Johannes Gaul

This study examines the compliance costs of OECD Pillar Two, i.e., the "Global Minimum Tax," for multinational enterprises headquartered in the European Union. Collecting data from chief financial officers and heads of finance or tax departments, we estimate compliance cost determinants and subsequently predict the overall compliance burden. Results indicate total one-off costs of about EUR 1.2 billion (up to EUR 2.0 billion) and total recurring costs of EUR 517 million EUR p.a. (up to EUR 865 million EUR p.a.). Our findings inform the public discourse by mitigating information asymmetries between policymakers and corporations. Moreover, we contribute by establishing a cost benchmark to facilitate a systematic cost-benefit evaluation of this policy.

We study the relationship between investors’ social media activity and earnings announcement returns. To distinguish between information contained in peer-to-peer interaction and user-posted content, we analyze conversation networks on Reddit using centrality metrics from network science and classify user sentiment with large language models. We show that pre-announcement sentiment is positively associated with short-term cumulative abnormal returns only if it does not spark pre-announcement controversy. If pre-announcement controversy arises, we document a negative association. Our findings present a more nuanced view on the wisdom of crowds hypothesis, highlighting that peer-to-peer interaction on social media exhibits a pattern of normalization, and thus contains informational value beyond content.

Although spatial interactions are in principle dependent on networks, the empirical literature on tax competition has thus far used matrices of generic form to model policy reactions. We address this gap in the literature in two ways. First, we analyze the arguments of local policy makers in debates on local tax reforms. We find that local politicians reference peers selectively to suit the direction of their argument. On average, their statements are in line with their political party's ideology, reflected in a preference for more equity or efficiency, respectively. However, the commonalities between the reference target and the municipality in question determine a set of references that are accepted across party lines. Second, we use this set of determinants to impute the network links as perceived by local politicians. Drawing upon a plausibly exogenous shock that affects a subset of peers, we analyze how tax reforms propagate in this network.

This paper presents descriptive evidence on economic activity reported under DAC7, the European Union's newly introduced third-party reporting regime for online marketplaces. Using novel administrative data from Germany, we study platform-mediated sales between businesses and consumers as well as among peers. We document the scale, composition, and distribution of online marketplace participation and sales across platforms and seller types. The analysis provides a comprehensive empirical characterization of activity reported under DAC7 and establishes a baseline for future research and policy evaluation.

As a team, we developed an interactive, computer game-based learning module to enhance engagement and conceptual understanding in financial accounting courses. Students play a computer opponent and take business decisions. They are in-game incentivized to conduct correct bookkeeping. We pilot the game in the Fundamentals of Financial Accounting course at the University of Mannheim with around 800 students per year.

We report on our results here (open-access, German):

Spielend lernen im digitalen Raum,
with M. Friedrich-Schieback. die hochschullehre, 37(1), 180–187, 2026.

Entwicklung und Anwendung des Lernspiels GeR Gamified für eine BWL-Grundlagen­veranstaltung,
with Andreas Reitzig, Ute Hager, Samuel Wissel, and Sabrina Navratil. In: Marina Friedrich-Schieback, Melanie Klinger, Niko Baldus (Hg.), Freiräume für innovative digitale Lehre: Gestaltungsprozesse, Lehrprojekte, Reflexionen. wbv Verlag, Bielefeld, 2026.

Funded by the University of Mannheim’s Teaching Innovation Program and Stiftung Innovation in der Hochschullehre.