduced for calculating the average end-to-end length, R_0, of polymers in complex-Langevin field-theoretic simulations (CL-FTSs). The statistical segment length, a, is then obtained by extrapolating R_0 to the long-chain limit. Because a has not been available to previous CL-FTSs, results have been expressed in terms of the bare statistical segment length, a_b, of an isolated polymer, which introduces inaccuracies even though the simulation method itself is inherently exact. In a few cases, a has been estimated by a weak-field approximation, but its accuracy remains uncertain. This study focuses on the fluctuation correction, a-a_b, for compressible melts of discrete Gaussian chains with finite-range interactions and compares it to the weak-field approximation. The approximation underestimates the fluctuation correction by up to 20%, but this is not particularly serious given that the correction itself is a small effect. Notably, our technique for evaluating R_0 can be generalized to any single-chain observable, which allows access to all the intramolecular correlations.
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    Accessing the universal phase behavior of block copolymer melts with complex-Langevin field-theoretic simulations
    (American Institute of Physics (AIP), 2026) Matsen, M. W.; Ramirez, J.; Willis, J. D.; Pina, P. D.
    The universal phase behavior of block copolymer melts demonstrated previously with particle-based simulations is reproduced using complex-Langevin field-theoretic simulations (CL-FTSs) combined with the Morse calibration. For comparison purposes, the calculations are repeated using conventional Langevin field-theoretic simulations (L-FTSs), where the partial saddle-point approximation (PSPA) is applied to the pressure field. Both FTS methods produce consistent results down to invariant polymerization indices of N ~ 10^5, implying that the inaccuracies in the PSPA are well compensated for by the Morse calibration. At lower N, however, the complex fields of the CL-FTSs become prone to the formation of hot spots, causing the simulations to fail. Previous studies have shown that finite-range interactions can help stabilize CL-FTSs. Aided by the L-FTSs, we locate conditions at N=10^4, under which the universality is expected to hold and the CL-FTSs are stable. While the L-FTSs continue to obey universality, the CL-FTSs deviate significantly. A number of potential explanations are considered, but only one appears credible. Given the documented problems with CL simulations of nonpolymeric models, it is likely that the inconsistency with universality results from a `silent failure' in the CL-FTSs, preceding the formation of hot spots.
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    Stabilizing complex-Langevin field-theoretic simulations for block copolymer melts
    (American Institute of Physics (AIP), 2024-12-28) Willis, J. D.; Matsen, M. W.
    Complex-Langevin field-theoretic simulations (CL-FTSs) provide an approximation-free method of calculating fluctuation corrections to the self-consistent field theory (SCFT) of block copolymer melts. However, the complex fields are prone to the formation of hot spots, which cause the method to fail. This problem has been attributed to an invariance under complex translations, which allows the system to drift away from the real-valued saddle-point of SCFT. Here, we apply dynamical stabilization to CL-FTSs of diblock copolymer melts, whereby the drift is suppressed by a small imaginary force on the composition field. The force needs to be sufficient to hold the system near the real saddle-point, but also small enough not to significantly bias the statistics. Although larger forces are required as the fluctuations become more intense, we are able to lower the invariant polymerization indices of the CL-FTSs by several orders of magnitude, before this becomes a problem. The new CL-FTS results are then used to test conventional Langevin simulations (L-FTSs), in which the instability is removed by a partial saddle-point approximation (PSPA) to the pressure field. As found previously, the L-FTSs agree accurately with the CL-FTSs, provided that the comparison is performed using a Morse calibration.