A Direct Proof of BCFW Recursion for Twistor-Strings

This paper gives a direct proof that the leading trace part of the genus zero twistor-string path integral obeys the BCFW recursion relation. This is the first complete proof that the twistor-string correctly computes all tree amplitudes in maximally supersymmetric Yang-Mills theory. The recursion has a beautiful geometric interpretation in twistor space that closely reflects the structure of BCFW recursion in momentum space, both on the one hand as a relation purely among tree amplitudes with shifted external momenta, and on the other as a relation between tree amplitudes and leading singularities of higher loop amplitudes. The proof works purely at the level of the string path integral and is intimately related to the recursive structure of boundary divisors in the moduli space of stable maps to CP^3.Comment: 23 pages, 5 figure

Chandra Observations of WR147 Reveal a Double X-ray Source

We report the first results from deep X-ray observations of the Wolf-Rayet binary system WR147 with the Chandra HETG. Analysis of the zeroth order data reveals that WR147 is a double X-ray source. The northern counterpart is likely associated with the colliding wind region, while the southern component is certainly identified with the WN star in this massive binary. The latter is the source of high energy X-rays (including the Fe K_alpha complex at 6.67 keV) whose production mechanism is yet unclear. For the first time, X-rays are observed directly from a WR star in a binary system.Comment: 15 pages, 3 figures, To Appear in The Astrophysical Journal Letter

[Review of] Bienvenido L. Lumbera. Tagalog Poetry: 1570-1898

Bienvenido Lumbera, in his Preface to this survey of Tagalog poetry, apologizes for the shortcomings of his book. Originally written twenty years ago as a doctoral dissertation, it does not take into account new information on Tagalog poetry and its discussion of precolonial poetry does not include new data on the oral poetry of contemporary Filipino groups. I have bailed myself out, say Lumbera, by persuading myself that many scholarly sins could be forgiven under the rubric of \u27pioneering.\u27\u27\u27 And indeed these omissions can be forgiven for what the reader gains in return is a pioneering study describing and analyzing the development of Tagalog poetry

Chemical potential and compressibility of quantum Hall bilayer excitons

This paper considers a system of two parallel quantum Hall layers with total filling factor $0$ or $1$. When the distance between the layers is small enough, electrons and holes in opposite layers form inter-layer excitons, which have a finite effective mass and interact via a dipole-dipole potential. Results are presented for the chemical potential $\mu$ of the resulting bosonic system as a function of the exciton concentration $n$ and the interlayer separation $d$. Both $\mu$ and the interlayer capacitance have an unusual nonmonotonic dependence on $d$, owing to the interplay between an increasing dipole moment and an increasing effective mass with increasing $d$. A phase transition between superfluid and Wigner crystal phases is shown to occur at $d \propto n^{-1/10}$. Results are derived first via simple intuitive arguments, and then verified with more careful analytic derivations and numeric calculations.Comment: 7 pages, 5 figures; improved discussion and references; published versio

The price of anarchy in basketball

Optimizing the performance of a basketball offense may be viewed as a network problem, wherein each play represents a "pathway" through which the ball and players may move from origin (the in-bounds pass) to goal (the basket). Effective field goal percentages from the resulting shot attempts can be used to characterize the efficiency of each pathway. Inspired by recent discussions of the "price of anarchy" in traffic networks, this paper makes a formal analogy between a basketball offense and a simplified traffic network. The analysis suggests that there may be a significant difference between taking the highest-percentage shot each time down the court and playing the most efficient possible game. There may also be an analogue of Braess's Paradox in basketball, such that removing a key player from a team can result in the improvement of the team's offensive efficiency.Comment: 9 pages, 6 figures; extra example and some discussion added; formatting errors fixed; typo in Sec. IIID fixe

Countersong: Rising or Falling

A recording, analysis and poetic translation of countersong between two Hermit thrushes (Catharus guttatis) recorded in the mountains of Northern New Mexico (United States) on 19 July 2015