7,244 research outputs found
A dilogarithmic integral arising in quantum field theory
Recently, an interesting dilogarithmic integral arising in quantum field
theory has been closed-form evaluated in terms of the Clausen function
by Coffey [J. Math. Phys.} 49 (2008), 093508]. It
represents the volume of an ideal tetrahedron in hyperbolic space and is
involved in two intriguing equivalent conjectures of Borwein and Broadhurst. It
is shown here, by simple and direct arguments, that this integral can be
expressed by the triplet of the Clausen function values which are involved in
one of the two above-mentioned conjectures.Comment: 6 page
An orientable, stabilized balloon-borne gondola for around-the-world flights
A system capable of pointing a balloon-borne telescope at selected celestial objects to an accuracy of approximately 10 arc minutes for an extended period (weeks to months) without reliance on telemetry is described. A unique combination of a sun/star tracker, an on-board computer, and a gyrocompass is utilized for navigation, source acquisition and tracking, and data compression and recording. The possibilities for intelligent activities by the computer are also discussed
Scalar Field Theory at Finite Temperature in D=2+1
We discuss the theory defined in -dimensional space-time and
assume that the system is in equilibrium with a thermal bath at temperature
. We use the expansion and the method of the composite
operator (CJT) for summing a large set of Feynman graphs.We demonstrate
explicitly the Coleman-Mermin-Wagner theorem at finite temperature.Comment: 12 pages, 1 figure. To be published in Journal Mathematical Physics,
typos adde
The end of HIV: Still a very long way to go, but progress continues.
In an Editorial accompanying PLOS Medicine's Special Issue on Advances in Prevention, Treatment and Cure of HIV/AIDS, Guest Editors Steven Deeks, Sharon Lewin, and Linda-Gail Bekker discuss priorities in the field and the content of the issue
Rapid fluctuations in the high-energy X-ray flux from a source in Crux
Balloonborne X ray telescopic observations of two point sources in Cru
Applications of DFT to the theory of twentieth-century harmony
Music theorists have only recently, following groundbreaking work by Quinn, recognized the potential for the DFT on pcsets, initially proposed by Lewin, to serve as the foundation of a theory of harmony for the twentieth century. This paper investigates pcset âarithmeticâ â subset structure, transpositional combination, and interval content â through the lens of the DFT. It discusses relationships between interval classes and DFT magnitudes, considers special properties of dyads, pcset products, and generated collections, and suggest methods of using the DFT in analysis, including interpreting DFT magnitudes, using phase spaces to understand subset structure, and interpreting the DFT of Lewinâs interval function. Webernâs op. 5/4 and Bartokâs String Quartet 4, iv, are discussed.Accepted manuscrip
Scalar one-loop integrals for QCD
We construct a basis set of infra-red and/or collinearly divergent scalar
one-loop integrals and give analytic formulas, for tadpole, bubble, triangle
and box integrals, regulating the divergences (ultra-violet, infra-red or
collinear) by regularization in dimensions. For scalar triangle
integrals we give results for our basis set containing 6 divergent integrals.
For scalar box integrals we give results for our basis set containing 16
divergent integrals. We provide analytic results for the 5 divergent box
integrals in the basis set which are missing in the literature. Building on the
work of van Oldenborgh, a general, publicly available code has been
constructed, which calculates both finite and divergent one-loop integrals. The
code returns the coefficients of and
as complex numbers for an arbitrary tadpole, bubble, triangle or box integral.Comment: 27 pages, 5 figures, associated fortran code available at
http://qcdloop.fnal.gov/. New version corrects typographical error in Eq. 5.
XMM-Newton Spectroscopy of the Accretion-Driven Millisecond X-ray Pulsar XTE J1751-305 in Outburst
We present an analysis of the first high-resolution spectra measured from an
accretion-driven millisecond X-ray pulsar in outburst. We observed XTE
J1751-305 with XMM-Newton on 2002 April 7 for approximately 35 ksec. Using a
simple absorbed blackbody plus power-law model, we measure an unabsorbed flux
of (6.6 +/- 0.1) * 10^(-10) erg/cm^2/s (0.5--10.0 keV). A hard power-law
component (Gamma = 1.44 +/- 0.01) contributes 83% of the unabsorbed flux in the
0.5-10.0 keV band, but a blackbody component (kT = 1.05 +/- 0.01 keV) is
required. We find no clear evidence for narrow or broad emission or absorption
lines in the time-averaged spectra, and the sensitivity of this observation has
allowed us to set constraining upper-limits on the strength of important
features. The lack of line features is at odds with spectra measured from some
other X-ray binaries which share some similarities with XTE J1751-305. We
discuss the implications of these findings on the accretion flow geometry in
XTE J1751-305.Comment: 5 pages, 3 figures (2 color). ApJ Letters, accepted. Uses
emulateapj.st
Ground state of two electrons on concentric spheres
We extend our analysis of two electrons on a sphere [Phys. Rev. A {\bf 79},
062517 (2009); Phys. Rev. Lett. {\bf 103}, 123008 (2009)] to electrons on
concentric spheres with different radii. The strengths and weaknesses of
several electronic structure models are analyzed, ranging from the mean-field
approximation (restricted and unrestricted Hartree-Fock solutions) to
configuration interaction expansion, leading to near-exact wave functions and
energies. The M{\o}ller-Plesset energy corrections (up to third-order) and the
asymptotic expansion for the large-spheres regime are also considered. We also
study the position intracules derived from approximate and exact wave
functions. We find evidence for the existence of a long-range Coulomb hole in
the large-spheres regime, and infer that unrestricted Hartree-Fock theory
over-localizes the electrons.Comment: 10 pages, 10 figure
Constraining Alternate Models of Black Holes: Type I X-ray Bursts on Accreting Fermion-Fermion and Boson-Fermion Stars
The existence of black holes remains open to doubt until other conceivable
options are excluded. With this motivation, we consider a model of a compact
star in which most of the mass consists of dark particles of some kind, and a
small fraction of the mass is in the form of ordinary nucleonic gas. The gas
does not interact with the dark matter other than via gravity, but collects at
the center as a separate fermionic fluid component. Depending on whether the
dark mass is made of fermions or bosons, the objects may be called
fermion-fermion stars or boson-fermion stars, respectively. For appropriate
choices of the mass of the dark matter particles, these objects are viable
models of black hole candidates in X-ray binaries. We consider models with a
dark mass of 10 solar masses and a range of gas mass from 10^{-6} to nearly one
solar mass, and analyse the bursting properties of the models when they accrete
gas. We show that all the models would experience thermonuclear Type I X-ray
bursts at appropriate mass accretion rates. Since no Type I bursts have been
reported from black hole candidates, the models are ruled out. The case for
identifying black hole candidates in X-ray binaries as true black holes is thus
strengthened.Comment: 29 pages, 7 figures, to appear in The Astrophysical Journa
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