Exact coefficients for higher dimensional operators with sixteen supersymmetries

We consider constraints on higher dimensional operators for supersymmetric effective field theories. In four dimensions with maximal supersymmetry and SU(4) R-symmetry, we demonstrate that the coefficients of abelian operators F^n with MHV helicity configurations must satisfy a recursion relation, and are completely determined by that of F^4. As the F^4 coefficient is known to be one-loop exact, this allows us to derive exact coefficients for all such operators. We also argue that the results are consistent with the SL(2,Z) duality symmetry. Breaking SU(4) to Sp(4), in anticipation for the Coulomb branch effective action, we again find an infinite class of operators whose coefficient that are determined exactly. We also consider three-dimensional N=8 as well as six-dimensional N=(2,0),(1,0) and (1,1) theories. In all cases, we demonstrate that the coefficient of dimension-six operator must be proportional to the square of that of dimension-four.Comment: typos corrected, minor modificatio

Synthesis, structural and property studies of bismuth containing perovskites

Several bismuth-containing transition metal perovskites that are of interest as potential multiferroic materials have been synthesised and studied. These materials have been structurally characterised and their physical properties have been examined at varying temperatures and pressures. The new series of substituted bismuth ferrite perovskites BixCa1-xFeO3, where x = 0.4 - 1.0, has been prepared. A disordered cubic phase (x = 0.4 - 0.67) and the coexistence of rhombohedral and cubic phases (x = 0.8 and 0.9) have been observed. The x = 0.8 sample is located at the phase boundary and shows a transformation from cubic to rhombohedral symmetry at 473 - 573 K. All samples are antiferromagnets at room temperature and have Néel temperature of 623 - 643 K. Ferroelectric order is suppressed in the disordered cubic phase. BixLa1-xMnO3 materials with x = 0.8, 0.9 and 1.0 were synthesised at 3 - 6 GPa. For x = 1.0 and 0.9 samples a highly distorted perovskite structure with monoclinic space group C2/c was adopted and ferromagnetic behaviour was observed with Curie temperatures of 101 and 94 K, respectively. Bi0.8La0.2MnO3 shows an O'-type orthorhombic Pnma structure and canted A-type antiferromagnetic ordering below 80 K. A new phase of BiNiO3 has been discovered at 4 - 5 GPa below 200 K, in which a Pb11 symmetry has been revealed with a = 5.2515(2) Å, b = 5.6012(3) Å, c = 7.6202(4) Å and β = 90.20(1) º at 4.3 GPa and 100 K. This new Phase Id is derived from the ambient Phase I Bi3+ 0.5Bi5+ 0.5Ni2+O3, where the charge disproportionated Bi3+/Bi5+ cations become disordered. The updated P-T phase diagram of BiNiO3 is presented. BiCu3Mn4O12 has been studied by neutron diffraction from 5 to 400 K. The incorporation of Mn3+ into the Cu site has been observed, showing that the true composition is BiCu2.5Mn4.5O12. The ordering of Mn and Cu moments below transition temperature 320 K is found to be ferromagnetic rather than ferrimagnetic as proposed previously

From U(1) to E8: soft theorems in supergravity amplitudes

It is known that for N=8 supergravity, the double-soft-scalar limit of a n-point amplitude is given by a sum of local SU(8) rotations acting on a (n-2)-point amplitude. For N<8 supergravity theories, complication arises due to the presence of a U(1) in the U(N) isotropy group, which introduces a soft-graviton singularity that obscures the action of the duality symmetry. In this paper, we introduce an anti-symmetrised extraction procedure that exposes the full duality group. We illustrate this procedure for tree-level amplitudes in 4<=N<8 supergravity in four dimensions, as well as N=16 supergravity in three dimensions. In three dimensions, as all bosonic degrees of freedom transform under the E8 duality group, supersymmetry ensures that the amplitude vanishes in the single-soft limit of all particle species, in contrast to its higher dimensional siblings. Using recursive formulas and generalized unitarity cuts in three dimensions, we demonstrate the action of the duality group for any tree-level and one-loop amplitudes. Finally we discuss the implications of the duality symmetry on possible counter terms for this theory. As a preliminary application, we show that the vanishing of single-soft limits of arbitrary component fields in three-dimensional supergravity rules out the direct dimensional reduction of D^8R^4 as a valid counter term.Comment: 29 pages, 5 figures, v2: minor modifications, published version; V3: typos correcte

Improper Ferroelectric Polarisation in a Perovskite driven by Inter-site Charge Transfer and Ordering

It is of great interest to design and make materials in which ferroelectric polarisation is coupled to other order parameters such as lattice, magnetic and electronic instabilities. Such materials will be invaluable in next-generation data storage devices. Recently, remarkable progress has been made in understanding improper ferroelectric coupling mechanisms that arise from lattice and magnetic instabilities. However, although theoretically predicted, a compact lattice coupling between electronic and ferroelectric (polar) instabilities has yet to be realised. Here we report detailed crystallographic studies of a novel perovskite Hg$^{\textbf{A}}$Mn$^{\textbf{A'}}_{3}$Mn$^{\textbf{B}}_{4}$O$_{12}$ that is found to exhibit a polar ground state on account of such couplings that arise from charge and orbital ordering on both the A' and B-sites, which are themselves driven by a highly unusual Mn$^{A'}$-Mn$^B$ inter-site charge transfer. The inherent coupling of polar, charge, orbital and hence magnetic degrees of freedom, make this a system of great fundamental interest, and demonstrating ferroelectric switching in this and a host of recently reported hybrid improper ferroelectrics remains a substantial challenge.Comment: 9 pages, 7 figure

Structural, magnetic, and electrical properties of Bi1-xLaxMnO3 (x=0.0, 0.1, and 0.2) solid solutions

Possible ferromagnetic and ferroelectric orders in ceramic Bi1–xLaxMnO3 (x = 0.0, 0.1, and 0.2) samples prepared under 3–6 GPa pressure have been investigated. Rietveld fits to powder neutron diffraction data show that BiMnO3 and Bi0.9La0.1MnO3 adopt a monoclinic C2/c perovskite superstructure whereas Bi0.8La0.2MnO3 has orthorhombic Pnma symmetry. Both structural analysis and Curie–Weiss fits to magnetic susceptibility data show that high spin d4 Mn3+ is present with no significant Bi deficiency or Mn4+ content apparent. La substitution suppresses the magnetic Curie temperature of the monoclinic phase from 105 K for x = 0 to 94 K at x = 0.1, but the x = 0.2 material shows antiferromagnetic order similar to that of LaMnO3. Impedance spectroscopy and dielectric measurements on the x = 0.1 and 0.2 materials show modest bulk permittivity values (45–80) down to 50 K, and there is no strong evidence for ferroelectric behavior. The two samples have thermally activated conductivities with activation energies of 0.21–0.24 eV.PostprintPeer reviewe

Acid-sensing ion channel 3 mediates peripheral anti-hyperalgesia effects of acupuncture in mice inflammatory pain

<p>Abstract</p> <p>Background</p> <p>Peripheral tissue inflammation initiates hyperalgesia accompanied by tissue acidosis, nociceptor activation, and inflammation mediators. Recent studies have suggested a significantly increased expression of acid-sensing ion channel 3 (ASIC3) in both carrageenan- and complete Freund's adjuvant (CFA)-induced inflammation. This study tested the hypothesis that acupuncture is curative for mechanical hyperalgesia induced by peripheral inflammation.</p> <p>Methods</p> <p>Here we used mechanical stimuli to assess behavioral responses in paw and muscle inflammation induced by carrageenan or CFA. We also used immunohistochemistry staining and western blot methodology to evaluate the expression of ASIC3 in dorsal root ganglion (DRG) neurons.</p> <p>Results</p> <p>In comparison with the control, the inflammation group showed significant mechanical hyperalgesia with both intraplantar carrageenan and CFA-induced inflammation. Interestingly, both carrageenan- and CFA-induced hyperalgesia were accompanied by ASIC3 up-regulation in DRG neurons. Furthermore, electroacupuncture (EA) at the ST36 rescued mechanical hyperalgesia through down-regulation of ASIC3 overexpression in both carrageenan- and CFA-induced inflammation.</p> <p>Conclusions</p> <p>In addition, electrical stimulation at the ST36 acupoint can relieve mechanical hyperalgesia by attenuating ASIC3 overexpression.</p