565 research outputs found
Affine spherical homogeneous spaces with good quotient by a maximal unipotent subgroup
For an affine spherical homogeneous space G/H of a connected semisimple
algebraic group G, we consider the factorization morphism by the action on G/H
of a maximal unipotent subgroup of G. We prove that this morphism is
equidimensional if and only if the weight semigroup of G/H satisfies some
simple condition.Comment: v2: title and abstract changed; v3: 16 pages, minor correction
Transcendental numbers and the topology of three-loop bubbles
We present a proof that all transcendental numbers that are needed for the
calculation of the master integrals for three-loop vacuum Feynman diagrams can
be obtained by calculating diagrams with an even simpler topology, the topology
of spectacles.Comment: 4 pages in REVTeX, 1 PostScript figure included, submitted to Phys.
Rev. Let
Contribution of matter fields to the Gell-Mann-Low function for N=1 supersymmetric Yang-Mills theory, regularized by higher covariant derivatives
Contribution of matter fields to the Gell-Mann-Low function for N=1
supersymmetric Yang-Mills theory, regularized by higher covariant derivatives,
is obtained using Schwinger-Dyson equations and Slavnov-Tailor identities. A
possible deviation of the result from the corresponding contribution in the
exact Novikov, Shifman, Vainshtein and Zakharov -function is discussed.Comment: 20 pages, 4 figure
Crystal Chemistry of Carbon-Substituted MgB2
Neutron powder diffraction has been used to characterize a sample of
C-substituted MgB2 synthesized from Mg and B4C (with isotopically enriched
11B). The sample is multiphase, with the major phase [73.4(1) wt.%] being
Mg(B1-xCx)2 with x=0.10(2). Minor phases include MgB2C2, Mg, and MgO. The major
Mg(B1-xCx)2 phase displays diffraction peak widths as sharp as for pure MgB2,
indicating good C homogeneity. There is no evidence for ordering of the
substituted C atoms or distortion of the host structure other than contraction
of the a axis and slight expansion of the c axis. The observed changes in
lattice parameters vs. C concentration provide a means for estimating the C
concentration in other Mg(B1-xCx)2 samples. The reduction in Tc resulting from
10% C substitution is much larger than previously reported, suggesting that
previous reports of the C concentration in Mg(B1-xCx)2 are overestimated. The
Mg site occupancy is determined to be 0.990(4) which is consistent with full Mg
occupancy. Given these results, the stoichiometry Mg(B0.9C0.1)2 should be used
by future attempts (band structural or otherwise) to explain (i) the dramatic
suppression of Tc (Tc ~ = 22 K) and (ii) the persistence of the
two-superconducting-gap feature in the specific heat data.Comment: 14 pages, 3 figure
The Four-Loop Konishi in N=4 SYM
We present the result of a full direct component calculation for the planar
four-loop anomalous dimension of the Konishi operator in N =4 Supersymmetric
Yang-Mills theory. Our result confirms the results obtained from superfield
(arXiv:0712.3522, arXiv:0806.2095) and superstring (arXiv:0807.0399)
computations, which take into account finite size corrections to the all-loop
asymptotic Bethe ansatz for the integrable models describing the spectrum of
the anomalous dimensions of the gauge-invariant operators and the spectrum of
the string states in the framework of the gauge/string duality.Comment: 7 pages, some detailes of calculations adde
Harmonic analysis on spherical homogeneous spaces with solvable stabilizer
For all spherical homogeneous spaces G/H, where G is a simply connected
semisimple algebraic group and H a connected solvable subgroup of G, we compute
the spectra of the representations of G on spaces of regular sections of
homogeneous line bundles over G/H.Comment: v2: 14 pages, minor correction
Supersymmetric States in Large N Chern-Simons-Matter Theories
In this paper we study the spectrum of BPS operators/states in N=2
superconformal U(N) Chern-Simons-matter theories with adjoint chiral matter
fields, with and without superpotential. The superconformal indices and
conjectures on the full supersymmetric spectrum of the theories in the large N
limit with up to two adjoint matter fields are presented. Our results suggest
that some of these theories may have supergravity duals at strong coupling,
while some others may be dual to higher spin theories of gravity at strong
coupling. For the N=2 theory with no superpotential, we study the
renormalization of R-charge at finite 't Hooft coupling using "Z-minimization".
A particularly intriguing result is found in the case of one adjoint matter.Comment: 53 pages, 18 figures. v2: improved numerics, additional comments
adde
Special case of sunset: reduction and epsilon-expansion
We consider two loop sunset diagrams with two mass scales m and M at the
threshold and pseudotreshold that cannot be treated by earlier published
formula. The complete reduction to master integrals is given. The master
integrals are evaluated as series in ratio m/M and in epsilon with the help of
differential equation method. The rules of asymptotic expansion in the case
when q^2 is at the (pseudo)threshold are given.Comment: LaTeX, 13 pages, 1 figur
Towards proof of new identity for Green functions in N=1 supersymmetric electrodynamics
For the N=1 supersymmetric massless electrodynamics, regularized by higher
derivatives, we describe a method, by which one can try to prove the new
identity for the Green functions, which was proposed earlier. Using this method
we show that some contribution to the new identity are really 0.Comment: 16 pages, 1 figure, an error corrected, significant change
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