812 research outputs found
How experimentally to detect a solitary superconductivity in dirty ferromagnet-superconductor trilayers?
We theoretically study the proximity effect in the thin-film layered
ferromagnet (F) - superconductor (S) heterostructures in FFS design. We
consider the boundary value problem for the Usadel-like equations in the case
of so-called "dirty" limit. The "latent" superconducting pairing interaction in
F layers taken into account. The focus is on the recipe of experimental
preparation the state with so-called solitary superconductivity. We also
propose and discuss the model of the superconducting spin valve based on
FFS trilayers in solitary superconductivity regime
Difficulties of an Infrared Extension of Differential Renormalization
We investigate the possibility of generalizing differential renormalization
of D.Z.Freedman, K.Johnson and J.I.Latorre in an invariant fashion to theories
with infrared divergencies via an infrared operation.
Two-dimensional models and the four-dimensional theory
diagrams with exceptional momenta are used as examples, while dimensional
renormalization serves as a test scheme for comparison. We write the basic
differential identities of the method simultaneously in co-ordinate and
momentum space, introducing two scales which remove ultraviolet and infrared
singularities. The consistent set of Fourier-transformation formulae is
derived. However, the values for tadpole-type Feynman integrals in higher
orders of perturbation theory prove to be ambiguous, depending on the order of
evaluation of the subgraphs. In two dimensions, even earlier than this
ambiguity manifests itself, renormalization-group calculations based on
infrared extension of differential renormalization lead to incorrect results.
We conclude that the extended differential renormalization procedure does not
perform the infrared operation in a self-consistent way, as the
original recipe does the ultraviolet operation.Comment: (minor changes have been made to make clear that no infrared problems
occur in the original ultraviolet procedure of [1]; subsection 2.1 has been
added to outline the ideas a simple example), 26 pages, LaTeX, JINR preprint
E2-92-538, Dubna (Dec.1992
Towards Automatic Analytic Evaluation of Diagrams with Masses
A method to calculate two-loop self-energy diagrams of the Standard Model is
demonstrated. A direct physical application is the calculation of the two-loop
electroweak contribution to the anomalous magnetic moment of the muon
. Presently, we confine ourselves to a ``toy'' model with
only , and a heavy neutral scalar particle (Higgs). The algorithm
is implemented as a FORM-based program package. For generating and
automatically evaluating any number of two-loop self-energy diagrams, a special
C-program has been written. This program creates the initial FORM-expression
for every diagram generated by QGRAF, executes the corresponding subroutines
and sums up the final results.Comment: LaTeX, 20 pages, 7 eps-figures included; extended version of talk
given at AIHEN96, Lausanne, 1-6 Sept. 1996; detailed description of C-program
is given; accepted for publication in Comp.Phys.Com
Ruling out an inflation driven by kinetic coupling
We demonstrate that the latest constraints on inflationary observables,
namely the tensor-to-scalar ratio and the scalar spectral index ,
from the Cosmic Background Radiation (CMB) observations are already strong
enough to rule out the model of a scalar field kinetically coupled to gravity
with a positive coupling constant and a power law potential. The case for a
negative coupling constant needs special treatment.Comment: 5 pages with 1 eps figure; minor changes, references adde
RadioAstron probes the ultra-fine spatial structure in the HO maser emission in the star forming region W49N
HO maser emission associated with the massive star formation region W49N
were observed with the Space-VLBI mission RadioAstron. The procedure for
processing of the maser spectral line data obtained in the RadioAstron
observations is described. Ultra-fine spatial structures in the maser emission
were detected on space-ground baselines of up to 9.6 Earth diameters. The
correlated flux densities of these features range from 0.1% to 0.6% of the
total flux density. These low values of correlated flux density are probably
due to turbulence either in the maser itself or in the interstellar medium.Comment: Accepted for publication in Advances in Space Researc
Thin accretion disk signatures in hybrid metric-Palatini f(R)-gravity
In the present work, accretion onto a spherically symmetric black hole in the
hybrid metric-Palatini f(R)-gravity is considered. The Novikov-Thorne model for
a relativistic thin accretion disk is used. The energy flux, temperature
distribution, emission spectrum and energy conversion efficiency of accretion
disks around such black holes are numerically calculated. A comparison with the
results for a Schwarzschild black hole is made and conclusions about the
viability of the model are drawn. As a result, it is obtained that the
accretion disks around black holes in hybrid metric-Palatini f(R)-gravity are
colder and less luminous than in general relativity.Comment: 27 pages, 26 figure
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