116 research outputs found
Non-supersymmetric D-Brane Configurations with Bose-Fermi Degenerate Open String Spectrum
The spectrum of open strings on various non-BPS D-brane configurations in
type II string theory on a K3 orbifold is analysed. At a generic point in the
corresponding moduli space the spectrum of open strings does not have any
degeneracy between bosonic and fermionic states. However, there exist special
values for these moduli for which many non-BPS D-brane configurations have an
exactly bose-fermi degenerate open string spectrum at all mass levels. In this
case the closed string exchange interaction between a pair of such D-brane
configurations vanishes at all distances.Comment: 28 pages, LaTe
AdS_3, Black Holes and Higher Derivative Corrections
Using AdS/CFT correspondence and the Euclidean action formalism for black
hole entropy Kraus and Larsen have argued that the entropy of a BTZ black hole
in three dimensional supergravity with (0,4) supersymmetry does not receive any
correction from higher derivative terms in the action. We argue that as a
consequence of AdS/CFT correspondence the action of a three dimensional
supergravity with (0,4) supersymmetry cannot receive any higher derivative
correction except for those which can be removed by field redefinition. The
non-renormalization of the entropy then follows as a consequence of this and
the invariance of Wald's formula under a field redefinition.Comment: LaTeX file, 12 pages; v2: reference adde
Product Representation of Dyon Partition Function in CHL Models
A formula for the exact partition function of 1/4 BPS dyons in a class of CHL
models has been proposed earlier. The formula involves inverse of Siegel
modular forms of subgroups of Sp(2,Z). In this paper we propose product
formulae for these modular forms. This generalizes the result of Borcherds and
Gritsenko and Nikulin for the weight 10 cusp form of the full Sp(2,Z) group.Comment: LaTeX file, 39 pages; minor change
Picture Changing Operators in Closed Fermionic String Field Theory
We discuss appropriate arrangement of picture changing operators required to
construct gauge invariant interaction vertices involving Neveu-Schwarz states
in heterotic and closed superstring field theory. The operators required for
this purpose are shown to satisfy a set of descent equations.Comment: 15 page
Kaluza-Klein Dyons in String Theory
S-duality of hetertotic / type II string theory compactified on a six
dimensional torus requires the existence of Kaluza-Klein dyons, carrying
winding charge. We identify the zero modes of the Kaluza-Klein monopole
solution which are responsible for these dyonic excitations, and show that we
get the correct degeneracy of dyons as predicted by S-duality. The self-dual
harmonic two form on the Euclidean Taub-NUT space plays a crucial role in this
construction.Comment: LaTeX file, 7 pages, reference adde
CHL Dyons and Statistical Entropy Function from D1-D5 System
We give a proof of the recently proposed formula for the dyon spectrum in CHL
string theories by mapping it to a configuration of D1 and D5-branes and
Kaluza-Klein monopole. We also give a prescription for computing the degeneracy
as a systematic expansion in inverse powers of charges. The computation can be
formulated as a problem of extremizing a duality invariant statistical entropy
function whose value at the extremum gives the logarithm of the degeneracy.
During this analysis we also determine the locations of the zeroes and poles of
the Siegel modular forms whose inverse give the dyon partition function in the
CHL models.Comment: LaTeX file, 48 pages; v2: typos correcte
Dyon Spectrum in Generic N=4 Supersymmetric Z_N Orbifolds
We find the exact spectrum of a class of quarter BPS dyons in a generic N=4
supersymmetric Z_N orbifold of type IIA string theory on K3\times T^2 or T^6.
We also find the asymptotic expansion of the statistical entropy to first
non-leading order in inverse power of charges and show that it agrees with the
entropy of a black hole carrying same set of charges after taking into account
the effect of the four derivative Gauss-Bonnet term in the effective action of
the theory.Comment: LaTeX file, 39 pages; minor change
Black Hole Entropy Function and the Attractor Mechanism in Higher Derivative Gravity
We study extremal black hole solutions in D dimensions with near horizon
geometry AdS_2\times S^{D-2} in higher derivative gravity coupled to other
scalar, vector and anti-symmetric tensor fields. We define an entropy function
by integrating the Lagrangian density over S^{D-2} for a general AdS_2\times
S^{D-2} background, taking the Legendre transform of the resulting function
with respect to the parameters labelling the electric fields, and multiplying
the result by a factor of 2\pi. We show that the values of the scalar fields at
the horizon as well as the sizes of AdS_2 and S^{D-2} are determined by
extremizing this entropy function with respect to the corresponding parameters,
and the entropy of the black hole is given by the value of the entropy function
at this extremum. Our analysis relies on the analysis of the equations of
motion and does not directly make use of supersymmetry or specific structure of
the higher derivative terms.Comment: LaTeX file, 12page
Orientifold Limit of F-theory Vacua
We show how an F-theory compactified on a Calabi-Yau (n+1)-fold in
appropriate weak coupling limit reduces formally to an orientifold of type IIB
theory compactified on an auxiliary complex n-fold. In some cases (but not
always) if the original (n+1)-fold is singular, then the auxiliary n-fold is
also singular. We illustrate this by analysing F-theory on elliptically fibered
Calabi-Yau 3-folds on base .Comment: LaTeX file, 11 pages, additional argument for Calabi-Yau nature of
the auxiliary manifold, one extra referenc
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