8,234 research outputs found
A -anaolg of the sixth Painlev\'e equation
A -difference analog of the sixth Painlev\'e equation is presented. It
arises as the condition for preserving the connection matrix of linear
-difference equations, in close analogy with the monodromy preserving
deformation of linear differential equations. The continuous limit and special
solutions in terms of -hypergeometric functions are also discussed.Comment: 8 pages, LaTeX file (Two misprints corrected
Stochastic Model and Equivalent Ferromagnetic Spin Chain with Alternation
We investigate a non-equilibrium reaction-diffusion model and equivalent
ferromagnetic spin 1/2 XY spin chain with alternating coupling constant. The
exact energy spectrum and the n-point hole correlations are considered with the
help of the Jordan-Wigner fermionization and the inter-particle distribution
function method. Although the Hamiltonian has no explicit translational
symmetry, the translational invariance is recovered after long time due to the
diffusion. We see the scaling relations for the concentration and the two-point
function in finite size analysis.Comment: 7 pages, LaTeX file, to appear in J. Phys. A: Math. and Ge
Local electronic nematicity in the one-band Hubbard model
Nematicity is a well known property of liquid crystals and has been recently
discussed in the context of strongly interacting electrons. An electronic
nematic phase has been seen by many experiments in certain strongly correlated
materials, in particular, in the pseudogap phase generic to many hole-doped
cuprate superconductors. Recent measurements in high superconductors has
shown even if the lattice is perfectly rotationally symmetric, the ground state
can still have strongly nematic local properties. Our study of the
two-dimensional Hubbard model provides strong support of the recent
experimental results on local rotational symmetry breaking. The
variational cluster approach is used here to show the possibility of an
electronic nematic state and the proximity of the underlying symmetry-breaking
ground state within the Hubbard model. We identify this nematic phase in the
overdoped region and show that the local nematicity decreases with increasing
electron filling. Our results also indicate that strong Coulomb interaction may
drive the nematic phase into a phase similar to the stripe structure. The
calculated spin (magnetic) correlation function in momentum space shows the
effects resulting from real-space nematicity
A giant planet imaged in the disk of the young star Beta Pictoris
Here we show that the ~10 Myr Beta Pictoris system hosts a massive giant
planet, Beta Pictoris b, located 8 to 15 AU from the star. This result confirms
that gas giant planets form rapidly within disks and validates the use of disk
structures as fingerprints of embedded planets. Among the few planets already
imaged, Beta Pictoris b is the closest to its parent star. Its short period
could allow recording the full orbit within 17 years.Comment: 4 pages, 2 figures. Published online 10 June 2010;
10.1126/science.1187187. To appear in Scienc
Thermodynamics of a black hole in a cavity
We present a unified thermodynamical description of the configurations
consisting on self-gravitating radiation with or without a black hole. We
compute the thermal fluctuations and evaluate where will they induce a
transition from metastable configurations towards stable ones. We show that the
probability of finding such a transition is exponentially small. This indicates
that, in a sequence of quasi equilibrium configurations, the system will remain
in the metastable states till it approaches very closely the critical point
beyond which no metastable configuration exists. Near that point, we relate the
divergence of the local temperature fluctuations to the approach of the
instability of the whole system, thereby generalizing the usual fluctuations
analysis in the cases where long range forces are present. When angular
momentum is added to the cavity, the above picture is slightly modified.
Nevertheless, at high angular momentum, the black hole loses most of its mass
before it reaches the critical point at which it evaporates completely.Comment: 27 pages, latex file, contains 3 figures available on request at
[email protected]
Frustrated trimer chain model and Cu3Cl6(H2O)2 2H8C4SO2 in a magnetic field
Recent magnetization and susceptibility measurements on Cu3Cl6(H2O)2 2H8C4SO2
by Ishii et.al. [J. Phys. Soc. Jpn. 69, 340 (2000)] have demonstrated the
existence of a spin gap. In order to explain the opening of a spin gap in this
copper-trimer system, Ishii et.al. have proposed a frustrated trimer chain
model. Since the exchange constants for this model have not yet been
determined, we develop a twelfth-order high-temperature series for the magnetic
susceptibility and fit it to the experimentally measured one. We find that some
of the coupling constants are likely to be ferromagnetic. The combination of
several arguments does not provide any evidence for a spin gap in the parameter
region with ferromagnetic coupling constants, but further results e.g. for the
magnetization process are in qualitative agreement with the experimental
observations.Comment: 9 pages REVTeX, 4 PostScript figures included using psfig.sty; for
series and supplementary material see http://www.tu-bs.de/~honecker/3mer/ or
http://www.itp.phys.ethz.ch/staff/laeuchli/3mer ; substantial reorganization
including shifting part of the discussion to WWW pages with "supplementary
material"; new appendix shows that antiferromagnetic J_i > 0 are not
compatible with the experimental data for the magnetic susceptibilit
The Ademollo-Gatto theorem for lattice semileptonic decays
We present the results of the calculation of the Kl3 semileptonic form factor
at zero momentum transfer, f(0), obtained at one-loop in partially quenched
Chiral Perturbation Theory (with either Nf=2, or Nf=3, and with generic valence
and sea quark masses). We show that for Nf=2, when the masses of the valence
and sea light quarks are equal, the correction is of the order (MK^2-Mpi^2)^3.
The formulae presented here can be useful for the mass extrapolation of the
results obtained in lattice simulations to the physical point.Comment: 7 page
Issues in the Blandford-Znajek Process for GRB Inner Engine
Several issues regarding the Blandford-Znajek process are discussed to
demonstrate that it can be an effective mechanism for powering the gamma ray
bursts. Using a simple circuit analysis it is argued that the disk power
increases the effective power of the black hole-accretion disk system, although
a part of disk power can be dissipated into black hole entropy. Within the
framework of the force-free magnetosphere with the strong magnetic field, the
magnetically dominated MHD flow is found to support the Blandford-Znajek
process and it is demonstrated that the possible magnetic repulsion by the
rotating black hole will not affect the efficiency substantially.Comment: 10 pages, 1 figure, 3 references added, more discussions on the
magnetic field on the black hole, accepted for publication in Ap
Resonant elastic soft x-ray scattering in oxygen-ordered YBa_2Cu_3O_{6+delta}
Static charge-density wave (CDW) and spin-density wave (SDW) order has been
convincingly observed in La-based cuprates for some time. However, more
recently it has been suggested by quantum oscillation, transport and
thermodynamic measurements that density wave order is generic to underdoped
cuprates and plays a significant role in YBa_2Cu_3O_{6+delta} (YBCO). We use
resonant soft x-ray scattering at the Cu L and O K edges to search for evidence
of density wave order in Ortho-II and Ortho-VIII oxygen-ordered YBCO. We report
a null result -- no evidence for static CDW order -- in both Ortho-II and
Ortho-VIII ordered YBCO. While this does not rule out static CDW order in the
CuO_2 planes of YBCO, these measurements place limits on the parameter space
(temperature, magnetic field, scattering vector) in which static CDW order may
exist. In addition, we present a detailed analysis of the energy and
polarization dependence of the Ortho-II superstructure Bragg reflection [0.5 0
0] at the Cu L edge. The intensity of this peak, which is due to the valence
modulations of Cu in the chain layer, is compared with calculations using
atomic scattering form factors deduced from x-ray absorption measurements. The
calculated energy and polarization dependence of the scattering intensity is
shown to agree very well with the measurement, validating the approach and
providing a framework for analyzing future resonant soft x-ray scattering
measurements.Comment: 11 pages, 9 figure
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