5,116 research outputs found
Remarks on Fundamental String Cosmology
In recent work, it was shown that velocity-dependent forces between moving
strings or branes lead to an accelerating expanding universe without assuming
the existence of a cosmological constant. Here we show that the repulsive
velocity-dependent force arises in more general contexts and can lead to cosmic
structure formation.Comment: 7 pages, harvma
Self-Gravitating Strings and String/Black Hole Correspondence
In a recent essay, we discussed the possibility of using polymer sizing to
model the collapse of a single, long excited string to a black hole. In this
letter, we apply this idea to bring further support to string/black hole
correspondence. In particular, we reproduce Horowitz and Polchinki's results
for self-gravitating fundamental strings and speculate on the nature of the
quantum degrees of freedom of black holes in string theory.Comment: 8 pages, harvma
Strings, Fivebranes and an Expanding Universe
It was recently shown that velocity-dependent forces between parallel
fundamental strings moving apart in a dimensional spacetime implied an
accelerating expanding universe in -dimensional space-time. Exact
solutions were obtained for the early time expansion in . Here we show
that this result also holds for fundamental strings in the background of a
fivebrane, and argue that the feature of an accelerating universe would hold
for more general -brane-seeded models.Comment: 8 pages, harvma
A Comment on the Stability of String Monopoles
In recent work a multimonopole solution of heterotic string theory was
obtained. The monopoles are noted to be stable, in contrast with analogous
solutions of Einstein-Maxwell or Yang-Mills-dilaton theory. The existence of
this and other classes of stable solitonic solutions in string theory thus
provides a possible test for low-energy string theory as distinct from other
gauge + gravity theories.Comment: 5 page
Existence of Black Holes Due to Concentration of Angular Momentum
We present a general sufficient condition for the formation of black holes
due to concentration of angular momentum. This is expressed in the form of a
universal inequality, relating the size and angular momentum of bodies, and is
proven in the context of axisymmetric initial data sets for the Einstein
equations which satisfy an appropriate energy condition. A brief comparison is
also made with more traditional black hole existence criteria based on
concentration of mass.Comment: 8 pages; final versio
Spacetime Supersymmetry and Duality in String Theory
I discuss the role of spacetime supersymmetry in the interplay between
strong/weak coupling duality and target space duality in string theory which
arises in string/string duality. This can be seen via the construction of
string soliton solutions which in compactifications of heterotic string
theory break more than of the spacetime supersymmetries but whose analogs
in and compactifications break precisely of the spacetime
supersymmetries. As a result, these solutions may be interpreted as stable
solitons in the latter two cases, and correspond to Bogomol'nyi-saturated
states in their respective spectra.Comment: 6 pages, harvma
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