arXiv subjects
Publications and source records attributed to Shohei Yanagita.
We formulate the voter's strategic information acquisition to control the future self's action as a Bayesian persuasion problem. Our main result shows that acquiring information that is irrelevant to the voter's objective can be a worst-case optimal solution: it can reduce the possibility that the future self is swayed by additional information whose content is ambiguous to the current voter.
We develop an axiomatic model of robust Bayesian persuasion where the sender cannot fully control the information available to the receiver. After selecting an information structure, the sender expects that more informative structures might be implemented. We model this by allowing the sender to assess each information structure under worst-case information leakage, represented by a set of more informative structures. The model encompasses a wide range of examples of information leakage, which we also explore.
Completeness and transitivity are standard rationality conditions in economics. However, under ambiguity, decision makers sometimes violate these requirements because of the difficulty of forming accurate predictions about ambiguous events. Motivated by this, we study various ambiguity preferences that partially satisfy completeness and transitivity. Our characterization results show that completeness and a novel yet natural weakening of transitivity correspond to two opposite ways of using multiple probability distributions in mind; that is, these two axioms have dual implications at the level of cognitive processes for ambiguity.
Gilboa and Schmeidler's (1989) uncertainty aversion plays a central role in decision theory and economics, yet many inconsistent behaviors have been observed in experiments. Motivated by this, we study an axiom postulating a minimal degree of uncertainty aversion. Our main result shows that this axiom yields a new class of representations, called cautious dual-self expected utility representations. In this model, two selves in the decision maker's mind play an extensive-form game to determine the belief used for evaluation, where the first mover is selected cautiously. As illustrated by two alternative representations, cautiously choosing between two "dual" scenarios is the key implication of our axiom.
When a collective decision maker presents a menu of uncertain prospects to her group members, each member's choice depends on their predictions about payoff-relevant states. In reality, however, these members hold different predictions; more precisely, they have different prior beliefs about states and predictions about the information they will receive. In this paper, we develop an axiomatic framework to examine collective decision making under such disagreements. First, we characterize two classes of representations: Bewley multiple learning (BML) representations, which are unanimity rules among predictions, and justifiable multiple learning (JML) representations, where a single prediction has veto power. Furthermore, we characterize a general class of representations called hierarchical multiple learning representations, which includes BML and JML representations as special cases. Finally, motivated by the fact that these representations violate completeness or intransitivity due to multiple predictions, we propose a rationalization procedure for constructing complete and transitive preferences from them.
Recent measurements of cosmic-ray light nuclei by AMS-02 have shown that there is an unexpected component of cosmic-ray (CR) lithium whose spectral index is harder than that expected from the secondary production scenario. We propose the nearby Type Ia supernova following a nova eruption as the origin of lithium nuclei in the CRs. By fitting the data of CR protons, helium, and lithium fluxes provided by AMS-02 with our theoretical model we show that this scenario is consistent with the observations. The observational tests that can check our hypothesis are briefly discussed.
We develop a method of stochastic differential equation to simulate electron acceleration at astrophysical shocks. Our method is based on Itô's stochastic differential equations coupled with a particle splitting, employing a skew Brownian motion where an asymmetric shock crossing probability is considered. Using this code, we perform simulations of electron acceleration at stationary plane parallel shock with various parameter sets, and studied how the cutoff shape, which is characterized by cutoff shape parameter $a$, changes with the momentum dependence of the diffusion coefficient $β$. In the age-limited cases, we reproduce previous results of other authors, $a\approx2β$. In the cooling-limited cases, the analytical expectation $a\approxβ+1$ is roughly reproduced although we recognize deviations to some extent. In the case of escape-limited acceleration, numerical result fits analytical stationary solution well, but deviates from the previous asymptotic analytical formula $a\approxβ$.
Transport equation of the galactic cosmic ray (GCR) is numerically solved for qA>0 and qA<0 based on the stochastic differential equation (SDE) method. We have developed a fully time-dependent and three-dimensional code adapted for the wavy heliospheric current sheet (HCS). Results anticipated by the drift pattern are obtained for sample trajectories and distributions of arrival points at the heliospheric boundary for GCR protons. Our simulation reproduced a 22-year cycle of solar modulation which is qualitatively consistent with observations. Energy spectra of protons at 1 AU are calculated and compared with the observation by BESS.
The structure of the cosmic ray electron halo of a starburst galaxy depends strongly on the nature of galactic wind and the configuration of the magnetic field. We have investigated these dependencies by solving numerically the propagation of electrons originating in starburst galaxies, most likely in supernova remnants. The calculations are made for several models for the galactic winds and for the configuration of the magnetic fields for comparison with observations. Our simulation of a quasi-radio halo reproduces both the extended structure of ~ 9 kpc and the subtle hollow structure near the polar region of the radio halo that are observed in the starburst galaxy NGC 253. These findings suggest the existence of strong galactic wind in NGC 253.
The existence of the spectral break around $\sim 3 \times 10^{15}$ eV in the cosmic ray spectrum (referred to as the `knee') is one of the biggest questions in cosmic ray astrophysics. At the same time, the origin of cosmic rays above the knee energies (between 10$^{15}$ and 10$^{18}$ eV) is also still unsettled. In this paper, we investigate how the hypothetical extragalactic CRs after modulated by the galactic wind contribute to the knee in the CR spectrum. We numerically calculate the modulated energy spectrum of the hypothetical cosmic rays coming into the galaxy from just outside of the ``galactic sphere'' where the galactic wind terminates. We show that the observed knee structure is reproduced well by a superposition of the modulated component and the galactic cosmic rays originating in supernova remnants.