Masses and widths of the rho(770)

Isospin violation in the $\rho(770)$ mass and width is considered within the $S$ matrix approach using combined fits to the $e^+e^- \to\pi^+\pi^-$ and $\tau^- \to \nu_{\tau}\pi^-\pi^0$ data performed by the ALEPH collaboration. We show that the pole position following from the parameters obtained from the ALEPH fits are not sensitive to the details of the parametrization. In this context, we have found that the pole mass difference and the pole width difference between the charged and neutral $\rho$ are consistent with zero. We show that a one loop calculation including vector, axial vector and pseudo-scalar mesons can satisfactorily describe the observed isospin breaking. We also give an estimate for the mass difference between the neutral and charged states of the $a_1(1260)$.Comment: 8 pages, 1 figur

How well do monetary fundamentals forecast exchange rates?

For many years after the seminal work of the Meese and Rogoff (1983a), conventional wisdom held that exchange rates could not be forecast from monetary fundamentals. Monetary models of exchange rate determination were generally unable to beat even a naive no-change model in out-of-sample forecasting. More recently, the use of sophisticated econometric techniques, panel data, and long spans of data has convinced some researchers (Mark and Sul, 2001) that monetary models can forecast a small, but statistically significant part of the variation in exchange rates. Others remain skeptical, however (Rapach and Wohar, 2001b; Faust, Rogers, and Wright, 2001). It remains a puzzle why even the most supportive studies find such a small predictable component to exchange rates. This article reviews the literature on forecasting exchange rates with monetary fundamentals and speculates as to why it remains so difficult.Foreign exchange rates ; Forecasting

Antigenic variation in the African trypanosome: molecular mechanisms and phenotypic complexity

Antigenic variation is an immune evasion strategy that has evolved in viral, bacterial and protistan pathogens. In the African trypanosome this involves stochastic switches in the composition of a variant surface glycoprotein (VSG) coat, using a massive archive of silent VSG genes to change the identity of the single VSG expressed at a time. VSG switching is driven primarily by recombination reactions that move silent VSGs into specialized expression sites, though transcription-based switching can also occur. Here we discuss what is being revealed about the machinery that underlies these switching mechanisms, including what parallels can be drawn with other pathogens. In addition, we discuss how such switching reactions act in a hierarchy and contribute to pathogen survival in the face of immune attack, including the establishment and maintenance of chronic infections, leading to host-host transmission

How well do monetary fundamentals forecast exchange rates?

For many years after the seminal work of Meese and Rogoff (1983a), conventional wisdom held that exchange rates could not be forecast from monetary fundamentals. Monetary models of exchange rate determination were generally unable to beat even a naïve no-change model in out-of-sample forecasting. More recently, the use of sophisticated econometric techniques, panel data, and long spans of data has convinced some researchers (Mark and Sul, 2001) that monetary models can forecast a small, but statistically significant part of the variation in exchange rates. Others remain skeptical, however (Rapach and Wohar, 2001b; Faust, Rogers, and Wright, 2001). It remains a puzzle why even the most supportive studies find such a small predictable component to exchange rates. This article reviews the literature on forecasting exchange rates with monetary fundamentals and speculates as to why it remains so difficult.Forecasting ; Foreign exchange rates

Algebraic deformations of toric varieties I. General constructions

We construct and study noncommutative deformations of toric varieties by combining techniques from toric geometry, isospectral deformations, and noncommutative geometry in braided monoidal categories. Our approach utilizes the same fan structure of the variety but deforms the underlying embedded algebraic torus. We develop a sheaf theory using techniques from noncommutative algebraic geometry. The cases of projective varieties are studied in detail, and several explicit examples are worked out, including new noncommutative deformations of Grassmann and flag varieties. Our constructions set up the basic ingredients for thorough study of instantons on noncommutative toric varieties, which will be the subject of the sequel to this paper.Comment: 54 pages; v2: Presentation of Grassmann and flag varieties improved, minor corrections; v3: Presentation of some parts streamlined, minor corrections, references added; final version to appear in Advances in Mathematic

On Scale Invariance and Anomalies in Quantum Mechanics

We re-consider the quantum mechanics of scale invariant potentials in two dimensions. The breaking of scale invariance by quantum effects is analyzed by the explicit evaluation of the phase shift and the self-adjoint extension method. We argue that the breaking of scale invariance reported in the literature for the $\delta$(r) potential, is an example of explicit and not an anomaly or quantum mechanical symmetry breaking.Comment: 15 pp in latex, no figure

Algebraic deformations of toric varieties II. Noncommutative instantons

We continue our study of the noncommutative algebraic and differential geometry of a particular class of deformations of toric varieties, focusing on aspects pertinent to the construction and enumeration of noncommutative instantons on these varieties. We develop a noncommutative version of twistor theory, which introduces a new example of a noncommutative four-sphere. We develop a braided version of the ADHM construction and show that it parametrizes a certain moduli space of framed torsion free sheaves on a noncommutative projective plane. We use these constructions to explicitly build instanton gauge bundles with canonical connections on the noncommutative four-sphere that satisfy appropriate anti-selfduality equations. We construct projective moduli spaces for the torsion free sheaves and demonstrate that they are smooth. We define equivariant partition functions of these moduli spaces, finding that they coincide with the usual instanton partition functions for supersymmetric gauge theories on C^2.Comment: 62 pages; v2: typos corrected, references updated; Final version to be published in Advances in Theoretical and Mathematical Physic

Tests of flavor symmetry in J/psi decays

We use SU(3) flavor symmetry to analyze the $PP', VP$ and baryon-antibaryon decays of $J/\psi$. Both, the SU(3)-invariant and -violating contributions are considered. Particular attention is paid to the interference of the electromagnetic and strong amplitudes.Comment: 8 pages, latex. Talk given at CAM-94 Physics Meetin

A Tiltable Single-Shot Miniature Dilution Refrigerator for Astrophysical Applications

We present a 3He / 4He dilution refrigerator designed for cooling astronomical mm-wave telescope receivers to around 100 mK. Used in combination with a Gifford-McMahon closed-cycle refrigerator, 4He and 3He sorption-pumped refrigerators, our cryogen-free system is capable of achieving 2 microW cooling power at 87 mK. A receiver attached directly to the telescope optics is required to rotate with respect to the downward direction. This scenario, of variable tilt, has proved difficult for typical dilution refrigerators, but our design has a geometry chosen to allow tilt to 45 degrees and beyond.Comment: 7 pages, 11 figures. Accepted by Cryogenic