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We perform a digital quantum simulation of a gauge theory with a topological term in Minkowski spacetime, which is practically inaccessible by standard lattice Monte Carlo simulations. We focus on $1+1$ dimensional quantum electrodynamics with the $\theta$-term known as the Schwinger model. We construct the true vacuum state of a lattice Schwinger model using adiabatic state preparation which, in turn, allows us to compute an expectation value of the fermion mass operator with respect to the vacuum. Upon taking a continuum limit we find that our result in massless case agrees with the known exact result. In massive case, we find an agreement with mass perturbation theory in small mass regime and deviations in large mass regime. We estimate computational costs required to take a reasonable continuum limit. Our results imply that digital quantum simulation is already useful tool to explore non-perturbative aspects of gauge theories with real time and topological terms., Comment: 13 pages, 6 figures; v3: accepted version in PRD

We propose a new neural sequence model training method in which the objective function is defined by $\alpha$-divergence. We demonstrate that the objective function generalizes the maximum-likelihood (ML)-based and reinforcement learning (RL)-based objective functions as special cases (i.e., ML corresponds to $\alpha \to 0$ and RL to $\alpha \to1$). We also show that the gradient of the objective function can be considered a mixture of ML- and RL-based objective gradients. The experimental results of a machine translation task show that minimizing the objective function with $\alpha > 0$ outperforms $\alpha \to 0$, which corresponds to ML-based methods., Comment: 2017 ICML Workshop on Learning to Generate Natural Language (LGNL 2017)

As articulated in economic growth theory, the accumulation of knowledge and human capital in higher education can be the essential sources of long-term economic growth. This PhD thesis carried out the following three empirical analyses on factors affecting these knowledge production and human capital accumulation. Focusing on the role carried out by universities in knowledge and human capital growth, Chapter 1 empirically analyzed the effects that university governance have on research activities by university researchers. Chapter 2 empirically analyzed the effects that post-graduate education has on human capital accumulation in research activities by PhD student. These analyses were treated as accumulations in intellectual human capital and mechanisms for cultivation. Moreover, Chapter 3 analyzed the effect of public and government research and development investment strongly linked to academic-industrial collaboration on businesses producing patents. Chapter 1 estimates the causal effects of university governance on their research activity through the analysis of the transformation of Japanese national universities into “national university corporation”, a juridical 0public body separated from central government. The Corporatization (or Partial Privatization) of the Japanese national universities since 2004 is characterized as exogenous source of promoting additive competitive environments within national universities, improving accountability, and expanding a range of some aspects of autonomous function of national universities. Some detailed estimation results were attained through DID estimations using private universities as the control group that had not affected by the corporatization of national universities bringing about a significantly positive impact for engineering and economics publication activity in national universities. Moreover, analyses of these fields of study that divided universities into less research-intensive universities and more research-intensive universities found that the more research-intensive universities had significantly robust positive effects, whereas significant effects couldn't be seen in the less research-intensive universities. The analyses largely indicated that the transformation into independent institutions resulted in the advancement of domestic competition and resources being concentrated on universities with superior research capabilities in line with the drastic decrease in subsidies for operations. Furthermore, the analyses suggest that the effect coincided with intensified efforts to acquire competitive-type research funding also induced by the reform. These results suggests the possibility that competitive research resources (perhaps more efficiently) have become concentrated towards universities that are achieving superior research results, and indicates a positive effect for research-intensive universities and no significant effect for less research-intensive universities. However, research output in medical science by national universities has shown a pronounced decrease. This result is consistent with the expectation that corporatization, which encourages income-generating activity, results in a decrease in the research output of university hospitals. This finding reflects the special characteristics of university hospitals that render them the main producers of research output and the greatest national university revenue earners from the provision of clinical services. The objective of Chapter 2, co-authored with Ryo Nakajima (Keio University), is to quantitatively elucidate the effectiveness of research guidance given by supervisors to student advisees, value-added, by focusing on post-graduate education as the provider of innovation in cultivating human capital. Here, a problem arises where the matching of the supervisor and student pair is endogenously determined making it difficult to deal with the resulting self-selection effect. Therefore, this research analyzed issues with matching by expanding on the value-added model technique used by Rivkin, Hanusheck and Kain (2005), and constructing data on supervisor and student pairs that exogenously broke down as a result of supervisor turnover during guidance based on data on supervisors and students from the Department of Physics at the University of Tokyo. We find that a one-standard-deviation increase in professor quality results in a 0.54 standard deviation increase in a doctoral student’s research achievement growth, increasing the number of first-authored papers that are published in top journals by 0.64 at the doctoral level. The purpose of Chapter 3, co-authored with Taro Akiyama (Yokohama National University), Tatsumi Ishizuka (Yokohama National University) and Ryuichi Tamura (Hitotsubashi University), is to analyze the influence of the Japanese government R&D investment on private sector patenting in the field of fuel cell. Specifically, using the data set on fuel cell-related patents between 1999 and 2011, we analyzed the patent productivity of companies following a partnership with NEDO (New Energy and Industrial Technology Development Organization.) The results of the estimation showed that, when analyzing without using the panel data structure, there was a significant positive influence on the number of patent applications, however, it was also revealed that there was no significant positive influence on the quality indexes such as the number of times those patents were cited. Furthermore, when analyzing while taking advantage of the characteristics of panel data, no significant influence was found in either of the two cases.

We discuss that a low-energy effective Lagrangian relying on SO(3) → SO(2) is applicable for a ferrimagnet as well as a ferromagnet and an antiferromagnet. We derive the Hamiltonian from the Lagrangian using the Poisson and Dirac brackets, and determine the particle states. The analysis of the particle states shows that there exist not only massless modes with the dispersion relations ω∝|k|, |k|2ω, i.e., the so-called type-I and type-II Nambu–Goldstone modes, respectively, but also gapped modes with ω∝m2+|k|2ω . We clarify how the coefficients of the terms with one time derivative and those with two time derivatives in the effective Lagrangian determine the order parameters specifying whether the system is in a ferromagnetic, antiferromagnetic, or ferrimagnetic state; we stress that the gapped mode resulting form the spontaneous symmetry breaking appears only in the ferrimagnetic system and not in the ferromagnetic and antiferromagnetic systems. We also establish the power-counting scheme and calculate the scattering amplitudes and thereby the scattering lengths between the two Nambu–Goldstone bosons. We show that the scattering length of the gapped mode is finite and proportional to the gap. This characteristic property of the gapped NG mode can be used to discriminate it from gapped excitations that originate in other mechanisms. Finally, we study the effects of the explicit symmetry breaking that are given by an external magnetic field and a single-ion anisotropy, and show that the external magnetic fields do not have any effects on the scattering amplitudes in all the spin systems, as was known for the ferromagnet system. In contrast, the anisotropy does affect the scattering amplitudes, the phase shift, and the scattering length except for spin 1/2 systems. This result supports the possibility of the Efimov effect in spin systems discussed in previous studies.

We give a detailed derivation of the second-order (local) hydrodynamics for Boltzmann equation with an external force by using the renormalization group method. In this method, we solve the Boltzmann equation faithfully to extract the hydrodynamics without recourse to any ansatz. Our method leads to microscopic expressions of not only all the transport coefficients that are of the same form as those in Chapman-Enskog method but also those of the viscous relaxation times $\tau_i$ that admit physically natural interpretations. As an example, we apply our microscopic expressions to calculate the transport coefficients and the relaxation times of the cold fermionic atoms in a quantitative way, where the transition probability in the collision term is given explicitly in terms of the $s$-wave scattering length $a_s$. We thereby discuss the quantum statistical effects, temperature dependence, and scattering-length dependence of the first-order transport coefficients and the viscous relaxation times: It is shown that as the temperature is lowered, the transport coefficients and the relaxation times increase rapidly because Pauli principle acts effectively. On the other hand, as $a_s$ is increased, these quantities decrease and become vanishingly small at unitarity because of the strong coupling. The numerical calculation shows that the relation $\tau_\pi=\eta/P$, which is derived in the relaxation-time approximation and used in most of literature without almost any foundation, turns out to be satisfied quite well, while the similar relation for the relaxation time $\tau_J$ of the heat conductivity is satisfied only approximately with a considerable error., Comment: 33 pages, 10 figures