31,848 research outputs found
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 N=4 Supersymmetric Type II String Theories
We compute the spectrum of quarter BPS dyons in freely acting Z_2 and Z_3
orbifolds of type II string theory compactified on a six dimensional torus. For
large charges the result for statistical entropy computed from the degeneracy
formula agrees with the corresponding black hole entropy to first non-leading
order after taking into account corrections due to the curvature squared terms
in the effective action. The result is significant since in these theories the
entropy of a small black hole, computed using the curvature squared corrections
to the effective action, fails to reproduce the statistical entropy associated
with elementary string states.Comment: LaTeX file, 32 pages; v2:minor change
Stable two--brane models with bulk tachyon matter
We explore the possibility of constructing stable, warped two--brane models
which solve the hierarchy problem, with a bulk non--canonical scalar field
(tachyon matter) as the source term in the action. Among our examples are two
models--one with a warp factor (denoted as ) which differs
from that of the standard Randall--Sundrum by the addition of a quadratic piece
in the and another, where the warping is super-exponential. We
investigate the issue of resolution of hierarchy and perform a stability
analysis by obtaining the effective inter-brane potentials, in each case. Our
analysis reveals that there does exist stable values of the modulus consistent
with hierarchy resolution in both the models. Thus, these models, in which the
bulk scalar field generates the geometry and also ensures stability, provide
viable alternatives to the standard Randall--Sundrum two-brane scenario.Comment: Final version published in Int. Jr. Mod. Phys
Phase transitions in Ising model on a Euclidean network
A one dimensional network on which there are long range bonds at lattice
distances with the probability has been taken
under consideration. We investigate the critical behavior of the Ising model on
such a network where spins interact with these extra neighbours apart from
their nearest neighbours for . It is observed that there is
a finite temperature phase transition in the entire range. For , finite size scaling behaviour of various quantities are consistent with
mean field exponents while for , the exponents depend on
. The results are discussed in the context of earlier observations on
the topology of the underlying network.Comment: 7 pages, revtex4, 7 figures; to appear in Physical Review E, minor
changes mad
H-Dyons and S-Duality
We present a relatively simple argument showing that the H-dyon states
required by S-duality of the heterotic string on are present provided
that the BPS dyons required by S-duality of N=4 supersymmetric Yang-Mills
theory are present. We also conjecture and provide evidence that H-dyons at
singularities where the nonperturbative gauge symmetry is completely broken are
actually BPS dyons.Comment: 16 pages, uses harvmac.tex, arguments are drastically changed but the
conclusions remain unchange
Dyon Spectrum in CHL Models
We propose a formula for the degeneracy of quarter BPS dyons in a class of
CHL models. The formula uses a modular form of a subgroup of the genus two
modular group Sp(2,Z). Our proposal is S-duality invariant and reproduces
correctly the entropy of a dyonic black hole to first non-leading order for
large values of the charges.Comment: LaTeX file, 38 pages, minor changes in section 3.3(v2), minor changes
in introduction, appendix A and C(v3
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