121385013
Perturbative QCD and the exclusive decay of heavy quarkonium into a photon and two mesons
We consider the radiative decays of the 3S1 ground state QQ into a real photon and two light pseudoscalar or vector mesons. For sufficiently large mass of the heavy quark Q, the decay, e.g. ϒ → γππ, can be calculated in perturbative QCD, provided that the photon does not carry away a predominant fraction of the available energy. We present differential and integrated Dalitz plot distributions and, for quarkonium states produced with transverse polarization in e+e− annihilation, angular distributions of the orientation of the decay triangle relative to the beam direction.
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.
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.
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.
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.
14800854
Application of Bayesian model inadequacy criterion for multiple data sets to radial velocity models of exoplanet systems
We present a simple mathematical criterion for determining whether a given statistical model does not describe several independent sets of measurements, or data modes, adequately. We derive this criterion for two data sets and generalise it to several sets by using the Bayesian updating of the posterior probability density. To demonstrate the usage of the criterion, we apply it to observations of exoplanet host stars by re-analysing the radial velocities of HD 217107, Gliese 581, and υ Andromedae and show that the currently used models are not necessarily adequate in describing the properties of these measurements. We show that while the two data sets of Gliese 581 can be modelled reasonably well, the noise model of HD 217107 needs to be revised. We also reveal some biases in the radial velocities of υ Andromedae and report updated orbital parameters for the recently proposed 4-planet model. Because of the generality of our criterion, no assumptions are needed on the nature of the measurements, models, or model parameters. The method we propose can be applied to any astronomical problems, as well as outside the field of astronomy, because it is a simple consequence of the Bayes’ rule of conditional probabilities.
14681463
Improved HCN/HNC linelist, model atmospheres and synthetic spectra for WZ Cas
We build an accurate database of 5200 HCN and HNC rotation-vibration energy levels, determined from existing laboratory data. 20 000 energy levels in the Harris et al. (2002b) linelist are assigned approximate quantum numbers. These assignments, lab determined energy levels and Harris et al. (2002b) energy levels are incorporated in to a new energy level list. A new linelist is presented, in which frequencies are computed using the lab determined energy levels where available, and the ab initio energy levels otherwise. The new linelist is then used to compute new model atmospheres and synthetic spectra for the carbon star WZ Cas. This results in better fit to the spectrum of WZ Cas in which the absorption feature at 3.56 µm is reproduced to a higher degree of accuracy than has previously been possible. We improve the reproduction of HCN absorption features by reducing the abundance of Si to [Si/H] = –0.5 dex, however, +
67841979
Carbon monoxide in low-mass dwarf stars
We compare high resolution infrared observations of the CO 3-1 bands in the 2.297– 2.310 µm region of M dwarfs and one L dwarf with theoretical expectations. We find a good match between the observational and synthetic spectra throughout the 20003500K temperature regime investigated. Nonetheless, for the 2500-3500 K temperature range the temperatures that we derive from synthetic spectral fits are higher than expected from more empirical methods by several hundred K. In order to reconcile our findings with the empirical temperature scale it is necessary to invoke warming of the model atmosphere used to construct the synthetic spectra. We consider that the most likely reason for the back-warming is missing high temperature opacity due to water vapour. We compare the water vapour opacity of the Partridge & Schwenke (1997) line list used for the model atmosphere with the output from a preliminary calculation by Barber & Tennyson (2004). While the Partridge & Schwenke line list is a reasonable spectroscopic match for the new line list at 2000 K, by 4000 K it is missing around 25% of the water vapour opacity. We thus consider that the offset between empirical and synthetic temperature scales is explained by the lack of hot water vapour used for computation of the synthetic spectra. For our coolest objects with temperatures below 2500 K we find best fits when using synthetic spectra which include dust emission. Our spectra also allow us to constrain the rotational velocities of our sources, and these velocities are consistent with the broad trend of rotational velocities increasing from M to L.
14668338
Parallaxes and physical properties of 11 mid-to-late T dwarfs
Aims. We present parallaxes of 11 mid-to-late T dwarfs observed in the UKIRT Infrared Deep Sky Survey. We use these results to test the reliability of model predictions in magnitude‐color space, determine a magnitude-spectral type calibration, and, estimate a bolometric luminosity and effective temperature range for the targets. Methods. We used observations from the UKIRT WFCAM instrument pipeline processed at the Cambridge Astronomical Survey Unit. The parallaxes and proper motions of the sample were calculated using standard procedures. The bolometric luminosity was estimated using near- and mid-infrared observations with two different methods. The corresponding effective temperature ranges were found adopting a large age-radius range. Results. We show the models are unable to predict the colors of the latest T dwarfs indicating the incompleteness of model opacities for NH3 ,C H4 and H2 as the temperature declines. We report the effective temperature ranges obtained.