121175185
Gluon effects and nonet mixing in the current quark picture
Abstract The effects on the meson mass spectrum of gluon interactions, and in particular of quark annihilation diagrams, are investigated in the current quark framework. The resulting mixing scheme leads to mixing angles θ p ≅ −13° and θ V ≅ − 52° for the pseudoscalar and vector nonets respectively, in moderate agreement with present data on radiative decays. For virtual electromagnetic processes additional gluon diagrams play a role. In η → 3 π the net effect is to almost double the current algebra prediction, while in ω → 2 π the ω → ϱ 0 transition amplitude is correctly predicted in both sign and magnitude. The relation between the Hamiltonian approach and the U(1) problem, as formulated in terms of axial divergences, is briefly discussed.
122803009
Gauge invariance and covariant Reggeization
SummaryBy the use of gauge-invariant couplings the formalism of covariant Reggeization is extended to deal with processes involving photons. Particular attention is paid to pion photoproduction, where Reggeized pion and nucleon exchange are shown to connect smoothly on to the elementary exchanges both from the form of the vertex couplings and form their respective contributions to the invariant amplitudes. In the latter approach the double-pole structure of the Coulomb Born terms is correctly reproduced. Pion Compton scattering is also studied as an archetypal two-photon process: here the problem of Pomeron Reggeization is similarly resolved. The Froissart-Gribov continuation is briefly discussed, as is the forward peak in π+ photoproduction.RiassuntoUsando gli accoppiamenti di invarianti di gauge si estende il formalismo della reggeizzazione covariante a trattare processi che coinvolgono i fotoni. Si dedica particolare attenzione alla fotoproduzione dei pioni, dimostrando che gli scambi reggeizzati del pione e del nucleone si raccordano agli scambi elementari sia per la forma degli accoppiamenti di vertice sia pei loro rispettivi contributi alle ampiezze invarianti. In quest'ultimo approccio si riproduce correttamente la struttura a poli doppi dei termini di Born coulombiani. Si studia anche lo scattering Compton del pione come un processo archetipo a due fotoni: in questo caso si risolve in modo analogo il problema della reggeizzazione del pomerone. Si discute brevemente la continuazione di Froissart-Gribov, come pure si discute il picco in avanti nella fotoproduzione del π+.РезюмеИспользуя калибровочно инвариантные связи, формлизм ковариантной реджеизации распространяется, чтобы рассмотреть процессы, включающие фотоны. Особенное внимание уделяется фоторождению пионов, где, как показывается, реджеизованный пионный и нуклонный обмен связаны плавно с элементарными обменами и из формы вершинных связей и из их сооттветствующих вкладов в инвариантные амплитуды. В последнем подходе корректно воспроизводится структура двойных полюсов кулоновских борновских членов. Также исследуется комптоновское рассеяние пионов, как архитипичный двух-фотонный процесс: где проблема реджеизации Померона разрешается аналогично. Вкратце обсуждается продолжение Фройссарта-Грибова, которое представляет пик вперед в π+ фоторождении.
42992493
Interpolating Lagrangians and SU(2) gauge theory on the lattice.
We apply the linear {delta} expansion to non-Abelian gauge theory on the lattice, with SU(2) as the gauge group. We establish an appropriate parametrization and evaluate the average plaquette energy {ital E}{sub {ital P}} to {ital O}({delta}). As a check on our results, we recover the large-{beta} expansion up to {ital O}(1/{beta}{sup 2}), which involves some {ital O}({delta}{sup 2}) contributions. Using these contributions we construct a variant of the 1/{beta} expansion which gives a good fit to the data down to the transition region.
117287068
A New Approach to QCD Sum Rules and Inclusive $\tau$ Decay
We show that renormalization group improvement, making use of analyticity and the structure of the operator product expansion, combined with a non-perturbative expansion method allows one to describe quarkonium states via QCD sum rules without the need for explicit power corrections. This technique also allows an accurate determination of parameters related to the inclusive decay of the $\tau$ lepton.
120377044
Electroproduction of isolated protons at high energy as a probe of the proton wave function in QCD
AbstractWe investigate the feasibility of using the process
$$eq \to ep\bar q\bar q$$
 as a means of determining the proton wave function which governs all exclusive processes involving protons. The calculation is performed in the limitŴ2≪Q2, whereŴ is the CM energy of the subprocess. The resulting expressions simplify considerably when an additional constraint is imposed excluding any hadrons accompanying the proton from a cone around it of half-angle θ≪1. However, a direct determination is still only possible in the case of a symmetric wave-function. A numerical exploration of the sensitivity of the cross-section to the parameters of an ansatz for the wave function shows a strong dependence on components which are not totally symmetric.
118655103
Comment on New ansatz for metric operator calculation in pseudo-Hermitian field theory
In a recent Brief Report by Shalaby, a new first-order perturbative calculation of the metric operator for an $i{\ensuremath{\phi}}^{3}$ scalar field theory is given. It is claimed that the incorporation of derivative terms in the ansatz for the metric operator results in a local solution, in contrast to the nonlocal solution previously obtained by Bender, Brody, and Jones. Unfortunately, Shalaby's calculation is not valid because of sign errors.
56264440
The current population of benchmark brown dwarfs
The number of brown dwarfs (BDs) now identified tops 700. Yet our understanding of these cool objects is still lacking, and models are struggling to accurately reproduce observations. What is needed is a method of calibrating the models, BDs whose properties (e.g. age, mass, distance, metallicity) that can be independently determined can provide such calibration. The ability to calculate properties based on observables is set to be of vital importance if we are to be able to measure the properties of fainter, more distant populations of BDs that near-future surveys will reveal, for which ground based spectroscopic studies will become increasingly difficult. We present here the state of the current population of age benchmark brown dwarfs.
14308791
Constraining the difference in convective blueshift between the components of alpha Centauri with precise radial velocities
New radial velocities of Cen A & B obtained in the framework the Anglo-Australian Planet Search programme as well as in the CORALIE programme are added to those by Endl et al. (2001) to improve the pre- cision of the orbital parameters. The resulting masses are 1:105 0:0070 M and 0:934 0:0061 M for A and B respectively. The factors limiting how accurately these masses can be derived from a combined visual-spectroscopic solution are investigated. The total eect of the convective blueshift and the gravitational redshift is also inves- tigated and estimated to dier by 215 8m s 1 between the components. This suggests that the dierence in convective blueshift between the components is much smaller than predicted from current hydrodynamical model atmosphere calculations.
17172233
A JUPITER-LIKE PLANET ORBITING THE NEARBY M DWARF GJ 832*
Precision Doppler velocity measurements from the Anglo-Australian Telescope reveal a planet with a 9.4 ± 0.4 year period orbiting the M1.5 dwarf GJ 832. Within measurement uncertainty the orbit is circular, and the minimum mass (msin i) of the planet is 0.64 ± 0.06 M JUP. GJ 832 appears to be depleted in metals by at least 50% relative to the Sun, as are a significant fraction of the M dwarfs known to host exoplanets. GJ 832 adds another Jupiter-mass planet to the known census of M dwarf exoplanets, which currently includes a significant number of Neptune-mass planets. GJ 832 is an excellent candidate for astrometric orbit determination with αsin i = 0.95 mas. GJ 832b has the second largest angular distance from its star among radial velocity detected exoplanets (0.69 arcsec) making it a potentially interesting target for future direct detection.
15452372
High-eccentricity planets from the Anglo-Australian Planet Search
We report Doppler measurements of the stars HD 187085 and HD 20782 which indicate two high eccentricity low-mass companions to the stars. We find HD 187085 has a Jupiter-mass companion with a �1000 d orbit. Our formal ‘best fit’ solution suggests an eccentricity of 0.47, however, it does not sample the periastron passage of the companion and we find that orbital solutions with eccentricities between 0.1 and 0.8 give only slightly poorer fits (based on RMS and � 2) and are thus plausible. Observations made during periastron passage in 2007 June should allow for the reliable determination of the orbital eccentricity for the companion to HD 187085. Our dataset for HD 20782 does sample periastron and so the orbit for its companion can be more reliably determined. We find the companion to HD 20782 has M sin i = 1.77±0.22 MJup, an orbital period of 595.86±0.03 d and an orbit with an eccentricity of 0.92±0.03. The detection of such high-eccentricity (and relatively low velocity amplitude) exoplanets appears to be facilitated by the long-term precision of the Anglo-Australian Planet Search. Looking at exoplanet detections as a whole, we find that those with higher eccentricity seem to have relatively higher velocity amplitudes indicating higher mass planets and/or an observational bias against the detection of high eccentricity systems.
7583247
A probable planetary companion to HD 39091 from the Anglo-Australian Planet Search
We report the detection of a extrasolar planet candidate orbiting the G1 V star HD 39091. The orbital period is 2083 d and the eccentricity is 0.62. With a minimum (M sin i) mass of 10.3 MJUP this object falls near the high mass end of the observed planet mass function, and may plausibly be a brown dwarf. Other characteristics of this system, including orbital eccentricity and metallicity, are typical of the well populated class of radial velocity planets in eccentric orbits around metal-rich stars.