Lattice QCD study of a five-quark hadronic molecule

We compute the ground-state energies of a heavy-light K-Lambda like system as a function of the relative distance r of the hadrons. The heavy quarks, one in each hadron, are treated as static. Then, the energies give rise to an adiabatic potential Va(r) which we use to study the structure of the five-quark system. The simulation is based on an anisotropic and asymmetric lattice with Wilson fermions. Energies are extracted from spectral density functions obtained with the maximum entropy method. Our results are meant to give qualitative insight: Using the resulting adiabatic potential in a Schroedinger equation produces bound state wave functions which indicate that the ground state of the five-quark system resembles a hadronic molecule, whereas the first excited state, having a very small rms radius, is probably better described as a five-quark cluster, or a pentaquark. We hypothesize that an all light-quark pentaquark may not exist, but in the heavy-quark sector it might, albeit only as an excited state.Comment: 11 pages, 15 figures, 4 table

Residual meson-meson interaction from lattice gauge simulation in a simple QED model

The residual interaction for a meson-meson system is computed utilizing the cumulant, or cluster, expansion of the momentum-space time correlation matrix. The cumulant expansion serves to define asymptotic, or free, meson-meson operators. The definition of an effective interaction is then based on a comparison of the full (interacting) and the free (noninteracting) time correlation matrices. The proposed method, which may straightforwardly be transcribed to other hadron-hadron systems, here is applied to a simple 2+1 dimensional U(1) lattice gauge model tuned such that it is confining. Fermions are treated in the staggered scheme. The effective interaction exhibits a repulsive core and attraction at intermediate relative distances. These findings are consistent with an earlier study of the same model utilizing L\"{u}scher's method where scattering phase shifts are obtained directly

Influence of strain on magnetization and magnetoelectric effect in La0.7A0.3MnO3 / PMN-PT(001) (A = Sr; Ca)

We investigate the influence of a well-defined reversible biaxial strain <=0.12 % on the magnetization (M) of epitaxial ferromagnetic manganite films. M has been recorded depending on temperature, strain and magnetic field in 20 - 50 nm thick films. This is accomplished by reversibly compressing the isotropic in-plane lattice parameter of the rhombohedral piezoelectric 0.72PMN-0.28PT (001) substrates by application of an electric field E <= 12 kV cm-1. The magnitude of the total variable in-plane strain has been derived. Strain-induced shifts of the ferromagnetic Curie temperature (Tc) of up to 19 K were found in La0.7Sr0.3MnO3 (LSMO) and La0.7Ca0.3MnO3 films and are quantitatively analysed for LSMO within a cubic model. The observed large magnetoelectric coupling coefficient alpha=mu0 dM/dE <= 6 10-8 s m-1 at ambient temperature results from the strain-induced M change in the magnetic-film-ferroelectric-substrate system. It corresponds to an enhancement of mu0 DeltaM <= 19 mT upon biaxial compression of 0.1 %. The extraordinary large alpha originates from the combination of three crucial properties: (i) the strong strain dependence of M in the ferromagnetic manganites, (ii) large piezo-strain of the PMN-PT substrates and (iii) effective elastic coupling at the film-substrate interface.Comment: 15 pages, 6 figures, 1 tabl

Time-resolved collapse and revival of the Kondo state near a quantum phase transition

One of the most successful paradigms of many-body physics is the concept of quasiparticles: excitations in strongly interacting matter behaving like weakly interacting particles in free space. Quasiparticles in metals are very robust objects. Yet, when a system's ground state undergoes a qualitative change at a quantum critical point (QCP), the quasiparticles may disintegrate and give way to an exotic quantum-fluid state of matter. The nature of this breakdown is intensely debated, because the emergent quantum fluid dominates the material properties up to high temperature and might even be related to the occurence of superconductivity in some compounds. Here we trace the dynamics of heavy-fermion quasiparticles in CeCu$_{6-x}$Au$_{x}$ and monitor their evolution towards the QCP in time-resolved experiments, supported by many-body calculations. A terahertz pulse disrupts the many-body heavy-fermion state. Under emission of a delayed, phase-coherent terahertz reflex the heavy-fermion state recovers, with a coherence time 100 times longer than typically associated with correlated metals. The quasiparticle weight collapses towards the QCP, yet its formation temperature remains constant -- phenomena believed to be mutually exclusive. Coexistence in the same experiment calls for revisions in our view on quantum criticality.Comment: Published version, including data on CeCu6, CeCu5.9Au0.1, and CeCu5Au1 and extended Supplementary Information. 7 pages, 4 figures, Supplementary Information: 5 pages, 3 figure

Exotic Meson Decay Widths using Lattice QCD

A decay width calculation for a hybrid exotic meson h, with JPC=1-+, is presented for the channel h->pi+a1. This quenched lattice QCD simulation employs Luescher's finite box method. Operators coupling to the h and pi+a1 states are used at various levels of smearing and fuzzing, and at four quark masses. Eigenvalues of the corresponding correlation matrices yield energy spectra that determine scattering phase shifts for a discrete set of relative pi+a1 momenta. Although the phase shift data is sparse, fits to a Breit-Wigner model are attempted, resulting in a decay width of about 60 MeV when averaged over two lattice sizes.Comment: 9 pages, 8 figures, RevTex4, minor change to Fig.

Unconventional spin fluctuations in the hexagonal antiferromagnet YMnO3_3

We used inelastic neutron scattering to show that well below its N\'{e}el temperature, $T_{\rm N}$, the two-dimensional (2D) XY nearly-triangular antiferromagnet YMnO$_{3}$ has a prominent {\it central peak} associated with 2D antiferromagnetic fluctuations with a characteristic life time of 0.55(5) ps, coexisting with the conventional long-lived spin-waves. Existence of the two time scales suggests competition between the N\'{e}el phase favored by weak interplane interactions, and the Kosterlitz-Thouless phase intrinsic to the 2D XY spin system.Comment: 4pages, 5figure

Residual meson-meson interaction from lattice gauge simulation in a simple QED model

The residual interaction for a meson-meson system is computed utilizing the cumulant, or cluster, expansion of the momentum-space time correlation matrix. The cumulant expansion serves to define asymptotic, or free, meson-meson operators. The definition of an effective interaction is then based on a comparison of the full (interacting) and the free (noninteracting) time correlation matrices. The proposed method, which may straightforwardly be transcribed to other hadron-hadron systems, here is applied to a simple 2+1 dimensional U(1) lattice gauge model tuned such that it is confining. Fermions are treated in the staggered scheme. The effective interaction exhibits a repulsive core and attraction at intermediate relative distances. These findings are consistent with an earlier study of the same model utilizing L\"{u}scher's method where scattering phase shifts are obtained directly.Comment: 28 pages, compressed postscript fil

Orbital ordering and enhanced magnetic frustration of strained BiMnO3 thin films

Epitaxial thin films of multiferroic perovskite BiMnO3 were synthesized on SrTiO3 substrates, and orbital ordering and magnetic properties of the thin films were investigated. The ordering of the Mn^{3+} e_g orbitals at a wave vector (1/4 1/4 1/4) was detected by Mn K-edge resonant x-ray scattering. This peculiar orbital order inherently contains magnetic frustration. While bulk BiMnO3 is known to exhibit simple ferromagnetism, the frustration enhanced by in-plane compressive strains in the films brings about cluster-glass-like properties.Comment: 8 pages, 4 figures, accepted to Europhysics Letter

Circular Polarization of Circumstellar Water Masers around S Per

We present the first circular polarization measurements of circumstellar H2O masers. Previously the magnetic field in circumstellar envelopes has been estimated using polarization observations of SiO and OH masers. SiO masers are probes of the high temperature and density regime close to the central star. OH masers are found at much lower densities and temperatures, generally much further out in the circumstellar envelope. The detection of the circular polarization of the (6_16 - 5_23) rotational transition of the H2O maser could be attributed to Zeeman splitting due to the magnetic field in the intermediate temperature and density regime. The fields inferred here agree well with predicted values for a combination of the r^{-2} dependence of a solar-type magnetic field, and the coupling of the field to the high density masing regions. We also discuss the unexpected narrowing of the circular polarization spectrum.Comment: 4 pages, 4 figures; accepted for publication in Astronomy and Astrophysics Letter