120814286
The Transverse Momentum Distribution of {Drell-Yan} Pairs in Perturbation Theory
Abstract We calculate, in lowest-order perturbation theory, the cumulative transverse momentum cross section for the Drell-Yan process in the regime m 2 ⪡ p T 2 ⪡ q 2 , keeping both single and double logarithmic terms. We verify that this distribution takes the proposed form of a product of structure functions evaluated at p T 2 and the square of the Sudakov form factor S ( p T 2 / q 2 ), evaluated to subleading order.
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.
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.
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.
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.
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.
16032606
The discovery of a very cool, very nearby brown dwarf in the Galactic plane
We report the discovery of a very cool, isolated brown dwarf, UGPS 0722-05, with the United Kingdom Infrared Telescope Deep Sky Survey (UKIDSS) Galactic Plane Survey. The near-infrared spectrum displays deeper H2O and CH4 troughs than the coolest known T dwarfs and an unidentified absorption feature at 1.275 mu m. We provisionally classify the object as a T10 dwarf but note that it may in future come to be regarded as the first example of a new spectral type. The distance is measured by trigonometric parallax as d = 4.1(-0.5)(+0.6) pc, making it the closest known isolated brown dwarf. With the aid of Spitzer/Infrared Array Camera (IRAC) we measure H - [4.5] = 4.71. It is the coolest brown dwarf presently known - the only known T dwarf that is redder in H - [4.5] is the peculiar T7.5 dwarf SDSS J1416+13B, which is thought to be warmer and more luminous than UGPS 0722-05. Our measurement of the luminosity, aided by Gemini/T-ReCS N-band photometry, is L = 9.2 +/- 3.1 x 10(-7) L-circle dot. Using a comparison with well-studied T8.5 and T9 dwarfs we deduce T-eff = 520 +/- 40 K. This is supported by predictions of the Saumon & Marley models. With apparent magnitude J = 16.52, UGPS 0722-05 is the brightest of the similar to 90 T dwarfs discovered by UKIDSS so far. It offers opportunities for future study via high-resolution near-infrared spectroscopy and spectroscopy in the thermal infrared.
55800969
Chromospheric activities and kinematics for solar type dwarfs and subgiants: analysis of the activity distribution and the AVR
Aims. In this work we present chromospheric activity indices, kinematics, radial-velocities, and rotational velocities for more than 850 FGK-type dwarfs and subgiant stars in the southern hemisphere and test how best to calibrate and measure S-indices from echelle spectra. Methods. We measured our parameters using the high-resolution and high-S /N FEROS echelle spectra acquired for this purpose. Results. We confirm the bimodal distribution of chromospheric activities for such stars and highlight the role that the more active K-dwarfs play in biasing the number of active stars. We show that the age-activity relationship does appear to continue to ages older than the Sun if we simply compare main sequence stars and subgiant stars with an offset of around 2.5 Gyr between the peaks of both distributions. Also we show evidence of an increased spin-down timescale for cool K dwarfs compared with earlier F and G type stars. We highlight that activities drawn from low-resolution spectra (R < 2500) significantly increase the rms scatter when calibrating onto common systems of measurements like the Mt. Wilson system. Also we show that older and widely used catalogues —————‐ ‐ ‐ ‐
15234437
NACO-SDI imaging of known companion host stars from the AAPS and Keck planet search surveys
Context. Direct imaging of brown dwarfs as companions to solar-type stars can provide a wealth of well-constrained data to “benchmark” the physics of such objects, since quantities like metallicity and age can be determined from their well-studied primaries. Aims. We present results from an adaptive optics imaging program on stars drawn from the Anglo-Australian and Keck Planet Search projects, with the aim of directly imaging known cool companions. Methods. Simulations have modeled the expected contrast ratios and separations of known companions using estimates of orbital parameters available from current radial-velocity data and then a selection of the best case objects were followed-up with high contrast imaging to attempt to directly image these companions. Results. These simulations suggest that only a very small number of radial-velocity detected exoplanets with consistent velocity fits and age estimates could potentially be directly imaged using the VLT’s Simultaneous Differential Imaging system and only under favorable conditions. We also present detectability confidence limits from the radial-velocity data sets and show how these can be used to gain a better understanding of these systems when combined with the imaging data. For HD32778 and HD91204 the detectabilities help little in constraining the companion and hence almost all our knowledge is drawn from the SDI images. Therefore, we can say that these stars do not host cool methane objects, out to on-sky separations of ∼2 �� , with contrasts less than 10−11 mag. However, for HD25874, HD120780 and HD145825, the contrasts and detectabilities can rule out a number of possible solutions, particularly at low angular separations, and for the best case, down to strong methane masses of 40 MJ at 1 �� separation. The contrast curves constructed for these five stars show 5σ contrasts (ΔF1) of ∼9.2–11.5 mag at separations of ≥0.6 �� , which correspond to contrasts of ∼9.7–12.0 mag for companions of mid-T spectral type. Such limits allow us to reach down to 40 MJ around fairly old field dwarfs that typically constitute high precision radial-velocity programs. Finally, the analysis performed here can serve as a template for future projects that will employ extreme-AO systems to directly image planets already indirectly discovered by the radial-velocity method.
7248338
Selection functions in doppler planet searches
We present a preliminary analysis of the sensitivity of Anglo-Australian Planet Search data to the orbital parameters of extrasolar planets. To do so, we have developed new tools for the automatic analysis of large-scale simulations of Doppler velocity planet search data. One of these tools is the two-dimensional Keplerian Lomb-Scargle (LS) periodogram that enables the straightforward detection of exoplanets with high eccentricities (something the standard LS periodogram routinely fails to do). We used this technique to redetermine the orbital parameters of HD20782b, with one of the highest known exoplanet eccentricities (e = 0.97 +/- 0.01). We also derive a set of detection criteria that do not depend on the distribution functions of fitted Keplerian orbital parameters (which we show are non-Gaussian with pronounced, extended wings). Using these tools, we examine the selection functions in orbital period, eccentricity and planet mass of Anglo-Australian Planet Search data for three planets with large-scale Monte Carlo like simulations. We find that the detectability of exoplanets declines at high eccentricities. However, we also find that exoplanet detectability is a strong function of epoch-to-epoch data quality, number of observations and period sampling. This strongly suggests that simple parametrizations of the detectability of exoplanets based on `whole-of-survey' metrics may not be accurate. We have derived empirical relationships between the uncertainty estimates for orbital parameters that are derived from least-squares Keplerian fits to our simulations and the true 99 per cent limits for the errors in those parameters, which are larger than equivalent Gaussian limits by the factors of 5-10. We quantify the rate at which false positives are made by our detection criteria, and find that they do not significantly affect our final conclusions. And finally, we find that there is a bias against measuring near-zero eccentricities, which becomes more significant in
18806294
Ultra-cool Dwarfs from Large Area Surveys
We selected brown dwarf candidates from the seventh Data Release of the Sloan Digital Sky Survey (SDSS DR7) with new photometric selectioncriteria based on a parameteriaztion of well-known L and T dwarfs. Then we confirmed their status with SDSS spectra. The candidates without SDSS spectra are cross matched in the Two Micron All Sky Survey (2MASS) and the Fourth Data Release of the UKIRT Infrared Deep Sky Survey (UKIDSS DR4). With the help of colors based on SDSS, 2MASS and UKIDSS, we are able to estimate spectral types of our candidates. We obtain reliable proper motions using positional and epoch information downloaded direct from the survey databases.