16,584 research outputs found
Visco-elastic regularization and strain softening
In this paper it is intended to verify the capacity of regularization of the numerical
solution of an elasto-plastic problem with linear strain softening. The finite element method
with a displacement approach is used. Drucker-Prager yield criteria is considered. The radial
return method is used for the integration of the elasto-plastic constitutive relations. An elastovisco-
plastic scheme is used to regularize the numerical solution. Two constitutive laws have
been developed and implemented in a FE-program, the first represent the radial return
method applied to Drucker-Prager yield criteria and the second is a time integration
procedure for the Maxwell visco-elastic model. Attention is paid to finite deformations. An
associative plastic flow is considered in the Drucker-Prager elasto-plastic model. The
algorithms are tested in two problems with softening. Figures showing the capability of the
algorithms to regularize the solution are presented
Duality Symmetries and Supersymmetry Breaking in String Compactifications
We discuss the spontaneous supersymetry breaking within the low-energy
effective supergravity action of four-dimensional superstrings. In particular,
we emphasize the non-universality of the soft supersymmetry breaking
parameters, the -problem and the duality symmetries.Comment: (invited talk to the 27th ICHEP, Glasgow, July 1994), 11 page
Entropy function for rotating extremal black holes in very special geometry
We use the relation between extremal black hole solutions in five- and in
four-dimensional N=2 supergravity theories with cubic prepotentials to define
the entropy function for extremal black holes with one angular momentum in five
dimensions. We construct two types of solutions to the associated attractor
equations.Comment: 15 pages, minor change
BPS Action and Superpotential for Heterotic String Compactifications with Fluxes
We consider N =1 compactifications to four dimensions of heterotic string
theory in the presence of fluxes. We show that up to order O(\alpha'^2) the
associated action can be written as a sum of squares of BPS-like quantities. In
this way we prove that the equations of motion are solved by backgrounds which
fulfill the supersymmetry conditions and the Bianchi identities. We also argue
for the expression of the related superpotential and discuss the radial modulus
stabilization for a class of examples.Comment: LaTeX, 28 pages. Minor changes, one more reference added. Final
version to appear on JHE
Heterotic String Theory on non-Kaehler Manifolds with H-Flux and Gaugino Condensate
We discuss compactifications of heterotic string theory to four dimensions in
the presence of H-fluxes, which deform the geometry of the internal manifold,
and a gaugino condensate which breaks supersymmetry. We focus on the
compensation of the two effects in order to obtain vacua with zero cosmological
constant and we comment on the effective superpotential describing these vacua.Comment: 6 page
BPS black holes, the Hesse potential, and the topological string
The Hesse potential is constructed for a class of four-dimensional N=2
supersymmetric effective actions with S- and T-duality by performing the
relevant Legendre transform by iteration. It is a function of fields that
transform under duality according to an arithmetic subgroup of the classical
dualities reflecting the monodromies of the underlying string compactification.
These transformations are not subject to corrections, unlike the
transformations of the fields that appear in the effective action which are
affected by the presence of higher-derivative couplings. The class of actions
that are considered includes those of the FHSV and the STU model. We also
consider heterotic N=4 supersymmetric compactifications. The Hesse potential,
which is equal to the free energy function for BPS black holes, is manifestly
duality invariant. Generically it can be expanded in terms of powers of the
modulus that represents the inverse topological string coupling constant,
, and its complex conjugate. The terms depending holomorphically on
are expected to correspond to the topological string partition function and
this expectation is explicitly verified in two cases. Terms proportional to
mixed powers of and are in principle present.Comment: 28 pages, LaTeX, added comment
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