The hot stove effect in repeated-play decision making under ambiguity

The ''hot stove effect'' has been studied for repeated-play decision making under uncertainty (also referred to as experience-based decision making) in which the decision makers repeatedly face the Allais-type binary choice problems, and have to learn about the outcome distributions through sampling as the decision makers are not explicitly provided with prior information on the payoff structure. The previous studies have found mixed evidence: some studies have found that the hot stove effect is strong in repeated-play decision making under uncertainty, while other studies have found that the effect is weak. Thus, the evidence is inconsistent. This paper reports an experimental investigation of the hot stove effect in repeated-play decision making under ambiguity. The current experiment involves an ambiguity treatment in which (1) the participants perform two binary repeated-play choice problems, each involving 400-fold choice between a risky option and a riskless option; and (2) in each problem, there are two states of nature available: a favourable state and an unfavourable state, but only one of them obtains on any given trial. The realisation of the actual state is not disclosed to the participants, thus they would be expected to discover the actual state through sampling with immediate feedback. The current results suggest that the magnitude of the hot stove effect is significantly different between repeated-play decision making under uncertainty and repeated-play decision making under ambiguity. I shall show that the hot stove effect is attenuated in repeated-play decision making under ambiguity.Allais-type choices; decisions from experience; risk; uncertainty

Dynamical Mean-Field Study of Metamagnetism in Heavy Fermion Systems

We investigate the metamagnetism in the periodic Anderson model with the $\bm{k}$-dependent $c-f$ mixing by using the dynamical mean-field theory combined with the exact diagonalization method. It is found that both effects of the $\bm{k}$-dependent $c-f$ mixing and strong correlation due to the Coulomb interaction between $f$ electrons are significant for determining both the magnetization and the mass enhancement factor. For the case away from the half-filling, the results is consistent with the metamagnetic behavior observed in CeRu$_2$Si$_2$.Comment: 3 pages, 4 figures, accepted in J. Phys. Soc. Jpn. 80 (2011) Suppl. (Proc. ICHE2010

Dynamical mean-field theory for the anisotropic Kondo semiconductor: Temperature and magnetic field dependence

We investigate the periodic Anderson model with $\bm{k}$-dependent $c$-$f$ mixing reproducing the point nodes of the hybridization gap by using the dynamical mean-field theory combined with the exact diagonalization method. At low temperature below a coherence temperature $T_0$, the imaginary part of the self-energy is found to be proportional to $T^2$ and the pseudogap with two characteristic energies $\tilde{\it \Delta}_1$ and $\tilde{\it \Delta}_2$ is clearly observed for $T\ll T_0$, while the pseudogap is smeared with increasing $T$ and then disappears at high temperature T \simg T_0 due to the evolution of the imaginary self-energy. When the Coulomb interaction between $f$ electrons $U$ increases, $\tilde{\it \Delta}_1$, $\tilde{\it \Delta}_2$, and $T_0$ together with $T_{\rm max}$ at which the magnetic susceptibility is maximum decrease in proportion to the renormalization factor $Z$ resulting in a heavy-fermion semiconductor with a large mass enhancement $m^*/m=Z^{-1}$ for large $U$. We also examine the effect of the external magnetic field $H$ and find that the magnetization $M$ shows two metamagnetic anomalies $H_1$ and $H_2$ corresponding to $\tilde{\it \Delta}_1$ and $\tilde{\it \Delta}_2$ which are reduced due to the effect of $H$ together with $Z$. Remarkably, $Z^{-1}$ is found to be largely enhanced due to $H$ especially for H_1 \siml H \siml H_2, where the field induced heavy-fermion state is realized. The obtained results seem to be consistent with the experimental results observed in the anisotropic Kondo semiconductors such as CeNiSn.Comment: 11 pages, 11 figure

The effects of background music and sound in economic decision making: Evidence from a laboratory experiment

This paper experimentally studies the effects of background music and sound on the preference of the decision makers for rewards in pairwise intertemporal choice tasks and lottery choice tasks. The participants took part in the current experiment, involving four treatments: (1) the familiar music treatment; (2) the unfamiliar music treatment; (3) the noise treatment and (4) the no music treatment. The experimental results confirm that background noise affects human performance in decision making under risk and intertemporal decision making, though the results do not indicate the significant familiarity effect that is a change of the preference in the presence of familiar background music and sound.Allais-type preferences; choice under risk; intertemporal choice; the familiarity effect

A High-Tc Mechanism of Iron Pnictide Superconductivity due to Cooperation of Ferro-orbital and Antiferromagnetic Fluctuations

The electronic states and superconductivity in iron pnictides are studied on the basis of the 16 band $d$-$p$ model which includes both the onsite Coulomb interaction between Fe $d$ electrons and the intersite one between Fe $d$ and pnictogen $p$ electrons. The model well accounts for experimentally observed two fluctuations: the $d$-$d$ interaction-enhanced antiferromagnetic (AFM) fluctuation and the $d$-$p$ interaction-enhanced ferro-orbital (FO) fluctuation responsible for the $C_{66}$ elastic softening. The AFM fluctuation induces the repulsive pairing interaction for $\bm{q}\sim \bm{Q}_{\rm AF}$ while the FO does the attractive one for $\bm{q}\sim \bm{0}$ resulting in the $s_{\pm}$-wave superconductivity where the two fluctuations cooperatively enhance the superconducting transition temperature $T_{c}$ without any competition by virtue of the $\bm{q}$-space segregation.Comment: 4 pages, 4 figure