Improving the locality of the overlap Dirac operator via approximate solutions of the Ginsparg-Wilson relation

We determine the free field hypercubic Dirac operator which is optimally close to satisfying the Ginsparg-Wilson relation. Inserting this operator into the overlap formula, we show that the analytic locality bound on the resulting overlap Dirac operator is substantially stronger than in the standard case. This improvement generally persists in gauge backgrounds when the plaquette variables are all close to unity.Comment: 3 pages, contributed to Proceedings of Lattice2003(chiral

Three Dimensional Periodic U(1)U(1) Gauge Theory and Strings

It will be argued that among the known systems in three dimensions that have string like excitations periodic U(1) pure gauge theories are the most likely candidates to lead to a string representation of their universal properties. Some recent work with F. David will also be reviewed.Comment: 5

Families index theory for Overlap lattice Dirac operator. I

The index bundle of the Overlap lattice Dirac operator over the orbit space of lattice gauge fields is introduced and studied. Obstructions to the vanishing of gauge anomalies in the Overlap formulation of lattice chiral gauge theory have a natural description in this context. Our main result is a formula for the topological charge (integrated Chern character) of the index bundle over even-dimensional spheres in the orbit space. It reduces under suitable conditions to the topological charge of the usual (continuum) index bundle in the classical continuum limit (this is announced and sketched here; the details will be given in a forthcoming paper). Thus we see that topology of the index bundle of the Dirac operator over the gauge field orbit space can be captured in a finite-dimensional lattice setting.Comment: Latex, 23 pages. v4: minor improvements, results unchanged; to appear in Nucl.Phys.

Fermionic topological charge of families of lattice gauge fields

Topological charge of families of lattice gauge fields is defined fermionically via families index theory for the overlap Dirac operator. Certain obstructions to gauge invariance of the overlap chiral fermion determinant, as well as the lattice analogues of certain obstructions to gauge fixings without the Gribov problem, have natural descriptions in this context.Comment: 4p., Lattice2002(chiral) (+ one paragraph not included in the proceedings version for length reasons

The UK Approach to Insuring Defined Benefit Pension Plans

The United Kingdom established the Pension Protection Fund (PPF) in 2005 to guarantee defined benefit pensions. We model the PPF and show that it is likely to face many years of low claims interspersed irregularly with periods of very large claims. There is a significant chance that these claims will be so large that the PPF will default on its liabilities, leaving the Government with no option but to bail it out. The cause of this problem is the double impact of a fall in equity prices on the PPF: it makes sponsor firms more likely to default, and it makes defaulted plans more likely to be underfunded. We use our model to derive a fair premium for PPF insurance under different circumstances, to estimate the extent of cross-subsidies in the PPF between strong and weak sponsors and to show that risk rated premiums are unlikely to have a substantial effect on either the size or the lumpiness of claims unless they are so powerful that they force weaker sponsors to cut fund deficits and improve the match between assets and liabilities

Global obstructions to gauge-invariance in chiral gauge theory on the lattice

It is shown that certain global obstructions to gauge-invariance in chiral gauge theory, described in the continuum by Alvarez-Gaume and Ginsparg, are exactly reproduced on the lattice in the Overlap formulation at small non-zero lattice spacing (i.e. close to the classical continuum limit). As a consequence, the continuum anomaly cancellation condition $d_R^{abc}=0$ is seen to be a necessary (although not necessarily sufficient) condition for anomaly cancellation on the lattice in the Overlap formulation.Comment: 31 pages, latex. v4: A few minor corrections, to appear in Nucl. Phys.

Thermal Infrared Sensor (TIRS) Instrument Thermal Subsystem Design and Lessons Learned

The Thermal Infrared Sensor (TIRS) is one of two instruments on the Landsat Data Continuity Mission (LDCM), which is scheduled to launch in February of 2013. The TIRS instrument was officially added to the mission later in the flow, which led to a highly aggressive schedule that became one of the main drivers during instrument development. The thermal subsystem design of the TIRS Sensor Unit is comprised of five thermal zones which range in temperature from less than 43 Kelvin to 330 Kelvin. Most zones are proportional heater controlled, and all are within a volume of 35 cu.ft. A two-stage cryocooler is used to cool the "cold stage" including three QWIP detectors to less than 43 Kelvin, and cool the "warm stage" to 105 Kelvin. The excess power dissipation from the cryocooler is rejected via ammonia transport heat pipes to a dedicated Cryocooler Radiator with embedded ammonia heat pipes. The cryogenic subsystem includes a series of shells used to radiatively and conductively isolate the cold stage from the warmer surroundings. The Optical System (telescope) is passively cooled to 180-190 Kelvin using a "thermal link" (comprised of a Flexible Conductive Thermal Strap and an APG Bar) which couples the telescope stage to a dedicated radiator with embedded ethane heat pipes. The Scene Select Mechanism, which is responsible for moving the Scene Select Mirror to three distinct positions (including Nadir, Space, and On-board Black Body Calibrator pointing), runs nominally at 278 Kelvin and is thermally isolated from the cryogenic thermal zones. The On-board Black Body Calibrator requires a dedicated radiator which allows for a temperature range of 260-330 Kelvin at the Source. The detectors are powered by the FPE Box, which is mounted to the nadir external surface of the composite honeycomb structure. There are two additional electronics boxes which are wet-mounted directly to the spacecraft shear panel, the Main Electronics Box and Cryocooler Electronics Box; thermal control of these boxes is the responsibility of Orbital Sciences Corporation, the spacecraft developer. The TIRS thermal subsystem design was successfully verified during months of testing campaign, from component & subsystem level to two instrument-level thermal vacuum tests. The Instrument, despite an aggressive schedule, was delivered to the spacecraft vendor in February of 2012 and is currently undergoing the final stages of spacecraft environmental testing in preparation for launch

Testing universality and the fractional power prescription for the staggered fermion determinant

In [Phys.Rev.Lett.92:162002 (2004), hep-lat/0312025] expressions for the continuous Euclidean time limits of various lattice fermion determinants were derived and compared in order to test universality expectations in Lattice QCD. Here we review that work with emphasis on its relevance for assessing the fractional power prescription for the determinant in dynamical staggered fermion simulations. Some new supplementary material is presented; in particular the status of the "universality anomaly" is clarified: it is shown to be gauge field-independent and therefore physically inconsequential.Comment: 7 pages, contributed to Lattice2004(plenary