4 research outputs found
Strings in Homogeneous Background Spacetimes
The string equations of motion for some homogeneous (Kantowski-Sachs, Bianchi
I and Bianchi IX) background spacetimes are given, and solved explicitly in
some simple cases. This is motivated by the recent developments in string
cosmology, where it has been shown that, under certain circumstances, such
spacetimes appear as string-vacua.
Both tensile and null strings are considered. Generally, it is much simpler
to solve for the null strings since then we deal with the null geodesic
equations of General Relativity plus some additional constraints.
We consider in detail an ansatz corresponding to circular strings, and we
discuss the possibility of using an elliptic-shape string ansatz in the case of
homogeneous (but anisotropic) backgrounds.Comment: 25 pages, REVTE
T-Duality and Penrose limits of spatially homogeneous and inhomogeneous cosmologies
Penrose limits of inhomogeneous cosmologies admitting two abelian Killing
vectors and their abelian T-duals are found in general. The wave profiles of
the resulting plane waves are given for particular solutions. Abelian and
non-abelian T-duality are used as solution generating techniques. Furthermore,
it is found that unlike in the case of abelian T-duality, non-abelian T-duality
and taking the Penrose limit are not commutative procedures.Comment: 16 pages, 4 figures. Discussion on non-abelian T-duality expande
Family Unification from Universality
A direct consequence of the occurrence of fermion families is the invariance
of currents under certain groups of (universality) transformations. We show how
these universality groups can themselves be used to find and study grand family
unification models. Identifying two independent - weak and strong -
universality groups and assuming that the grand unification group is SU(8N),
its subgroup respecting either weak or strong universality is shown to be G =
SU(2)xU(1)xSU(3). The fundamental representation of SU(8N) decomposes as N
families of leptons and quarks. In the G-invariant limit, all fermions are
left-handed. A mechanism for generating the correct number of right-handed
fermions with the correct couplings so as to give pure vector colour and
electromagnetic currents is exhibited. Universality is shown to result most
naturally from a preonic structure of fermions. In such a preonic picture there
are no ultraheavy gauge bosons and no anomaly or hierarchy problem.Comment: 30 page