884 research outputs found
Ion Beam Analysis of He-implanted fusion solid breedes
Introduction
Lithium-based ceramics (silicates, titanates, ?) possess a series of advantages as alternative over liquid lithium and lithium-lead alloys for fusion breeders. They have a sufficient lithium atomic density (up to 540 kg*m-3), high temperature stability (up to 1300 K), and good chemical compatibility with structural materials. Nevertheless, few research is made on the diffusion behavior of He and H isotopes through polycrystalline structures of porous ceramics which is crucial in order to understand the mobility of gas coolants as well as, the release of tritium. Moreover, in the operating conditions of actual breeder blanket concepts, the extraction rate of the helium produced during lithium transmutation can be affected by the composition and the structure of the near surface region modifying the performance of BB material
Explicit construction of nilpotent covariants in N=4 SYM
Some aspects of correlation functions in N=4 SYM are discussed. Using N=4
harmonic superspace we study two and three-point correlation functions which
are of contact type and argue that these contact terms will not affect the
non-renormalisation theorem for such correlators at non-coincident points. We
then present a perturbative calculation of a five-point function at two loops
in N=2 harmonic superspace and verify that it reproduces the derivative of the
previously found four-point function with respect to the coupling. The
calculation of this four-point function via the five-point function turns out
to be significantly simpler than the original direct calculation. This
calculation also provides an explicit construction of an N=2 component of an
N=4 five-point nilpotent covariant that violates U(1)_Y symmetry.Comment: 20 pages, standard late
Non-renormalization of next-to-extremal correlators in N=4 SYM and the AdS/CFT correspondence
We show that next-to-extremal correlators of chiral primary operators in N=4
SYM theory do not receive quantum corrections to first order in perturbation
theory. Furthermore we consider next-to-extremal correlators within AdS
supergravity. Here the exchange diagrams contributing to these correlators
yield results of the same free-field form as obtained within field theory. This
suggests that quantum corrections vanish at strong coupling as well.Comment: 21 pages, LaTex, 9 eps figures, typos corrected and references adde
Simplifications of four-point functions in N=4 supersymmetric Yang-Mills theory at two loops
The superconformal Ward identities combined with N=2 harmonic analyticity are
used to evaluate two-loop four-point correlation functions of gauge-invariant
operators in D=4, N=4 supersymmetric Yang-Mills theory in terms of the
well-known one-loop box integral. The result is confirmed by a direct numerical
computation
Four-point functions in N=2 superconformal field theories
Four-point correlation functions of hypermultiplet bilinear composites are
analysed in N=2 superconformal field theory using the superconformal Ward
identities and the analyticity properties of the composite operator
superfields. It is shown that the complete amplitude is determined by a single
arbitrary function of the two conformal cross-ratios of the space-time
variables.Comment: 36 pp LaTeX2e, uses amsfonts, amssymb. Some references adde
Double-vector multiplet and partially broken N=4, d=3 supersymmetry
We elaborate on a new N=2, d=3 supermultiplet (double-vector multiplet) with
a non-trivial off-shell realization of the central charge. Its bosonic sector
comprises two abelian gauge vector fields forming an SO(2) vector. We present a
superfield formulation of this multiplet in the central-charge extended N=2,
d=3 superspace and then employ it, in the framework of the nonlinear
realizations approach, as the Goldstone one for the partial breaking N=4 -> N=2
in three dimensions. The covariant equations of motion for the self-interacting
Goldstone superfield arise as a natural generalization of the free ones and are
interpreted as the worldvolume supersymmetric form of the equations of motion
of a N=4 D2-brane. For the vector fields we find a coupled nonlinear system of
Born-Infeld type and demonstrate its dual equivalence to the d=5 membrane. The
double-vector multiplet can be fused with some extra N=2, d=3 multiplet to form
an off-shell N=4, d=3 supermultiplet.Comment: 11 pages, no figures, typos corrected, version to be published in PL
Partial non-renormalisation of the stress-tensor four-point function in N=4 SYM and AdS/CFT
We show that, although the correlator of four stress-tensor multiplets in N=4
SYM is known to have radiative corrections, certain linear combinations of its
components are protected from perturbative renormalisation and remain at their
free-field values. This result is valid for weak as well as for strong coupling
and for any gauge group. Our argument uses Intriligator's insertion formula,
and includes a proof that the possible contact term contributions cannot change
the form of the amplitudes. Combining this new non-renormalisation theorem with
Maldacena's conjecture allows us to make a prediction for the structure of the
corresponding correlator in AdS supergravity. This is verified by first
considerably simplifying the strong coupling expression obtained by recent
supergravity calculations, and then showing that it does indeed exhibit the
expected structure.Comment: 21 pages, no figure
1/4 Partial Breaking of Global Supersymmetry and New Superparticle Actions
We construct the worldline superfield massive superparticle actions which
preserve 1/4 portion of the underlying higher-dimensional supersymmetry. The
rest of supersymmetry is spontaneously broken and realized by nonlinear
transformations. We consider the cases of N=4 to N=1 and N=8 to N=2 partial
breaking. In the first case we present the corresponding Green-Schwarz type
target superspace action with one -supersymmetry. It is related to the
superfield action via a field redefinition. In the second case we find out two
possible models, one of which is a direct generalization of the N=4 to N=1
case, while another is essentially different. For the first model we formulate
Green-Schwarz type action with two kappa supersymmetries. We elaborate on the
bosonic part of the superfield action for the second model and find that only
in two special limits it takes the standard Nambu-Goto form. In the general
case it is determined by a fourth-order algebraic equation. The characteristic
common feature of these new superparticle models is that the algebras of their
spontaneously broken supersymmetries are non-trivial truncations of the general
extensions of N=1 and N=2 Poincare D=4 superalgebras by tensorial central
charges.Comment: 22 page
Static Potential in N=4 Supersymmetric Yang-Mills Theory
We compute the leading order perturbative correction to the static potential
in supersymmetric Yang-Mills theory. We show that the perturbative
expansion contains infrared logarithms which, when resummed, become logarithms
of the coupling constant. The resulting correction goes in the right direction
to match the strong coupling behavior obtained from the AdS/CFT correspondence.
We find that the strong coupling extrapolation of the sum of ladder diagrams
goes as , as in the supergravity approach.Comment: 8 pages, four figures using feynm
Six-dimensional Supergravity and Projective Superfields
We propose a superspace formulation of N=(1,0) conformal supergravity in six
dimensions. The corresponding superspace constraints are invariant under
super-Weyl transformations generated by a real scalar parameter. The known
variant Weyl super-multiplet is recovered by coupling the geometry to a
super-3-form tensor multiplet. Isotwistor variables are introduced and used to
define projective superfields. We formulate a locally supersymmetric and
super-Weyl invariant action principle in projective superspace. Some families
of dynamical supergravity-matter systems are presented.Comment: 39 pages; v3: some modifications in section 2; equations (2.3),
(2.14b), (2.16) and (2.17) correcte
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