18,822 research outputs found
Resonating-valence-bond structure of Gutzwiller-projected superconducting wave functions
Gutzwiller-projected (GP) wave functions have been widely used for describing
spin-liquid physics in frustrated magnets and in high-temperature
superconductors. Such wave functions are known to represent states of the
resonating-valence-bond (RVB) type. In the present work I discuss the RVB
structure of a GP singlet superconducting state with nodes in the spectrum. The
resulting state for the undoped spin system may be described in terms of the
"path integral" over loop coverings of the lattice, thus extending the known
construction for RVB states. The problem of the topological order in GP states
may be reformulated in terms of the statistical behavior of loops. The simple
example of the projected d-wave state on the square lattice demonstrates that
the statistical behavior of loops is renormalized in a nontrivial manner by the
projection.Comment: 6 pages, 4 figures, some numerical data adde
Exclusive diffractive electroproduction of dijets in collinear factorization
Exclusive electroproduction of hard dijets can be described within the
collinear factorization. This process has clear experimental signature and
provides one with an interesting alternative venue to test QCD description of
hard diffractive processes and extract information on generalized nucleon
parton distributions. In this work we present detailed leading-order QCD
calculations of the relevant cross sections, including longitudinal momentum
fraction distribution of the dijets and their azimuthal angle dependence.Comment: 11 pages, 14 Postscript figures, uses revtex4.st
Coulomb effects in a ballistic one-channel S-S-S device
We develop a theory of Coulomb oscillations in superconducting devices in the
limit of small charging energy . We consider a small
superconducting grain of finite capacity connected to two superconducting leads
by nearly ballistic single-channel quantum point contacts. The temperature is
supposed to be very low, so there are no single-particle excitations on the
grain. Then the behavior of the system may be described as quantum mechanics of
the superconducting phase on the island. The Josephson energy as a function of
this phase has two minima which become degenerate at the phase difference on
the leads equal to , the tunneling amplitude between them being controlled
by the gate voltage at the grain. We find the Josephson current and its
low-frequency fluctuations and predict their periodic dependence on the induced
charge with period .Comment: 11 pages, REVTeX, 10 figures, uses eps
Siberian flood basalt magmatism and Mongolia-Okhotsk slab dehydration
Experimental data combined with numerical calculations suggest that fast subducting slabs are cold enough to carry into the deep mantle a significant portion of the water in antigorite, which transforms with increasing depth to phase A and then to phase E and/or wadsleyite by solid-solid phase transition. Clathrate hydrates and ice VII are also stable at PT conditions of cold slabs and represent other potential phases for water transport into the deep mantle. Some cold slabs are expected to deflect while crossing the 410 km and stagnate in transition zone being unable to penetrate through 660 km discontinuity. In this way slabs can move a long way beneath continents after long-lived subduction. With time, the stagnant slabs are heated to the temperature of the ambient transition zone and release free H~2~O-bearing fluid. Combining with transition zone water filter model this may cause voluminous melting of overlying upper mantle rocks. If such process operates in nature, magmas geochemically similar to island-arc magmas are expected to appear in places relatively remote from active arcs at the time of their emplacement. Dolerites of the south-eastern margin of the Siberian flood basalt province, located about 700 km from suggested trench, were probably associated with fast subduction of the Mongolia-Okhotsk slab and originated by dehydration of the stagnant slab in the transition zone. We show that influence of the subduction-related deep water cycle on Siberian flood basalt magmatism gradually reduced with increasing distance from the subduction zone
Relativistic Heavy-Ion Collisions within 3-Fluid Hydrodynamics: Hadronic Scenario
A 3-fluid hydrodynamic model for simulating relativistic heavy-ion collisions
is introduced. Alongside with two baryon-rich fluids, the new model considers
time-delayed evolution of a third, baryon-free (i.e. with zero net baryonic
charge) fluid of newly produced particles. Its evolution is delayed due to a
formation time, during which the baryon-free fluid neither thermalizes nor
interacts with the baryon-rich fluids. After the formation it starts to
interact with the baryon-rich fluids and quickly gets thermalized. Within this
model with pure hadronic equation of state, a systematic analysis of various
observables at incident energies between few and about 160A GeV has been done
as well as comparison with results of transport models. We have succeeded to
reasonably reproduce a great body of experimental data in the incident energy
range of E_{lab} = (1-160)A GeV. The list includes proton and pion rapidity
distributions, proton transverse-mass spectra, rapidity distributions of Lambda
and antiLambda hyperons, elliptic flow of protons and pions (with the exception
of proton v2 at 40A GeV), multiplicities of pions, positive kaons, phi-mesons,
hyperons and antihyperons, including multi-strange particles. This agreement is
achieved on the expense of substantial enhancement of the interflow friction as
compared to that estimated proceeding from hadronic free cross sections.
However, we have also found out certain problems. The calculated yield of K^-
is approximately by a factor of 1.5 higher than that in the experiment. We have
also failed to describe directed transverse flow of protons and pion at E_{lab}
> 40A GeV. This failure apparently indicates that the used EoS is too hard and
thereby leaves room for a phase transition.Comment: 30 pages, 20 figures, 2 tables. Version accepted for publication in
Phys. Rev.
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