1,607 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
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
Geodesic Scattering of Solitonic Strings
We compute the metric on moduli space for the Dabholkar-Harvey string soliton
in to lowest nontrivial order in the string tension. The metric is found
to be flat, which implies trivial scattering of the solitons. This result is
consistent with an earlier test-string calculation of the leading order
dynamical force and a computation of the Veneziano amplitude for the scattering
of macroscopic strings.Comment: 6 page
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
Supersymmetry, Duality and Bound States
-brane solutions of low-energy string actions have traditionally provided
the first evidence for the existence of string dualities, in which fundamental
and solitonic -branes are identified with perturbative and non-perturbative
BPS states. In this talk we discuss the composite nature of solutions, which
allows for the interpretation of general solutions as bound states or
intersections of maximally supersymmetric fundamental constituents. This
feature lies at the heart of the recent success of string theory in reproducing
the Beckenstein-Hawking black hole entropy formula.Comment: 8 pages, harvmac, talk given at Strings '9
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