590 research outputs found
The Two-Boson-Exchange Correction to Parity-Violating Elastic Electron-Proton Scattering
We calculate the two-boson-exchange (TBE) corrections to the parity-violating
asymmetry of the elastic electron-proton scattering in a simple hadronic model
including the nucleon and the intermediate states. We find that
contribution is, in general, comparable with the
nucleon contribution and the current experimental measurements of
strange-quark effects in the proton neutral weak current. The total TBE
corrections to the current extracted values of
in recent experiments are found to lie in the
range of .Comment: 3 pages, 2 figs, 1 table, talk given at International Conference of
Particle and Nuclei (PANIC08) Eilat, Israel, 9-14 Nov,200
Spin-orbit scattering in quantum diffusion of massive Dirac fermions
Effect of spin-orbit scattering on quantum diffusive transport of
two-dimensional massive Dirac fermions is studied by the diagrammatic
technique. The quantum diffusion of massive Dirac fermions can be viewed as a
singlet Cooperon in the massless limit and a triplet Cooperon in the large-mass
limit. The spin-orbit scattering behaves like random magnetic fields only to
the triplet Cooperon, and suppresses the weak localization of Dirac fermions in
the large-mass regime. This behavior suggests an experiment to detect the weak
localization of bulk subbands in topological insulator thin films, in which a
narrowing of the cusp of the negative magnetoconductivity is expected after
doping heavy-element impurities. Finally, a detailed comparison between the
conventional two-dimensional electrons and Dirac fermions is presented for
impurities of orthogonal, symplectic, and unitary symmetries.Comment: 5 pages, 3 figures, 2 tables. To be submitted, comments are welcom
A balancing act: Evidence for a strong subdominant d-wave pairing channel in
We present an analysis of the Raman spectra of optimally doped based on LDA band structure calculations and the
subsequent estimation of effective Raman vertices. Experimentally a narrow,
emergent mode appears in the () Raman spectra only below
, well into the superconducting state and at an energy below twice the
energy gap on the electron Fermi surface sheets. The Raman spectra can be
reproduced quantitatively with estimates for the magnitude and momentum space
structure of the s pairing gap on different Fermi surface sheets, as
well as the identification of the emergent sharp feature as a
Bardasis-Schrieffer exciton, formed as a Cooper pair bound state in a
subdominant channel. The binding energy of the exciton relative
to the gap edge shows that the coupling strength in this subdominant
channel is as strong as 60% of that in the dominant
channel. This result suggests that may be the dominant pairing
symmetry in Fe-based sperconductors which lack central hole bands.Comment: 10 pages, 6 Figure
Raman-Scattering Detection of Nearly Degenerate -Wave and -Wave Pairing Channels in Iron-Based BaKFeAs and RbFeSe Superconductors
We show that electronic Raman scattering affords a window into the essential
properties of the pairing potential of
iron-based superconductors. In BaKFeAs we observe band
dependent energy gaps along with excitonic Bardasis-Schrieffer modes
characterizing, respectively, the dominant and subdominant pairing channel. The
symmetry of all excitons allows us to identify the subdominant
channel to originate from the interaction between the electron bands.
Consequently, the dominant channel driving superconductivity results from the
interaction between the electron and hole bands and has the full lattice
symmetry. The results in RbFeSe along with earlier ones in
Ba(FeCo)As highlight the influence of the Fermi
surface topology on the pairing interactions.Comment: 5 pages, 4 figure
Pairing via Index theorem
This work is motivated by a specific point of view: at short distances and
high energies the undoped and underdoped cuprates resemble the -flux phase
of the t-J model. The purpose of this paper is to present a mechanism by which
pairing grows out of the doped -flux phase. According to this mechanism
pairing symmetry is determined by a parameter controlling the quantum tunneling
of gauge flux quanta. For zero tunneling the symmetry is ,
while for large tunneling it is . A zero-temperature critical
point separates these two limits
Down-Regulation of Cytokinin Oxidase 2 Expression Increases Tiller Number and Improves Rice Yield
Lower critical field and SNS-Andreev spectroscopy of 122-arsenides: Evidence of nodeless superconducting gap
Using two experimental techniques, we studied single crystals of the 122-FeAs
family with almost the same critical temperature, Tc. We investigated the
temperature dependence of the lower critical field of a single crystal under
static magnetic fields parallel to the axis. The temperature dependence of the
London penetration depth can be described equally well either by a single
anisotropic -wave-like gap or by a two-gap model, while a d-wave approach
cannot be used to fit the London penetration depth data. Intrinsic multiple
Andreev reflection effect spectroscopy was used to detect bulk gap values in
single crystals of the intimate compound, with the same Tc. We estimated the
range of the large gap value 6-8 meV (depending on small variation of and its a
space anisotropy of about 30%, and the small gap 1.7 meV. This clearly
indicates that the gap structure of our investigated systems more likely
corresponds to a nodeless s-wave two gaps.Comment: 9 pages, 6 figure
The Chalker-Coddington Network Model is Quantum Critical
We show that the localization transition in the integer quantum Hall effect
as described by the Chalker-Coddington network model is quantum critical. We
first map the anisotropic network model to the problem of diagonalizing a
one-dimensional non-Hermitian non-compact supersymmetric lattice Hamiltonian of
interacting bosons and fermions. Its behavior is investigated numerically using
the density matrix renormalization group method, and critical behavior is found
at the plateau transition. This result is confirmed by an exact, analytic,
generalization of the Lieb-Schultz-Mattis theorem.Comment: Version accepted for publication in PRL. 4 pages, 2 eps figure
Hadronic Annihilation Decay Rates of P-wave Heavy Quarkonia with Both Relativistic and QCD Radiative Corrections
Hadronic annihilation decay rates of P-wave heavy quarkonia are given to
next-to-leading order in both and . They include ten
nonperturbative parameters, which can be rigorously defined as the matrix
elements of color-singlet and color-octet operators in NRQCD. We expect these
papameters will be determined from lattice calculations in future.Comment: 5 Pages RevTex. The paper is withdraw
Suppression of Immunodeficiency Virus-Associated Neural Damage by the p75 Neurotrophin Receptor Ligand, LM11A-31, in an In Vitro Feline Model
Feline immunodeficiency virus (FIV) infection like human immunodeficiency virus (HIV), produces systemic and central nervous system disease in its natural host, the domestic cat, that parallels the pathogenesis seen in HIV-infected humans. The ability to culture feline nervous system tissue affords the unique opportunity to directly examine interactions of infectious virus with CNS cells for the development of models and treatments that can then be translated to a natural infectious model. To explore the therapeutic potential of a new p75 neurotrophin receptor ligand, LM11A-31, we evaluated neuronal survival, neuronal damage and calcium homeostasis in cultured feline neurons following inoculation with FIV. FIV resulted in the gradual appearance of dendritic beading, pruning of processes and shrinkage of neuronal perikarya in the neurons. Astrocytes developed a more activated appearance and there was an enhanced accumulation of microglia, particularly at longer times post-inoculation. Addition of 10 nM LM11A-31, to the cultures greatly reduced or eliminated the neuronal pathology as well as the FIV effects on astrocytes and microglia. LM11A-31 also, prevented the development of delayed calcium deregulation in feline neurons exposed to conditioned medium from FIV treated macrophages. The suppression of calcium accumulation prevented the development of foci of calcium accumulation and beading in the dendrites. FIV replication was unaffected by LM11A-31. The strong neuroprotection afforded by LM11A-31 in an infectious in vitro model indicates that LM11A-31 may have excellent potential for the treatment of HIV-associated neurodegeneration
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