Uncertainties in constraining low-energy constants from 3^3H β\beta decay

We discuss the uncertainties in constraining low-energy constants of chiral effective field theory from $^3$H $\beta$ decay. The half-life is very precisely known, so that the Gamow-Teller matrix element has been used to fit the coupling $c_D$ of the axial-vector current to a short-range two-nucleon pair. Because the same coupling also describes the leading one-pion-exchange three-nucleon force, this in principle provides a very constraining fit, uncorrelated with the $^3$H binding energy fit used to constrain another low-energy coupling in three-nucleon forces. However, so far such $^3$H half-life fits have only been performed at a fixed cutoff value. We show that the cutoff dependence due to the regulators in the axial-vector two-body current can significantly affect the Gamow-Teller matrix elements and consequently also the extracted values for the $c_D$ coupling constant. The degree of the cutoff dependence is correlated with the softness of the employed NN interaction. As a result, present three-nucleon forces based on a fit to $^3$H $\beta$ decay underestimate the uncertainty in $c_D$. We explore a range of $c_D$ values that is compatible within cutoff variation with the experimental $^3$H half-life and estimate the resulting uncertainties for many-body systems by performing calculations of symmetric nuclear matter.Comment: 9 pages, 11 figures, published version, includes Erratum, which corrects Figs. 2-6 due to the incorrect c_D relation between 3N forces and two-body currents use

Current voltage characteristics and excess noise at the trap filling transition in polyacenes

Experiments in organic semiconductors (polyacenes) evidence a strong super quadratic increase of the current-voltage (I-V) characteristic at voltages in the transition region between linear (Ohmic) and quadratic (trap free space-charge-limited-current) behaviours. Similarly, excess noise measurements at a given frequency and increasing voltages evidence a sharp peak of the relative spectral density of the current noise in concomitance with the strong super-quadratic I-V characteristics. Here we discuss the physical interpretation of these experiments in terms of an essential contribution from field assisted trapping-detrapping processes of injected carriers. To this purpose, the fraction of filled traps determined by the I-V characteristics is used to evaluate the excess noise in the trap filled transition (TFT) regime. We have found an excellent agreement between the predictions of our model and existing experimental results in tetracene and pentacene thin films of different length in the range $0.65 \div 35 \ \mu m$.Comment: 20 pg, 13 figures, in pres

Measuring the LISA test mass magnetic proprieties with a torsion pendulum

Achieving the low frequency LISA sensitivity requires that the test masses acting as the interferometer end mirrors are free-falling with an unprecedented small degree of deviation. Magnetic disturbances, originating in the interaction of the test mass with the environmental magnetic field, can significantly deteriorate the LISA performance and can be parameterized through the test mass remnant dipole moment $\vec{m}_r$ and the magnetic susceptibility $\chi$. While the LISA test flight precursor LTP will investigate these effects during the preliminary phases of the mission, the very stringent requirements on the test mass magnetic cleanliness make ground-based characterization of its magnetic proprieties paramount. We propose a torsion pendulum technique to accurately measure on ground the magnetic proprieties of the LISA/LTP test masses.Comment: 6 pages, 3 figure

Transport anisotropy in biaxially strained La(2/3)Ca(1/3)MnO(3) thin films

Due to the complex interplay of magnetic, structural, electronic, and orbital degrees of freedom, biaxial strain is known to play an essential role in the doped manganites. For coherently strained La(2/3)Ca(1/3)MnO(3) thin films grown on SrTiO(3) substrates, we measured the magnetotransport properties both parallel and perpendicular to the substrate and found an anomaly of the electrical transport properties. Whereas metallic behavior is found within the plane of biaxial strain, for transport perpendicular to this plane an insulating behavior and non-linear current-voltage characteristics (IVCs) are observed. The most natural explanation of this anisotropy is a strain induced transition from an orbitally disordered ferromagnetic state to an orbitally ordered state associated with antiferromagnetic stacking of ferromagnetic manganese oxide planes.Comment: 5 pages, 4 figure

Inconsistent Distances in Substitution Matrices can be Avoided by Properly Handling Hydrophobic Residues

The adequacy of substitution matrices to model evolutionary relationships between amino acid sequences can be numerically evaluated by checking the mathematical property of triangle inequality for all triplets of residues. By converting substitution scores into distances, one can verify that a direct path between two amino acids is shorter than a path passing through a third amino acid in the amino acid space modeled by the matrix. If the triangle inequality is not verified, the intuition is that the evolutionary signal is not well modeled by the matrix, that the space is locally inconsistent and that the matrix construction was probably based on insufficient biological data. Previous analysis on several substitution matrices revealed that the number of triplets violating the triangle inequality increases with sequence divergence. Here, we compare matrices which are dedicated to the alignment of highly divergent proteins. The triangle inequality is tested on several classical substitution matrices as well as in a pair of “complementary” substitution matrices recording the evolutionary pressures inside and outside hydrophobic blocks in protein sequences. The analysis proves the crucial role of hydrophobic residues in substitution matrices dedicated to the alignment of distantly related proteins

Coupling of a high-energy excitation to superconducting quasiparticles in a cuprate from Coherent Charge Fluctuation Spectroscopy

Dynamical information on spin degrees of freedom of proteins or solids can be obtained by Nuclear Magnetic Resonance (NMR) and Electron Spin Resonance (ESR). A technique with similar versatility for charge degrees of freedom and their ultrafast correlations could move forward the understanding of systems like unconventional superconductors. By perturbing the superconducting state in a high-Tc cuprate using a femtosecond laser pulse, we generate coherent oscillations of the Cooper pair condensate which can be described by an NMR/ESR formalism. The oscillations are detected by transient broad-band reflectivity and found to resonate at the typical scale of Mott physics (2.6 eV), suggesting the existence of a non-retarded contribution to the pairing interaction, as in unconventional (non Migdal-Eliashberg) theories.Comment: Accepted for publication in the Proceedings of the National Academy of Sciences of the U.S.A. (PNAS

Position and velocity space diffusion of test particles in stochastic electromagnetic fields

The two--dimensional diffusive dynamics of test particles in a random electromagnetic field is studied. The synthetic electromagnetic fluctuations are generated through randomly placed magnetised ``clouds'' oscillating with a frequency $\omega$. We investigate the mean square displacements of particles in both position and velocity spaces. As $\omega$ increases the particles undergo standard (Brownian--like) motion, anomalous diffusion and ballistic motion in position space. Although in general the diffusion properties in velocity space are not trivially related to those in position space, we find that energization is present only when particles display anomalous diffusion in position space. The anomalous character of the diffusion is only in the non--standard values of the scaling exponents while the process is Gaussian.Comment: 10 pages, 4 figure

Characterization of disturbance sources for LISA: torsion pendulum results

A torsion pendulum allows ground-based investigation of the purity of free-fall for the LISA test masses inside their capacitive position sensor. This paper presents recent improvements in our torsion pendulum facility that have both increased the pendulum sensitivity and allowed detailed characterization of several important sources of acceleration noise for the LISA test masses. We discuss here an improved upper limit on random force noise originating in the sensor. Additionally, we present new measurement techniques and preliminary results for characterizing the forces caused by the sensor's residual electrostatic fields, dielectric losses, residual spring-like coupling, and temperature gradients.Comment: 11 pages, 8 figures, accepted for publication Classical and Quantum Gravit