在面臨2008年金融危機後嚴峻之需求面衝擊下，多國央行紛紛調降利率，甚至調降至零利率，以期望國家能盡速脫離經濟衰退。在利率調降的過程中，由於受零利率下限的限制，單純藉由傳統貨幣政策之調控，仍可能無法使經濟從嚴峻的需求面衝擊下恢復。因此，非傳統貨幣政策也在美國、日本、英國、歐元區等國家被央行所採行做為對抗經濟衰退的政策工具。在此背景下，我們想了解如何實施最適非傳統貨幣政策。 在最適貨幣政策理論發展中，最適傳統貨幣政策發展較早，因此也較為完備。而在最適非傳統貨幣政策方面，前瞻指引(forward guidance)這項政策工具已被引入最適理論中來進行討論，但量化寬鬆(quantitative easing)直至今日還未被引入最適理論中來討論。 因此，本文建構一個封閉的新興凱因斯模型(New Keynesian)，開創性的將量化寬鬆引入最適貨幣政策理論中，來討論最適傳統與非傳統貨幣政策，也藉此與過去文獻比較施行量化寬鬆與未施行量化寬鬆之影響。 / After financial crisis occurred in 2008, countries, such as United States of America, United Kingdom, Japan and the euro area, have been mired in slow economic growth, compared with long-term, and have confronted with severe negative demand shocks which can’t be offset by zero interest-rate policy. Under the circumstance where zero lower bound was present, unconventional monetary policy was implemented by central bank of each country to end up the economic recession prospectively. As a result, we are interested in how to implement optimal unconventional monetary policy. The literatures regarding implementing conventional optimal monetary policy under demand shock were developed maturely. Forward guidance, one of unconventional monetary policy, was already developed in field of optimal monetary policy under impacted by demand shock, but quantitative easing has not been conducted in the theory of optimal monetary policy so far. Thus, we construct a close-economy by New Keynesian model to conduct quantitative easing into the theory of optimal monetary policy to discuss the optimal conventional and unconventional monetary policy, and to compare the difference corresponding to the previous literatures which without quantitative easing.

自從2008年全球經濟衰退以來，歐元區經濟顯著的衰退，特別是歐元區各成員國的經濟表現有明顯的差異。在本文中，我們試就成員國「貿易開放程度」和「財政基本面」這兩個重要特徵，來詮釋歐元區經濟穩定這個議題。在第二章中，我們在貿易開放程度不同的國家下，比較貨幣同盟制度與浮動匯率制度對於負向衝擊產生的影響。我們發現當貨幣當局愈重視產出穩定時，相較於浮動匯率制度，貨幣同盟制度將使產出下降的更多。在第三章中，我們將短期私人債券及長期政府債券引入貨幣同盟的兩國DSGE模型。我們推斷，歐洲央行(ECB)的公共部門債券購買計劃（PSPP），對於不同財政狀況的成員國，有著不對稱的總體經濟影響。在第四章中，我們建立貨幣同盟經濟的最適貨幣政策模型。我們發現成員國間經濟差異，將影響貨幣同盟的整體福利水準。相較於傳統零利率最適貨幣政策文獻，本研究的結果顯示不論是權衡或承諾制度，增加公共部門債券購買將緩和貨幣同盟的經濟波動。 / Since the global recession in 2008, the economic performance of the Euro area has declined significantly. In particular, there have been great differences in the economic performance among member states in the Euro area. In this dissertation, we attempt to address the issue of economic stability by focusing on two key features: the trade openness and the fiscal fundamentals among member states. In Chapter 2, we compare the impacts of the adverse shocks on countries with different degrees of openness under the monetary union regime, and our finding shows that the monetary union will result in a greater decline in output if the monetary authority attaches a higher weight to output stabilization. In Chapter 3, we build a two-country DSGE model representing a monetary union with both short-term and long-term government bonds. We deduce that the ECB’s public sector purchase programme (PSPP) has asymmetric macroeconomic effects on member states under different fiscal fundamentals. In Chapter 4, we set up an optimal monetary policy model of a monetary union. We find that the differences in the economic performance of individual member states will influence the union-wide welfare. Comparing our results with classical literature of optimal monetary policy at zero lower bound, by adding the PSPP, our study indeed reflects lower volatility of the union-wide economy under either discretion or commitment.