120270283
s - channel helicity conservation and the stress-tensor
Abstract We discuss the general form of covariant helicity-conserving couplings and their relation to the stress-tensor.
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.
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.
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.
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.
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.
13406335
A search for southern ultracool dwarfs and wide binary systems in young moving groups
We associate 135 low-mass ultracool dwarfs in the southern hemisphere as candidate members of five moving groups using photometric and astrometric selection techniques. Of these objects, three candidates possess published radial velocities allowing a galactic space motion to be calculated, and the kinematic membership of the moving groups to be assessed. One object is a possible member of the IC2391 or Hyades moving groups. We also re-identify a previously known member of the Castor moving group. Also identified is a possible member of the Pleiades moving group, although the large uncertainties associated with the space motion of this object mean that it remains unconfirmed kinematically. Possible membership of moving groups has allowed possible ages and metallicities to be constrained for these objects and evolutionary models have been used to estimate their mass. In addition, the SuperCOSMOS and Hipparcos catalogues were searched for common proper motion binary companions to the 135 candidate moving group members. Three potential binary systems have been found. Further investigation is required to determine if one of these is the widest double brown dwarf binary system known, and another may consist of a low-mass star and a dwarf carbon star. We estimate that up to ∼75 of our candidate moving group members should be genuine, and discuss future work that will confirm and exploit this major new sample.
15911991
A long-period planet orbiting a nearby Sun-like star
Original article can be found at: http://www3.interscience.wiley.com/ Copyright Royal Astronomical Society
118608411
MID-INFRARED PHOTOMETRY OF COLD BROWN DWARFS: DIVERSITY IN AGE, MASS, AND METALLICITY
Original article can be found at: http://www.iop.org/EJ/journal/apj [Full text of this article is not available in the UHRA]
16160180
Probabilities of exoplanet signals from posterior samplings
M. Tuomi and H. R. A. Jones, 'Probabilities of exoplanet signals from posterior samplings', Astronomy & Astrophysics, Vol 544, A166, (2012), the version of record is available online at DOI: 10.1051/0004-6361/201118114. © 2012 ESO
8583739
The electronic bands of CrD, CrH, MgD and MgH: application to the 'deuterium test'
We compute opacities for the electronic molecular band systems A 6 � + – X 6 � + of CrH and CrD, and A 2 � – X 2 � + of MgH and MgD. The opacities are computed by making use of existing spectroscopic constants for MgH and CrH. These constants are adjusted for the different reduced masses of MgD and CrD. Frank-Condon factors are used to provide intensities for the individual vibronic bands. These results are used in the computation of synthetic spectra between Teff = 1800 and 1200 K with an emphasis on the realisation of “deuterium test”, first proposed by Bejar et al. (1999) to distinguish brown dwarfs from planetary mass objects. We discuss the possible use of CrD and MgD electronic bands for the “deuterium test”. We find CrD to be the more promising of the two deuterides, potentially, the most useful bands of ′′ ′′ ′′ ! × "