18,467 research outputs found
Magnon Heat Conductivity and Mean Free Paths in Two-Leg Spin Ladders: A Model-Independent Determination
The magnon thermal conductivity of the spin ladders
in has been investigated at low doping levels
, 0.125, 0.25, 0.5 and 0.75. The Zn-impurities generate nonmagnetic
defects which define an upper limit for and therefore allow
a clear-cut relation between and to
be established independently of any model. Over a large temperature range we
observe a progressive suppression of with increasing
Zn-content and find in particular that with respect to pure is strongly suppressed even in
the case of tiny impurity densities where ~{\AA}.
This shows unambiguously that large ~{\AA} which
have been reported for and on basis of a kinetic model are in the correct order
of magnitude
Predictions of the pseudo-complex theory of Gravity for EHT observations- II. Theory and predictions
We present a resum\'e on the modified theory of gravity, called
pseudo-complex General Relativity (pc-GR). It is the second in a series of
papers, where the first one (Boller et al. 2019, referred to as paper I)
discussed the observational consequences of pc-GR. In this paper, we
concentrate on the underlying theory. PC-GR involves an algebraic extension of
the standard theory of GR and it depends on two phenomenological parameters. An
element included in pc-GR that is not present in standard GR is the
energy-momentum tensor corresponding to an anisotropic ideal fluid, which we
call dark energy. The two parameters are related to the coupling of mass to the
dark energy and its fall-off as a function of r. The consequences and
predictions of this theory will be discussed in the context of the
observational results of the Even Horizon Telescope, expected soon. Our main
result is that due to the accumulation of dark energy near a large mass, the
modified theory predicts a dark ring followed by a bright ring in the emission
profile of the accretion disc. We also discuss the light ring in the equatorial
plane.Comment: 2 figure
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Seasonal changes in the transport of pollutants into the Arctic troposphere-model study
Regge Behaviour from an Environmentally Friendly Renormalization Group
The asymptotic behaviour of cubic field theories is investigated in the Regge
limit using the techniques of environmentally friendly renormalization,
environmentally friendly in the present context meaning asymmetric in its
momentum dependence. In particular we consider the crossover between large and
small energies at fixed momentum transfer for a model scalar theory of the type
phi^2 psi. The asymptotic forms of the crossover scaling functions are
exhibited for all two particle scattering processes in this channel to one loop
in a renormalization group improved perturbation theory.Comment: 9 pages text, one figure, LaTeX, uses psfig.sty. Revised version
submitted to Phys. Lett. B., besides minor changes a figure to illustrate the
conventions and a discussion of the full crossover function have been adde
Hidden assumptions in the derivation of the Theorem of Bell
John Bell's inequalities have already been considered by Boole in 1862. Boole
established a one-to-one correspondence between experimental outcomes and
mathematical abstractions of his probability theory. His abstractions are
two-valued functions that permit the logical operations AND, OR and NOT and are
the elements of an algebra. Violation of the inequalities indicated to Boole an
inconsistency of definition of the abstractions and/or the necessity to revise
the algebra. It is demonstrated in this paper, that a violation of Bell's
inequality by Einstein-Podolsky-Rosen type of experiments can be explained by
Boole's ideas. Violations of Bell's inequality also call for a revision of the
mathematical abstractions and corresponding algebra. It will be shown that this
particular view of Bell's inequalities points toward an incompleteness of
quantum mechanics, rather than to any superluminal propagation or influences at
a distance
An exactly solvable limit of low energy QCD
Starting from the QCD Hamiltonian, we derive a schematic Hamiltonian for low
energy quark dynamics with quarks restricted to the lowest s-level. The
resulting eigenvalue problem can be solved analytically. Even though the
Hamiltonian exhibits explicit chiral symmetry the severe restriction of the
number of degrees of freedom breaks the pattern of chiral symmetry breaking for
finite quark masses.Comment: 7 page
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