Determination of f+K(0)f_+^K(0) and Extraction of ∣Vcs∣|V_{cs}| from Semileptonic DD Decays

By globally analyzing all existing measured branching fractions and partial rates in different four momentum transfer-squared $q^2$ bins of $D\to Ke^+\nu_e$ decays, we obtain the product of the form factor and magnitude of CKM matrix element $V_{cs}$ to be $f_+^K(0)|V_{cs}|=0.717\pm0.004$. With this product, we determine the $D\to K$ semileptonic form factor $f_+^K(0)=0.737\pm0.004\pm0.000$ in conjunction with the value of $|V_{cs}|$ determined from the SM global fit. Alternately, with the product together with the input of the form factor $f_+^K(0)$ calculated in lattice QCD recently, we extract $|V_{cs}|^{D\to Ke^+\nu_e}=0.962\pm0.005\pm0.014$, where the error is still dominated by the uncertainty of the form factor calculated in lattice QCD. Combining the $|V_{cs}|^{D_s^+\to\ell^+\nu_\ell}=1.012\pm0.015\pm0.009$ extracted from all existing measurements of $D^+_s\to\ell^+\nu_\ell$ decays and $|V_{cs}|^{D\to Ke^+\nu_e}=0.962\pm0.005\pm0.014$ together, we find the most precisely determined $|V_{cs}|$ to be $|V_{cs}|=0.983\pm0.011$, which improves the accuracy of the PDG'2014 value $|V_{cs}|^{\rm PDG'2014}=0.986\pm0.016$ by $45\%$

Effective potential for composite operators and for an auxiliary scalar field in a Nambu-Jona-Lasinio model

We derive the effective potentials for composite operators in a Nambu-Jona-Lasinio (NJL) model at zero and finite temperature and show that in each case they are equivalent to the corresponding effective potentials based on an auxiliary scalar field. The both effective potentials could lead to the same possible spontaneous breaking and restoration of symmetries including chiral symmetry if the momentum cutoff in the loop integrals is large enough, and can be transformed to each other when the Schwinger-Dyson (SD) equation of the dynamical fermion mass from the fermion-antifermion vacuum (or thermal) condensates is used. The results also generally indicate that two effective potentials with the same single order parameter but rather different mathematical expressions can still be considered physically equivalent if the SD equation corresponding to the extreme value conditions of the two potentials have the same form.Comment: 7 pages, no figur

Spin transfer in a ferromagnet-quantum dot and tunnel barrier coupled Aharonov-Bohm ring system with Rashba spin-orbit interactions

The spin transfer effect in ferromagnet-quantum dot (insulator)-ferromagnet Aharonov-Bohm (AB) ring system with Rashba spin-orbit (SO) interactions is investigated by means of Keldysh nonequilibrium Green function method. It is found that both the magnitude and direction of the spin transfer torque (STT) acting on the right ferromagnet electrode can be effectively controlled by changing the magnetic flux threading the AB ring or the gate voltage on the quantum dot. The STT can be greatly augmented by matching a proper magnetic flux and an SO interaction at a cost of low electrical current. The STT, electrical current, and spin current are uncovered to oscillate with the magnetic flux. The present results are expected to be useful for information storage in nanospintronics.Comment: 17pages, 7figure

Determination of f+π(0)f_+^\pi(0) and Extraction of ∣Vcd∣|V_{cd}| from Semileptonic DD Decays

By globally analyzing all existing measured branching fractions for $D\to \pi e^+\nu_e$ decays, partial decay rates in different four momentum transfer-squared $q^2$ bins, as well as products of the decay form factor $f_+^\pi(q^2)$ and the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix element $|V_{cd}|$, we obtain $f_+^\pi(0)|V_{cd}|=0.1428\pm0.0019$. This product, in conjunction with $|V_{cd}|$ from a global Standard Model fit, implies a value for the $D\to\pi$ semileptonic form factor $f_+^\pi(0)=0.634\pm0.008\pm0.002$, which is consistent within error with those calculated in theory based on QCD, but with higher precision than the most accurate $f_+^\pi(0)_{\rm LQCD}=0.666\pm0.020\pm0.021$ calculated in LQCD by a factor of 3.3. Alternately, using this product together with the most accurate form factor calculated in LQCD, we find $|V_{cd}|^{D\to \pi e^+\nu_e}=0.2144\pm0.0029_{\rm exp}\pm 0.0093_{\rm LQCD}$. Combining this $|V_{cd}|^{D\to \pi e^+\nu_e}$ together with $|V_{cd}|^{D^+\to\mu^+\nu_\mu}=0.2160\pm0.0049\pm0.0014$ extracted from both the BESIII and CLEO-c measurements of $D^+\to\mu^+\nu_\mu$ decays, we find the most precisely extracted $|V_{cd}|$ to be $|V_{cd}|=0.2157\pm0.0045$ up to date, which improves the accuracy of the PDG'2014 value $|V_{cd}|_{\rm PDG'2014}=0.225\pm0.008$ by over $70$. Using this $|V_{cd}|$ together with the PDG'2014 $|V_{ud}|$ and $|V_{td}|$, we check for first column unitarity and find $|V_{ud}|^2+|V_{cd}|^2+|V_{td}|^2-1=-0.004\pm0.002$, which deviates from unitarity by $2\sigma$. In addition, we find the ratio of $f_+^\pi(0)$ and $D^+$ decay constant $f_{D^+}$ to be $f_+^\pi(0)/f_{D^+}=(3.11\pm0.08)$ GeV$^{-1}$, which can be used to validate LQCD calculations for these two quantities.Comment: arXiv admin note: substantial text overlap with arXiv:1409.804

Managing Risk of Bidding in Display Advertising

In this paper, we deal with the uncertainty of bidding for display advertising. Similar to the financial market trading, real-time bidding (RTB) based display advertising employs an auction mechanism to automate the impression level media buying; and running a campaign is no different than an investment of acquiring new customers in return for obtaining additional converted sales. Thus, how to optimally bid on an ad impression to drive the profit and return-on-investment becomes essential. However, the large randomness of the user behaviors and the cost uncertainty caused by the auction competition may result in a significant risk from the campaign performance estimation. In this paper, we explicitly model the uncertainty of user click-through rate estimation and auction competition to capture the risk. We borrow an idea from finance and derive the value at risk for each ad display opportunity. Our formulation results in two risk-aware bidding strategies that penalize risky ad impressions and focus more on the ones with higher expected return and lower risk. The empirical study on real-world data demonstrates the effectiveness of our proposed risk-aware bidding strategies: yielding profit gains of 15.4% in offline experiments and up to 17.5% in an online A/B test on a commercial RTB platform over the widely applied bidding strategies

Joint source and relay design for MIMO multi-relay systems using projected gradient approach

In this paper, we develop the optimal source precoding matrix and relay amplifying matrices for non-regenerative multiple-input multiple-output (MIMO) relay communication systems with parallel relay nodes using the projected gradient (PG) approach. We show that the optimal relay amplifying matrices have a beamforming structure. Exploiting the structure of relay matrices, an iterative joint source and relay matrices optimization algorithm is developed to minimize the mean-squared error (MSE) of the signal waveform estimation at the destination using the PG approach. The performance of the proposed algorithm is demonstrated through numerical simulations