D-instantons, Strings and M-theory

The R^4 terms in the effective action for M-theory compactified on a two-torus are motivated by combining one-loop results in type II superstring theories with the Sl(2,Z) duality symmetry. The conjectured expression reproduces precisely the tree-level and one-loop R^4 terms in the effective action of the type II string theories compactified on a circle, together with the expected infinite sum of instanton corrections. This conjecture implies that the R^4 terms in ten-dimensional string type II theories receive no perturbative corrections beyond one loop and there are also no non-perturbative corrections in the ten-dimensional IIA theory. Furthermore, the eleven-dimensional M-theory limit exists, in which there is an R^4 term that originates entirely from the one-loop contribution in the type IIA theory and is related by supersymmetry to the eleven-form C^{(3)}R^4. The generalization to compactification on T^3 as well as implications for non-renormalization theorems in D-string and D-particle interactions are briefly discussed.Comment: harvmac (b) 17 pages. v4: Some formulae corrected. Dimensions corrected for eleven-dimensional expression

Atmospheric Calorimetry above 1019^{19} eV: Shooting Lasers at the Pierre Auger Cosmic-Ray Observatory

The Pierre Auger Cosmic-Ray Observatory uses the earth's atmosphere as a calorimeter to measure extensive air-showers created by particles of astrophysical origin. Some of these particles carry joules of energy. At these extreme energies, test beams are not available in the conventional sense. Yet understanding the energy response of the observatory is important. For example, the propagation distance of the highest energy cosmic-rays through the cosmic microwave background radiation (CMBR) is predicted to be strong function of energy. This paper will discuss recently reported results from the observatory and the use of calibrated pulsed UV laser "test-beams" that simulate the optical signatures of ultra-high energy cosmic rays. The status of the much larger 200,000 km$^3$ companion detector planned for the northern hemisphere will also be outlined.Comment: 6 pages, 11 figures XIII International Conference on Calorimetry in High Energy Physic

Proof of a modular relation between 1-, 2- and 3-loop Feynman diagrams on a torus

The coefficients of the higher-derivative terms in the low energy expansion of genus-one graviton Type II superstring scattering amplitudes are determined by integrating sums of non-holomorphic modular functions over the complex structure modulus of a torus. In the case of the four-graviton amplitude, each of these modular functions is a multiple sum associated with a Feynman diagram for a free massless scalar field on the torus. The lines in each diagram join pairs of vertex insertion points and the number of lines defines its weight $w$, which corresponds to its order in the low energy expansion. Previous results concerning the low energy expansion of the genus-one four-graviton amplitude led to a number of conjectured relations between modular functions of a given $w$, but different numbers of loops $\le w-1$. In this paper we shall prove the simplest of these conjectured relations, namely the one that arises at weight $w=4$ and expresses the three-loop modular function $D_4$ in terms of modular functions with one and two loops. As a byproduct, we prove three intriguing new holomorphic modular identities.Comment: 38 pages, 9 figures, in version 2: Appendix D added and corrections made in section

Production of the X(3872) at the Tevatron and the LHC

We predict the differential cross sections for production of the X(3872) at the Tevatron and the Large Hadron Collider from both prompt QCD mechanisms and from decays of b hadrons. The prompt cross section is calculated using the NRQCD factorization formula. Simplifying assumptions are used to reduce the nonperturbative parameters to a single NRQCD matrix element that is determined from an estimate of the prompt cross section at the Tevatron. For X(3872) with transverse momenta greater than about 4 GeV, the predicted cross section is insensitive to the simplifying assumptions. We also discuss critically a recent analysis that concluded that the prompt production rate at the Tevatron is too large by orders of magnitude for the X(3872) to be a weakly-bound charm-meson molecule. We point out that if charm-meson rescattering is properly taken into account, the upper bound is increased by orders of magnitude and is compatible with the observed production rate at the Tevatron.Comment: 29 pages, 5 figure

Topological Origin of Equatorial Waves

Topology sheds new light on the emergence of unidirectional edge waves in a variety of physical systems, from condensed matter to artificial lattices. Waves observed in geophysical flows are also robust to perturbations, which suggests a role for topology. We show a topological origin for two celebrated equatorially trapped waves known as Kelvin and Yanai modes, due to the Earth's rotation that breaks time-reversal symmetry. The non-trivial structure of the bulk Poincar\'e wave modes encoded through the first Chern number of value $2$ guarantees existence for these waves. This invariant demonstrates that ocean and atmospheric waves share fundamental properties with topological insulators, and that topology plays an unexpected role in the Earth climate system

The Macroeconomics of Delegated Management

We are interested in the macroeconomic implications of the separation of ownership and control. An alternative decentralized interpretation of the stochastic growth model is proposed, one where shareholders hire a self-interested manager who is in charge of the firm’s hiring and investment decisions. Delegation is seen to give rise to a generic conflict of interests between shareholders and managers. This conflict fundamentally results from the different income base of the two types of agents, once aggregate market clearing conditions are taken into account. An optimal contract exists resulting in an observational equivalence between the delegated management economy and the standard representative agent business cycle model. The optimal contract, however, appears to be miles away from standard practice: the manager’s remuneration is tied to the firm’s total income net of investment expenses, abstracting totally from wage costs. In order to align the interest of a manager more conventionally remunerated on the basis of the firm’s operating results to those of stockholder-workers, the manager must be made nearly risk neutral. We show the limited power of convex contracts to accomplish this goal and the necessity, if the manager is too risk averse (log or higher than log), of considerably downplaying the incentive features of his remuneration. The difficulty in reconciling the viewpoints of a manager with powers of delegation and of a representative firm owner casts doubt on the descriptive validity of the macro-dynamics highlighted in the representative agent macroeconomic model.business cycles, delegated management, contracting

The Macroeconomics of Delegated Management

We are interested in the macroeconomic implications of the separation of ownership and control. An alternative decentralized interpretation of the stochastic growth model is proposed, one where shareholders hire a self-interested manager who is in charge of the firm's hiring and investment decisions. Delegation is seen to give rise to a generic conflict of interests between shareholders and managers. This conflict fundamentally results from the different income base of the two types of agents, once aggregate market clearing conditions are taken into account. An optimal contract exists resulting in an observational equivalence between the delegated management economy and the standard representative agent business cycle model. The optimal contract, however, appears to be miles away from standard practice: the manager's remuneration is tied to the firm's total income net of investment expenses, abstracting totally from wage costs. In order to align the interest of a manager more conventionally remunerated on the basis of the firm's operating results to those of stockholder-workers, the manager must be made nearly risk neutral. We show the limited power of convex contracts to accomplish this goal and the necessity, if the manager is too risk averse (log or higher than log), of considerably downplaying the incentive features of his remuneration. The difficulty in reconciling the viewpoints of a manager with powers of delegation and of a representative firm owner casts doubt on the descriptive validity of the macro-dynamics highlighted in the representative agent macroeconomic model.business cycles; delegated management; contracting

Macroeconomic Frictions: What have we Learned from the Real Business Cycle Research Programm ?

One interpretation of the RBC research program is that it was meant to identify and incorporate into dynamic general equilibrium models those market imperfections which are most relevant for macroeconomic theory and policy. This paper reviews the methodological basis for this interpretation. It then discusses the empirical foundations for some of the many frictions that have found their way into RBC models including efficiency wages, labour contracts, nominal price rigidities, limited market participation, imperfect competition and expectational errors. We find that the 'necessity' of these frictions is better established in some cases than in others. While one is lead to the prediction that the 'next neo-classical synthesis' will be a dynamic stochastic general equilibrium with frictions, it is premature to decide which specific friction will necessarily be taken on board.Business cycle; neo-classical synthesis; market frictions