Combinatorics in N = 1 Heterotic Vacua

We briefly review an algorithmic strategy to explore the landscape of heterotic E8 \times E8 vacua, in the context of compactifying smooth Calabi-Yau three-folds with vector bundles. The Calabi-Yau three-folds are algebraically realised as hypersurfaces in toric varieties and a large class of vector bundles are constructed thereon as monads. In the spirit of searching for Standard-like heterotic vacua, emphasis is placed on the integer combinatorics of the model-building programme.Comment: 14 pages. An introductory review prepared for the special issue "Computational Algebraic Geometry in String and Gauge Theory" of Advances in High Energy Physic

Economic fundamentals and exchange rates under different exchange rate regimes: Korean experience

Korea provides a unique opportunity to study the different behaviors or roles, if any, of limited flexibility and free floating exchange rate regimes. Korea shifted from a limited flexibility to a free floating exchange rate regime after the 1997 economic crisis. It is well documented that the exchange rate is very difficult to predict using any theoretical models for exchange rate determination. Based on a simple monetary model, we find that the impact of economic fundamentals on the exchange rate is very similar under both exchange rate regimes according to OLS estimates, but the difference is statistically significant with GARCH(1,1) results. We also find that the size of the exchange rate shock is much bigger under the free floating regime than under the limited flexibility regime. VAR results show that the exchange rate shock impact on inflation is not statistically different under the two regimes. These findings are generally in line with Baxter and Stockman (1989) for regime neutrality.Korean exchange rate regimes, economic fundamentals, exchange rate pass-through

Uncovered Interest Parity: Cross-sectional Evidence

This paper proposes a different empirical approach to estimate the UIP by analyzing a large number of cross-country bilateral exchange rates using cross-section analysis. Different from conventional time-series UIP, cross-sectional UIP is examined with single equation estimation and panel regression model estimation. The exchange rates analyzed here include a broad spectrum of countries: developed, developing, low inflation and high inflation countries. Based on the empirical evidence, there does not appear to be a well-publicized UIP puzzle for cross-sectional UIP, and the slope estimates remain largely between zero and one throughout the sample periods, with a few exceptions. Evidence of UIP is more clear for low inflation countries than for high inflation countries. As interest rate maturity becomes longer, UIP relationship becomes weaker.Uncovered interest parity, Cross-sectional UIP

Swampland Bounds on the Abelian Gauge Sector

We derive bounds on the number of abelian gauge group factors in six-dimensional gravitational theories with minimal supersymmetry and in their F-theoretic realisations. These bounds follow by requiring consistency of certain BPS strings in the spectrum of the theory, as recently proposed in the literature. Under certain assumptions this approach constrains the number of abelian gauge group factors in six-dimensional supergravity theories with at least one tensor multiplet to be $N \leq 20$ (or $N \leq 22$ in absence of charged matter). For any geometric F-theory realisation with at least one tensor multiplet we establish the bound $N \leq 16$ by demanding unitarity of a heterotic solitonic string which exists even in absence of a perturbative heterotic dual. This result extends to four-dimensional F-theory vacua on any blowup of a rational fibration. Our findings lead to universal bounds on the rank of the Mordell-Weil group of elliptically fibered Calabi-Yau threefolds.Comment: 10 pages, 2-column forma

Mobile Innovation and the Music Business in Japan: The Case of Ringing Tone Melody ("Chaku-Mero") (Research Note)

This paper examines the development process and successful factors of the ringing tone melody downloading service, or "Chaku-Mero," in Japan. Chaku-Mero is a mobile Internet service in which a subscriber could download from a wide selection of music melodies his/her favorite with some fee to get it ring when the mobile phone receives a call message. This service is arguably the most successful m-commerce business in the world. According to three major mobile communication carriers, NTT DoCoMo, KDDI, and J-Phone, Chaku-Mero accounts for 40 to 60% of their paid service sales on the mobile Internet. Industry sources estimate that annual payment for Chaku-Mero reached approximately 80-90 billion yen in 2002 (currently US$1=120yen). Also, it has been argued that the Japanese Chaku-Mero service is the sole example of Internet cultural content business, be it fixed or mobile, in the world that has successfully overcome complicated conflicts and concerns of copyrights among different parties and created a significant market. The paper describes the process of how this business has evolved. It traces back the pre-mobile-Internet phase of related services such as the "Sky Melody" service by J-Phone and the wireless Karaoke business, which served as precursors of Chaku-Mero. Then the paper examines the business structure: the parties involved in the business, their relations, and how values are created and distributed among them. Also, the paper analyzes why some content providers have been more successful than others. A leading Chaku-Mero provider, for example, maintains more than 6.5 million subscribers and annual sales of 12 billion yen. Over all, the paper provides a preliminary study of mobile innovation in the music business, which is a part of a larger study of the history of interactions between technologies to create, record, distribute, and promote music and the music business. It would give some implications for the prospects of mobile Internet businesses for music and other cultural contents.

Emergent Strings, Duality and Weak Coupling Limits for Two-Form Fields

We systematically analyse weak coupling limits for 2-form tensor fields in the presence of gravity. Such limits are significant for testing various versions of the Weak Gravity and Swampland Distance Conjectures, and more broadly, the phenomenon of emergence. The weak coupling limits for 2-forms correspond to certain infinite-distance limits in the moduli space of string compactifications, where asymptotically tensionless, solitonic strings arise. These strings are identified as weakly coupled fundamental strings in a dual frame, which makes the idea of emergence manifest. Concretely we first consider weakly coupled tensor fields in six-dimensional compactifications of F-theory, where the arising tensionless strings play the role of dual weakly coupled heterotic strings. As the main part of this work, we consider certain infinite distance limits of Type IIB strings on K3 surfaces, for which we show that the asymptotically tensionless strings describe dual fundamental Type IIB strings, again on K3 surfaces. By contrast the analogous weak coupling limits of M-theory compactifications are found to correspond to an F-theory limit where an extra dimension emerges rather than tensionless strings. We comment on extensions of our findings to four-dimensional compactifications.Comment: 30 pages, 1 figure; v2: cosmetic changes and minor comments adde