Longitudinal Polarization at future e+e−e^+e^- Colliders and Virtual New Physics Effects

The theoretical merits of longitudinal polarization asymmetries of electron-positron annihilation into two final fermions at future colliders are examined, using a recently proposed theoretical description. A number of interesting features, valid for searches of virtual effects of new physics, is underlined, that is reminiscent of analogous properties valid on top of $Z$ resonance. As an application to a concrete example, we consider the case of a model with triple anomalous gauge couplings and show that the additional information provided by these asymmetries would lead to a drastic reduction of the allowed domain of the relevant parameters.Comment: 18 pages and 1 figure. e-mail: [email protected]

Magnetic Order and Spin Dynamics in Ferroelectric HoMnO3_{3}

Hexagonal HoMnO$_{3}$ is a frustrated antiferromagnet (T$_{N}$=72 K) ferroelectric (T$_{C}$=875 K) in which these two order parameters are coupled. Our neutron measurements of the spin wave dispersion for the S=2 Mn$^{3+}$ on the layered triangular lattice are well described by a two-dimensional nearest-neighbor Heisenberg exchange J=2.44 meV, and an anisotropy $D$ that is 0.093 meV above the spin reorientation transition at 40 K, and 0.126 meV below. For $H\parallel c$ the magnetic structures and phase diagram have been determined, and reveal additional transitions below 8 K where the ferroelectrically displaced Ho$^{3+}$ ions are ordered magnetically.Comment: To be published in Physical Review Letter

Origin of Electric Field Induced Magnetization in Multiferroic HoMnO3

We have performed polarized and unpolarized small angle neutron scattering experiments on single crystals of HoMnO3 and have found that an increase in magnetic scattering at low momentum transfers begins upon cooling through temperatures close to the spin reorientation transition at TSR ~ 40 K. We attribute the increase to an uncompensated magnetization arising within antiferromagnetic domain walls. Polarized neutron scattering experiments performed while applying an electric field show that the field suppresses magnetic scattering below T ~ 50 K, indicating that the electric field affects the magnetization via the antiferromagnetic domain walls rather than through a change to the bulk magnetic order

Antiferromagnetic Order of the Ru and Gd in Superconducting RuSr2GdCu2O8

Neutron diffraction has been used to study the magnetic order in RuSr{2}GdCu2O8. The Ru moments order antiferromagnetically at T{N}=136(2)K, coincident with the previously reported onset of ferromagnetism. Neighboring spins are antiparallel in all three directions, with a low T moment of 1.18(6) mu {B} along the c-axis. Our measurements put an upper limit of ~0.1 mu{B} to any net zero-field moment, with fields exceeding ~0.4T needed to induce a measurable magnetization. The Gd ions order independently at T{N}=2.50(2)K with the same spin configuration. PACS numbers: 74.72.Jt, 75.25.+z, 74.25.Ha, 75.30.KzComment: Four pages, Latex, 5 eps figure

Structural Anomalies at the Magnetic and Ferroelectric Transitions in RMn2O5RMn_2O_5 (R=Tb, Dy, Ho)

Strong anomalies of the thermal expansion coefficients at the magnetic and ferroelectric transitions have been detected in multiferroic $RMn_2O_5$. Their correlation with anomalies of the specific heat and the dielectric constant is discussed. The results provide evidence for the magnetic origin of the ferroelectricity mediated by strong spin-lattice coupling in the compounds. Neutron scattering data for $HoMn_2O_5$ indicate a spin reorientation at the two low-temperature phase transitions

Magnetic inversion symmetry breaking and ferroelectricity in TbMnO3

TbMnO3 is an orthorhombic insulator where incommensurate spin order for temperature T_N < 41K is accompanied by ferroelectric order for T < 28K. To understand this, we establish the magnetic structure above and below the ferroelectric transition using neutron diffraction. In the paraelectric phase, the spin structure is incommensurate and longitudinally-modulated. In the ferroelectric phase, however, there is a transverse incommensurate spiral. We show that the spiral breaks spatial inversion symmetry and can account for magnetoelectricity in TbMnO3.Comment: 4 pages revtex, accepted by Phys. Rev. Lett. on June 21, 200

Antiferromagnetic critical pressure in URu2Si2 under hydrostatic conditions

The onset of antiferromagnetic order in URu2Si2 has been studied via neutron diffraction in a helium pressure medium, which most closely approximates hydrostatic conditions. The antiferromagnetic critical pressure is 0.80 GPa, considerably higher than values previously reported. Complementary electrical resistivity measurements imply that the hidden order-antiferromagnetic bicritical point far exceeds 1.02 GPa. Moreover, the redefined pressure-temperature phase diagram suggests that the superconducting and antiferromagnetic phase boundaries actually meet at a common critical pressure at zero temperature.Comment: 5 pgs, 4 figs; AFM ordered moment revised to 0.5 muB, added and corrected citations and reference