A unified description of superconducting pairing symmetry in electron-doped Fe-based-122 compounds

The pairing symmetry is examined in highly electron-doped Ba(Fe$_{1-x}$Co$_x$As)$_2$ and A$_y$Fe$_2$Se$_2$ (with A=K, Cs) compounds, with similar crystallographic and electronic band structures. Starting from a phenomenological two-orbital model, we consider nearest-neighbor and next-nearest-neighbor intraorbital pairing interactions on the Fe square lattice. In this model, we find a unified description of the evolution from $s_pm$-wave pairing ($2.0 < n lesssim 2.4$) to $d$-wave pairing ($2.4 lesssim n lesssim 2.5$) as a function of electron filling. In the crossover region a novel time-reversal symmetry breaking state with $s_pm+id$ pairing symmetry emerges. This minimal model offers an overall picture of the evolution of superconductivity with electron doping for both $s_pm$-wave [Ba(Fe$_{1-x}$Co$_x$As)$_2$] and $d$-wave [A$_y$Fe$_2$Se$_2$] pairing, as long as the dopants only play the role of a charge reservoir. However, the situation is more complicated for Ba(Fe$_{1-x}$Co$_x$As)$_2$. A real-space study further shows that when the impurity scattering effects of Co dopants are taken into account, the superconductivity is completely suppressed for $n > 2.4$. This preempts any observation of $d$-wave pairing in this compound, in contrast to A$_y$Fe$_2$Se$_2$.

Coverage versus Supply Cost in Facility Location: Physics of Frustrated Spin Systems

A comprehensive coverage is crucial for communication, supply and transportation networks, yet it is limited by the requirement of extensive infrastructure and heavy energy consumption. Here we draw an analogy between spins in antiferromagnet and outlets in supply networks, and apply techniques from the studies of disordered systems to elucidate the effects of balancing the coverage and supply costs on the network behavior. A readily applicable, coverage optimization algorithm is derived. Simulation results show that magnetized and antiferromagnetic domains emerge and coexist to balance the need for coverage and energy saving. The scaling of parameters with system size agrees with the continuum approximation in two dimensions and the tree approximation in random graphs. Due to frustration caused by the competition between coverage and supply cost, a transition between easy and hard computation regimes is observed. We further suggest a local expansion approach to greatly simplify the message updates which shed light on simplifications in other problems.

Quantum advantage by weak measurements

Weak measurements may result in extra quantity of quantumness of correlations compared with standard projective measurement on a bipartite quantum state. We show that the quantumness of correlations by weak measurements can be consumed for information encoding which is only accessible by coherent quantum interactions. Then it can be considered as a resource for quantum information processing and can quantify this quantum advantage. We conclude that weak measurements can create more valuable quantum correlation.

Interpretation of the coronal magnetic field configuration of the Sun

The origin of the heliospheric magnetic flux on the Sun, and hence the origin of the solar wind, is a topic of hot debate.While the prevailing view is that the solar wind originates from outside coronal streamer helmets, there also exists the suggestion that the open magnetic field spans a far wider region.Without the definitive measurement of the coronal magnetic field, it is difficult to resolve the conflict between the two scenarios without doubt.We present two 2-dimensional, Alfvenic-turbulence-based models of the solar corona and solar wind, one with and the other without a closed magnetic field region in the inner corona.The purpose of the latter model is to test whether it is possible to realize a picture suggested by polarimetric measurements of the corona using the FeXIII 10747AA line, where open magnetic field lines seem to penetrate the streamer base.The boundary conditions at the coronal base are able to account for important observational constraints, especially those on the magnetic flux distribution.Interestingly, the two models provide similar polarized brightness (pB) distributions in the field of view (FOV) of SOHO/LASCO C2 and C3 coronagraphs.In particular, a dome-shaped feature is present in the C2 FOV even for the model without any closed magnetic field.Moreover, both models fit equally well the Ulysses data scaled to 1 AU.We suggest that: 1) The pB observations cannot be safely taken as a proxy for the magnetic field topology, as often implicitly assumed.2) The Ulysses measurements, especially the one showing a nearly uniform distribution with heliocentric latitude of the radial magnetic field, do not rule out the ubiquity of open magnetic fields on the Sun.

A possible signature of new physics at BES-III

The recent observations of the purely leptonic decay $Ds to mu^+ u_{mu}$ and $tau^+ u_{tau}$ at CLEO-c and $B$ factory may allow a possible contribution from a charged Higgs boson. One such measurement of the decay constant $f_{D_s}$ differs from the most precise unquenched lattice QCD calculation by 4 $sigma$ level. Meanwhile, the measured ratio, ${cal BR}(Ds to mu^+ u_{mu})$ / ${cal BR}(Dp to mu^+ u_{mu})$, is larger than the standard model prediction at 2.0$sigma$ level. We discuss that the precise measurement of the ratio ${cal BR}(Ds to mu^+ u_{mu})$ / ${cal BR}(Dp to mu^+ u_{mu})$ at BES-III will shed light on the presence of new intermediate particles by comparing the theoretical predictions, especially, the predictions of high precise unquenched lattice QCD calculation.

Rare Semileptonic Decays of Heavy Mesons with Flavor SU(3) Symmetry

In this paper, we calculate the decay rates of $D^+ to D^0 e^+ u$, $D^+_S to D^0 e^+ u$, $B^0_S to B^+ e^- bar{ u}$, $D^+_S to D^+ e^- e^+$ and $B^0_S to B^0 e^-e^+$ semileptonic decay processes, in which only the light quarks decay, while the heavy flavors remain unchanged. The branching ratios of these decay processes are calculated with the flavor SU(3) symmetry. The uncertainties are estimated by considering the SU(3) breaking effect. We find that the decay rates are very tiny in the framework of the Standard Model. We also estimate the sensitivities of the measurements of these rare decays at the future experiments, such as BES-III, super-$B$ and LHC-$b$.

Rare and forbidden decay of charm mesons at CLEO-c and BES-III

This paper presents the results of searches for the flavor-changing neutral current, lepton-number-violating and lepton-flavor-violating processes in the charm mesons decays. Recent results from charged $D$ mesons decays to final states with dielectrons from CLEO-c are reported. The prospects of the searches for the rare charm decays at BES-III are also discussed.

Strong Phase and $D^0-D^0bar$ mixing at BES-III

Most recently, both BaBar and Belle experiments found evidences of neutral $D$ mixing. In this paper, we discuss the constraints on the strong phase difference in $D^0 to Kpi$ decay from the measurements of the mixing parameters, $y^prime$, $y_{CP}$ and $x$ at the $B$ factories. The sensitivity of the measurement of the mixing parameter $y$ is estimated in BES-III experiment at $psi(3770)$ peak. We also make an estimate on the measurements of the mixing rate $R_M$. Finally, the sensitivity of the strong phase difference at BES-III are obtained by using data near the $Dbar{D}$ threshold with CP tag technique at BES-III experiment.