Matching factors for Delta S=1 four-quark operators in RI/SMOM schemes

The non-perturbative renormalization of four-quark operators plays a significant role in lattice studies of flavor physics. For this purpose, we define regularization-independent symmetric momentum-subtraction (RI/SMOM) schemes for Delta S=1 flavor-changing four-quark operators and provide one-loop matching factors to the MS-bar scheme in naive dimensional regularization. The mixing of two-quark operators is discussed in terms of two different classes of schemes. We provide a compact expression for the finite one-loop amplitudes which allows for a straightforward definition of further RI/SMOM schemes.Comment: 22 pages, 5 figure

Pion transition form factor at the two-loop level vis-\`a-vis experimental data

We use light-cone QCD sum rules to calculate the pion-photon transition form factor, taking into account radiative corrections up to the next-to-next-to-leading order of perturbation theory. We compare the obtained predictions with all available experimental data from the CELLO, CLEO, and the BaBar Collaborations. We point out that the BaBar data are incompatible with the convolution scheme of QCD, on which our predictions are based, and can possibly be explained only with a violation of the factorization theorem. We pull together recent theoretical results and comment on their significance.Comment: 10 pages, 4 figures, 3 tables. Presented by the first author at Workshop "Recent Advances in Perturbative QCD and Hadronic Physics", 20--25 July 2009, ECT*, Trento (Italy), in Honor of Prof. Anatoly Efremov's 75th Birthday. v2 wrong reference tag removed. v3 Fig. 4 and Ref. [27] correcte

Meson distribution amplitudes in holographic models

We study the wave functions of light and heavy mesons in both hard-wall (HW) and soft-wall (SW) holographic models which use AdS/CFT correspondence. In the case of massless constituents, the asymptotic behaviors of the electromagnetic form factor, the distribution amplitudes, and the decay constants for the two models are the same, if the relation between the dilaton scale parameter and the size of meson is an inverse proportion. On the other hand, by introducing a quark mass dependence in the wave function, the differences of the distribution amplitudes between the two models are obvious. In addition, for the SW model, the dependences of the decay constants of meson on the dilaton scale parameter $\kappa$ differ; especially f_{Qq}\sim \kappa^3/m_Q^2 is consistent with the prediction of the heavy quark effective theory if \kappa\sim m_Q^{1/2}. Thus the parameters of the two models are fit by the decay constants of the distinct mesons; the distribution amplitudes and the \xi-moments are calculated and compared.Comment: 30 pages, 11 figures, 2 tables, minor modifications and one short paragraph added, some references added and removed, accepted for publication in PR

Parental Co‐Construction of 5‐ to 13‐Year‐Olds\u27 Global Self‐Esteem Through Reminiscing About Past Events

The current study explored parental processes associated with children\u27s global self‐esteem development. Eighty 5‐ to 13‐year‐olds and one of their parents provided qualitative and quantitative data through questionnaires, open‐ended questions, and a laboratory‐based reminiscing task. Parents who included more explanations of emotions when writing about the lowest points in their lives were more likely to discuss explanations of emotions experienced in negative past events with their child, which was associated with child attachment security. Attachment was associated with concurrent self‐esteem, which predicted relative increases in self‐esteem 16 months later, on average. Finally, parent support also predicted residual increases in self‐esteem. Findings extend prior research by including younger ages and uncovering a process by which two theoretically relevant parenting behaviors impact self‐esteem development

Generalized parton distributions of the pion in chiral quark models and their QCD evolution

We evaluate Generalized Parton Distributions of the pion in two chiral quark models: the Spectral Quark Model and the Nambu-Jona-Lasinio model with a Pauli-Villars regularization. We proceed by the evaluation of double distributions through the use of a manifestly covariant calculation based on the alpha representation of propagators. As a result polynomiality is incorporated automatically and calculations become simple. In addition, positivity and normalization constraints, sum rules and soft pion theorems are fulfilled. We obtain explicit formulas, holding at the low-energy quark-model scale. The expressions exhibit no factorization in the t-dependence. The QCD evolution of those parton distributions is carried out to experimentally or lattice accessible scales. We argue for the need of evolution by comparing the Parton Distribution Function and the Parton Distribution Amplitude of the pion to the available experimental and lattice data, and confirm that the quark-model scale is low, about 320 MeV.Comment: 25 pages, 15 figures, added discussion of the end-point behavio

Endpoint behavior of the pion distribution amplitude in QCD sum rules with nonlocal condensates

Starting from the QCD sum rules with nonlocal condensates for the pion distribution amplitude, we derive another sum rule for its derivative and its "integral" derivatives---defined in this work. We use this new sum rule to analyze the fine details of the pion distribution amplitude in the endpoint region $x\sim 0$. The results for endpoint-suppressed and flat-top (or flat-like) pion distribution amplitudes are compared with those we obtained with differential sum rules by employing two different models for the distribution of vacuum-quark virtualities. We determine the range of values of the derivatives of the pion distribution amplitude and show that endpoint-suppressed distribution amplitudes lie within this range, while those with endpoint enhancement---flat-type or CZ-like---yield values outside this range.Comment: 20 pages, 10 figures, 1 table, conclusions update

O(a^2) cutoff effects in lattice Wilson fermion simulations

In this paper we propose to interpret the large discretization artifacts affecting the neutral pion mass in maximally twisted lattice QCD simulations as O(a^2) effects whose magnitude is roughly proportional to the modulus square of the (continuum) matrix element of the pseudoscalar density operator between vacuum and one-pion state. The numerical size of this quantity is determined by the dynamical mechanism of spontaneous chiral symmetry breaking and turns out to be substantially larger than its natural magnitude set by the value of Lambda_QCD.Comment: 38 pages, 1 figure, 2 table

Pulsed Feedback Defers Cellular Differentiation

Environmental signals induce diverse cellular differentiation programs. In certain systems, cells defer differentiation for extended time periods after the signal appears, proliferating through multiple rounds of cell division before committing to a new fate. How can cells set a deferral time much longer than the cell cycle? Here we study Bacillus subtilis cells that respond to sudden nutrient limitation with multiple rounds of growth and division before differentiating into spores. A well-characterized genetic circuit controls the concentration and phosphorylation of the master regulator Spo0A, which rises to a critical concentration to initiate sporulation. However, it remains unclear how this circuit enables cells to defer sporulation for multiple cell cycles. Using quantitative time-lapse fluorescence microscopy of Spo0A dynamics in individual cells, we observed pulses of Spo0A phosphorylation at a characteristic cell cycle phase. Pulse amplitudes grew systematically and cell-autonomously over multiple cell cycles leading up to sporulation. This pulse growth required a key positive feedback loop involving the sporulation kinases, without which the deferral of sporulation became ultrasensitive to kinase expression. Thus, deferral is controlled by a pulsed positive feedback loop in which kinase expression is activated by pulses of Spo0A phosphorylation. This pulsed positive feedback architecture provides a more robust mechanism for setting deferral times than constitutive kinase expression. Finally, using mathematical modeling, we show how pulsing and time delays together enable “polyphasic” positive feedback, in which different parts of a feedback loop are active at different times. Polyphasic feedback can enable more accurate tuning of long deferral times. Together, these results suggest that Bacillus subtilis uses a pulsed positive feedback loop to implement a “timer” that operates over timescales much longer than a cell cycle

Fabrication of a planar micro Penning trap and numerical investigations of versatile ion positioning protocols

We describe a versatile planar Penning trap structure, which allows to dynamically modify the trapping conguration almost arbitrarily. The trap consists of 37 hexagonal electrodes, each with a circumcirle-diameter of 300 m, fabricated in a gold-on-sapphire lithographic technique. Every hexagon can be addressed individually, thus shaping the electric potential. The fabrication of such a device with clean room methods is demonstrated. We illustrate the variability of the device by a detailed numerical simulation of a lateral and a vertical transport and we simulate trapping in racetrack and articial crystal congurations. The trap may be used for ions or electrons, as a versatile container for quantum optics and quantum information experiments.Comment: 10 pages, 7 figures, pdflatex, to be published in New Journal of Physics (NJP) various changes according to the wishes of the NJP referees. Text added and moved around, title changed, abstract changed, references added rev3: one reference had a typo (ref 15), fixed (phys rev a 72, not 71