1,103,946 research outputs found
Critical -equivariant biharmonic maps
We study -equivariant biharmonic maps in the critical dimension. A
major consequence of our study concerns the corresponding heat flow. More
precisely, we prove that blowup occurs in the biharmonic map heat flow from
into . To our knowledge, this was the first example of blowup
for the biharmonic map heat flow. Such results have been hard to prove, due to
the inapplicability of the maximum principle in the biharmonic case.
Furthermore, we classify the possible -equivariant biharmonic maps from
into , and we show that there exists, in contrast to the
harmonic map analogue, equivariant biharmonic maps from into
that wind around as many times as we wish. We believe that the ideas
developed herein could be useful in the study of other higher-order parabolic
equations.Comment: 24 pages, 1 figure. Published online in Calculus of Variations and
Partial Differential Equations, 201
-Covariant String Cosmology
The recently discovered symmetry of the space of slowly varying
cosmological string vacua in dimensions is shown to be preserved in the
presence of bulk string matter. The existence of conserved currents
allows all the equations of string cosmology to be reduced to first-order
differential equations. The perfect-fluid approximation is not
-invariant, implying that stringy fluids possess in general a
non-vanishing viscosity.Comment: 13 page
O(d,d)-Duality in String Theory
A new method for obtaining dual string theory backgrounds is presented.
Preservation of the Hamiltonian density and the energy momentum tensor induced
by O(d,d)-transformations leads to a relation between dual sets of coordinate
one-forms accompanied by a redefinition of the background fields and a shift of
the dilaton. The necessity of isometric directions arises as integrability
condition for this map. The isometry algebra is studied in detail using
generalised geometry. In particular, non-abelian dualities and
beta-transformations are contained in this approach. The latter are exemplified
by the construction of a new approximate non-geometric background.Comment: 19+5 pages; v2: minor corrections and references added; v3: comments
and references adde
Ehlers Transformations and String Effective Action
We explicitly obtain the generalization of the Ehlers transformation for
stationary axisymmetric Einstein equations to string theory. This is
accomplished by finding the twist potential corresponding to the moduli fields
in the effective two dimensional theory. Twist potential and symmetric moduli
are shown to transform under an which is a manifest symmetry of the
equations of motion. The non-trivial action of this is given by the
Ehlers transformation and belongs to the set .Comment: 13 pages, minor corrections, version to appear in Physics Letters
B35
A worldsheet extension of O(d,d;Z)
We study superconformal interfaces between N=(1,1) supersymmetric sigma
models on tori, which preserve a u(1)^{2d} current algebra. Their fusion is
non-singular and, using parallel transport on CFT deformation space, it can be
reduced to fusion of defect lines in a single torus model. We show that the
latter is described by a semi-group extension of O(d,d;Q), and that (on the
level of Ramond charges) fusion of interfaces agrees with composition of
associated geometric integral transformations. This generalizes the well-known
fact that T-duality can be geometrically represented by Fourier-Mukai
transformations. Interestingly, we find that the topological interfaces between
torus models form the same semi-group upon fusion. We argue that this
semi-group of orbifold equivalences can be regarded as the \alpha' deformation
of the continuous O(d,d) symmetry of classical supergravity.Comment: 71 pages, 1 figure, minor additions and correction
Higher order effects in the and transfer reactions
Full Coupled Channels Calculations were performed for the
and transfer reactions at several deuteron incident
energies from MeV up to 3.27 MeV. A strong polarization effect
between the entrance channel and the transfer channels
and was
observed. This polarization effect had to be taken into account in order to
obtain realistic spectroscopic factors from these reactions.Comment: 15 papes, 13 figures, accepted for publication in Phys. Rev.
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