2,361 research outputs found
The Role of Higher Twist in Determining Polarized Parton Densities from DIS data
Different methods to extract the polarized parton densities from the world
polarized DIS data are considered. The higher twist corrections to
the spin dependent proton and neutron structure functions are found to be
non-negligible and important in the QCD analysis of the present experimental
data. Their role in determining the polarized parton densities in the framework
of the different approaches is discussed.Comment: To appear in the Proceedings of the Spin2004 Symposium, Trieste,
11-16 Oct 200
Semiclassical correlators of three states with large S^5 charges in string theory in AdS_5 x S^5
We consider semiclassical computation of 3-point correlation functions of
(BPS or non-BPS) string states represented by vertex operators carrying large
charges in S5. We argue that the AdS5 part of the construction of relevant
semiclassical solution involves the two basic ingredients: (i) configuration of
three glued geodesics in AdS2 suggested by Klose and McLoughlin in
arXiv:1106.0495 and (ii) a particular Schwarz-Christoffel map of the 3-geodesic
solution in cylindrical (tau, sigma) domain into the complex plane with three
marked points. This map is constructed using the expression for the AdS2 string
stress tensor which is uniquely determined by the 3 scaling dimensions as noted
by Janik and Wereszczynski in arXiv:1109.6262 (our solution, however, is
different from theirs). We also find the S5 part of the solution and thus the
full expression for the semiclassical part of the 3-point correlator for
several examples: extremal and non-extremal correlators of BPS states and a
particular correlator of "small" circular spinning strings in S3 part of S5. We
demonstrate that for the BPS correlators the results agree with the large
charge limit of the corresponding supergravity and free gauge theory
expressions.Comment: 43 pages, 4 figures; v2: minor corrections; v3: comments added at the
end of section 3 and in section 5; v4: minor corrections; v5: discussion in
subsection 3.3 correcte
Superconducting and Normal State Properties of Heavily Hole-Doped Diamond
We report measurements of the specific heat, Hall effect, upper critical
field and resistivity on bulk, B-doped diamond prepared by reacting amorphous B
and graphite under high-pressure/high-temperature conditions. These experiments
establish unambiguous evidence for bulk superconductivity and provide a
consistent set of materials parameters that favor a conventional, weak coupling
electron-phonon interpretation of the superconducting mechanism at high hole
doping.Comment: 10 pages, 3 figure
Theoretical and experimental study of high-pressure synthesized B20-type compounds Mn(Co,Rh)Ge
The search and exploration of new materials not found in nature is one of
modern trends in pure and applied chemistry. In the present work, we report on
experimental and \textit{ab initio} density-functional study of the
high-pressure-synthesized series of compounds Mn(Co,Rh)Ge. These
high-pressure phases remain metastable at normal conditions, therewith they
preserve their inherent noncentrosymmetric B20-type structure and chiral
magnetism. Of particular interest in these two isovalent systems is the
comparative analysis of the effect of (Co) and (Rh) substitution for
Mn, since the orbitals are characterized by higher localization and
electron interaction than the orbitals. The behavior of
Mn(Co,Rh)Ge systems is traced as the concentration changes in the
range . We applied a sensitive experimental and theoretical
technique which allowed to refine the shape of the temperature dependencies of
magnetic susceptibility and thereby provide a new and detailed
magnetic phase diagram of MnCoGe. It is shown that both systems
exhibit a helical magnetic ordering that very strongly depends on the
composition . However, the phase diagram of MnCoGe differs from
that of MnRhGe in that it is characterized by coexistence of two
helices in particular regions of concentrations and temperatures.Comment: 12 pages, 11 figure
Two-channel point-contact tunneling theory of superconductors
We introduce a two-channel tunneling model to generalize the widely used BTK
theory of point-contact conductance between a normal metal contact and
superconductor. Tunneling of electrons can occur via localized surface states
or directly, resulting in a Fano resonance in the differential conductance
. We present an analysis of within the two-channel model when
applied to soft point-contacts between normal metallic silver particles and
prototypical heavy-fermion superconductors CeCoIn and CeRhIn at high
pressures. In the normal state the Fano line shape of the measured is well
described by a model with two tunneling channels and a large
temperature-independent background conductance. In the superconducting state a
strongly suppressed Andreev reflection signal is explained by the presence of
the background conductance. We report Andreev signal in CeCoIn consistent
with standard -wave pairing, assuming an equal mixture of
tunneling into [100] and [110] crystallographic interfaces. Whereas in
CeRhIn at 1.8 and 2.0 GPa the signal is described by a -wave
gap with reduced nodal region, i.e., increased slope of the gap opening on the
Fermi surface. A possibility is that the shape of the high-pressure Andreev
signal is affected by the proximity of a line of quantum critical points that
extends from 1.75 to 2.3 GPa, which is not accounted for in our description of
the heavy-fermion superconductor.Comment: 13 pages, 13 figure
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