Improving alpha_QED(M_Z^2) and the charm mass by analytic continuation

The standard determination of the QED coupling on the Z pole is performed using the latest available data for R. The direct application of analytic continuation techniques is found not to improve the accuracy of the value of \alpha(M_Z^2). However they help to resolve an ambiguity in the values of R in the energy region \sqrt{s} < 2 GeV, which, in turn, reduces the uncertainty in \alpha(M_Z^2). Moreover, they provide a sensitive determination of the mass of the charm quark. The favoured solution, which uses the inclusive data for R for \sqrt{s} < 2 GeV, has a pole mass m_c = 1.33-1.40 GeV and \alpha^{-1}(M_Z^2) = 128.972 +/- 0.026; whereas if the sum of the exclusive channels is used to determine R in this region, we find \alpha^{-1}(M_Z^2) = 128.941 +/- 0.029.Comment: LaTeX, 23 pages, 7 eps figures, typos removed, accepted by Eur. Phys. J.

A novel and sensitive method for measuring very weak magnetic fields of DA white dwarfs: A search for a magnetic field at the 250 G level in 40 Eri B

Searches for magnetic fields in white dwarfs have clarified both the frequency of occurrence and the global structure of the fields found down to field strengths of the order of 500 kG. Below this level, the situation is still very unclear. We are studying the weakest fields found in white dwarfs to determine the frequency of such fields and their structure. We describe a very sensitive new method of measuring such fields in DA (H-rich) white dwarfs, and search for a field in the brightest such star, 40 Eri B. Our new method makes use of the strongly enhanced polarisation signal in the sharp core of Halpha. We find that with one-hour integrations with the high-resolution spectropolarimeter ESPaDOnS on the 3.6-m CFHT, we can reach a standard error fo the longitudinal field of about 85 G, the smallest error ever achieved for any white dwarf. Nevertheless, we do not detect a magnetic field in this star. Observations with ISIS at the WHT, and the Main Stellar Spectrograph at the SAO, support the absence of a field at somewhat lower precision. The new method is very efficient; it is shown that for suitable DA stars the integration time, with ESPaDOnS on a 3.6-m telescope, to reach a 500 G standard error on a white dwarf of V = 12.5, is about half an hour, about the same as the time required on an ESO 8-m telescope with FORS using conventional low-resolution spectropolarimetry.Comment: Accepted by Astronomy & Astrophysics on 20/06/201

Bryophytes of Uganda : 1., BBS Tropical Bryology Group expeditions, 1996-1998 ; introduction and collecting sites

The British Bryological Society Tropical Bryology Group (TBG) undertook three expeditions to Uganda, in Jan-Feb 1996, Jan-Feb 1997 and June-Jul 1998. Collections were made from 134 sites, mainly from national parks and forest reserves in western and southern Uganda

Discovery of an extremely weak magnetic field in the white dwarf LTT 16093 = WD2047+372

Magnetic fields have been detected in several hundred white dwarfs, with strengths ranging from a few kG to several hundred MG. Only a few of the known fields have a mean magnetic field modulus below about 1 MG. We are searching for new examples of magnetic white dwarfs with very weak fields, and trying to model the few known examples. Our search is intended to be sensitive enough to detect fields at the few kG level. We have been surveying bright white dwarfs for very weak fields using spectropolarimeters at the Canada-France-Hawaii telescope, the William Herschel telescope, the European Southern Observatory, and the Russian Special Astrophysical Observatory. We discuss in some detail tests of the WHT spectropolarimeter ISIS using the known magnetic strong-field Ap star HD 215441 (Babcock's star) and the long-period Ap star HD 201601 (gamma Equ). We report the discovery of a field with a mean field modulus of about 57 kG in the white dwarf LTT 16093 = WD2047+372. The field is clearly detected through the Zeeman splitting of Halpha seen in two separate circularly polarised spectra from two different spectropolarimeters. Zeeman circular polarisation is also detected, but only barely above the 3 sigma level. The discovery of this field is significant because it is the third weakest field ever unambiguously discovered in a white dwarf, while still being large enough that we should be able to model the field structure in some detail with future observations

A Mission to Test the Pioneer Anomaly

Analysis of the radio tracking data from the Pioneer 10/11 spacecraft has consistently indicated the presence of an anomalous small Doppler frequency drift. The drift can be interpreted as being due to a constant acceleration of a_P= (8.74 +/- 1.33) x 10^{-8} cm/s^2 directed towards the Sun. Although it is suspected that there is a systematic origin to the effect, none has been found. The nature of this anomaly has become of growing interest in the fields of relativistic cosmology, astro- and gravitational physics as well as in the areas of spacecraft design and high-precision navigation. We present a concept for a designated deep-space mission to test the discovered anomaly. A number of critical requirements and design considerations for such a mission are outlined and addressed.Comment: Final changes for publication. Honorable Mention, 2002 Gravity Research Foundation Essay

Nucleon-Nucleon Interactions from Dispersion Relations: Coupled Partial Waves

We consider nucleon-nucleon interactions from chiral effective field theory applying the N/D method. The case of coupled partial waves is now treated, extending Ref. [1] where the uncoupled case was studied. As a result three N/D elastic-like equations have to be solved for every set of three independent partial waves coupled. As in the previous reference the input for this method is the discontinuity along the left-hand cut of the nucleon-nucleon partial wave amplitudes. It can be calculated perturbatively in chiral perturbation theory because it involves only irreducible two-nucleon intermediate states. We apply here our method to the leading order result consisting of one-pion exchange as the source for the discontinuity along the left-hand cut. The linear integral equations for the N/D method must be solved in the presence of L - 1 constraints, with L the orbital angular momentum, in order to satisfy the proper threshold behavior for L>= 2. We dedicate special attention to satisfy the requirements of unitarity in coupled channels. We also focus on the specific issue of the deuteron pole position in the 3S1-3D1 scattering. Our final amplitudes are based on dispersion relations and chiral effective field theory, being independent of any explicit regulator. They are amenable to a systematic improvement order by order in the chiral expansion.Comment: 11 pages. Extends the work of uncoupled partial waves of M. Albaladejo and J. A. Oller, Phys. Rev. C 84, 054009 (2011) to the case of coupled partial waves. This version matches the published version. Discussion about the deuteron enlarged. Some references adde

Extracting the Proton ubar content from pp->Direct Photon plus Jet Cross Sections

An analysis procedure is proposed to measure the antiquark distributions in the proton over the region 0.01 < x < 0.1. The procedure involves the measurement of high p_t asymmetric direct photon and jet final states in pp interactions. This measurement can be made at the RHIC collider running in pp mode at an energy of sqrt(s)=500 GeV/c. This analysis identifies a region of phase space where the contribution from quark-antiquark annihilation uncharacteristically approaches the magnitude of the contribution from the leading process, quark-gluon Compton scattering. The forward-backward angular asymmetry in the parton center of mass is sensitive to the antiquark content of the proton and the ubar parton density function can be extracted.Comment: 21 pages, 7 figure