46321890
Complex square well - a new exactly solvable quantum mechanical model
Recently, a class ofPT -invariant quantum mechanical models described by the non- Hermitian HamiltonianHDp2 +x2.ix/ was studied. It was found that the energy levels for this theory are real for all > 0. Here, the limit as !1is examined. It is shown that in this limit, the theory becomes exactly solvable. A generalization of this Hamiltonian, H D p 2 +x 2M.ix/ (MD 1;2;3;:::) is also studied, and thisPT -symmetric Hamiltonian becomes exactly solvable in the large- limit as well. In effect, what is obtained in each case is a complex analogue of the Hamiltonian for the square-well potential. Expansions about the large- limit are obtained.
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.
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.
17310918
The discovery of a very cool binary system
The definitive version can be found at: http://www3.interscience.wiley.com/ Copyright Royal Astronomical Society
14171934
The Properties of the 500 K Dwarf UGPS J072227.51-054031.2, and a Study of the Far-Red Flux of Cold Brown Dwarfs
We present i and z photometry for 25 T dwarfs and 1 L dwarf. Combined with published photometry, the data show that the i – z, z – Y, and z – J colors of T dwarfs are very red, and continue to increase through to the late-type T dwarfs, with a hint of a saturation for the latest types with T eff 600 K. We present new 0.7-1.0 μm and 2.8-4.2 μm spectra for the very late type T dwarf UGPS J072227.51–054031.2, as well as improved astrometry for this dwarf. Examination of the spectral energy distribution using new and published data, with Saumon & Marley models, shows that the dwarf has T eff = 505 ± 10 K, a mass of 3-11 M Jupiter, and an age between 60 Myr and 1 Gyr. This young age is consistent with the thin disk kinematics of the dwarf. The mass range overlaps with that usually considered to be planetary, despite this being an unbound object discovered in the field near the Sun. This apparently young rapid rotator is also undergoing vigorous atmospheric mixing, as determined by the IRAC and WISE 4.5 μm photometry and the Saumon & Marley models. The optical spectrum for this 500 K object shows clearly detected lines of the neutral alkalis Cs and Rb, which are emitted from deep atmospheric layers with temperatures of 900-1200 K.
285922
Brown dwarfs and low-mass stars in the Pleiades and Praesepe: membership and binarity
We present near-infrared J-, H- and K-band photometry and optical spectroscopy of low-mass star and brown dwarf (BD) candidates in the Pleiades and Praesepe open clusters. We flag non-members from their position in K, I−K and J, J−K colour–magnitude diagrams (CMDs), and J−H, H−K two-colour diagrams. In general, the dust-free NextGen model isochrones of the Lyon Group fit the K, I−K CMDs well for stars with I−K∼ 1.5–3.5. However, Pleiades stars with K≃ 10.5–13 (MK≃ 5–7.5) are rather redder than the isochrones. We also identify this effect amongst αPer sources from the literature, but find no evidence of it for field stars from the literature. The NextGen isochrones fit the J, J−K CMDs of both clusters very well in this photometric range. It is possible that the I−K colour of youthful stars is affected by the presence of magnetic activity. The Lyon Group's Dusty isochrones fit both K, I−K and K, J−K Pleiades CMDs well for I−K≃ 4.3–6/J−K≃ 1.1–1.4. In between these colour ranges the Pleiades cluster sequence comprises three portions. Starting at the bluer side, there is a gap where very few sources are found (the gap size is ΔI∼ 0.5, ΔJ∼ΔK∼ 0.3), probably resulting from a sharp local drop in the magnitude–mass relation. Then the sequence is quite flat from I−K∼ 3.5–4. Finally, the sequence turns over and drops down to join the Dusty isochrone. We also compare model atmosphere colours to the two-colour diagrams of the clusters. The NextGen models are seen to be ∼0.1 too blue in H−K and ∼0.1 too red in J−H for Teff > 4000 K. However, they are in reasonable agreement with the data at Teff∼ 3200 K. For Teff∼ 2800–3150 K, the colours of Pleiades and Praesepe sources are significantly different, where Praesepe sources are ∼0.1 bluer in J−H and up to ∼0.1 redder in H−K. These differences could result from gravity-sensitive molecular opacities. Cooler Praesepe sources then agree well with the dusty models, suggesting that dust is beginning to form in Praesepe sources around 2500 K. However, Pleiades sources remain consistent with the NextGen models (and inconsistent with the dusty models) down to Teff values of ∼2000 K. It is possible that dust formation does not begin until lower Teff values in sources with lower surface gravities (and hence lower atmospheric pressures). We also identify unresolved binaries in both clusters, and estimate mass ratios (q) for Pleiades BDs. Most of these have q > 0.7, however, 3/18 appear to have lower q values. We determine the binary fraction (BF) for numerous mass ranges in each cluster, and find that it is generally rising towards lower masses. We find a BD BF of 50+11−10 per cent. We also find some evidence suggesting that the BF–q distribution is flat for 0.5–0.35 M⊙, in contrast to solar-type stars.
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.
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, +