18,466 research outputs found

    Magnon Heat Conductivity and Mean Free Paths in Two-Leg Spin Ladders: A Model-Independent Determination

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    The magnon thermal conductivity κmag\kappa_{\mathrm{mag}} of the spin ladders in Sr14Cu24−xZnxO41\rm Sr_{14}Cu_{24-x}Zn_xO_{41} has been investigated at low doping levels x=0x=0, 0.125, 0.25, 0.5 and 0.75. The Zn-impurities generate nonmagnetic defects which define an upper limit for lmagl_{\mathrm{mag}} and therefore allow a clear-cut relation between lmagl_{\mathrm{mag}} and κmag\kappa_{\mathrm{mag}} to be established independently of any model. Over a large temperature range we observe a progressive suppression of κmag\kappa_{\mathrm{mag}} with increasing Zn-content and find in particular that with respect to pure Sr14Cu24O41\rm Sr_{14}Cu_{24}O_{41} κmag\kappa_{\mathrm{mag}} is strongly suppressed even in the case of tiny impurity densities where lmag≲374l_{\mathrm{mag}}\lesssim 374~{\AA}. This shows unambiguously that large lmag≈3000l_{\mathrm{mag}}\approx 3000~{\AA} which have been reported for Sr14Cu24O41\rm Sr_{14}Cu_{24}O_{41} and La5Ca9Cu24O41\rm La_{5}Ca_9Cu_{24}O_{41} 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

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    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

    Regge Behaviour from an Environmentally Friendly Renormalization Group

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    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

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    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

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    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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