373 research outputs found
Duality without Supersymmetry: The Case of the SO(16)xSO(16) String
We extend strong/weak coupling duality to string theories without spacetime
supersymmetry, and focus on the case of the unique ten-dimensional,
nonsupersymmetric, tachyon-free heterotic string. We
construct a tachyon-free heterotic string model that interpolates smoothly
between this string and the ten-dimensional supersymmetric heterotic
string, and we construct a dual for this interpolating model. We find that the
perturbative massless states of our dual theories precisely match within a
certain range of the interpolation. Further evidence for this proposed duality
comes from a calculation of the one-loop cosmological constant in both
theories, as well as the presence of a soliton in the dual theory. This is
therefore the first known duality relation between nonsupersymmetric
tachyon-free string theories. Using this duality, we then investigate the
perturbative and nonperturbative stability of the string,
and present a conjecture concerning its ultimate fate.Comment: 15 pages, LaTeX, 3 figure
Supersymmetric Electroweak Cosmic Strings
We study the connection between supersymmetry and a topological bound
in a two-Higgs-doublet system with an gauge group. We derive the Bogomol'nyi equations from
supersymmetry considerations showing that they hold provided certain conditions
on the coupling constants, which are a consequence of the huge symmetry of the
theory, are satisfied. Their solutions, which can be interpreted as electroweak
cosmic strings breaking one half of the supersymmetries of the theory, are
studied. Certain interesting limiting cases of our model which have recently
been considered in the literature are finally analyzed.Comment: 20 pages, RevTe
Holographic Gauge Theories in Background Fields and Surface Operators
We construct a new class of supersymmetric surface operators in N=4 SYM and
find the corresponding dual supergravity solutions. We show that the insertion
of the surface operator - which is given by a WZW model supported on the
surface - appears by integrating out the localized degrees of freedom along the
surface which arise microscopically from a D3/D7 brane intersection.
Consistency requires constructing N=4 SYM in the D7 supergravity background and
not in flat space. This enlarges the class of holographic gauge theories dual
to string theory backgrounds to gauge theories in non-trivial supergravity
backgrounds. The dual Type IIB supergravity solutions we find reveal - among
other features - that the holographic dual gauge theory does indeed live in the
D7-brane background.Comment: 42 pages, harvmac, corrected typo
Exotic Differentiable Structures and General Relativity
We review recent developments in differential topology with special concern
for their possible significance to physical theories, especially general
relativity. In particular we are concerned here with the discovery of the
existence of non-standard (``fake'' or ``exotic'') differentiable structures on
topologically simple manifolds such as , \R and
Because of the technical difficulties involved in the smooth case, we begin
with an easily understood toy example looking at the role which the choice of
complex structures plays in the formulation of two-dimensional vacuum
electrostatics. We then briefly review the mathematical formalisms involved
with differentiable structures on topological manifolds, diffeomorphisms and
their significance for physics. We summarize the important work of Milnor,
Freedman, Donaldson, and others in developing exotic differentiable structures
on well known topological manifolds. Finally, we discuss some of the geometric
implications of these results and propose some conjectures on possible physical
implications of these new manifolds which have never before been considered as
physical models.Comment: 11 pages, LaTe
In vivo activity of a mixture of two human monoclonal antibodies (anti-HBs) in a chronic hepatitis B virus carrier chimpanzee
A 35-year-old female hepatitis B virus carrier chimpanzee was infused with
one dose of a mixture of human monoclonal antibodies 9H9 and 4-7B
(antibodies against hepatitis B virus surface antigen; HBsAg). Blood
samples were taken before and up to 3 weeks after infusion. HBsAg and
antibodies against HBsAg (anti-HBs) were quantified by radioimmunoassay
and enzyme immunoassay. Free anti-HBs was never detected. Thirty min after
the start of the infusion the HBsAg level was minimal with maximum loading
of the chimpanzee HBsAg with human immunoglobulin. HBsAg complexes could
be dissociated by acid treatment. The HBsAg level was completely restored
on day 7. Similar results were obtained for the preS1-containing particles
that may represent the infectious viral particles in the chimpanzee serum.
A mouse monoclonal anti-HBs (HBs.OT40) was found to compete with 9H9 in
artificial immune complexes with the pre-treatment HBsAg from the
chimpanzee. Used as a conjugate, HBs.OT40 yielded a maximum decrease in
the signal in the 30 min sample compared to non-competing anti-HBs
conjugates. This indicates binding of HBsAg with 9H9 in the circulation of
the chimpanzee. Immune-complexed 4-7B could not be detected by its
corresponding 4-7B peptide conjugate, probably due to its low
concentration in the complexes. It is concluded that human monoclonal
anti-HBs can effectively reduce the level of HBsAg in serum from this
chronic carrier. Monoclonals 9H9 and 4-7B may complement each other due to
their different mechanisms of inactivation, probably with higher
efficiency than that monitored by our HBsAg screening assays
Moduli Stabilisation in Heterotic Models with Standard Embedding
In this note we analyse the issue of moduli stabilisation in 4d models
obtained from heterotic string compactifications on manifolds with SU(3)
structure with standard embedding. In order to deal with tractable models we
first integrate out the massive fields. We argue that one can not only
integrate out the moduli fields, but along the way one has to truncate also the
corresponding matter fields. We show that the effective models obtained in this
way do not have satisfactory solutions. We also look for stabilised vacua which
take into account the presence of the matter fields. We argue that this also
fails due to a no-go theorem for Minkowski vacua in the moduli sector which we
prove in the end. The main ingredient for this no-go theorem is the constraint
on the fluxes which comes from the Bianchi identity.Comment: 20 pages, LaTeX; references adde
Black Holes and Five-brane Thermodynamics
The phase diagram for Dp-branes in M-theory compactified on , ,
, and is constructed. As for the lower-dimensional tori considered
in our previous work (hep-th/9810224), the black brane phase at high entropy
connects onto matrix theory at low entropy; we thus recover all known instances
of matrix theory as consequences of the Maldacena conjecture. The difficulties
that arise for are reviewed. We also analyze the D1-D5 system on ;
we exhibit its relation to matrix models of M5-branes, and use spectral flow as
a tool to investigate the dependence of the phase structure on angular
momentum.Comment: 57 pages, 6 eps figures, latex. v2: DLCQ limit of 5-brane corrected;
typos corrected, references added. v3: reference added, typos corrected v4:
comments on DLCQ limit of 5-brane corrected one last time. Final version, to
appear in Phys. Rev.
Supersymmetry breaking on orbifolds from Wilson lines
We consider five dimensional theories compactified on the orbifold S^1/Z_2
and prove that spontaneous local supersymmetry breaking by Wilson lines and by
the Scherk-Schwarz mechanism are equivalent. Wilson breaking is triggered by
the SU(2)_R symmetry which is gauged in off-shell N=2 supergravity by auxiliary
fields. The super-Higgs mechanism disposes of the would-be Goldstinos which are
absorbed by the gravitinos to become massive. The breaking survives in the flat
limit, where we decouple all gravitational interactions, and the theory becomes
softly broken global supersymmetry.Comment: 9 pages, some comments in the discussion of the super-Higgs effect
and some references adde
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