Restoration of kTk_T factorization for low pTp_T hadron hadroproduction

We discuss the applicability of the $k_T$ factorization theorem to low-$p_T$ hadron production in hadron-hadron collision in a simple toy model, which involves only scalar particles and gluons. It has been shown that the $k_T$ factorization for high-$p_T$ hadron hadroproduction is broken by soft gluons in the Glauber region, which are exchanged among a transverse-momentum-dependent (TMD) parton density and other subprocesses of the collision. We explain that the contour of a loop momentum can be deformed away from the Glauber region at low $p_T$, so the above residual infrared divergence is factorized by means of the standard eikonal approximation. The $k_T$ factorization is then restored in the sense that a TMD parton density maintains its universality. Because the resultant Glauber factor is independent of hadron flavors, experimental constraints on its behavior are possible. The $k_T$ factorization can also be restored for the transverse single-spin asymmetry in hadron-hadron collision at low $p_T$ in a similar way, with the residual infrared divergence being factorized into the same Glauber factor.Comment: 12 pages, 2 figures, version to appear in EPJ

Theory of Current-Induced Magnetization Precession

We solve appropriate drift-diffusion and Landau-Lifshitz-Gilbert equations to demonstrate that unpolarized current flow from a non-magnet into a ferromagnet can produce a precession-type instability of the magnetization. The fundamental origin of the instability is the difference in conductivity between majority spins and minority spins in the ferromagnet. This leads to spin accumulation and spin currents that carry angular momentum across the interface. The component of this angular momentum perpendicular to the magnetization drives precessional motion that is opposed by Gilbert damping. Neglecting magnetic anisotropy and magnetostatics, our approximate analytic and exact numerical solutions using realistic values for the material parameters show (for both semi-infinite and thin film geometries) that a linear instability occurs when both the current density and the excitation wave vector parallel to the interface are neither too small nor too large. For many aspects of the problem, the variation of the magnetization in the direction of the current flows makes an important contribution.Comment: Submitted to Physical Review

Influence of constitution and charge on radical pairing interactions in tris-radical tricationic complexes

The results of a systematic investigation of trisradical tricationic complexes formed between cyclobis(paraquat-p-phenylene) bisradical dicationic (CBPQT2(•+)) rings and a series of 18 dumbbells, containing centrally located 4,4′-bipyridinium radical cationic (BIPY•+) units within oligomethylene chains terminated for the most part by charged 3,5-dimethylpyridinium (PY+) and/or neutral 3,5-dimethylphenyl (PH) groups, are reported. The complexes were obtained by treating equimolar amounts of the CBPQT4+ ring and the dumbbells containing BIPY2+ units with zinc dust in acetonitrile solutions. Whereas UV–Vis–NIR spectra revealed absorption bands centered on ca. 1100 nm with quite different intensities for the 1:1 complexes depending on the constitutions and charges on the dumbbells, titration experiments showed that the association constants (Ka) for complex formation vary over a wide range, from 800 M–1 for the weakest to 180 000 M–1 for the strongest. While Coulombic repulsions emanating from PY+ groups located at the ends of some of the dumbbells undoubtedly contribute to the destabilization of the trisradical tricationic complexes, solid-state superstructures support the contention that those dumbbells with neutral PH groups at the ends of flexible and appropriately constituted links to the BIPY•+ units stand to gain some additional stabilization from C–H···π interactions between the CBPQT2(•+) rings and the PH termini on the dumbbells. The findings reported in this Article demonstrate how structural changes implemented remotely from the BIPY•+ units influence their non-covalent bonding interactions with CBPQT2(•+) rings. Different secondary effects (Coulombic repulsions versus C–H···π interactions) are uncovered, and their contributions to both binding strengths associated with trisradical interactions and the kinetics of associations and dissociations are discussed at some length, supported by extensive DFT calculations at the M06-D3 level. A fundamental understanding of molecular recognition in radical complexes has relevance when it comes to the design and synthesis of non-equilibrium systems

FMRF-NH2-related neuropeptides in Biomphalaria spp., intermediate hosts for schistosomiasis: Precursor organization and immunohistochemical localization

Freshwater snails of the genus Biomphalaria serve as intermediate hosts for the digenetic trematode Schistosoma mansoni, the etiological agent for the most widespread form of intestinal schistosomiasis. As neuropeptide signaling in host snails can be altered by trematode infection, a neural transcriptomics approach was undertaken to identify peptide precursors in Biomphalaria glabrata, the major intermediate host for S. mansoni in the Western Hemisphere. Three transcripts that encode peptides belonging to the FMRF-NH2-related peptide (FaRP) family were identified in B. glabrata. One transcript encoded a precursor polypeptide (Bgl-FaRP1; 292 amino acids) that included eight copies of the tetrapeptide FMRF-NH2 and single copies of FIRF-NH2, FLRF-NH2, and pQFYRI-NH2. The second transcript encoded a precursor (Bgl-FaRP2; 347 amino acids) that comprised 14 copies of the heptapeptide GDPFLRF-NH2 and 1 copy of SKPYMRF-NH2. The precursor encoded by the third transcript (Bgl-FaRP3; 287 amino acids) recapitulated Bgl-FaRP2 but lacked the full SKPYMRF-NH2 peptide. The three precursors shared a common signal peptide, suggesting a genomic organization described previously in gastropods. Immunohistochemical studies were performed on the nervous systems of B. glabrata and B. alexandrina, a major intermediate host for S. mansoni in Egypt. FMRF-NH2-like immunoreactive (FMRF-NH2-li) neurons were located in regions of the central nervous system associated with reproduction, feeding, and cardiorespiration. Antisera raised against non-FMRF-NH2 peptides present in the tetrapeptide and heptapeptide precursors labeled independent subsets of the FMRF-NH2-li neurons. This study supports the participation of FMRF-NH2-related neuropeptides in the regulation of vital physiological and behavioral systems that are altered by parasitism in Biomphalaria

Transverse Momentum Dependent Parton Distribution/Fragmentation Functions at an Electron-Ion Collider

We present a summary of a recent workshop held at Duke University on Partonic Transverse Momentum in Hadrons: Quark Spin-Orbit Correlations and Quark-Gluon Interactions. The transverse momentum dependent parton distribution functions (TMDs), parton-to-hadron fragmentation functions, and multi-parton correlation functions, were discussed extensively at the Duke workshop. In this paper, we summarize first the theoretical issues concerning the study of partonic structure of hadrons at a future electron-ion collider (EIC) with emphasis on the TMDs. We then present simulation results on experimental studies of TMDs through measurements of single spin asymmetries (SSA) from semi-inclusive deep-inelastic scattering (SIDIS) processes with an EIC, and discuss the requirement of the detector for SIDIS measurements. The dynamics of parton correlations in the nucleon is further explored via a study of SSA in D (`D) production at large transverse momenta with the aim of accessing the unexplored tri-gluon correlation functions. The workshop participants identified the SSA measurements in SIDIS as a golden program to study TMDs in both the sea and valence quark regions and to study the role of gluons, with the Sivers asymmetry measurements as examples. Such measurements will lead to major advancement in our understanding of TMDs in the valence quark region, and more importantly also allow for the investigation of TMDs in the sea quark region along with a study of their evolution.Comment: 44 pages 23 figures, summary of Duke EIC workshop on TMDs accepted by EPJ

Forward Jets and Energy Flow in Hadronic Collisions

We observe that at the Large Hadron Collider, using forward + central detectors, it becomes possible for the first time to carry out calorimetric measurements of the transverse energy flow due to "minijets" accompanying production of two jets separated by a large rapidity interval. We present parton-shower calculations of energy flow observables in a high-energy factorized Monte Carlo framework, designed to take into account QCD logarithmic corrections both in the large rapidity interval and in the hard transverse momentum. Considering events with a forward and a central jet, we examine the energy flow in the interjet region and in the region away from the jets. We discuss the role of these observables to analyze multiple parton collision effects.Comment: 9 pages, 5 figures. Version2: added results on azimuthal distributions and more discussion of energy flow definition using jet clusterin

Transverse field muon-spin rotation signature of the skyrmion-lattice phase in Cu2OSeO3

We present the results of transverse field (TF) muon-spin rotation (μ+SR) measurements on Cu2OSeO3, which has a skyrmion-lattice (SL) phase. We measure the response of the TF μ+SR signal in that phase along with the surrounding ones, and suggest how the phases might be distinguished using the results of these measurements. Dipole field simulations support the conclusion that the muon is sensitive to the SL via the TF line shape and, based on this interpretation, our measurements suggest that the SL is quasistatic on a time scale τ > 100 ns

Magnetic ground state of the one-dimensional ferromagnetic chain compounds M(NCS)2(thiourea)2 (M=Ni,Co)

The magnetic properties of the two isostructural molecule-based magnets—Ni(NCS)2(thiourea)2, S = 1 [thiourea = SC(NH2 )2] and Co(NCS)2 (thiourea)2, S = 3/2—are characterized using several techniques in order to rationalize their relationship with structural parameters and to ascertain magnetic changes caused by substitution of the spin. Zero-field heat capacity and muon-spin relaxation measurements reveal low-temperature long-range ordering in both compounds, in addition to Ising-like (D < 0) single-ion anisotropy (DCo ∼ −100 K, DNi ∼ −10 K). Crystal and electronic structure, combined with dc-field magnetometry, affirm highly quasi-onedimensional behavior, with ferromagnetic intrachain exchange interactions JCo ≈ +4 K and JNi ∼ +100 K and weak antiferromagnetic interchain exchange, on the order of J ∼ −0.1 K. Electron charge- and spin-density mapping reveals through-space exchange as a mechanism to explain the large discrepancy in J-values despite, from a structural perspective, the highly similar exchange pathways in both materials. Both species can be compared to the similar compounds MCl2(thiourea)4, M = Ni(II) (DTN) and Co(II) (DTC), where DTN is known to harbor two magnetic-field-induced quantum critical points. Direct comparison of DTN and DTC with the compounds studied here shows that substituting the halide Cl− ion for the NCS− ion results in a dramatic change in both the structural and magnetic properties

Possible Z2 phase and spin-charge separation in electron doped cuprate superconductors

The SU(2) slave-boson mean-field theory for the tt'J model is analyzed. The role of next-nearest-neighbor hopping t' on the phase-diagram is studied. We find a pseudogap phase in hole-doped materials (where t'<0). The pseudo-gap phase is a U(1) spin liquid (the staggered-flux phase) with a U(1) gauge interaction and no fractionalization. This agrees with experiments on hole doped samples. The same calculation also indicates that a positive t' favors a Z2 state with true spin-charge separation. The Z2 state that exists when t' > 0.5J can be a candidate for the pseudo-gap phase of electron-doped cuprates (if such a phase exists). The experimental situation in electron-doped materials is also addressed.Comment: 6 pages, 2 figures, RevTeX4. Homepage http://dao.mit.edu/~wen

Nonlinear wave transmission and pressure on the fixed truncated breakwater using NURBS numerical wave tank

Fully nonlinear wave interaction with a fixed breakwater is investigated in a numerical wave tank (NWT). The potential theory and high-order boundary element method are used to solve the boundary value problem. Time domain simulation by a mixed Eulerian-Lagrangian (MEL) formulation and high-order boundary integral method based on non uniform rational B-spline (NURBS) formulation is employed to solve the equations. At each time step, Laplace equation is solved in Eulerian frame and fully non-linear free-surface conditions are updated in Lagrangian manner through material node approach and fourth order Runge-Kutta time integration scheme. Incident wave is fed by specifying the normal flux of appropriate wave potential on the fixed inflow boundary. To ensure the open water condition and to reduce the reflected wave energy into the computational domain, two damping zones are provided on both ends of the numerical wave tank. The convergence and stability of the presented numerical procedure are examined and compared with the analytical solutions. Wave reflection and transmission of nonlinear waves with different steepness are investigated. Also, the calculation of wave load on the breakwater is evaluated by first and second order time derivatives of the potential