Recent developments in bimetric theory

This review is dedicated to recent progress in the field of classical, interacting, massive spin-2 theories, with a focus on ghost-free bimetric theory. We will outline its history and its development as a nontrivial extension and generalisation of nonlinear massive gravity. We present a detailed discussion of the consistency proofs of both theories, before we review Einstein solutions to the bimetric equations of motion in vacuum as well as the resulting mass spectrum. We introduce couplings to matter and then discuss the general relativity and massive gravity limits of bimetric theory, which correspond to decoupling the massive or the massless spin-2 field from the matter sector, respectively. More general classical solutions are reviewed and the present status of bimetric cosmology is summarised. An interesting corner in the bimetric parameter space which could potentially give rise to a nonlinear theory for partially massless spin-2 fields is also discussed. Relations to higher-curvature theories of gravity are explained and finally we give an overview of possible extensions of the theory and review its formulation in terms of vielbeins.Comment: 124 pages, 4 figures; minor changes, corrected typos; matches published versio

Networks of micro and small enterprise banks : a contribution to financial sector development : [Version March 2005]

The paper is a follow-up to an article published in Technique Financière et Developpement in 2000 (see the appendix to the hardcopy version), which portrayed the first results of a new strategy in the field of development finance implemented in South-East Europe. This strategy consists in creating microfinance banks as greenfield investments, that is, of building up new banks which specialise in providing credit and other financial services to micro and small enterprises, instead of transforming existing credit-granting NGOs into formal banks, which had been the dominant approach in the 1990s. The present paper shows that this strategy has, in the course of the last five years, led to the emergence of a network of microfinance banks operating in several parts of the world. After discussing why financial sector development is a crucial determinant of general social and economic development and contrasting the new strategy to former approaches in the area of development finance, the paper provides information about the shareholder composition and the investment portfolio of what is at present the world's largest and most successful network of microfinance banks. This network is a good example of a well-functioning "private public partnership". The paper then provides performance figures and discusses why the creation of such a network seems to be a particularly promising approach to the creation of financially self-sustaining financial institutions with a clear developmental objective

Networks of micro and small enterprise banks : a contribution to financial sector development :[Version January 2004]

The paper is a follow-up to an article published in Technique Financière et Developpement in 2000 (see the appendix to the hardcopy version), which portrayed the first results of a new strategy in the field of development finance implemented in South-East Europe. This strategy consists in creating microfinance banks as greenfield investments, that is, of building up new banks which specialise in providing credit and other financial services to micro and small enterprises, instead of transforming existing credit-granting NGOs into formal banks, which had been the dominant approach in the 1990s. The present paper shows that this strategy has, in the course of the last five years, led to the emergence of a network of microfinance banks operating in several parts of the world. After discussing why financial sector development is a crucial determinant of general social and economic development and contrasting the new strategy to former approaches in the area of development finance, the paper provides information about the shareholder composition and the investment portfolio of what is at present the world's largest and most successful network of microfinance banks. This network is a good example of a well-functioning "private public partnership". The paper then provides performance figures and discusses why the creation of such a network seems to be a particularly promising approach to the creation of financially self-sustaining financial institutions with a clear developmental objective

Choosing and using payment instruments: evidence from German microdata

Germans are still very fond of using cash. Of all direct payment transactions, cash accounts for an astounding 82% in terms of number, and for 58% in terms of value. With a new and unique dataset that combines transaction information with survey data on payment behaviour of German consumers, we shed light on how individuals choose payment instruments and why cash remains so important. We propose a two-stage empirical framework which jointly explains credit card ownership and the use of cash. Our results indicate that the pattern of cash usage is compatible with systematic economic decision making. Consumers decide upon the adoption of payment cards and then use available payment media according to their transaction and personal characteristics, the relative costs of cash and card usage, and their assessment of payment instruments’ characteristics. Whereas older consumers use significantly more cash, the comparison with younger consumers shows that the difference in payment behaviour is not explained by age as such but to a large extent by differences in the characteristics of these two groups. It is interesting that the possession of a credit card, especially alongside a debit card, does not significantly affect the use of cash in Germany. JEL Classification: E41, E58, D12cash substitution, cash usage, credit cards, debit cards, payment behaviour, payment cards, payment innovation, Payment instruments, survey data

Particular Solutions in Bimetric Theory and Their Implications

Ghost-free bimetric theory can describe gravity in the presence of an extra spin-2 field. We study certain aspects of dynamics in this theory: (1) It is shown that if either of the metrics is an Einstein solution then the other is always forced to be Einstein, too. For a class of bimetric models this constraint is stronger and as soon as one metric is Einstein, the other metric is forced to be proportional to it. As a consequence, the models in this class avoid a branch of pathological solutions that exhibit determinant singularities or nonlinear ghosts. These constraints persists in a generalized form when sources are included, but are destroyed in the massive gravity limit of the theory. (2) For another class of bimetric models, we show the existence of solutions that do not admit a massive gravity limit. A bimetric model that could exhibit a nonlinear version of "partially massless" symmetry belongs to both these classes. It is argued that if such a model exits, its symmetry will not survive in the massive gravity limit.Comment: Latex, 18 pages. Published versio

Choosing and using payment instruments: evidence from German microdata

Germans are still very fond of using cash. Of all direct payment transactions, cash accounts for an astounding 82% in terms of number, and for 58% in terms of value. With a new and unique dataset that combines transaction information with survey data on payment behaviour of German consumers, we shed light on how individuals choose payment instruments and why cash remains so important. We propose a two-stage empirical framework which jointly explains credit card ownership and the use of cash. Our results indicate that the pattern of cash usage is compatible with systematic economic decision making. Consumers decide upon the adoption of payment cards and then use available payment media according to their transaction and personal characteristics, the relative costs of cash and card usage, and their assessment of payment instruments' characteristics. Whereas older consumers use significantly more cash, the comparison with younger consumers shows that the difference in payment behaviour is not explained by age as such but to a large extent by differences in the characteristics of these two groups. It is interesting that the possession of a credit card, especially alongside a debit card, does not significantly affect the use of cash in Germany. --Payment instruments,payment cards,payment behaviour,payment innovation,cash usage,cash substitution,debit cards,credit cards,survey data

Does wage rigidity really exist? New evidence from US panel data

Downward nominal wage rigidity (DNWR) could prevent real wage adjustments in times of low inflation rates. Nominal wage rigidity based on annual wages can at least be reduced, if the number of working hours is considered. This leads to a lower degree of DNWR in hourly wage changes. In this paper, we use a histogram-location approach to investigate to what extent annual as well as hourly wages are subject to downward nominal wage rigidity. Using data from the Panel Study of Income Dynamics (PSID) we find that annual wage changes exhibit a substantially higher level of wage rigidity than hourly wage changes which also holds for males compared to females. --Wage Rigidity,Histogram-Location Approach