原文：Merger Policy and Tax CompetitionIn many situations governments have sector-specific tax and regulation policies at their disposal to influence the market outcome after a national or an international merger has taken place. We find that whether national or international mergers are more likely to be enacted in the presence of nationally optimal tax policies depends crucially on the ownership structure of firms. When all firms are owned domestically in the premerger situation, non-cooperative tax policies are more efficient in the national merger case and smaller synergy effects are needed for this type of merger to be proposed and cleared. These results are reversed when there is a high degree of foreign firm ownership prior to the merger.Mergers have played a prominent role over the past decade, and international merger activity has grown particularly fast. During the period 1981-1998 the annual number of mergers and acquisitions (M&A) has increased more than fivefold and the share of cross-border mergers has reached more than one quarter of the total by the end of this period. This increase in merger activity has led to situations where a national or an international merger have been in direct competition with each other. A recent example has been the bidding race for the leading Spanish electricity provider Endesa, where the German-based E.ON company initially competed with the Spanish-based rival Gas Natural. The Spanish authorities favored the national merger and formulated severe obstacles to an international take-over by E.ON, which was one of the reasons why E.ON eventually withdrew its bid. A different approach has been taken by the British government, which has fully liberalized its electricity market in the early 1990s. In this process, foreign electricity providers (among them E.ON ) took over a large part of the British electricity industry. The British government responded to high profits in this and other privatized industries by imposing a one-time, sector-specific windfall profit tax in 1997. Since then, a renewed imposition of this tax has been repeatedly discussed as a complement to the regulation of prices through the regulation authority Ofgem (Office of Gas and Electricity Markets).The last example shows clearly that national governments dispose over additional policy instruments in an industry where a merger or a foreign acquisition has taken place. Price regulation in privatized network industries is one important way to increase domestic consumer surplus at the expense of corporate profits, which often accrue, at least in part, to foreign shareholders. Sector-specific profit taxes have very similar effects, if their proceeds are redistributed to consumers in compensation for higher goods prices. On the other hand, there are also many industries where subsidies are granted in order to improve the competitiveness of domestic products in world markets. One set of examples are direct subsidies to specific sectors, such as mining, shipbuilding, steel production, or airplane construction. Moreover, several of these sectors and several others (e.g. air transportation) also receive indirect subsidies by paying reduced rates of excise taxes, in particular mineral oil or electricity taxes. To the extent that these eco taxes represent Pigouvian taxes that cause firms to internalize the true social cost of their products, such tax rebates also represent subsidies to the involved sectors and, importantly, to the electricity and energy sector itself. In all these cases, sector-specific tax or subsidy policies can be adjusted by national policymakers in response to a change in market structure caused by a merger.we argue that the possibility to levy industry-specific taxes or subsidies in a nationally optimal way has important repercussions on the position that national regulation authorities take vis-a-vis a national or an international merger proposal. At the same time, merging firms will incorporate a possible change in policy when deciding about a merger in a particular country. To analyze this interaction between tax and merger policies we set up a model where both firms and merger regulation authorities anticipate that taxes will be optimally adjusted in the host country after a merger has taken place. More specifically, we investigate a setting of Cournot quantity competition between four producing firms where two firms are located in each of two symmetric countries. Importantly, these firms may have foreign shareholders, thus giving an incentive to each government to employ profit taxes that can be partly exported to foreigners. Starting from a market structure of double duopoly, our focus is on the comparison between a national merger in one of the countries and an international merger between a home and a foreign firm.Our analysis shows that the relative attractiveness of a national versus an international merger depends critically on the degree of foreign firm