B_s^0 - bar{B}_s^0 Mixing and the B_s -> J/psi phi Asymmetry in Supersymmetric Models

We analyse supersymmetric contributions to B_s mixing and their impact on mixing-induced CP asymmetries, using the mass insertion approximation. We discuss in particular the correlation of SUSY effects in the CP asymmetries of B_s -> J/psi phi and B_d -> phi K_S and find that the mass insertions dominant in B_s mixing and B_d -> phi K_S are (delta_{23}^d)_{LL, RR} and (delta_{23}^d)_{LR, RL}, respectively. We show that models with dominant (delta_{23}^d)_{LR, RL} can accomodate a negative value of S_{phi K_S}, in agreement with the BELLE measurement of that observable, but yield a B_s mixing phase too small to be observed. On the other hand, models with dominant (delta_{23}^d)_{LL, RR} predict sizeable SUSY contributions to both Delta M_s and the mixing phase, but do not allow the asymmetry in B_d -> phi K_S to become negative, except for small values of the average down squark mass, which, in turn, entail a value of Delta M_s too large to be observed at the Tevatron and the LHC. We conclude that the observation of B_s mixing at hadron machines, together with the confirmation of a negative value of S_{phi K_S}, disfavours models with a single dominant mass insertion.Comment: 17 pages, 5 figure

Probing New Physics using top quark polarization in the e+e- -> t \bar{t} process at future Linear Colliders

We investigate the sensitivity to new physics of the process e+e- -> t bar{t} when the top polarization is analyzed using leptonic final states e+e- -> t \bar{t} -> l+l- b \bar{b} nu_l \bar{nu}_l. We first show that the kinematical reconstruction of the complete kinematics is experimentally tractable for this process. Then we apply the matrix element method to study the sensitivity to the Vt\bar{t} coupling (V being a vector gauge boson), at the tree level and in the narrow width approximation. Assuming the ILC baseline configuration, sqrt{S}=500 GeV, and a luminosity of 500 fb^{-1}, we conclude that this optimal analysis allows to determine simultaneously the ten form factors that parameterize the Vt\bar{t} coupling, below the percent level. We also discuss the effects of the next leading order (NLO) electroweak corrections using the GRACE program with polarized beams. It is found that the NLO corrections to different beam polarization lead to significantly different patterns of contributions.Comment: 14 pages, 4 figures, Proceedings for the TYL-FJPPL workshops on "Top Physics at ILC

Topological Gauge Structure and Phase Diagram for Weakly Doped Antiferromagnets

We show that the topological gauge structure in the phase string theory of the {\rm t-J} model gives rise to a global phase diagram of antiferromagnetic (AF) and superconducting (SC) phases in a weakly doped regime. Dual confinement and deconfinement of holons and spinons play essential roles here, with a quantum critical point at a doping concentration $x_c\simeq 0.043$. The complex experimental phase diagram at low doping is well described within such a framework.Comment: 4 pages, 2 figures, modified version, to appear in Phys. Rev. Let

Anomalous Spin Dynamics of Hubbard Model on Honeycomb Lattices

In this paper, the honeycomb Hubbard model in optical lattices is investigated using O(3) non-linear sigma model. A possible quantum non-magnetic insulator in a narrow parameter region is found near the metal-insulator transition. We study the corresponding dynamics of magnetic properties, and find that the narrow region could be widened by hole doping.Comment: 9 pages, 12 figure

Nonleptonic charmless B_c decays and their search at LHCb

International audienceWe discuss the decay of B_c mesons into two light (pseudoscalar and vector) mesons. All these decay channels come from a single type of diagram, namely tree annihilation which allows us to derive simple relations among these processes. The size of annihilation contributions is an important issue in B physics, and we provide two different estimates in the case of non-leptonic charmless B_c decays, either a comparison with annihilation decays of heavy-light mesons or a perturbative model inspired by QCD factorisation. We finally discuss a possible search for these channels at LHCb

Realization of Topological Quantum Computation with surface codes

In this paper, the degenerate ground states of Z2 topological order on a plane with holes (the so-called surface codes) are used as the protected code subspace to build a topological quantum computer by tuning their quantum tunneling effect. Using a designer Hamiltonian - the Kitaev toric-code model as an example, we study quantum tunneling effects of the surface codes and obtain its effective theory. Finally, we show how to do topological quantum computation including the initialization, the unitary transformation and the measurement

Quantum spin Hall states in graphene interacting with WS2_2 or WSe2_2

In the framework of first-principles calculations, we investigate the structural and electronic properties of graphene in contact with as well as sandwiched between WS$_2$ and WSe$_2$ monolayers. We report the modification of the band characteristics due to the interaction at the interface and demonstrate that the presence of the dichalcogenides results in quantum spin Hall states in the absence of a magnetic field

B->gamma e nu Transitions from QCD Sum Rules

B->gamma e nu transitions have recently been studied in the framework of QCD factorization. The attractiveness of this channel for such an analysis lies in the fact that, at least in the heavy quark limit, the only hadron involved is the B meson itself, so one expects a very simple description of the form factor in terms of a convolution of the B meson distribution amplitude with a perturbative kernel. This description, however, does not include contributions suppressed by powers of the b quark mass. In this letter, we calculate corrections to the factorized expression which are induced by the ``soft'' hadronic component of the photon. We demonstrate that the power-suppression of these terms is numerically not effective for physical values of the $b$ quark mass and that they increase the form factor by about 30% at zero momentum transfer. We also derive a sum rule for lambda_B, the first negative moment of the B meson distribution amplitude, and find lambda_B = 0.6 GeV (to leading order in QCD).Comment: 13 pages, 5 figure

Mutual-Chern-Simons effective theory of doped antiferromagnets

A mutual-Chern-Simons Lagrangian is derived as a minimal field theory description of the phase-string model for doped antiferromagnets. Such an effective Lagrangian is shown to retain the full symmetries of parity, time-reversal, and global SU(2) spin rotation, in contrast to conventional Chern-Simons theories where first two symmetries are usually broken. Two ordered phases, i.e., antiferromagnetic and superconducting states, are found at low temperatures as characterized by dual Meissner effects and dual flux quantization conditions due to the mutual-Chern-Simons gauge structure. A dual confinement in charge/spin degrees of freedom occurs such that no true spin-charge separation is present in these ordered phases, but the spin-charge separation/deconfinement serves as a driving force in the unconventional phase transitions of these ordered states to disordered states.Comment: 16 pages, 2 figures; published versio