K+ -> pi+ nu nu(bar) and FCNC from non-universal Z' bosons

Motivated by the E787 and E949 result for K+ -> pi+ nu nu(bar) we examine the effects of a new non-universal right-handed Z' boson on flavor changing processes. We place bounds on the tree-level FCNC from K-K(bar) and B-B(bar) mixing as well as from the observed CP violation in kaon decay. We discuss the implications for K -> pi nu nu(bar), B -> X nu nu(bar) and B -> tau+ tau-. We find that existing bounds allow substantial enhancements in the K+ -> pi+ nu nu(bar) rate, particularly through a new one-loop Z' penguin operator.Comment: Typos corrected, references added, version to appear in PR

Spin chirality fluctuation in two-dimensional ferromagnets with perpendicular anisotropy

Non-coplanar spin textures with scalar spin chirality can generate effective magnetic field that deflects the motion of charge carriers, resulting in topological Hall effect (THE), a powerful probe of the ground state and low-energy excitations of correlated systems. However, spin chirality fluctuation in two-dimensional ferromagnets with perpendicular anisotropy has not been considered in prior studies. Herein, we report direct evidence of universal spin chirality fluctuation by probing the THE above the transition temperatures in two different ferromagnetic ultra-thin films, SrRuO$_3$ and V doped Sb$_2$Te$_3$. The temperature, magnetic field, thickness, and carrier type dependences of the THE signal, along with our Monte-Carlo simulations, unambiguously demonstrate that the spin chirality fluctuation is a universal phenomenon in two-dimensional Ising ferromagnets. Our discovery opens a new paradigm of exploring the spin chirality with topological Hall transport in two-dimensional magnets and beyondComment: accepted by nature material

Culture-independent analysis of microflora in Gayals (Bos frontalis) feces

Comparative DNA sequence analysis of 16S/18S rRNA genes (rDNA) were undertaken to further our understanding of the make-up of micro-organisms communities in the feces of Gayals. Total DNA wereextracted from the feces of 5 Gayals. Two rDNA libraries (16S/18S rDNA) were constructed. In the 16S rDNA library, phylogenetic and sequence similarity analyses of the resultant 71 clone sequences revealed the presence of 67 operational taxonomic units (OTUs) or phylotypes and defined as having more than 97% of sequence similarity. The sequences were affiliated with the following phyla: Firmicutes (34.3%), Bacteroidetes (6.0%), Proteobacteria (4.5%), and uncultured bacteria (55.2%). A setof 58 sequences were analyzed in the 18S rDNA library, which were classified into 27 OTUs. They were mainly affiliated with the following phyla: Protozoa (25.9%), Basidiomycota (3.7%), Ascomycota (11.1%),and uncultured eukaryotes (59.3%). The sequence analysis indicated that more than half of the species, harbored in Gayals fecal belonged to the not-yet-cultured groups at 90% 16S/18S similarity levels with cultured species. In addition, micro-organisms of Chytridiomycetes was one of the most significant cellulose producing species obtained from the Gayal feces as well

B_c meson rare decays in the light-cone quark model

We investigate the rare decays $B_c \rightarrow D_s(1968) \ell \bar{\ell}$ and $B_c\rightarrow D_s^*(2317) \ell \bar{\ell}$ in the framework of the light-cone quark model (LCQM). The transition form factors are calculated in the space-like region and then analytically continued to the time-like region via exponential parametrization. The branching ratios and longitudinal lepton polarization asymmetries (LPAs) for the two decays are given and compared with each other. The results are helpful to investigating the structure of $B_c$ meson and to testing the unitarity of CKM quark mixing matrix. All these results can be tested in the future experiments at the LHC.Comment: 9 pages, 11 figures, version accepted for publication in EPJ

Sharp and Smooth Boundaries of Quantum Hall Liquids

We study the transition between sharp and smooth density distributions at the edges of Quantum Hall Liquids in the presence of interactions. We find that, for strong confining potentials, the edge of a $\nu=1$ liquid is described by the $Z_F=1$ Fermi Liquid theory, even in the presence of interactions, a consequence of the chiral nature of the system. When the edge confining potential is decreased beyond a point, the edge undergoes a reconstruction and electrons start to deposit a distance $\sim 2$ magnetic lengths away from the initial QH Liquid. Within the Hartree-Fock approximation, a new pair of branches of gapless edge excitations is generated after the transition. We show that the transition is controlled by the balance between a long-ranged repulsive Hartree term and a short-ranged attractive exchange term. Such transition also occurs for Quantum Dots in the Quantum Hall Regime, and should be observable in resonant tunneling experiments. Electron tunneling into the reconstructed edge is also discussed.Comment: 28 pages, REVTeX 3.0, 18 figures available upon request, cond-mat/yymmnn

Field induced spin reorientation and giant spin-lattice coupling in EuFe2As2

We have studied a EuFe2As2 single crystal by neutron diffraction under magnetic fields up to 3.5 T and temperatures down to 2 K. A field induced spin reorientation is observed in the presence of a magnetic field along both the a and c axes, respectively. Above critical field, the ground state antiferromagnetic configuration of Eu$^{2+}$ moments transforms into a ferromagnetic structure with moments along the applied field direction. The magnetic phase diagram for Eu magnetic sublattice in EuFe2As2 is presented. A considerable strain ($\sim$0.9%) is induced by the magnetic field, caused by the realignment of the twinning structure. Furthermore, the realignment of the twinning structure is found to be reversible with the rebound of magnetic field, which suggested the existence of magnetic shape-memory effect. The Eu moment ordering exhibits close relationship with the twinning structure. We argue that the Zeeman energy in combined with magnetic anisotropy energy is responsible for the observed spin-lattice coupling.Comment: 5 pages, 4 figure

Excitation of nightside magnetosonic waves observedby Van Allen Probes

Abstract During the recovery phase of the geomagnetic storm on 30-31 March 2013, Van Allen Probe A detected enhanced magnetosonic (MS) waves in a broad range of L = 1.8-4.7 and magnetic local time (MLT) = 17-22 h, with a frequency range ∼10-100 Hz. In the meanwhile, distinct proton ring distributions with peaks at energies of ∼10 keV, were also observed in L = 3.2-4.6 and L = 5.0-5.6. Using a subtracted bi-Maxwellian distribution to model the observed proton ring distribution, we perform three-dimensional ray tracing to investigate the instability, propagation, and spatial distribution of MS waves. Numerical results show that nightside MS waves are produced by proton ring distribution and grow rapidly from the source location L = 5.6 to the location L = 5.0 but remain nearly stable at locations L \u3c 5.0. Moreover, waves launched toward lower L shells with different initial azimuthal angles propagate across different MLT regions with divergent paths at first, then gradually turn back toward higher L shells and propagate across different MLT regions with convergent paths. The current results further reveal that MS waves are generated by a ring distribution of ∼10 keV proton and proton ring in one region can contribute to the MS wave power in another region. Key Points: Correlated Van Allen Probe data of MS wave and proton ringGrowth rates are peaked at the harmonics of the proton gyrofrequencyMS waves propagate inward divergently and outward convergently